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wine/documentation/winedev-kernel.sgml
Eric Pouech 3bebb0fed9 - Using uniform DocBook tags for DLLs, commands, environment vars... 
- Moved detailed memory management from archi to kernel(s) part.
- Enhanced process handling description.
- Added section about 16 bit processes' support.
- Added section about DOS support.
2005-04-18 09:53:39 +00:00

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<chapter>
<title>Kernel modules</title>
<para>
This section covers the kernel modules. As already stated, Wine
implements the NT architecture, hence provides <filename>NTDLL</filename>
for the core kernel functions, and <filename>KERNEL32</filename>, which is
the implementation of the basis of the Win32 subsystem, on top of
<filename>NTDLL</filename>.
</para>
<para>
This chapter is made of two types of material (depending of their point of
view). Some items will be tackled from a global point of view and then,
when needed, explaining the split of work between
<filename>NTDLL</filename> and <filename>KERNEL32</filename>; some others
will be tackled from a DLL point of view (<filename>NTDLL</filename> or
<filename>KERNEL32</filename>). The choice is made so that the output is
more readable and understantable. At least, that's the intend (sigh).
</para>
<sect1 id="initialization">
<title>The Wine initialization process</title>
<para>
Wine has a rather complex startup procedure, so unlike many programs the
best place to begin exploring the code-base is
<emphasis>not</emphasis> in fact at the <function>main()</function>
function but instead at some of the more straightforward DLLs that
exist on the periphery such as MSI, the widget library (in
<filename>USER</filename> and <filename>COMCTL32</filename>) etc. The
purpose of this section is to document and explain how Wine starts up
from the moment the user runs "<command>wine myprogram.exe</command>" to
the point at which <filename>myprogram</filename> gets control.
</para>
<sect2>
<title>First Steps</title>
<para>
The actual wine binary that the user runs does not do very much, in
fact it is only responsible for checking the threading model in use
(NPTL vs LinuxThreads) and then invoking a new binary which performs
the next stage in the startup sequence. See the beginning of this
chapter for more information on this check and why it's necessary. You
can find this code in <filename>loader/glibc.c</filename>. The result
of this check is an exec of either <command>wine-pthread</command> or
<command>wine-kthread</command>, potentially (on Linux) via the
<emphasis>preloader</emphasis>. We need to use separate binaries here
because overriding the native pthreads library requires us to exploit
a property of ELF symbol fixup semantics: it's not possible to do this
without starting a new process.
</para>
<para>
The Wine preloader is found in
<filename>loader/preloader.c</filename>, and is required in order to
impose a Win32 style address space layout upon the newly created Win32
process. The details of what this does is covered in the address space
layout chapter. The preloader is a statically linked ELF binary which
is passed the name of the actual Wine binary to run (either
<command>wine-kthread</command> or <command>wine-pthread</command>)
along with the arguments the user passed in from the command line. The
preloader is an unusual program: it does not have a
<function>main()</function> function. In standard ELF applications,
the entry point is actually at a symbol named
<function>_start()</function>: this is provided by the
standard <command>gcc</command> infrastructure and normally jumps to
<function>__libc_start_main()</function> which initializes glibc before
passing control to the main function as defined by the programmer.
</para>
<para>
The preloader takes control direct from the entry point for a few
reasons. Firstly, it is required that glibc is not initialized twice:
the result of such behaviour is undefined and subject to change
without notice. Secondly, it's possible that as part of initializing
glibc, the address space layout could be changed - for instance, any
call to <function>malloc()</function> will initialize a heap arena
which modifies the VM mappings. Finally, glibc does not return to
<function>_start()</function> at any point, so by reusing it we avoid
the need to recreate the ELF bootstrap stack
(<varname>env</varname>, <varname>argv</varname>, auxiliary array etc).
</para>
<para>
The preloader is responsible for two things: protecting important
regions of the address space so the dynamic linker does not map shared
libraries into them, and once that is done loading the real Wine
binary off disk, linking it and starting it up. Normally all this is
automatically by glibc and the kernel but as we intercepted this
process by using a static binary it's up to us to restart the
process. The bulk of the code in the preloader is about loading
<command>wine-[pk]thread</command> and
<filename>ld-linux.so.2</filename> off disk, linking them together,
then starting the dynamic linking process.
</para>
<para>
One of the last things the preloader does before jumping into the
dynamic linker is scan the symbol table of the loaded Wine binary and
set the value of a global variable directly: this is a more efficient
way of passing information to the main Wine program than flattening
the data structures into an environment variable or command line
parameter then unpacking it on the other side, but it achieves pretty
much the same thing. The global variable set points to the preload
descriptor table, which contains the VMA regions protected by the
preloader. This allows Wine to unmap them once the dynamic linker has
been run, so leaving gaps we can initialize properly later on.
</para>
</sect2>
<sect2>
<title>Starting the emulator</title>
<para>
The process of starting up the emulator itself is mostly one of
chaining through various initializer functions defined in the core
libraries and DLLs: <filename>libwine</filename>, then
<filename>NTDLL</filename>, then <filename>KERNEL32</filename>.
</para>
<para>
Both the <command>wine-pthread</command> and
<command>wine-kthread</command> binaries share a common
<function>main()</function> function, defined in
<filename>loader/main.c</filename>, so no matter which binary is
selected after the preloader has run we start here. This passes the
information provided by the preloader into
<filename>libwine</filename> and then calls
<function>wine_init()</function>, defined in
<filename>libs/wine/loader.c</filename>. This is where the emulation
really starts:
<function>wine_init()</function> can, with the correct preparation,
be called from programs other than the wine loader itself.
</para>
<para>
<function>wine_init()</function> does some very basic setup tasks such
as initializing the debugging infrastructure, yet more address space
manipulation (see the information on the 4G/4G VM split in the address
space chapter), before loading <filename>NTDLL</filename> - the core
of both Wine and the Windows NT series - and jumping to the
<function>__wine_process_init()</function> function defined
in <filename>dlls/ntdll/loader.c</filename>
</para>
<para>
This function is responsible for initializing the primary Win32
environment. In <function>thread_init()</function>, it sets up the
TEB, the <command>wineserver</command> connection for the main thread
and the process heap. See the beginning of this chapter for more
information on this.
</para>
<para>
Finally, it loads and jumps to
<function>__wine_kernel_init()</function> in
<filename>KERNEL32.DLL</filename>: this is defined in
<filename>dlls/kernel32/process.c</filename>. This is where the bulk
of the work is done. The <filename>KERNEL32</filename> initialization
code retrieves the startup info for the process from the server,
initializes the registry, sets up the drive mapping system and locale
data, then begins loading the requested application itself. Each
process has a <structname>STARTUPINFO</structname> block that can be
passed into <function>CreateProcess</function> specifying various
things like how the first window should be displayed: this is sent to
the new process via the <command>wineserver</command>.
</para>
<para>
After determining the type of file given to Wine by the user (a Win32
EXE file, a Win16 EXE, a Winelib app etc), the program is loaded into
memory (which may involve loading and initializing other DLLs, the
bulk of Wines startup code), before control reaches the end of
<function>__wine_kernel_init()</function>. This function ends with the
new process stack being initialized, and start_process being called on
the new stack. Nearly there!
</para>
<para>
The final element of initializing Wine is starting the newly loaded
program itself. <function>start_process()</function> sets up the SEH
backstop handler, calls <function>LdrInitializeThunk()</function>
which performs the last part of the process initialization (such as
performing relocations and calling the <function>DllMain()</function>
with <constant>PROCESS_ATTACH</constant>), grabs the entry point of
the executable and then on this line:
</para>
<programlisting>
ExitProcess( entry( peb ) );
</programlisting>
<para>
... jumps to the entry point of the program. At this point the users
program is running and the API provided by Wine is ready to be
used. When entry returns, the <function>ExitProcess()</function> API
will be used to initialize a graceful shutdown.
</para>
</sect2>
</sect1>
<sect1>
<title>Detailed memory management</title>
<para>
As already explained in previous chapter (see <xref linkend="arch-mem">
for the details), Wine creates every 32-bit Windows process in its own
32 address space. Wine also tries to map at the relevant addresses what
Windows would do. There are however a few nasty bits to look at.
</para>
<sect2>
<title>Implementation</title>
<para>
Wine (with a bit of black magic) is able to map the main module at
it's desired address (likely <constant>0x400000</constant>), to create
the process heap, its stack (as a Windows executable can ask for a
specific stack size), Wine simply use the initial stack of the ELF
executable for its initialisation, but creates a new stack (as a Win32
one) for the main thread of the executable. Wine also tries to map all
native DLLs at their desired address, so that no relocation has to be
performed.
</para>
<para>
Wine also implements the shared heap so native win9x DLLs can be
used. This heap is always created at the
<constant>SYSTEM_HEAP_BASE</constant> address or
<constant>0x80000000</constant> and defaults to 16 megabytes in size.
</para>
<para>
There are a few other magic locations. The bottom 64k of memory is
deliberately left unmapped to catch null pointer dereferences. The
region from 64k to 1mb+64k are reserved for DOS compatibility and
contain various DOS data structures. Finally, the address space also
contains mappings for the Wine binary itself, any native libaries
Wine is using, the glibc malloc arena and so on.
</para>
</sect2>
<sect2 id="address-space">
<title>Laying out the address space</title>
<para>
Up until about the start of 2004, the Linux address space very much
resembled the Windows 9x layout: the kernel sat in the top gigabyte,
the bottom pages were unmapped to catch null pointer dereferences, and
the rest was free. The kernels mmap algorithm was predictable: it
would start by mapping files at low addresses and work up from there.
</para>
<para>
The development of a series of new low level patches violated many of
these assumptions, and resulted in Wine needing to force the Win32
address space layout upon the system. This section looks at why and
how this is done.
</para>
<para>
The exec-shield patch increases security by randomizing the kernels
mmap algorithms. Rather than consistently choosing the same addresses
given the same sequence of requests, the kernel will now choose
randomized addresses. Because the Linux dynamic linker
(<filename>ld-linux.so.2</filename>) loads DSOs into memory by using
mmap, this means that DSOs are no longer loaded at predictable
addresses, so making it harder to attack software by using buffer
overflows. It also attempts to relocate certain binaries into a
special low area of memory known as the ASCII armor so making it
harder to jump into them when using string based attacks.
</para>
<para>
Prelink is a technology that enhances startup times by precalculating
ELF global offset tables then saving the results inside the native
binaries themselves. By grid fitting each DSO into the address space,
the dynamic linker does not have to perform as many relocations so
allowing applications that heavily rely on dynamic linkage to be
loaded into memory much quicker. Complex C++ applications such as
Mozilla, OpenOffice and KDE can especially benefit from this
technique.
</para>
<para>
The 4G VM split patch was developed by Ingo Molnar. It gives the Linux
kernel its own address space, thereby allowing processes to access the
maximum addressable amount of memory on a 32-bit machine: 4
gigabytes. It allows people with lots of RAM to fully utilise that in
any given process at the cost of performance: the reason behind giving
the kernel a part of each processes address space was to avoid the
overhead of switching on each syscall.
</para>
<para>
Each of these changes alter the address space in a way incompatible
with Windows. Prelink and exec-shield mean that the libraries Wine
uses can be placed at any point in the address space: typically this
meant that a library was sitting in the region that the EXE you wanted
to run had to be loaded (remember that unlike DLLs, EXE files cannot
be moved around in memory). The 4G VM split means that programs could
receive pointers to the top gigabyte of address space which some are
not prepared for (they may store extra information in the high bits of
a pointer, for instance). In particular, in combination with
exec-shield this one is especially deadly as it's possible the process
heap could be allocated beyond
<constant>ADDRESS_SPACE_LIMIT</constant> which causes Wine
initialization to fail.
</para>
<para>
The solution to these problems is for Wine to reserve particular parts
of the address space so that areas that we don't want the system to
use will be avoided. We later on (re/de)allocate those areas as
needed. One problem is that some of these mappings are put in place
automatically by the dynamic linker: for instance any libraries that
Wine is linked to (like <filename>libc</filename>,
<filename>libwine</filename>, <filename>libpthread</filename> etc)
will be mapped into memory before Wine even gets control. In order to
solve that, Wine overrides the default ELF initialization sequence at
a low level and reserves the needed areas by using direct syscalls
into the kernel (ie without linking against any other code to do it)
before restarting the standard initialization and letting the dynamic
linker continue. This is referred to as the preloader and is found in
<filename>loader/preloader.c</filename>.
</para>
<para>
Once the usual ELF boot sequence has been completed, some native
libraries may well have been mapped above the 3gig limit: however,
this doesn't matter as 3G is a Windows limit, not a Linux limit. We
still have to prevent the system from allocating anything else above
there (like the heap or other DLLs) though so Wine performs a binary
search over the upper gig of address space in order to iteratively
fill in the holes with <constant>MAP_NORESERVE</constant> mappings so
the address space is allocated but the memory to actually back it is
not. This code can be found in
<filename>libs/wine/mmap.c</filename>:<function>reserve_area</function>.
</para>
</sect2>
</sect1>
<sect1>
<title>Multi-processing in Wine</title>
<para>
Let's take a closer look at the way Wine loads and run processes in memory.
</para>
<sect2>
<title>Starting a process from command line</title>
<para>
When starting a Wine process from command line (we'll get later on to
the differences between NE, PE and Winelib executables), there are a
couple of things Wine need to do first. A first executable is run to
check the threading model of the underlying OS (see
<xref linkend="threading"> for the details) and will start the real
Wine loader corresponding to the choosen threading model.
</para>
<para>
Then Wine graps a few elements from the Unix world: the environment,
the program arguments. Then the <filename>ntdll.dll.so</filename> is
loaded into memory using the standard shared library dynamic
loader. When loaded, <filename>NTDLL</filename> will mainly first
create a decent Windows environment:
<itemizedlist>
<listitem>
<para>
create a PEB (Process Environment Block) and a TEB (Thread
Environment Block).
</para>
</listitem>
<listitem>
<para>
set up the connection to the Wine server - and eventually
launching the Wine server if none runs
</para>
</listitem>
<listitem>
<para>create the process heap</para>
</listitem>
</itemizedlist>
</para>
<para>
Then <filename>Kernel32</filename> is loaded (but now using the
Windows dynamic loading capabilities) and a Wine specific entry point
is called <function>__wine_kernel_init</function>. This function will
actually handle all the logic of the process loading and execution,
and will never return from it's call.
</para>
<para>
<function>__wine_kernel_init</function> will undergo the following
tasks:
<itemizedlist>
<listitem>
<para>
initialization of program arguments from Unix program arguments
</para>
</listitem>
<listitem>
<para>lookup of executable in the file system</para>
</listitem>
<listitem>
<para>
If the file is not found, then an error is printed and the Wine
loader stops.
</para>
</listitem>
<listitem>
<para>
We'll cover the non-PE file type later on, so assume for now
it's a PE file. The PE module is loaded in memory using the
same mechanisms as for a native DLLs (mainly mapping the file
data and code sections into memory, and handling relocation if
needed). Note that the dependencies on the module are not
resolved at this point.
</para>
</listitem>
<listitem>
<para>
A new stack is created, which size is given in the PE header,
and this stack is made the one of the running thread (which is
still the only one in the process). The stack used at startup
will no longer be used.
</para>
</listitem>
<listitem>
<para>
Which this new stack,
<function>ntdll.LdrInitializeThunk</function> is called which
performs the remaining initialization parts, including resolving
all the DLL imports on the PE module, and doing the init of the
TLS slots.
</para>
</listitem>
<listitem>
<para>
Control can now be passed to the <function>EntryPoint</function>
of the PE module, which will let the executable run.
</para>
</listitem>
</itemizedlist>
</para>
</sect2>
<sect2>
<title>Creating a child process from a running process</title>
<para>
The steps used are closely link to what is done in the previous case.
</para>
<para>
There are however a few points to look at a bit more closely. The
inner implementation creates the child process using the
<function>fork()</function> and <function>exec()</function>
calls. This means that we don't need to check again for the threading
model, we can use what the parent (or the grand-parent process...)
started from command line has found.
</para>
<para>
The Win32 process creation allows to pass a lot of information between
the parent and the child. This includes object handles, windows title,
console parameters, environment strings... Wine makes use of both the
standard Unix inheritance mechanisms (for environment for example) and
the Wine server (to pass from parent to child a chunk of data
containing the relevant information).
</para>
<para>
The previously described loading mechanism will check in the Wine
server if such a chunk exists, and, if so, will perform the relevant
initialization.
</para>
<para>
Some further synchronization is also put in place: a parent will wait
until the child has started, or has failed. The Wine server is also
used to perform those tasks.
</para>
</sect2>
<sect2>
<title>Starting a Winelib process</title>
<para>
Before going into the gory details, let's first go back to what a
Winelib application is. It can be either a regular Unix executable, or
a more specific Wine beast. This later form in fact creates two files
for a given executable (say <filename>foo.exe</filename>). The first
one, named <filename>foo</filename> will be a symbolic link to the
Wine loader (<filename>wine</filename>). The second one, named
<filename>foo.exe.so</filename>, is the equivalent of the
<filename>.dll.so</filename> files we've already described for
DLLs. As in Windows, an executable is, among other things, a module
with its import and export information, as any DLL, it makes sense
Wine uses the same mechanisms for loading native executables and
DLLs.
</para>
<para>
When starting a Winelib application from the command line (say with
<command>foo arg1 arg2</command>), the Unix shell will execute
<command>foo</command> as a Unix executable. Since this is in fact the
Wine loader, Wine will fire up. However, will notice that it hasn't
been started as <command>wine</command> but as <command>foo</command>,
and hence, will try to load (using Unix shared library mechanism) the
second file <filename>foo.exe.so</filename>. Wine will recognize a 32
bit module (with its descriptor) embedded in the shared library, and
once the shared library loaded, it will proceed the same path as when
loading a standard native PE executable.
</para>
<para>
Wine needs to implement this second form of executable in order to
maintain the order of initialization of some elements in the
executable. One particular issue is when dealing with global C++
objects. In standard Unix executable, the call of the constructor to
such objects is stored in the specific section of the executable
(<function>.init</function> not to name it). All constructors in this
section are called before the <function>main()</function> or
<function>WinMain</function> function is called. Creating a Wine
executable using the first form mentionned above will let those
constructors being called before Wine gets a chance to initialize
itself. So, any constructor using a Windows API will fail, because
Wine infrastructure isn't in place. The use of the second form for
Winelib executables ensures that we do the initialization using the
following steps:
<itemizedlist>
<listitem>
<para>
initialize the Wine infrastructure
</para>
</listitem>
<listitem>
<para>
load the executable into memory
</para>
</listitem>
<listitem>
<para>
handle the import sections for the executable
</para>
</listitem>
<listitem>
<para>
call the global object constructors (if any). They now can
properly call the Windows APIs
</para>
</listitem>
<listitem>
<para>
call the executable entry point
</para>
</listitem>
</itemizedlist>
</para>
<para>
The attentive reader would have noted that the resolution of imports
for the executable is done, as for a DLL, when the executable/DLL
descriptor is registered. However, this is done also by adding a
specific constructor in the <function>.init</function> section. For
the above describe scheme to function properly, this constructor must
be the first constructor to be called, before all the other
constructors, generated by the executable itself. The Wine build chain
takes care of that, and also generating the executable/DLL descriptor
for the Winelib executable.
</para>
</sect2>
</sect1>
<sect1 id="threading">
<title>Multi-threading in Wine</title>
<para>
This section will assume you understand the basics of multithreading. If
not there are plenty of good tutorials available on the net to get you
started.
</para>
<para>
Threading in Wine is somewhat complex due to several factors. The first
is the advanced level of multithreading support provided by Windows -
there are far more threading related constructs available in Win32 than
the Linux equivalent (pthreads). The second is the need to be able to
map Win32 threads to native Linux threads which provides us with
benefits like having the kernel schedule them without our
intervention. While it's possible to implement threading entirely
without kernel support, doing so is not desirable on most platforms that
Wine runs on.
</para>
<sect2>
<title>Threading support in Win32</title>
<para>
Win32 is an unusually thread friendly API. Not only is it entirely
thread safe, but it provides many different facilities for working
with threads. These range from the basics such as starting and
stopping threads, to the extremely complex such as injecting threads
into other processes and COM inter-thread marshalling.
</para>
<para>
One of the primary challenges of writing Wine code therefore is
ensuring that all our DLLs are thread safe, free of race conditions
and so on. This isn't simple - don't be afraid to ask if you aren't
sure whether a piece of code is thread safe or not!
</para>
<para>
Win32 provides many different ways you can make your code thread safe
however the most common are <emphasis>critical section</emphasis> and
the <emphasis>interlocked functions</emphasis>. Critical sections are
a type of mutex designed to protect a geographic area of code. If you
don't want multiple threads running in a piece of code at once, you
can protect them with calls to
<function>EnterCriticalSection()</function> and
<function>LeaveCriticalSection()</function>. The first call to
<function>EnterCriticalSection()</function> by a thread will lock the
section and continue without stopping. If another thread calls it then
it will block until the original thread calls
<function>LeaveCriticalSection()</function> again.
</para>
<para>
It is therefore vitally important that if you use critical sections to
make some code thread-safe, that you check every possible codepath out
of the code to ensure that any held sections are left. Code like this:
</para>
<programlisting>
if (res != ERROR_SUCCESS) return res;
</programlisting>
<para>
is extremely suspect in a function that also contains a call to
<function>EnterCriticalSection()</function>. Be careful.
</para>
<para>
If a thread blocks while waiting for another thread to leave a
critical section, you will see an error from the
<function>RtlpWaitForCriticalSection()</function> function, along with
a note of which thread is holding the lock. This only appears after a
certain timeout, normally a few seconds. It's possible the thread
holding the lock is just being really slow which is why Wine won't
terminate the app like a non-checked build of Windows would, but the
most common cause is that for some reason a thread forgot to call
<function>LeaveCriticalSection()</function>, or died while holding the
lock (perhaps because it was in turn waiting for another lock). This
doesn't just happen in Wine code: a deadlock while waiting for a
critical section could be due to a bug in the app triggered by a
slight difference in the emulation.
</para>
<para>
Another popular mechanism available is the use of functions like
<function>InterlockedIncrement()</function>
and <function>InterlockedExchange()</function>. These make use of native
CPU abilities to execute a single instruction while ensuring any other
processors on the system cannot access memory, and allow you to do
common operations like add/remove/check a variable in thread-safe code
without holding a mutex. These are useful for reference counting
especially in free-threaded (thread safe) COM objects.
</para>
<para>
Finally, the usage of TLS slots are also popular. TLS stands for
thread-local storage, and is a set of slots scoped local to a thread
which you can store pointers in. Look on MSDN for the
<function>TlsAlloc()</function> function to learn more about the Win32
implementation of this. Essentially, the contents of a given slot will
be different in each thread, so you can use this to store data that is
only meaningful in the context of a single thread. On recent versions
of Linux the __thread keyword provides a convenient interface to this
functionality - a more portable API is exposed in the pthread
library. However, these facilities are not used by Wine, rather, we
implement Win32 TLS entirely ourselves.
</para>
</sect2>
<sect2>
<title>POSIX threading vs. kernel threading</title>
<para>
Wine runs in one of two modes: either pthreads (posix threading) or
kthreads (kernel threading). This section explains the differences
between them. The one that is used is automatically selected on
startup by a small test program which then execs the correct binary,
either <command>wine-kthread</command> or
<command>wine-pthread</command>. On NPTL-enabled systems pthreads
will be used, and on older non-NPTL systems kthreads is selected.
</para>
<para>
Let's start with a bit of history. Back in the dark ages when Wine's
threading support was first implemented a problem was faced - Windows
had much more capable threading APIs than Linux did. This presented a
problem - Wine works either by reimplementing an API entirely or by
mapping it onto the underlying systems equivalent. How could Win32
threading be implemented using a library which did not have all the
needed features? The answer, of course, was that it couldn't be.
</para>
<para>
On Linux the pthreads interface is used to start, stop and control
threads. The pthreads library in turn is based on top of so-called
"kernel threads" which are created using the
<function>clone(2)</function> syscall. Pthreads provides a nicer (more
portable) interface to this functionality and also provides APIs for
controlling mutexes. There is a <ulink
url="http://www.llnl.gov/computing/tutorials/pthreads/"> good
tutorial on pthreads</ulink> available if you want to learn more.
</para>
<para>
As pthreads did not provide the necessary semantics to implement Win32
threading, the decision was made to implement Win32 threading on top
of the underlying kernel threads by using syscalls like
<function>clone()</function> directly. This provided maximum
flexibility and allowed a correct implementation but caused some bad
side effects. Most notably, all the userland Linux APIs assumed that
the user was utilising the pthreads library. Some only enabled thread
safety when they detected that pthreads was in use - this is true of
glibc, for instance. Worse, pthreads and pure kernel threads had
strange interactions when run in the same process yet some libraries
used by Wine used pthreads internally. Throw in source code porting
using Winelib - where you have both UNIX and Win32 code in the same
process - and chaos was the result.
</para>
<para>
The solution was simple yet ingenious: Wine would provide its own
implementation of the pthread library <emphasis>inside</emphasis> its
own binary. Due to the semantics of ELF symbol scoping, this would
cause Wine's own implementation to override any implementation loaded
later on (like the real libpthread.so). Therefore, any calls to the
pthread APIs in external libraries would be linked to Wine's instead
of the system's pthreads library, and Wine implemented pthreads by
using the standard Windows threading APIs it in turn implemented
itself.
</para>
<para>
As a result, libraries that only became thread-safe in the presence of
a loaded pthreads implementation would now do so, and any external
code that used pthreads would actually end up creating Win32 threads
that Wine was aware of and controlled. This worked quite nicely for a
long time, even though it required doing some extremely un-kosher
things like overriding internal libc structures and functions. That
is, it worked until NPTL was developed at which point the underlying
thread implementation on Linux changed dramatically.
</para>
<para>
The fake pthread implementation can be found in
<filename>loader/kthread.c</filename>, which is used to
produce the <command>wine-kthread</command> binary. In contrast,
<filename>loader/pthread.c</filename> produces the
<command>wine-pthread</command> binary which is used on newer NPTL
systems.
</para>
<para>
NPTL is a new threading subsystem for Linux that hugely improves its
performance and flexibility. By allowing threads to become much more
scalable and adding new pthread APIs, NPTL made Linux competitive with
Windows in the multi-threaded world. Unfortunately it also broke many
assumptions made by Wine (as well as other applications such as the
Sun JVM and RealPlayer) in the process.
</para>
<para>
There was, however, some good news. NPTL made Linux threading powerful
enough that Win32 threads could now be implemented on top of pthreads
like any other normal application. There would no longer be problems
with mixing win32-kthreads and pthreads created by external libraries,
and no need to override glibc internals. As you can see from the
relative sizes of the <filename>loader/kthread.c</filename> and
<filename>loader/pthread.c</filename> files, the difference in code
complexity is considerable. NPTL also made several other semantic
changes to things such as signal delivery so changes were required in
many different places in Wine.
</para>
<para>
On non-Linux systems the threading interface is typically not powerful
enough to replicate the semantics Win32 applications expect and so
kthreads with the pthread overrides are used.
</para>
</sect2>
<sect2>
<title>The Win32 thread environment</title>
<para>
All Win32 code, whether from a native EXE/DLL or in Wine itself,
expects certain constructs to be present in its environment. This
section explores what those constructs are and how Wine sets them
up. The lack of this environment is one thing that makes it hard to
use Wine code directly from standard Linux applications - in order to
interact with Win32 code a thread must first be
"adopted" by Wine.
</para>
<para>
The first thing Win32 code requires is the
<emphasis>TEB</emphasis> or "Thread Environment Block". This is an
internal (undocumented) Windows structure associated with every thread
which stores a variety of things such as TLS slots, a pointer to the
threads message queue, the last error code and so on. You can see the
definition of the TEB in <filename>include/thread.h</filename>, or at
least what we know of it so far. Being internal and subject to change,
the layout of the TEB has had to be reverse engineered from scratch.
</para>
<para>
A pointer to the TEB is stored in the %fs register and can be accessed
using <function>NtCurrentTeb()</function> from within Wine code. %fs
actually stores a selector, and setting it therefore requires
modifying the processes local descriptor table (LDT) - the code to do
this is in <filename>lib/wine/ldt.c</filename>.
</para>
<para>
The TEB is required by nearly all Win32 code run in the Wine
environment, as any <command>wineserver</command> RPC will use it,
which in turn implies that any code which could possibly block for
instance by using a critical section) needs it. The TEB also holds the
SEH exception handler chain as the first element, so if disassembling
you see code like this:
</para>
<programlisting>movl %esp, %fs:0</programlisting>
<para>
... then you are seeing the program set up an SEH handler frame. All
threads must have at least one SEH entry, which normally points to the
backstop handler which is ultimately responsible for popping up the
all-too-familiar This program has performed an illegal operation and
will be terminated" message. On Wine we just drop straight into the
debugger. A full description of SEH is out of the scope of this
section, however there are some good articles in MSJ if you are
interested.
</para>
<para>
All Win32-aware threads must have a <command>wineserver</command>
connection. Many different APIs require the ability to communicate
with the <command>wineserver</command>. In turn, the
<command>wineserver</command> must be aware of Win32 threads in order
to be able to accurately report information to other parts of the
program and do things like route inter-thread messages, dispatch APCs
(asynchronous procedure calls) and so on. Therefore a part of thread
initialization is initializing the thread server-side. The result is
not only correct information in the server, but a set of file
descriptors the thread can use to communicate with the server - the
request fd, reply fd and wait fd (used for blocking).
</para>
</sect2>
</sect1>
<sect1 id="seh">
<title>Structured Exception Handling</title>
<para>
Structured Exception Handling (or SEH) is an implementation of
exceptions inside the Windows core. It allows code written in different
languages to throw exceptions across DLL boundaries, and Windows reports
various errors like access violations by throwing them. This section
looks at how it works, and how it's implemented in Wine.
</para>
<sect2>
<title>How SEH works</title>
<para>
SEH is based on embedding
<structname>EXCEPTION_REGISTRATION_RECORD</structname> structures in
the stack. Together they form a linked list rooted at offset zero in
the TEB (see the threading section if you don't know what this is). A
registration record points to a handler function, and when an
exception is thrown the handlers are executed in turn. Each handler
returns a code, and they can elect to either continue through the
handler chain or it can handle the exception and then restart the
program. This is referred to as unwinding the stack. After each
handler is called it's popped off the chain.
</para>
<para>
Before the system begins unwinding the stack, it runs vectored
handlers. This is an extension to SEH available in Windows XP, and
allows registered functions to get a first chance to watch or deal
with any exceptions thrown in the entire program, from any thread.
</para>
<para>
A thrown exception is represented by an
<structname>EXCEPTION_RECORD</structname> structure. It consists of a
code, flags, an address and an arbitrary number of <type>DWORD</type>
parameters. Language runtimes can use these parameters to associate
language-specific information with the exception.
</para>
<para>
Exceptions can be triggered by many things. They can be thrown
explicitly by using the RaiseException API, or they can be triggered
by a crash (ie, translated from a signal). They may be used internally
by a language runtime to implement language-specific exceptions. They
can also be thrown across DCOM connections.
</para>
<para>
Visual C++ has various extensions to SEH which it uses to implement,
eg, object destruction on stack unwind as well as the ability to throw
arbitrary types. The code for this is in
<filename>dlls/msvcrt/except.c</filename>
</para>
</sect2>
<sect2>
<title>Translating signals to exceptions</title>
<para>
In Windows, compilers are expected to use the system exception
interface, and the kernel itself uses the same interface to
dynamically insert exceptions into a running program. By contrast on
Linux the exception ABI is implemented at the compiler level
(inside GCC and the linker) and the kernel tells a thread of
exceptional events by sending <emphasis>signals</emphasis>. The
language runtime may or may not translate these signals into native
exceptions, but whatever happens the kernel does not care.
</para>
<para>
You may think that if an app crashes, it's game over and it really
shouldn't matter how Wine handles this. It's what you might
intuitively guess, but you'd be wrong. In fact some Windows programs
expect to be able to crash themselves and recover later without the
user noticing, some contain buggy binary-only components from third
parties and use SEH to swallow crashes, and still others execute
priviledged (kernel-level) instructions and expect it to work. In
fact, at least one set of APIs (the <function>IsBad*Ptr()</function>
series) can only be implemented by performing an operation that may
crash and returning <constant>TRUE</constant> if it does, and
<constant>FALSE</constant> if it doesn't! So, Wine needs to not only
implement the SEH infrastructure but also translate Unix signals into
SEH exceptions.
</para>
<para>
The code to translate signals into exceptions is a part of
<filename>NTDLL</filename>, and can be found in
<filename>dlls/ntdll/signal_i386.c</filename>. This file sets up
handlers for various signals during Wine startup, and for the ones
that indicate exceptional conditions translates them into
exceptions. Some signals are used by Wine internally and have nothing
to do with SEH.
</para>
<para>
Signal handlers in Wine run on their own stack. Each thread has its
own signal stack which resides 4k after the TEB. This is important for
a couple of reasons. Firstly, because there's no guarantee that the
app thread which triggered the signal has enough stack space for the
Wine signal handling code. In Windows, if a thread hits the limits of
its stack it triggers a fault on the stack guard page. The language
runtime can use this to grow the stack if it wants to.
<!-- fixme: is it really the language runtime that does this? i
can't find any code in Wine to reallocate the stack on
STATUS_GUARD_PAGE_VIOLATION -->
However, because a guard page violation is just a regular segfault to
the kernel, that would lead to a nested signal handler and that gets
messy really quick so we disallow that in Wine. Secondly, setting up
the exception to throw requires modifying the stack of the thread
which triggered it, which is quite hard to do when you're still
running on it.
</para>
<para>
Windows exceptions typically contain more information than the Unix
standard APIs provide. For instance, a
<constant>STATUS_ACCESS_VIOLATION</constant> exception
(<constant>0xC0000005</constant>) structure contains the faulting
address, whereas a standard Unix <constant>SIGSEGV</constant> just
tells the app that it crashed. Usually this information is passed as
an extra parameter to the signal handler, however its location and
contents vary between kernels (BSD, Solaris, etc). This data is
provided in a <structname>SIGCONTEXT</structname> structure, and on
entry to the signal handler it contains the register state of the CPU
before the signal was sent. Modifying it will cause the kernel to
adjust the context before restarting the thread.
</para>
</sect2>
</sect1>
<sect1>
<title>File management</title>
<para>
With time, Windows API comes closer to the old Unix paradigm "Everything
is a file". Therefore, this whole section dedicated to file management
will cover firstly the file management, but also some other objects like
directories, and even devices, which are manipulated in Windows in a
rather coherent way. We'll see later on some other objects fitting
(more or less) in this picture (pipes or consoles to name a few).
</para>
<para>
First of all, Wine, while implementing the file interface from Windows,
needs to maps a file name (expressed in the Windows world) onto a file
name in the Unix world. This encompasses several aspects: how to map
the file names, how to map access rights (both on files and
directories), how to map physical devices (hardisks, but also other
devices - like serial or parallel interfaces - and even VxDs).
</para>
<sect2>
<title>Various Windows formats for file names</title>
<para>
Let's first review a bit the various forms Windows uses when it comes
to file names.
</para>
<sect3>
<title>The DOS inheritance</title>
<para>
At the beginning was DOS, where each file has to sit on a drive,
called from a single letter. For separating device names from
directory or file names, a ':' was appended to this single letter,
hence giving the (in)-famous <filename>C:</filename> drive
designations. Another great invention was to use some fixed names
for accessing devices: not only where these named fixed, in a way
you couldn't change the name if you'd wish to, but also, they were
insensible to the location where you were using them. For example,
it's well known that <filename>COM1</filename> designates the first
serial port, but it's also true that
<filename>c:\foo\bar\com1</filename> also designates the first
serial port. It's still true today: on XP, you still cannot name a
file <filename>COM1</filename>, whatever the directory!!!
</para>
<para>
Well later on (with Windows 95), Microsoft decided to overcome some
little details in file names: this included being able to get out of
the 8+3 format (8 letters for the name, 3 letters for the
extension), and so being able to use "long names" (that's the
"official" naming; as you can guess, the 8+3 format is a short
name), and also to use very strange characters in a file name (like
a space, or even a '.'). You could then name a file
<filename>My File V0.1.txt</filename>, instead of
<filename>myfile01.txt</filename>. Just to keep on the fun side of
things, for many years the format used on the disk itself for
storing the names has been the short name as the real one and to use
some tricky aliasing techniques to store the long name. When some
newer disk file systems have been introduced (NTFS with NT), in
replacement of the old FAT system (which had little evolved since
the first days of DOS), the long name became the real name while the
short name took the alias role.
</para>
<para>
Windows also started to support mounting network shares, and see
them as they were a local disk (through a specific drive letter).
The way it has been done changed along the years, so we won't go
into all the details (especially on the DOS and Win9x side).
</para>
</sect3>
<sect3>
<title>The NT way</title>
<para>
The introduction of NT allowed a deep change in the ways DOS had
been handling devices:
<itemizedlist>
<listitem>
<para>
There's no longer a forest of DOS drive letters (even if the
<command>assign</command> was a way to create symbolic links
in the forest), but a single hierarchical space.
</para>
</listitem>
<listitem>
<para>
This hierarchy includes several distinct elements. For
example, <filename>\Device\Hardisk0\Partition0</filename>
refers to the first partition on the first physical hard disk
of the system.
</para>
</listitem>
<listitem>
<para>
This hierarchy covers way more than just the files and drives
related objects, but most of the objects in the system. We'll
only cover here the file related part.
</para>
</listitem>
<listitem>
<para>
This hierarchy is not directly accessible for the Win32 API,
but only the <filename>NTDLL</filename> API. The Win32 API
only allows to manipulate part of this hierarchy (the rest
being hidden from the Win32 API). Of course, the part you see
from Win32 API looks very similar to the one that DOS
provided.
</para>
</listitem>
<listitem>
<para>
Mounting a disk is performed by creating a symbol link in this
hierarchy from <filename>\Global??\C:</filename> (the name
seen from the Win32 API) to
<filename>\Device\Harddiskvolume1</filename> which determines
the partition on a physical disk where C: is going to be seen.
</para>
</listitem>
<listitem>
<para>
Network shares are also accessible through a symbol link.
However in this case, a symbol link is created from
<filename>\Global??\UNC\host\share\</filename> for the share
<filename>share</filename> on the machine
<filename>host</filename>) to what's called a network
redirector, and which will take care of 1/ the connection to
the remote share, 2/ handling with that remote share the rest
of the path (after the name of the server, and the name of the
share on that server).
</para>
<note>
<para>
In NT naming convention, <filename>\Global??</filename> can
also be called <filename>\??</filename> to shorten the
access.
</para>
</note>
</listitem>
</itemizedlist>
</para>
<para>
All of these things, make the NT system pretty much more flexible
(you can add new types of filesystems if you want), you provide a
unique name space for all objects, and most operations boil down to
creating relationship between different objects.
</para>
</sect3>
<sect3>
<title>Wrap up</title>
<para>
Let's end this chapter about files in Windows with a review of the
different formats used for file names:
<itemizedlist>
<listitem>
<para><filename>c:\foo\bar</filename> is a full path.</para>
</listitem>
<listitem>
<para>
<filename>\foo\bar</filename> is an absolute path; the full
path is created by appending the default drive (ie. the drive
of the current directory).
</para>
</listitem>
<listitem>
<para>
<filename>bar</filename> is a relative path; the full path is
created by adding the current directory.
</para>
</listitem>
<listitem>
<para>
<filename>c:bar</filename> is a drive relative path. Note
that the case where <filename>c:</filename> is the drive of
the current directory is rather easy; it's implemented the
same way as the case just below (relative path). In the rest
of this chapter, drive relative path will only cover the case
where the drive in the path isn't the drive of the default
directory. The resolution of this to a full pathname defers
according to the version of Windows, and some parameters.
Let's take some time browsing through these issues. On
Windows 9x (as well as on DOS), the system maintains a process
wide set of default directories per drive. Hence, in this
case, it will resolve <filename>c:bar</filename> to the
default directory on drive <filename>c:</filename> plus file
<filename>bar</filename>. Of course, the default per drive
directory is updated each time a new current directory is set
(only the current directory of the drive specified is
modified). On Windows NT, things differ a bit. Since NT
implements a namespace for file closer to a single tree
(instead of 26 drives), having a current directory per drive
is a bit ackward. Hence, Windows NT default behavior is to
have only one current directory across all drives (in fact, a
current directory expressed in the global tree) - this
directory is of course related to a given process -,
<filename>c:bar</filename> is resolved this way:
<itemizedlist>
<listitem>
<para>
If <filename>c:</filename> is the drive of the default
directory, the final path is the current directory plus
<filename>bar</filename>.
</para>
</listitem>
<listitem>
<para>
Otherwise it's resolved into
<filename>c:\bar</filename>.
</para>
</listitem>
<listitem>
<para>
In order to bridge the gap between the two
implementations (Windows 9x and NT), NT adds a bit of
complexity on the second case. If the
<envar>=C:</envar> environment variable is defined, then
it's value is used as a default directory for drive
<filename>C:</filename>. This is handy, for example,
when writing a DOS shell, where having a current drive
per drive is still implemented, even on NT. This
mechanism (through environment variables) is implemented
on <command>CMD.EXE</command>, where those variables are
set when you change directories with the
<command>cd</command>. Since environment variables are
inherited at process creation, the current directories
settings are inherited by child processes, hence
mimicing the behavior of the old DOS shell. There's no
mechanism (in <filename>NTDLL</filename> or
<filename>KERNEL32</filename>) to set up, when current
directory changes, the relevant environment variables.
This behavior is clearly band-aid, not a full featured
extension of current directory behavior.
</para>
</listitem>
</itemizedlist>
Wine fully implements all those behaviors (the Windows 9x vs
NT ones are triggered by the version flag in Wine).
</para>
</listitem>
<listitem>
<para>
<filename>\\host\share</filename> is <firstterm>UNC</firstterm>
(Universal Naming Convention) path, ie. represents a file on a
remote share.
</para>
</listitem>
<listitem>
<para>
<filename>\\.\device</filename> denotes a physical device
installed in the system (as seen from the Win32 subsystem). A
standard NT system will map it to the
<filename>\??\device</filename> NT path. Then, as a standard
configuration, <filename>\??\device</filename> is likely to be
a link to in a physical device described and hooked into the
<filename>\Device\</filename> tree. For example,
<filename>COM1</filename> is a link to
<filename>\Device\Serial0</filename>.
</para>
</listitem>
<listitem>
<para>
On some versions of Windows, paths were limited to
<constant>MAX_PATH</constant> characters. To circumvent this,
Microsoft allowed paths to be <constant>32,767</constant>
characters long, under the conditions that the path is
expressed in Unicode (no Ansi version), and that the path is
prefixed with <filename>\\?\</filename>. This convention is
applicable to any of the cases described above.
</para>
</listitem>
</itemizedlist>
</para>
<para>
To summarize, what we've discussed so, let's put everything into a
single table...
<table>
<title>DOS, Win32 and NT paths equivalences</title>
<tgroup cols="3" align="left">
<thead>
<row>
<entry>Type of path</entry>
<entry>Win32 example</entry>
<entry>NT equivalent</entry>
<entry>Rule to construct</entry>
</row>
</thead>
<tbody>
<row>
<entry>Full path</entry>
<entry><filename>c:\foo\bar.txt</filename></entry>
<entry><filename>\Global??\C:\foo\bar.txt</filename></entry>
<entry>Simple concatenation</entry>
</row>
<row>
<entry>Absolute path</entry>
<entry><filename>\foo\bar.txt</filename></entry>
<entry><filename>\Global??\J:\foo\bar.txt</filename></entry>
<entry>
Simple concatenation using the drive of the default
directory (here J:)
</entry>
</row>
<row>
<entry>Relative path</entry>
<entry><filename>gee\bar.txt</filename></entry>
<entry>
<filename>
\Global??\J:\mydir\mysubdir\gee\bar.txt
</filename>
</entry>
<entry>
Simple concatenation using the default directory
(here <filename>J:\mydir\mysubdir</filename>)
</entry>
</row>
<row>
<entry>Drive relative path</entry>
<entry><filename>j:gee\bar.txt</filename></entry>
<entry>
<msgtext>
<para>
<itemizedlist>
<listitem>
<para>
On Windows 9x (and DOS),
<filename>J:\toto\gee\bar.txt</filename>.
</para>
</listitem>
<listitem>
<para>
On Windows NT,
<filename>J:\gee\bar.txt</filename>.
</para>
</listitem>
<listitem>
<para>
On Windows NT,
<filename>J:\tata\titi\bar.txt</filename>.
</para>
</listitem>
</itemizedlist>
</para>
</msgtext>
</entry>
<entry>
<msgtext>
<para>
<itemizedlist>
<listitem>
<para>
On Windows NT (and DOS),
<filename>\toto</filename> is the default
directory on drive <filename>J:</filename>.
</para>
</listitem>
<listitem>
<para>
On Windows NT, if <envar>=J:</envar> isn't set.
</para>
</listitem>
<listitem>
<para>
On Windows NT, if <envar>=J:</envar> is set to
<filename>J:\tata\titi</filename>.
</para>
</listitem>
</itemizedlist>
</para>
</msgtext>
</entry>
</row>
<row>
<entry>UNC (Uniform Naming Convention) path</entry>
<entry><filename>\\host\share\foo\bar.txt</filename></entry>
<entry>
<filename>\Global??\UNC\host\share\foo\bar.txt</filename>
</entry>
<entry>
Simple concatenation.
</entry>
</row>
<row>
<entry>Device path</entry>
<entry><filename>\\.\device</filename></entry>
<entry><filename>\Global??\device</filename></entry>
<entry>Simple concatenation</entry>
</row>
<row>
<entry>Long paths</entry>
<entry><filename>\\?\...</filename></entry>
<entry></entry>
<entry>
With this prefix, paths can take up to
<constant>32,767</constant> characters, instead of
<constant>MAX_PATH</constant> for all the others). Once
the prefix stripped, to be handled like one of the
previous ones, just providing internal buffers large
enough).
</entry>
</row>
</tbody>
</tgroup>
</table>
</para>
</sect3>
</sect2>
<sect2>
<title>Wine implementation</title>
<para>
We'll mainly cover in this section the way Wine opens a file (in the
Unix sense) when given a Windows file name. This will include mapping
the Windows path onto a Unix path (including the devices case),
handling the access rights, the sharing attribute if any...
</para>
<sect3>
<title>Mapping a Windows path into an absolute Windows path</title>
<para>
First of all, we described in previous section the way to convert
any path in an absolute path. Wine implements all the previous algorithms
in order to achieve this. Note also, that this transformation is
done with information local to the process (default directory,
environment variables...). We'll assume in the rest of this section
that all paths have now been transformed into absolute from.
</para>
</sect3>
<sect3>
<title>Mapping a Windows (absolute) path onto a Unix path</title>
<para>
When Wine is requested to map a path name (in DOS form, with a drive
letter, e.g. <filename>c:\foo\bar\myfile.txt</filename>), Wine
converts this into the following Unix path
<filename>$(WINEPREFIX)/dosdevices/c:/foo/bar/myfile.txt</filename>.
The Wine configuration process is responsible for setting
<filename>$(WINEPREFIX)/dosdevices/c:</filename> to be a symbolic
link pointing to the directory in Unix hierarchy the user wants to
expose as the <filename>C:</filename> drive in the DOS forest of
drives.
</para>
<para>
This scheme allows:
<itemizedlist>
<listitem>
<para>
a very simple algorithm to map a DOS path name into a Unix one
(no need of Wine server calls)
</para>
</listitem>
<listitem>
<para>
a very configurable implementation: it's very easy to change a
drive mapping
</para>
</listitem>
<listitem>
<para>
a rather readable configuration: no need of sophisticated
tools to read a drive mapping, a <command>ls -l
$(WINEPREFIX)/dosdevices</command>
says it all.
</para>
</listitem>
</itemizedlist>
</para>
<para>
This scheme is also used to implement UNC path names. For example,
Wine maps <filename>\\host\share\foo\bar\MyRemoteFile.txt</filename>
into
<filename>$(WINEPREFIX)/dosdevices/unc/host/share/foo/bar/MyRemoteFile.txt</filename>.
It's then up to the user to decide where
<filename>$(WINEPREFIX)/dosdevices/unc/host/share</filename> shall
point to (or be). For example, it can either be a symbolic link to a
directory inside the local machine (just for emulation purpose), or
a symbolic link to the mount point of a remote disk (done through
Samba or NFS), or even the real mount point. Wine will not do any
checking here, nor will help in actually mounting the remote drive.
</para>
<para>
We've seen how Wine maps a drive letter or a UNC path onto the Unix
hierarchy, we now have to look on a the filename is searched within
this hierarchy. The main issue is about case sensivity. Here's a
reminder of the various properties for the file systems in the
field.
<table>
<title>File systems' properties</title>
<tgroup cols="4" align="left">
<thead>
<row>
<entry>FS Name</entry>
<entry>Length of elements</entry>
<entry>Case sensitivity (on disk)</entry>
<entry>Case sensitivity for lookup</entry>
</row>
</thead>
<tbody>
<row>
<entry>FAT, FAT16 or FAT32</entry>
<entry>Short name (8+3)</entry>
<entry>Names are always stored in upper-case</entry>
<entry>Case insensitive</entry>
</row>
<row>
<entry>VFAT</entry>
<entry>Short name (8+3) + alias on long name</entry>
<entry>
Short names are always stored in upper-case. Long names
are stored with case preservation.
</entry>
<entry>Case insensitive</entry>
</row>
<row>
<entry>NTFS</entry>
<entry>Long name + alias on short name (8+3).</entry>
<entry>
Long names are stored with case preservation. Short names
are always stored in upper-case.
</entry>
<entry>Case insentivite</entry>
</row>
<row>
<entry>Linux FS (ext2fs, ext3fs, reiserfs...)</entry>
<entry>Long name</entry>
<entry>Case preserving</entry>
<entry>Case sensitive</entry>
</row>
</tbody>
</tgroup>
</table>
</para>
<para>
<note>
<title>Case sensitivity vs. preservation</title>
<para>
When we say that most systems in NT are case insensitive, this
has to be understood for looking up for a file, where the
matches are made in a case insensitive mode. This is different
from VFAT or NTFS "case preservation" mechanism, which stores
the file names as they are given when creating the file, while
doing case insensitive matches.
</para>
</note>
Since most file systems used in NT are case insensitive and since
most Unix file systems are case sensitive, Wine undergo a case
insensitive search when it has found the Unix path is has to look
for. This means, for example, that for opening the
<filename>$(WINEPREFIX)/dosdevices/c:/foo/bar/myfile.txt</filename>,
Wine will recursively open all directories in the path, and check,
in this order, for the existence of the directory entry in the form
given in the file name (ie. case sensitive), and if it's not found,
in a case insensitive form. This allows to also pass, in most Win32
file API also a Unix path (instead of a DOS or NT path), but we'll
come back to this later. This also means that the algorithm
described doesn't correctly handle the case of two files in the same
directory, which names only differ on the case of the letters. This
means, that if, in the same directory, two files (which names match
in a case sensitive comparison), Wine will pick-up the right one if
the filename given matches on of the name (in a case sensitive way),
but will pickup one of the two (without defining the one it's going
to pickup) if the filename given matches none of the two names in a
case sensitive way (but in a case insensitive way). For example, if
the two filenames are <filename>my_neat_file.txt</filename> and
<filename>My_Neat_File.txt</filename>, Wine's behavior when opening
<filename>MY_neat_FILE.txt</filename> is undefined.
</para>
<para>
As Windows, at the early days, didn't support the notion of symbolic
links on directories, lots of applications (and some old native
DLLs) are not ready for this feature. Mainly, they imply that the
directory structure is a tree, which has lots of consequences on
navigating in the forest of directories (ie: there cannot be two
ways for going from directory to another, there cannot be
cycles...). In order to prevent some bad behavior for such
applications, Wine sets up an option. By default, symbolic links on
directories are not followed by Wine. There's an options to follow
them (see the Wine User Guide), but this could be harmful.
</para>
<para>
Wine considers that Unix file names <emphasis>are</emphasis> long
filename. This seems a reasonable approach; this is also the
approach followed by most of the Unix OSes while mounting Windows
partitions (with filesystems like FAT, FAT32 or NTFS). Therefore,
Wine tries to support short names the best it can. Basically, they
are two options:
<itemizedlist>
<listitem>
<para>
The filesystem on which the inspected directory lies in a real
Windows FS (like FAT, or FAT32, or NTFS) and the OS has
support to access the short filename (for example, Linux does
this on FAT, FAT32 or VFAT). In this case, Wine makes full use
of this information and really mimics the Windows behavior:
the short filename used for any file is the same than on
Windows.
</para>
</listitem>
<listitem>
<para>
If conditions listed above are not met (either, FS has no
physical short name support, or OS doesn't provide the access
access to the short name), Wine decides and computes on its
own the short filename for a given long filename. We cannot
ensure that the generated short name is the same than on
Windows (because the algorithm on Windows takes into account
the order of creation of files, which cannot be implemented in
Wine: Wine would have to cache the short names of every
directory it uses!). The short name is made up of part of the
long name (first characters) and the rest with a hashed
value. This has several advantages:
<itemizedlist>
<listitem>
<para>
The algorithm is rather simple and low cost.
</para>
</listitem>
<listitem>
<para>
The algorithm is stateless (doesn't depend of the other
files in the directory).
</para>
</listitem>
</itemizedlist>
But, it also has the drawbacks (of the advantages):
<itemizedlist>
<listitem>
<para>
The algorithm isn't the same as on Windows, which means
a program cannot use short names generated on
Windows. This could happen when copying an existing
installed program from Windows (for example, on a dual
boot machine).
</para>
</listitem>
<listitem>
<para>
Two long file names can end up with the same short name
(Windows handles the collision in this case, while Wine
doesn't). We rely on our hash algorithm to lower at most
this possibility (even if it exists).
</para>
</listitem>
</itemizedlist>
</para>
</listitem>
</itemizedlist>
</para>
<para>
Wine also allows in most file API to give as a parameter a full Unix
path name. This is handy when running a Wine (or Winelib) program
from the command line, and one doesn't need to convert the path into
the Windows form. However, Wine checks that the Unix path given can
be accessed from one of the defined drives, insuring that only part
of the Unix <filename>/</filename> hierarchy can be accessed.
</para>
<para>
As a side note, as Unix doesn't widely provide a Unicode interface
to the filenames, and that Windows implements filenames as Unicode
strings (even on the physical layer with NTFS, the FATs variant are
ANSI), we need to properly map between the two. At startup, Wine
defines what's called the Unix Code Page, that's is the code page
the Unix kernel uses as a reference for the strings. Then Wine uses
this code page for all the mappings it has to do between a Unicode
path (on the Windows side) and a Ansi path to be used in a Unix path
API. Note, that this will work as long as a disk isn't mounted with
a different code page than the one the kernel uses as a default.
</para>
<para>
We describe below how Windows devices are mapped to Unix devices.
Before that, let's finish the pure file round-up with some basic
operations.
</para>
</sect3>
<sect3>
<title>Access rights and file attributes</title>
<para>
Now that we have looked how Wine converts a Windows pathname into a
Unix one, we need to cover the various meta-data attached to a file
or a directory.
</para>
<para>
In Windows, access rights are simplistic: a file can be read-only or
read-write. Wine sets the read-only flag if the file doesn't have
the Unix user-write flag set. As a matter of fact, there's no way
Wine can return that a file cannot be read (that doesn't exist under
Windows). The file will be seen, but trying to open it will return
an error. The Unix exec-flag is never reported. Wine doesn't use
this information to allow/forbid running a new process (as Unix does
with the exec-flag). Last but not least: hidden files. This exists
on Windows but not really on Unix! To be exact, in Windows, the
hidden flag is a metadata associated to any file or directoy; in
Unix, it's a convention based on the syntax of the file name
(whether it starts with a '.' or not). Wine implements two behaviors
(chosen by configuration). This impacts file names and directory
names starting by a '.'. In first mode
(<option>ShowDotFile</option> is <constant>FALSE</constant>), every
file or directory starting by '.' is returned with the hidden flag
turned on. This is the natural behavior on Unix (for
<command>ls</command> or even file explorer). In the second mode
(<option>ShowDotFile</option> is <constant>TRUE</constant>), Wine
never sets the hidden flag, hence every file will be seen.
</para>
<para>
Last but not least, before opening a file, Windows makes use of
sharing attributes in order to check whether the file can be opened;
for example, a process, being the first in the system to open a
given file, could forbid, while it maintains the file opened, that
another process opens it for write access, whereas open for read
access would be granted. This is fully supported in Wine by moving
all those checks in the Wine server for a global view on the system.
Note also that what's moved in the Wine server is the check, when
the file is opened, to implement the Windows sharing semantics.
Further operation on the file (like reading and writing) will not
require heavy support from the server.
</para>
<para>
The other good reason for putting the code for actually opening a
file in the server is that an opened files in Windows is managed
through a handle, and handles can only be created in Wine server!
</para>
<para>
Just a note about attributes on directories: while we can easily map
the meaning of Windows' <constant>FILE_ATTRIBUTE_READONLY</constant>
on a file, we cannot do it for a directory. Windows' semantic (when
this flag is set) means do not delete the directory, while the
<constant>w</constant> attribute in Unix means don't write nor
delete it. Therefore, Wine uses an asymetric mapping here: if the
directory (in Unix) isn't writable, then Wine reports the
<constant>FILE_ATTRIBUTE_READONLY</constant> attribute; on the other
way around, when asked to set a directory with
<constant>FILE_ATTRIBUTE_READONLY</constant> attribute, Wine simply
does nothing.
</para>
</sect3>
<sect3>
<title>Operations on file</title>
<sect4>
<title>Reading and writing</title>
<para>
Reading and writing are the basic operations on files. Wine of
course implements this, and bases the implementation on client
side calls to Unix equivalents (like <function>read()</function>
or <function>write()</function>). Note, that the Wine server is
involved in any read or write operation, as Wine needs to
transform the Windows-handle to the file into a Unix file
descriptor it can pass to any Unix file function.
</para>
</sect4>
<sect4>
<title>Getting a Unix fd</title>
<para>
This is major operation in any file related operation. Basically,
each file opened (at the Windows level), is first opened in the
Wine server, where the fd is stored. Then, Wine (on client side)
uses <function>recvmsg()</function> to pass the fd from the wine
server process to the client process. Since this operation could
be lengthy, Wine implement some kind of cache mechanism to send it
only once, but getting a fd from a handle on a file (or any other
Unix object which can be manipulated through a file descriptor)
still requires a round trip to the Wine server.
</para>
</sect4>
<sect4>
<title>Locking</title>
<para>
Windows provides file locking capabilities. When a lock is set
(and a lock can be set on any contiguous range in a file), it
controls how other processes in the system will have access to the
range in the file. Since locking range on a file are defined on a
system wide manner, its implementation resides in
<command>wineserver</command>. It tries to make use Unix file
locking (if the underlying OS and the mounted disk where the file
sits support this feature) with <function>fcntl()</function> and
the <constant>F_SETLK</constant> command. If this isn't
supported, then <command>wineserver</command> just pretends it
works.
</para>
</sect4>
<sect4>
<title>I/O control</title>
<para>
There's no need (so far) to implement support (for files and
directories) for <function>DeviceIoControl()</function>, even if
this is supported by Windows, but for very specific needs
(like compression management, or file system related information).
This isn't the case for devices (including disks), but we'll cover
this in the hereafter section related to devices.
</para>
</sect4>
<sect4>
<title>Buffering</title>
<para>
Wine doesn't do any buffering on file accesses but rely on the
underlying Unix kernel for that (when possible). This scheme is
needed because it's easier to implement multiple accesses on the
same file at the kernel level, rather than at Wine levels. Doing
lots of small reads on the same file can turn into a performance
hog, because each read operation needs a round trip to the server
in order to get a file descriptor (see above).
</para>
</sect4>
<sect4>
<title>Overlapped I/O</title>
<para>
Windows introduced the notion of overlapped I/O. Basically, it
just means that an I/O operation (think read / write to start
with) will not wait until it's completed, but rather return to the
caller as soon as possible, and let the caller handle the wait
operation and determine when the data is ready (for a read
operation) or has been sent (for a write operation). Note that the
overlapped operation is linked to a specific thread.
</para>
<para>
There are several interests to this: a server can handle several
clients without requiring multi-threading techniques; you can
handle an event driven model more easily (ie how to kill properly
a server while waiting in the lengthy <function>read()</function>
operation).
</para>
<para>
Note that Microsoft's support for this feature evolved along the
various versions of Windows. For example, Windows 95 or 98 only
supports overlapped I/O for serial and parallel ports, while NT
supports also files, disks, sockets, pipes, or mailslots.
</para>
<para>
Wine implements overlapped I/O operations. This is mainly done by
queueing in the server a request that will be triggered when
something the current state changes (like data available for a
read operation). This readiness is signaled to the calling
processing by queueing a specific APC, which will be called within
the next waiting operation the thread will have. This specific
APC will then do the hard work of the I/O operation. This scheme
allows to put in place a wait mechanism, to attach a routine to be
called (on the thread context) when the state changes, and to be
done is a rather transparent manner (embedded any the generic wait
operation). However, it isn't 100% perfect. As the heavy
operations are done in the context of the calling threads, if
those operations are lengthy, there will be an impact on the
calling thread, especially its latency. In order to provide an
effective support for this overlapped I/O operations, we would
need to rely on Unix kernel features (AIO is a good example).
</para>
</sect4>
</sect3>
<sect3>
<title>Devices & volume management</title>
<para>
We've covered so far the ways file names are mapped into Unix
paths. There's still need to cover it for devices. As a regular
file, devices are manipulated in Windows with both read / write
operations, but also control mechanisms (speed or parity of a serial
line; volume name of a hard disk...). Since, this is also supported
in Linux, there's also a need to open (in a Unix sense) a device
when given a Windows device name. This section applies to DOS device
names, which are seen in NT as nicknames to other devices.
</para>
<para>
Firstly, Wine implements the Win32 to NT mapping as described above,
hence every device path (in NT sense) is of the following form:
<filename>/??/devicename</filename> (or
<filename>/DosDevices/devicename</filename>). As Windows device
names are case insensitive, Wine also converts them to lower case
before any operation. Then, the first operation Wine tries is to
check whether
<filename>$(WINEPREFIX)/dosdevices/devicename</filename> exists. If
so, it's used as the final Unix path for the device. The
configuration process is in charge of creating for example, a
symbolic link between
<filename>$(WINEPREFIX)/dosdevices/PhysicalDrive0</filename> and
<filename>/dev/hda0</filename>. If such a link cannot be found, and
the device name looks like a DOS disk name (like
<filename>C:</filename>), Wine first tries to get the Unix device
from the path <filename>$(WINEPREFIX)/dosdevices/c:</filename>
(i.e. the device which is mounted on the target of the symbol link);
if this doesn't give a Unix device, Wine tries whether
<filename>$(WINEPREFIX)/dosdevices/c::</filename> exists. If so,
it's assumed to be a link to the actual Unix device. For example,
for a CD Rom, <filename>$(WINEPREFIX)/dosdevices/e::</filename>
would be a symbolic link to <filename>/dev/cdrom</filename>. If
this doesn't exist (we're still handling the a device name of the
<filename>C:</filename> form), Wine tries to get the Unix device
from the system information (<filename>/etc/mtab</filename> and
<filename>/etc/fstab</filename> on Linux). We cannot apply this
method in all the cases, because we have no insurance that the
directory can actually be found. One could have, for example, a CD
Rom which he/she want only to use as audio CD player (ie never
mounted), thus not having any information of the device itself. If
all of this doesn't work either, some basic operations are checked:
if the devicename is <filename>NUL</filename>, then
<filename>/dev/null</filename> is returned. If the device name is a
default serial name (<filename>COM1</filename> up to
<filename>COM9</filename>) (resp. printer name
<filename>LPT1</filename> up to <filename>LPT9</filename>), then
Wine tries to open the Nth serial (resp. printer) in the system.
Otherwise, some basic old DOS name support is done
<filename>AUX</filename> is transformed into
<filename>COM1</filename> and <filename>PRN</filename> into
<filename>LPT1</filename>), and the whole process is retried with
those new names.
</para>
<para>
To sum up:
<table>
<title>
Mapping of Windows device names into Unix device names
</title>
<tgroup cols="3" align="left">
<thead>
<row>
<entry>Windows device name</entry>
<entry>NT device name</entry>
<entry>Mapping to Unix device name</entry>
</row>
</thead>
<tbody>
<row>
<entry><filename>&lt;any_path&gt;AUX</filename></entry>
<entry<filename>>\Global??\AUX</filename></entry>
<entry>
Treated as an alias to <filename>COM1</filename>
</entry>
</row>
<row>
<entry><filename>&lt;any_path&gt;PRN</filename></entry>
<entry><filename>\Global??\PRN</filename></entry>
<entry>Treated as an alias to <filename>LPT1</filename></entry>
</row>
<row>
<entry><filename>&lt;any_path&gt;COM1</filename></entry>
<entry><filename>\Global??\COM1</filename></entry>
<entry>
<filename>$(WINEPREFIX)/dosdevices/com1</filename>
(if the symbol link exists) or the Nth serial
line in the system (on Linux,
<filename>/dev/ttyS0</filename>).
</entry>
</row>
<row>
<entry><filename>&lt;any_path&gt;LPT1</filename></entry>
<entry><filename>\Global??\LPT1</filename></entry>
<entry>
<filename>$(WINEPREFIX)/dosdevices/lpt1</filename>
(if the symbol link exists) or the Nth printer
in the system (on Linux,
<filename>/dev/lp0</filename>).
</entry>
</row>
<row>
<entry><filename>&lt;any_path&gt;NUL</filename></entry>
<entry><filename>\Global??\NUL</filename></entry>
<entry><filename>/dev/null</filename></entry>
</row>
<row>
<entry><filename>\\.\E:</filename></entry>
<entry><filename>\Global??\E:</filename></entry>
<entry>
<filename>$(WINEPREFIX)/dosdevices/e::</filename> (if the
symbolic link exists) or guessing the device from
<filename>/etc/mtab</filename> or
<filename>/etc/fstab</filename>.
</entry>
</row>
<row>
<entry><filename>\\.\&lt;device_name&gt;</filename></entry>
<entry>
<filename>\Global??\&lt;device_name&gt;</filename>
</entry>
<entry>
<filename>$(WINEPREFIX)/dosdevices/&lt;device_name&gt;</filename>
(if the symbol link exists).
</entry>
</row>
</tbody>
</tgroup>
</table>
</para>
<para>
Now that we know which Unix device to open for a given Windows
device, let's cover the operation on it. Those operations can either
be read / write, io control (and even others).
</para>
<para>
Read and write operations are supported on Real disks & CDROM
devices, under several conditions:
<itemizedlist>
<listitem>
<para>
Foremost, as the <function>ReadFile()</function> and
<function>WriteFile()</function> calls are mapped onto the
Unix <function>read()</function> and
<function>write()</function> calls, the user (from the Unix
perspective of the one running the Wine executable) must have
read (resp. write) access to the device. It wouldn't be wise
to let a user write directly to a hard disk!!!
</para>
</listitem>
<listitem>
<para>
Blocks' size for read and write but be of the size of a
physical block (generally 512 for a hard disk, depends on the
type of CD used), and offsets must also be a multiple of the
block size.
</para>
</listitem>
</itemizedlist>
</para>
<para>
Wine also reads (if the first condition above about access rights is
met) the volume information from a hard disk or a CD ROM to be
displayed to a user.
</para>
<!--
<para>
Handling of old DOS devices (<filename>COMx</filename>,
<filename>LPTx</filename>, <filename>NUL</filename>...)
</para>
-->
<para>
Wine also recognizes VxD as devices. But those VxD must be the
Wine builtin ones (Wine will never allow to load native VxD). Those
are configured with symbolic links in the
<filename>$(WINEPREFIX)/dosdevices/</filename> directory, and point
to the actual builtin DLL. This DLL exports a single entry point,
that Wine will use when a call to
<function>DeviceIoControl</function> is made, with a handle opened
to this VxD. This allows to provide some kind of compatibility for
old Win9x apps, still talking directly to VxD. This is no longer
supported on Windows NT, newest programs are less likely to make use
of this feature, so we don't expect lots of development in this
area, even though the framework is there and working. Note also that
Wine doesn't provide support for native VxDs (as a game, report how
many times this information is written in the documentation; as an
advanced exercise, find how many more occurrences we need in order to
stop questions whether it's possible or not).
</para>
</sect3>
</sect2>
</sect1>
<sect1 id="ntdll">
<title><filename>NTDLL</filename> module</title>
<para>
<filename>NTDLL</filename> provides most of the services you'd expect
from a kernel. In lots of cases, <filename>KERNEL32</filename> APIs are
just wrappers to <filename>NTDLL</filename> APIs. There are however,
some difference in the APIs (the <filename>NTDLL</filename> ones have
quite often a bit wider semantics than their
<filename>KERNEL32</filename> counterparts). All the detailed functions
we've described since the beginning of this chapter are in fact
implemented in <filename>NTDLL</filename>, plus a great numbers of
others we haven's written about yet.
</para>
</sect1>
<sect1>
<title><filename>KERNEL32</filename> Module</title>
<para>
As already explained, <filename>KERNEL32</filename> maps quite a few of
its APIs to <filename>NTDLL</filename>. There are however a couple of
things which are handled directly in
<filename>KERNEL32</filename>. Let's cover a few of them...
</para>
<sect2 id="consoles">
<title>Console</title>
<sect3>
<title>NT implementation</title>
<para>
Windows implements console solely in the Win32 subsystem. Under NT,
the real implementation uses a dedicated subsystem
<filename>csrss.exe</filename> Client/Server Run-time SubSystem)
which is in charge, amont other things, of animating the consoles.
Animating includes for example handling several processes on the
same console (write operations must be atomic, but also a character
keyed on the console must be read by a single process), or sending
some information back to the processes (changing the size or
attributes of the console, closing the console). Windows NT uses a
dedicated (RPC based) protocol between each process being attached
to a console and the <command>csrss.exe</command> subsystem, which
is in charge of the UI of every console in the system.
</para>
</sect3>
<sect3>
<title>Wine implementation</title>
<para>
Wine tries to integrate as much as possible into the Unix consoles,
but the overall situation isn't perfect yet. Basically, Wine
implements three kinds of consoles:
<itemizedlist>
<listitem>
<para>
the first one is a direct mapping of the Unix console into the
Windows environment. From the windows program point of view,
it won't run in a Windows console, but it will see its
standard input and output streams redirected to files; thoses
files are hooked into the Unix console's output and input
streams respectively. This is handy for running programs from
a Unix command line (and use the result of the program as it
was a Unix programs), but it lacks all the semantics of the
Windows consoles.
</para>
</listitem>
<listitem>
<para>
the second and third ones are closer to the NT scheme, albeit
different from what NT does. The <command>wineserver</command>
plays the role of the <filename>csrss.exe</filename> subsystem
(all requests are sent to it), and are then dispatched to a
dedicated wine process, called (surprise!)
<command>wineconsole</command> which manages the UI of the
console. There is a running instance of
<command>wineconsole</command> for every console in the
system. Two flavors of this scheme are actually implemented:
they vary on the backend for the
<command>wineconsole</command>. The first one, dubbed
<constant>user</constant>, creates a real GUI window
(hence the USER name) and renders the console in this window.
The second one uses the <filename>(n)curses</filename> library
to take full control of an existing Unix console; of course,
interaction with other Unix programs will not be as smooth as
the first solution.
</para>
</listitem>
</itemizedlist>
</para>
<para>
The following table describes the main implementation differences
between the three approaches.
<table>
<title>Function consoles implementation comparison</title>
<tgroup cols="4" align="left">
<thead>
<row>
<entry>Function</entry>
<entry>Bare streams</entry>
<entry>
<command>Wineconsole</command> &amp; user backend
</entry>
<entry>
<command>Wineconsole</command> &amp; curses backend
</entry>
</row>
</thead>
<tbody>
<row>
<entry>
Console as a Win32 Object (and associated handles)
</entry>
<entry>
No specific Win32 object is used in this case. The
handles manipulated for the standard Win32 streams are in
fact "bare handles" to their corresponding Unix streams.
The mode manipulation functions
(<function>GetConsoleMode()</function> /
<function>SetConsoleMode()</function>) are not supported.
</entry>
<entry>
Implemented in server, and a specific Winelib program
(<command>wineconsole</command>) is in charge of the
rendering and user input. The mode manipulation functions
behave as expected.
</entry>
<entry>
Implemented in server, and a specific Winelib program
(<command>wineconsole</command>) is in charge of the
rendering and user input. The mode manipulation functions
behave as expected.
</entry>
</row>
<row>
<entry>
Inheritance (including handling in
<function>CreateProcess()</function> of
<constant>CREATE_DETACHED</constant>,
<constant>CREATE_NEW_CONSOLE</constant> flags).
</entry>
<entry>
Not supported. Every process child of a process will
inherit the Unix streams, so will also inherit the Win32
standard streams.
</entry>
<entry>
Fully supported (each new console creation will be handled
by the creation of a new <filename>USER32</filename> window)
</entry>
<entry>
Fully supported, except for the creation of a new console,
which will be rendered on the same Unix terminal as the
previous one, leading to unpredictable results.
</entry>
</row>
<row>
<entry>
<function>ReadFile()</function> /
<function>WriteFile()</function> operations
</entry>
<entry>Fully supported</entry>
<entry>Fully supported</entry>
<entry>Fully supported</entry>
</row>
<row>
<entry>
Screen-buffer manipulation (creation, deletion, resizing...)
</entry>
<entry>Not supported</entry>
<entry>Fully supported</entry>
<entry>
Partly supported (this won't work too well as we don't
control (so far) the size of underlying Unix terminal
</entry>
</row>
<row>
<entry>
APIs for reading/writing screen-buffer content, cursor position
</entry>
<entry>Not supported</entry>
<entry>Fully supported</entry>
<entry>Fully supported</entry>
</row>
<row>
<entry>APIs for manipulating the rendering window size</entry>
<entry>Not supported</entry>
<entry>Fully supported</entry>
<entry>
Partly supported (this won't work too well as we don't
control (so far) the size of underlying Unix terminal
</entry>
</row>
<row>
<entry>
Signaling (in particular, Ctrl-C handling)
</entry>
<entry>
Nothing is done, which means that Ctrl-C will generate (as
usual) a <constant>SIGINT</constant> which will terminate
the program.
</entry>
<entry>
Partly supported (Ctrl-C behaves as expected, however the
other Win32 CUI signaling isn't properly implemented).
</entry>
<entry>
Partly supported (Ctrl-C behaves as expected, however the
other Win32 CUI signaling isn't properly implemented).
</entry>
</row>
</tbody>
</tgroup>
</table>
</para>
<para>
The Win32 objects behind a console can be created in several
occasions:
<itemizedlist>
<listitem>
<para>
When the program is started from
<command>wineconsole</command>, a new console object is
created and will be used (inherited) by the process launched
from <command>wineconsole</command>.
</para>
</listitem>
<listitem>
<para>
When a program, which isn't attached to a console, calls
<function>AllocConsole()</function>, Wine then launches
<command>wineconsole</command>, and attaches the current
program to this console. In this mode, the
<filename>USER32</filename> mode is always selected as Wine
cannot tell the current state of the Unix console.
</para>
</listitem>
</itemizedlist>
</para>
<para>
Please also note, that starting a child process with the
<constant>CREATE_NEW_CONSOLE</constant> flag, will end-up calling
<function>AllocConsole()</function> in the child process, hence
creating a <command>wineconsole</command> with the
<filename>USER32</filename> backend.
</para>
<para>
Another interesting point to note is that Windows implements handles
to console objects (input and screen buffers) only in the
<filename>KERNEL32</filename> DLL, and those are not sent nor seen
from the <filename>NTDLL</filename> level, albeit, for example,
console are waitable on input. How is this possible? Well, Windows
NT is a bit tricky here. Regular handles have an interesting
property: their integral value is always a multiple of four (they
are likely to be offsets from the beginning of a table). Console
handles, on the other hand, are not multiple of four, but have the
two lower bit set (being a multiple of four means having the two
lower bits reset). When <filename>KERNEL32</filename> sees a handle
with the two lower bits set, it then knows it's a console handle and
takes appropriate decisions. For example, in the various
<function>kernel32!WaitFor*()</function> functions, it transforms
any console handle (input and <emphasis>output</emphasis> -
strangely enough handles to console's screen buffers are waitable)
into a dedicated wait event for the targetted console. There's an
(undocumented) <filename>KERNEL32</filename> function
<function>GetConsoleInputWaitHandle()</function> which returns the
handle to this event in case you need it. Another interesting
handling of those console's handles is in
<function>ReadFile()</function>
(resp. <function>WriteFile()</function>), which behavior, for
console's handles, is transferred to
<function>ReadConsole()</function> (resp.
<function>WriteConsole()</function>). Note that's always the ANSI
version of
<function>ReadConsole()</function> /
<function>WriteConsole()</function>
which is called, hence using the default console's code page. There
are some other spots affected, but you can look in
<filename>dlls/kernel</filename> to find them all. All of this is
implemented in Wine.
</para>
<para>
Wine also implements the same layout of the registry for storing the
preferences of the console as Windows does. Those settings can
either be defined globally, or on a per process name basis.
<command>wineconsole</command> provides the choice to the user to
pick you which registry part (global, current running program) it
wishes to modify the settings for.
<table>
<title>Console registry settings</title>
<tgroup cols="3" align="left">
<thead>
<row>
<entry>Name</entry>
<entry>Default value</entry>
<entry>Purpose</entry>
</row>
</thead>
<tbody>
<row>
<entry>CursorSize</entry>
<entry>25</entry>
<entry>
Percentage of cell height to which the cursor extents
</entry>
</row>
<row>
<entry>CursorVisible</entry>
<entry>1</entry>
<entry>Whether the cursor is visible or not</entry>
</row>
<row>
<entry>EditionMode</entry>
<entry>0</entry>
<entry>
The way the edition takes place in the console: 0 is
insertion mode, 1 is overwrite mode.
</entry>
</row>
<row>
<entry>ExitOnDie</entry>
<entry>1</entry>
<entry>
Whether the console should close itself when last running
program attached to it dies
</entry>
</row>
<row>
<entry>FaceName</entry>
<entry>No default</entry>
<entry>
Name of the font to be used for display. When none is
given, <command>wineconsole</command> tries its best to
pick up a decent font
</entry>
</row>
<row>
<entry>FontSize</entry>
<entry>0x0C08</entry>
<entry>
The high word in the font's cell height, and the low word
is the font cell's width. The default value is 12 pixels
in height and 8 pixels in width.
</entry>
</row>
<row>
<entry>FontWeight</entry>
<entry>0</entry>
<entry>
Weigth of the font. If none is given (or 0)
<command>wineconsole</command> picks up a decent font size
</entry>
</row>
<row>
<entry>HistoryBufferSize</entry>
<entry>50</entry>
<entry>
Number of entries in history buffer (not actually used)
</entry>
</row>
<row>
<entry>HistoryNoDup</entry>
<entry>0</entry>
<entry>
Whether the history should store twice the same entry
</entry>
</row>
<row>
<entry>MenuMask</entry>
<entry>0</entry>
<entry>
This mask only exists for Wine console handling. It
allows to know which combination of extra keys are need to
open the configuration window on right click. The mask
can include <constant>MK_CONTROL</constant> or
<constant>MK_SHIFT</constant> bits. This can be needed
when programs actually need the right click to be passed
to them instead of being intercepted by
<command>wineconsole</command>.
</entry>
</row>
<row>
<entry>QuickEdit</entry>
<entry>0</entry>
<entry>
If null, mouse events are sent to the application. If non
null, mouse events are used to select text on the window.
This setting must really be set on a application per
application basis, because it deals with the fact the CUI
application will use or not the mouse events.
</entry>
</row>
<row>
<entry>ScreenBufferSize</entry>
<entry>0x1950</entry>
<entry>
The high word is the number of font cells in the height of
the screen buffer, while the low word is the number of
font cells in the width of the screen buffer.
</entry>
</row>
<row>
<entry>ScreenColors</entry>
<entry>0x000F</entry>
<entry>
Default color attribute for the screen buffer (low char is
the foreground color, and high char is the background
color)
</entry>
</row>
<row>
<entry>WindowSize</entry>
<entry>0x1950</entry>
<entry>
The high word is the number of font cells in the height of
the window, while the low word is the number of font cells
in the width of the window. This window is the visible
part of the screen buffer: this implies that a screen
buffer must always be bigger than its window, and that the
screen buffer can be scrolled so that every cell of the
screen buffer can be seen in the window.
</entry>
</row>
</tbody>
</tgroup>
</table>
</para>
</sect3>
</sect2>
<sect2>
<title>Win16 processes support</title>
<sect3>
<title>Starting a NE (Win16) process</title>
<para>
Wine is also able to run 16 bit processes, but this feature is only
supported on Intel IA-32 architectures.
</para>
<para>
When Wine is requested to run a NE (Win 16 process), it will in fact
hand over the execution of it to a specific executable
<command>winevdm</command>. VDM stands for Virtual DOS
Machine. This <command>winevdm</command> is a Winelib application,
but will in fact set up the correct 16 bit environment to run the
executable. We will get back later on in details to what this means.
</para>
<para>
Any new 16 bit process created by this executable (or its children)
will run into the same <command>winevdm</command> instance. Among
one instance, several functionalities will be provided to those 16
bit processes, including the cooperative multitasking, sharing the
same address space, managing the selectors for the 16 bit segments
needed for code, data and stack.
</para>
<para>
Note that several <command>winevdm</command> instances can run in
the same Wine session, but the functionalities described above are
only shared among a given instance, not among all the
instances. <command>winevdm</command> is built as Winelib
application, and hence has access to any facility a 32 bit
application has.
</para>
<para>
Each Win16 application is implemented in
<command>winevdm</command> as a Win32
thread. <command>winevdm</command> then implements its own
scheduling facilities (in fact, the code for this feature is in the
<filename>krnl386.exe</filename> DLL). Since the required Win16
scheduling is non pre-emptive, this doesn't require any underlying
OS kernel support.
</para>
</sect3>
<sect3>
<title>SysLevels</title>
<para>
SysLevels are an undocumented Windows-internal thread-safety system
dedicated to 16 bit applications (or 32 bit applications that call -
directly or indirectly - 16 bit code). They are basically critical
sections which must be taken in a particular order. The mechanism is
generic but there are always three syslevels:
<itemizedlist>
<listitem>
<para>level 1 is the Win16 mutex,</para>
</listitem>
<listitem>
<para>level 2 is the <filename>USER</filename> mutex,</para>
</listitem>
<listitem>
<para>level 3 is the <filename>GDI</filename> mutex.</para>
</listitem>
</itemizedlist>
</para>
<para>
When entering a syslevel, the code (in
<filename>dlls/kernel/syslevel.c</filename>) will check that a
higher syslevel is not already held and produce an error if so. This
is because it's not legal to enter level 2 while holding level 3 -
first, you must leave level 3.
</para>
<para>
Throughout the code you may see calls to
<function>_ConfirmSysLevel()</function> and
<function>_CheckNotSysLevel()</function>. These functions are
essentially assertions about the syslevel states and can be used to
check that the rules have not been accidentally violated. In
particular, <function>_CheckNotSysLevel()</function> will break
probably into the debugger) if the check fails. If this happens the
solution is to get a backtrace and find out, by reading the source
of the wine functions called along the way, how Wine got into the
invalid state.
</para>
</sect3>
<sect3>
<title>Memory management</title>
<para>
Every Win16 address is expressed in the form of selector:offset. The
selector is an entry in the LDT, but a 16 bit entry, limiting each
offset to 64 KB. Hence, the maximum available memory to a Win16
process is 512 MB. Note, that the processor runs in protected mode,
but using 16 bit selectors.
</para>
<para>
Windows, for a 16 bit process, defines a few selectors to access the
"real" memory (the one provided) by DOS. Basically, Wine also
provides this area of memory.
</para>
</sect3>
</sect2>
<sect2>
<title>DOS processes support</title>
<para>
The behaviour we just described also applies to DOS executables, which
are handled the same way by <command>winevdm</command>. This is only
supported on Intel IA-32 architectures.
</para>
<para>
Wine implements also most of the DOS support in a Wine specific DLL
(<filename>winedos</filename>). This DLL is called under certain
conditions, like:
<itemizedlist>
<listitem>
<para>
In <command>winevdm</command>, when trying to launch a DOS
application (<filename>.EXE</filename> or
<filename>.COM</filename>, <filename>.PIF</filename>).
</para>
</listitem>
<listitem>
<para>
In <filename>kernel32</filename>, when an attempt is made in the
binary code to call some DOS or BIOS interrupts (like Int 21h
for example).
</para>
</listitem>
</itemizedlist>
</para>
<para>
When <command>winevdm</command> runs a DOS program, this one runs in
real mode (in fact in V86 mode from the IA-32 point of view).
</para>
<para>
Wine also supports part of the DPMI (DOS Protected Mode Interface).
</para>
<para>
Wine, when running a DOS programs, needs to map the 1 MB of virtual
memory to the real memory (as seen by the DOS program). When this is
not possible (like when someone else is already using this area), the
DOS support is not possible. Not also that by doing so, access to
linear address 0 is enabled (as it's also real mode address 0 which is
valid). Hence, NULL pointer derefence faults are no longer catched.
</para>
</sect2>
</sect1>
</chapter>
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