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darling-gdb/gdb/solib-svr4.c
Andrew Cagney 4b38d6f1a4 2004-06-09 Andrew Cagney <cagney@gnu.org> 
* solib-svr4.c [HANDLE_SVR4_EXEC_EMULATORS]: Delete #ifdef code.
2004-06-09 20:03:33 +00:00

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/* Handle SVR4 shared libraries for GDB, the GNU Debugger.
Copyright 1990, 1991, 1992, 1993, 1994, 1995, 1996, 1998, 1999,
2000, 2001, 2003, 2004
Free Software Foundation, Inc.
This file is part of GDB.
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 59 Temple Place - Suite 330,
Boston, MA 02111-1307, USA. */
#include "defs.h"
#include "elf/external.h"
#include "elf/common.h"
#include "elf/mips.h"
#include "symtab.h"
#include "bfd.h"
#include "symfile.h"
#include "objfiles.h"
#include "gdbcore.h"
#include "target.h"
#include "inferior.h"
#include "solist.h"
#include "solib-svr4.h"
#include "bfd-target.h"
#include "exec.h"
#ifndef SVR4_FETCH_LINK_MAP_OFFSETS
#define SVR4_FETCH_LINK_MAP_OFFSETS() svr4_fetch_link_map_offsets ()
#endif
static struct link_map_offsets *svr4_fetch_link_map_offsets (void);
static struct link_map_offsets *legacy_fetch_link_map_offsets (void);
static int svr4_have_link_map_offsets (void);
/* fetch_link_map_offsets_gdbarch_data is a handle used to obtain the
architecture specific link map offsets fetching function. */
static struct gdbarch_data *fetch_link_map_offsets_gdbarch_data;
/* legacy_svr4_fetch_link_map_offsets_hook is a pointer to a function
which is used to fetch link map offsets. It will only be set
by solib-legacy.c, if at all. */
struct link_map_offsets *(*legacy_svr4_fetch_link_map_offsets_hook)(void) = 0;
/* Link map info to include in an allocated so_list entry */
struct lm_info
{
/* Pointer to copy of link map from inferior. The type is char *
rather than void *, so that we may use byte offsets to find the
various fields without the need for a cast. */
char *lm;
};
/* On SVR4 systems, a list of symbols in the dynamic linker where
GDB can try to place a breakpoint to monitor shared library
events.
If none of these symbols are found, or other errors occur, then
SVR4 systems will fall back to using a symbol as the "startup
mapping complete" breakpoint address. */
static char *solib_break_names[] =
{
"r_debug_state",
"_r_debug_state",
"_dl_debug_state",
"rtld_db_dlactivity",
"_rtld_debug_state",
/* On the 64-bit PowerPC, the linker symbol with the same name as
the C function points to a function descriptor, not to the entry
point. The linker symbol whose name is the C function name
prefixed with a '.' points to the function's entry point. So
when we look through this table, we ignore symbols that point
into the data section (thus skipping the descriptor's symbol),
and eventually try this one, giving us the real entry point
address. */
"._dl_debug_state",
NULL
};
#define BKPT_AT_SYMBOL 1
#if defined (BKPT_AT_SYMBOL)
static char *bkpt_names[] =
{
#ifdef SOLIB_BKPT_NAME
SOLIB_BKPT_NAME, /* Prefer configured name if it exists. */
#endif
"_start",
"__start",
"main",
NULL
};
#endif
static char *main_name_list[] =
{
"main_$main",
NULL
};
/* Macro to extract an address from a solib structure. When GDB is
configured for some 32-bit targets (e.g. Solaris 2.7 sparc), BFD is
configured to handle 64-bit targets, so CORE_ADDR is 64 bits. We
have to extract only the significant bits of addresses to get the
right address when accessing the core file BFD.
Assume that the address is unsigned. */
#define SOLIB_EXTRACT_ADDRESS(MEMBER) \
extract_unsigned_integer (&(MEMBER), sizeof (MEMBER))
/* local data declarations */
/* link map access functions */
static CORE_ADDR
LM_ADDR (struct so_list *so)
{
struct link_map_offsets *lmo = SVR4_FETCH_LINK_MAP_OFFSETS ();
return (CORE_ADDR) extract_signed_integer (so->lm_info->lm + lmo->l_addr_offset,
lmo->l_addr_size);
}
static CORE_ADDR
LM_NEXT (struct so_list *so)
{
struct link_map_offsets *lmo = SVR4_FETCH_LINK_MAP_OFFSETS ();
/* Assume that the address is unsigned. */
return extract_unsigned_integer (so->lm_info->lm + lmo->l_next_offset,
lmo->l_next_size);
}
static CORE_ADDR
LM_NAME (struct so_list *so)
{
struct link_map_offsets *lmo = SVR4_FETCH_LINK_MAP_OFFSETS ();
/* Assume that the address is unsigned. */
return extract_unsigned_integer (so->lm_info->lm + lmo->l_name_offset,
lmo->l_name_size);
}
static int
IGNORE_FIRST_LINK_MAP_ENTRY (struct so_list *so)
{
struct link_map_offsets *lmo = SVR4_FETCH_LINK_MAP_OFFSETS ();
/* Assume that the address is unsigned. */
return extract_unsigned_integer (so->lm_info->lm + lmo->l_prev_offset,
lmo->l_prev_size) == 0;
}
static CORE_ADDR debug_base; /* Base of dynamic linker structures */
static CORE_ADDR breakpoint_addr; /* Address where end bkpt is set */
/* Local function prototypes */
static int match_main (char *);
static CORE_ADDR bfd_lookup_symbol (bfd *, char *, flagword);
/*
LOCAL FUNCTION
bfd_lookup_symbol -- lookup the value for a specific symbol
SYNOPSIS
CORE_ADDR bfd_lookup_symbol (bfd *abfd, char *symname, flagword sect_flags)
DESCRIPTION
An expensive way to lookup the value of a single symbol for
bfd's that are only temporary anyway. This is used by the
shared library support to find the address of the debugger
interface structures in the shared library.
If SECT_FLAGS is non-zero, only match symbols in sections whose
flags include all those in SECT_FLAGS.
Note that 0 is specifically allowed as an error return (no
such symbol).
*/
static CORE_ADDR
bfd_lookup_symbol (bfd *abfd, char *symname, flagword sect_flags)
{
long storage_needed;
asymbol *sym;
asymbol **symbol_table;
unsigned int number_of_symbols;
unsigned int i;
struct cleanup *back_to;
CORE_ADDR symaddr = 0;
storage_needed = bfd_get_symtab_upper_bound (abfd);
if (storage_needed > 0)
{
symbol_table = (asymbol **) xmalloc (storage_needed);
back_to = make_cleanup (xfree, symbol_table);
number_of_symbols = bfd_canonicalize_symtab (abfd, symbol_table);
for (i = 0; i < number_of_symbols; i++)
{
sym = *symbol_table++;
if (strcmp (sym->name, symname) == 0
&& (sym->section->flags & sect_flags) == sect_flags)
{
/* Bfd symbols are section relative. */
symaddr = sym->value + sym->section->vma;
break;
}
}
do_cleanups (back_to);
}
if (symaddr)
return symaddr;
/* On FreeBSD, the dynamic linker is stripped by default. So we'll
have to check the dynamic string table too. */
storage_needed = bfd_get_dynamic_symtab_upper_bound (abfd);
if (storage_needed > 0)
{
symbol_table = (asymbol **) xmalloc (storage_needed);
back_to = make_cleanup (xfree, symbol_table);
number_of_symbols = bfd_canonicalize_dynamic_symtab (abfd, symbol_table);
for (i = 0; i < number_of_symbols; i++)
{
sym = *symbol_table++;
if (strcmp (sym->name, symname) == 0
&& (sym->section->flags & sect_flags) == sect_flags)
{
/* Bfd symbols are section relative. */
symaddr = sym->value + sym->section->vma;
break;
}
}
do_cleanups (back_to);
}
return symaddr;
}
/*
LOCAL FUNCTION
elf_locate_base -- locate the base address of dynamic linker structs
for SVR4 elf targets.
SYNOPSIS
CORE_ADDR elf_locate_base (void)
DESCRIPTION
For SVR4 elf targets the address of the dynamic linker's runtime
structure is contained within the dynamic info section in the
executable file. The dynamic section is also mapped into the
inferior address space. Because the runtime loader fills in the
real address before starting the inferior, we have to read in the
dynamic info section from the inferior address space.
If there are any errors while trying to find the address, we
silently return 0, otherwise the found address is returned.
*/
static CORE_ADDR
elf_locate_base (void)
{
struct bfd_section *dyninfo_sect;
int dyninfo_sect_size;
CORE_ADDR dyninfo_addr;
char *buf;
char *bufend;
int arch_size;
/* Find the start address of the .dynamic section. */
dyninfo_sect = bfd_get_section_by_name (exec_bfd, ".dynamic");
if (dyninfo_sect == NULL)
return 0;
dyninfo_addr = bfd_section_vma (exec_bfd, dyninfo_sect);
/* Read in .dynamic section, silently ignore errors. */
dyninfo_sect_size = bfd_section_size (exec_bfd, dyninfo_sect);
buf = alloca (dyninfo_sect_size);
if (target_read_memory (dyninfo_addr, buf, dyninfo_sect_size))
return 0;
/* Find the DT_DEBUG entry in the the .dynamic section.
For mips elf we look for DT_MIPS_RLD_MAP, mips elf apparently has
no DT_DEBUG entries. */
arch_size = bfd_get_arch_size (exec_bfd);
if (arch_size == -1) /* failure */
return 0;
if (arch_size == 32)
{ /* 32-bit elf */
for (bufend = buf + dyninfo_sect_size;
buf < bufend;
buf += sizeof (Elf32_External_Dyn))
{
Elf32_External_Dyn *x_dynp = (Elf32_External_Dyn *) buf;
long dyn_tag;
CORE_ADDR dyn_ptr;
dyn_tag = bfd_h_get_32 (exec_bfd, (bfd_byte *) x_dynp->d_tag);
if (dyn_tag == DT_NULL)
break;
else if (dyn_tag == DT_DEBUG)
{
dyn_ptr = bfd_h_get_32 (exec_bfd,
(bfd_byte *) x_dynp->d_un.d_ptr);
return dyn_ptr;
}
else if (dyn_tag == DT_MIPS_RLD_MAP)
{
char *pbuf;
int pbuf_size = TARGET_PTR_BIT / HOST_CHAR_BIT;
pbuf = alloca (pbuf_size);
/* DT_MIPS_RLD_MAP contains a pointer to the address
of the dynamic link structure. */
dyn_ptr = bfd_h_get_32 (exec_bfd,
(bfd_byte *) x_dynp->d_un.d_ptr);
if (target_read_memory (dyn_ptr, pbuf, pbuf_size))
return 0;
return extract_unsigned_integer (pbuf, pbuf_size);
}
}
}
else /* 64-bit elf */
{
for (bufend = buf + dyninfo_sect_size;
buf < bufend;
buf += sizeof (Elf64_External_Dyn))
{
Elf64_External_Dyn *x_dynp = (Elf64_External_Dyn *) buf;
long dyn_tag;
CORE_ADDR dyn_ptr;
dyn_tag = bfd_h_get_64 (exec_bfd, (bfd_byte *) x_dynp->d_tag);
if (dyn_tag == DT_NULL)
break;
else if (dyn_tag == DT_DEBUG)
{
dyn_ptr = bfd_h_get_64 (exec_bfd,
(bfd_byte *) x_dynp->d_un.d_ptr);
return dyn_ptr;
}
else if (dyn_tag == DT_MIPS_RLD_MAP)
{
char *pbuf;
int pbuf_size = TARGET_PTR_BIT / HOST_CHAR_BIT;
pbuf = alloca (pbuf_size);
/* DT_MIPS_RLD_MAP contains a pointer to the address
of the dynamic link structure. */
dyn_ptr = bfd_h_get_64 (exec_bfd,
(bfd_byte *) x_dynp->d_un.d_ptr);
if (target_read_memory (dyn_ptr, pbuf, pbuf_size))
return 0;
return extract_unsigned_integer (pbuf, pbuf_size);
}
}
}
/* DT_DEBUG entry not found. */
return 0;
}
/*
LOCAL FUNCTION
locate_base -- locate the base address of dynamic linker structs
SYNOPSIS
CORE_ADDR locate_base (void)
DESCRIPTION
For both the SunOS and SVR4 shared library implementations, if the
inferior executable has been linked dynamically, there is a single
address somewhere in the inferior's data space which is the key to
locating all of the dynamic linker's runtime structures. This
address is the value of the debug base symbol. The job of this
function is to find and return that address, or to return 0 if there
is no such address (the executable is statically linked for example).
For SunOS, the job is almost trivial, since the dynamic linker and
all of it's structures are statically linked to the executable at
link time. Thus the symbol for the address we are looking for has
already been added to the minimal symbol table for the executable's
objfile at the time the symbol file's symbols were read, and all we
have to do is look it up there. Note that we explicitly do NOT want
to find the copies in the shared library.
The SVR4 version is a bit more complicated because the address
is contained somewhere in the dynamic info section. We have to go
to a lot more work to discover the address of the debug base symbol.
Because of this complexity, we cache the value we find and return that
value on subsequent invocations. Note there is no copy in the
executable symbol tables.
*/
static CORE_ADDR
locate_base (void)
{
/* Check to see if we have a currently valid address, and if so, avoid
doing all this work again and just return the cached address. If
we have no cached address, try to locate it in the dynamic info
section for ELF executables. There's no point in doing any of this
though if we don't have some link map offsets to work with. */
if (debug_base == 0 && svr4_have_link_map_offsets ())
{
if (exec_bfd != NULL
&& bfd_get_flavour (exec_bfd) == bfd_target_elf_flavour)
debug_base = elf_locate_base ();
}
return (debug_base);
}
/*
LOCAL FUNCTION
first_link_map_member -- locate first member in dynamic linker's map
SYNOPSIS
static CORE_ADDR first_link_map_member (void)
DESCRIPTION
Find the first element in the inferior's dynamic link map, and
return its address in the inferior. This function doesn't copy the
link map entry itself into our address space; current_sos actually
does the reading. */
static CORE_ADDR
first_link_map_member (void)
{
CORE_ADDR lm = 0;
struct link_map_offsets *lmo = SVR4_FETCH_LINK_MAP_OFFSETS ();
char *r_map_buf = xmalloc (lmo->r_map_size);
struct cleanup *cleanups = make_cleanup (xfree, r_map_buf);
read_memory (debug_base + lmo->r_map_offset, r_map_buf, lmo->r_map_size);
/* Assume that the address is unsigned. */
lm = extract_unsigned_integer (r_map_buf, lmo->r_map_size);
/* FIXME: Perhaps we should validate the info somehow, perhaps by
checking r_version for a known version number, or r_state for
RT_CONSISTENT. */
do_cleanups (cleanups);
return (lm);
}
/*
LOCAL FUNCTION
open_symbol_file_object
SYNOPSIS
void open_symbol_file_object (void *from_tty)
DESCRIPTION
If no open symbol file, attempt to locate and open the main symbol
file. On SVR4 systems, this is the first link map entry. If its
name is here, we can open it. Useful when attaching to a process
without first loading its symbol file.
If FROM_TTYP dereferences to a non-zero integer, allow messages to
be printed. This parameter is a pointer rather than an int because
open_symbol_file_object() is called via catch_errors() and
catch_errors() requires a pointer argument. */
static int
open_symbol_file_object (void *from_ttyp)
{
CORE_ADDR lm, l_name;
char *filename;
int errcode;
int from_tty = *(int *)from_ttyp;
struct link_map_offsets *lmo = SVR4_FETCH_LINK_MAP_OFFSETS ();
char *l_name_buf = xmalloc (lmo->l_name_size);
struct cleanup *cleanups = make_cleanup (xfree, l_name_buf);
if (symfile_objfile)
if (!query ("Attempt to reload symbols from process? "))
return 0;
if ((debug_base = locate_base ()) == 0)
return 0; /* failed somehow... */
/* First link map member should be the executable. */
if ((lm = first_link_map_member ()) == 0)
return 0; /* failed somehow... */
/* Read address of name from target memory to GDB. */
read_memory (lm + lmo->l_name_offset, l_name_buf, lmo->l_name_size);
/* Convert the address to host format. Assume that the address is
unsigned. */
l_name = extract_unsigned_integer (l_name_buf, lmo->l_name_size);
/* Free l_name_buf. */
do_cleanups (cleanups);
if (l_name == 0)
return 0; /* No filename. */
/* Now fetch the filename from target memory. */
target_read_string (l_name, &filename, SO_NAME_MAX_PATH_SIZE - 1, &errcode);
if (errcode)
{
warning ("failed to read exec filename from attached file: %s",
safe_strerror (errcode));
return 0;
}
make_cleanup (xfree, filename);
/* Have a pathname: read the symbol file. */
symbol_file_add_main (filename, from_tty);
return 1;
}
/* LOCAL FUNCTION
current_sos -- build a list of currently loaded shared objects
SYNOPSIS
struct so_list *current_sos ()
DESCRIPTION
Build a list of `struct so_list' objects describing the shared
objects currently loaded in the inferior. This list does not
include an entry for the main executable file.
Note that we only gather information directly available from the
inferior --- we don't examine any of the shared library files
themselves. The declaration of `struct so_list' says which fields
we provide values for. */
static struct so_list *
svr4_current_sos (void)
{
CORE_ADDR lm;
struct so_list *head = 0;
struct so_list **link_ptr = &head;
/* Make sure we've looked up the inferior's dynamic linker's base
structure. */
if (! debug_base)
{
debug_base = locate_base ();
/* If we can't find the dynamic linker's base structure, this
must not be a dynamically linked executable. Hmm. */
if (! debug_base)
return 0;
}
/* Walk the inferior's link map list, and build our list of
`struct so_list' nodes. */
lm = first_link_map_member ();
while (lm)
{
struct link_map_offsets *lmo = SVR4_FETCH_LINK_MAP_OFFSETS ();
struct so_list *new
= (struct so_list *) xmalloc (sizeof (struct so_list));
struct cleanup *old_chain = make_cleanup (xfree, new);
memset (new, 0, sizeof (*new));
new->lm_info = xmalloc (sizeof (struct lm_info));
make_cleanup (xfree, new->lm_info);
new->lm_info->lm = xmalloc (lmo->link_map_size);
make_cleanup (xfree, new->lm_info->lm);
memset (new->lm_info->lm, 0, lmo->link_map_size);
read_memory (lm, new->lm_info->lm, lmo->link_map_size);
lm = LM_NEXT (new);
/* For SVR4 versions, the first entry in the link map is for the
inferior executable, so we must ignore it. For some versions of
SVR4, it has no name. For others (Solaris 2.3 for example), it
does have a name, so we can no longer use a missing name to
decide when to ignore it. */
if (IGNORE_FIRST_LINK_MAP_ENTRY (new))
free_so (new);
else
{
int errcode;
char *buffer;
/* Extract this shared object's name. */
target_read_string (LM_NAME (new), &buffer,
SO_NAME_MAX_PATH_SIZE - 1, &errcode);
if (errcode != 0)
{
warning ("current_sos: Can't read pathname for load map: %s\n",
safe_strerror (errcode));
}
else
{
strncpy (new->so_name, buffer, SO_NAME_MAX_PATH_SIZE - 1);
new->so_name[SO_NAME_MAX_PATH_SIZE - 1] = '\0';
xfree (buffer);
strcpy (new->so_original_name, new->so_name);
}
/* If this entry has no name, or its name matches the name
for the main executable, don't include it in the list. */
if (! new->so_name[0]
|| match_main (new->so_name))
free_so (new);
else
{
new->next = 0;
*link_ptr = new;
link_ptr = &new->next;
}
}
discard_cleanups (old_chain);
}
return head;
}
/* Get the address of the link_map for a given OBJFILE. Loop through
the link maps, and return the address of the one corresponding to
the given objfile. Note that this function takes into account that
objfile can be the main executable, not just a shared library. The
main executable has always an empty name field in the linkmap. */
CORE_ADDR
svr4_fetch_objfile_link_map (struct objfile *objfile)
{
CORE_ADDR lm;
if ((debug_base = locate_base ()) == 0)
return 0; /* failed somehow... */
/* Position ourselves on the first link map. */
lm = first_link_map_member ();
while (lm)
{
/* Get info on the layout of the r_debug and link_map structures. */
struct link_map_offsets *lmo = SVR4_FETCH_LINK_MAP_OFFSETS ();
int errcode;
char *buffer;
struct lm_info objfile_lm_info;
struct cleanup *old_chain;
CORE_ADDR name_address;
char *l_name_buf = xmalloc (lmo->l_name_size);
old_chain = make_cleanup (xfree, l_name_buf);
/* Set up the buffer to contain the portion of the link_map
structure that gdb cares about. Note that this is not the
whole link_map structure. */
objfile_lm_info.lm = xmalloc (lmo->link_map_size);
make_cleanup (xfree, objfile_lm_info.lm);
memset (objfile_lm_info.lm, 0, lmo->link_map_size);
/* Read the link map into our internal structure. */
read_memory (lm, objfile_lm_info.lm, lmo->link_map_size);
/* Read address of name from target memory to GDB. */
read_memory (lm + lmo->l_name_offset, l_name_buf, lmo->l_name_size);
/* Extract this object's name. Assume that the address is
unsigned. */
name_address = extract_unsigned_integer (l_name_buf, lmo->l_name_size);
target_read_string (name_address, &buffer,
SO_NAME_MAX_PATH_SIZE - 1, &errcode);
make_cleanup (xfree, buffer);
if (errcode != 0)
{
warning ("svr4_fetch_objfile_link_map: Can't read pathname for load map: %s\n",
safe_strerror (errcode));
}
else
{
/* Is this the linkmap for the file we want? */
/* If the file is not a shared library and has no name,
we are sure it is the main executable, so we return that. */
if ((buffer && strcmp (buffer, objfile->name) == 0)
|| (!(objfile->flags & OBJF_SHARED) && (strcmp (buffer, "") == 0)))
{
do_cleanups (old_chain);
return lm;
}
}
/* Not the file we wanted, continue checking. Assume that the
address is unsigned. */
lm = extract_unsigned_integer (objfile_lm_info.lm + lmo->l_next_offset,
lmo->l_next_size);
do_cleanups (old_chain);
}
return 0;
}
/* On some systems, the only way to recognize the link map entry for
the main executable file is by looking at its name. Return
non-zero iff SONAME matches one of the known main executable names. */
static int
match_main (char *soname)
{
char **mainp;
for (mainp = main_name_list; *mainp != NULL; mainp++)
{
if (strcmp (soname, *mainp) == 0)
return (1);
}
return (0);
}
/* Return 1 if PC lies in the dynamic symbol resolution code of the
SVR4 run time loader. */
static CORE_ADDR interp_text_sect_low;
static CORE_ADDR interp_text_sect_high;
static CORE_ADDR interp_plt_sect_low;
static CORE_ADDR interp_plt_sect_high;
static int
svr4_in_dynsym_resolve_code (CORE_ADDR pc)
{
return ((pc >= interp_text_sect_low && pc < interp_text_sect_high)
|| (pc >= interp_plt_sect_low && pc < interp_plt_sect_high)
|| in_plt_section (pc, NULL));
}
/* Given an executable's ABFD and target, compute the entry-point
address. */
static CORE_ADDR
exec_entry_point (struct bfd *abfd, struct target_ops *targ)
{
/* KevinB wrote ... for most targets, the address returned by
bfd_get_start_address() is the entry point for the start
function. But, for some targets, bfd_get_start_address() returns
the address of a function descriptor from which the entry point
address may be extracted. This address is extracted by
gdbarch_convert_from_func_ptr_addr(). The method
gdbarch_convert_from_func_ptr_addr() is the merely the identify
function for targets which don't use function descriptors. */
return gdbarch_convert_from_func_ptr_addr (current_gdbarch,
bfd_get_start_address (abfd),
targ);
}
/*
LOCAL FUNCTION
enable_break -- arrange for dynamic linker to hit breakpoint
SYNOPSIS
int enable_break (void)
DESCRIPTION
Both the SunOS and the SVR4 dynamic linkers have, as part of their
debugger interface, support for arranging for the inferior to hit
a breakpoint after mapping in the shared libraries. This function
enables that breakpoint.
For SunOS, there is a special flag location (in_debugger) which we
set to 1. When the dynamic linker sees this flag set, it will set
a breakpoint at a location known only to itself, after saving the
original contents of that place and the breakpoint address itself,
in it's own internal structures. When we resume the inferior, it
will eventually take a SIGTRAP when it runs into the breakpoint.
We handle this (in a different place) by restoring the contents of
the breakpointed location (which is only known after it stops),
chasing around to locate the shared libraries that have been
loaded, then resuming.
For SVR4, the debugger interface structure contains a member (r_brk)
which is statically initialized at the time the shared library is
built, to the offset of a function (_r_debug_state) which is guaran-
teed to be called once before mapping in a library, and again when
the mapping is complete. At the time we are examining this member,
it contains only the unrelocated offset of the function, so we have
to do our own relocation. Later, when the dynamic linker actually
runs, it relocates r_brk to be the actual address of _r_debug_state().
The debugger interface structure also contains an enumeration which
is set to either RT_ADD or RT_DELETE prior to changing the mapping,
depending upon whether or not the library is being mapped or unmapped,
and then set to RT_CONSISTENT after the library is mapped/unmapped.
*/
static int
enable_break (void)
{
int success = 0;
#ifdef BKPT_AT_SYMBOL
struct minimal_symbol *msymbol;
char **bkpt_namep;
asection *interp_sect;
/* First, remove all the solib event breakpoints. Their addresses
may have changed since the last time we ran the program. */
remove_solib_event_breakpoints ();
interp_text_sect_low = interp_text_sect_high = 0;
interp_plt_sect_low = interp_plt_sect_high = 0;
/* Find the .interp section; if not found, warn the user and drop
into the old breakpoint at symbol code. */
interp_sect = bfd_get_section_by_name (exec_bfd, ".interp");
if (interp_sect)
{
unsigned int interp_sect_size;
char *buf;
CORE_ADDR load_addr = 0;
int load_addr_found = 0;
struct so_list *so;
bfd *tmp_bfd = NULL;
struct target_ops *tmp_bfd_target;
int tmp_fd = -1;
char *tmp_pathname = NULL;
CORE_ADDR sym_addr = 0;
/* Read the contents of the .interp section into a local buffer;
the contents specify the dynamic linker this program uses. */
interp_sect_size = bfd_section_size (exec_bfd, interp_sect);
buf = alloca (interp_sect_size);
bfd_get_section_contents (exec_bfd, interp_sect,
buf, 0, interp_sect_size);
/* Now we need to figure out where the dynamic linker was
loaded so that we can load its symbols and place a breakpoint
in the dynamic linker itself.
This address is stored on the stack. However, I've been unable
to find any magic formula to find it for Solaris (appears to
be trivial on GNU/Linux). Therefore, we have to try an alternate
mechanism to find the dynamic linker's base address. */
tmp_fd = solib_open (buf, &tmp_pathname);
if (tmp_fd >= 0)
tmp_bfd = bfd_fdopenr (tmp_pathname, gnutarget, tmp_fd);
if (tmp_bfd == NULL)
goto bkpt_at_symbol;
/* Make sure the dynamic linker's really a useful object. */
if (!bfd_check_format (tmp_bfd, bfd_object))
{
warning ("Unable to grok dynamic linker %s as an object file", buf);
bfd_close (tmp_bfd);
goto bkpt_at_symbol;
}
/* Now convert the TMP_BFD into a target. That way target, as
well as BFD operations can be used. Note that closing the
target will also close the underlying bfd. */
tmp_bfd_target = target_bfd_reopen (tmp_bfd);
/* On a running target, we can get the dynamic linker's base
address from the shared library table. */
solib_add (NULL, 0, NULL, auto_solib_add);
so = master_so_list ();
while (so)
{
if (strcmp (buf, so->so_original_name) == 0)
{
load_addr_found = 1;
load_addr = LM_ADDR (so);
break;
}
so = so->next;
}
/* Otherwise we find the dynamic linker's base address by examining
the current pc (which should point at the entry point for the
dynamic linker) and subtracting the offset of the entry point. */
if (!load_addr_found)
load_addr = (read_pc ()
- exec_entry_point (tmp_bfd, tmp_bfd_target));
/* Record the relocated start and end address of the dynamic linker
text and plt section for svr4_in_dynsym_resolve_code. */
interp_sect = bfd_get_section_by_name (tmp_bfd, ".text");
if (interp_sect)
{
interp_text_sect_low =
bfd_section_vma (tmp_bfd, interp_sect) + load_addr;
interp_text_sect_high =
interp_text_sect_low + bfd_section_size (tmp_bfd, interp_sect);
}
interp_sect = bfd_get_section_by_name (tmp_bfd, ".plt");
if (interp_sect)
{
interp_plt_sect_low =
bfd_section_vma (tmp_bfd, interp_sect) + load_addr;
interp_plt_sect_high =
interp_plt_sect_low + bfd_section_size (tmp_bfd, interp_sect);
}
/* Now try to set a breakpoint in the dynamic linker. */
for (bkpt_namep = solib_break_names; *bkpt_namep != NULL; bkpt_namep++)
{
/* On ABI's that use function descriptors, there are usually
two linker symbols associated with each C function: one
pointing at the actual entry point of the machine code,
and one pointing at the function's descriptor. The
latter symbol has the same name as the C function.
What we're looking for here is the machine code entry
point, so we are only interested in symbols in code
sections. */
sym_addr = bfd_lookup_symbol (tmp_bfd, *bkpt_namep, SEC_CODE);
if (sym_addr != 0)
break;
}
/* We're done with both the temporary bfd and target. Remember,
closing the target closes the underlying bfd. */
target_close (tmp_bfd_target, 0);
if (sym_addr != 0)
{
create_solib_event_breakpoint (load_addr + sym_addr);
return 1;
}
/* For whatever reason we couldn't set a breakpoint in the dynamic
linker. Warn and drop into the old code. */
bkpt_at_symbol:
warning ("Unable to find dynamic linker breakpoint function.\nGDB will be unable to debug shared library initializers\nand track explicitly loaded dynamic code.");
}
/* Scan through the list of symbols, trying to look up the symbol and
set a breakpoint there. Terminate loop when we/if we succeed. */
breakpoint_addr = 0;
for (bkpt_namep = bkpt_names; *bkpt_namep != NULL; bkpt_namep++)
{
msymbol = lookup_minimal_symbol (*bkpt_namep, NULL, symfile_objfile);
if ((msymbol != NULL) && (SYMBOL_VALUE_ADDRESS (msymbol) != 0))
{
create_solib_event_breakpoint (SYMBOL_VALUE_ADDRESS (msymbol));
return 1;
}
}
/* Nothing good happened. */
success = 0;
#endif /* BKPT_AT_SYMBOL */
return (success);
}
/*
LOCAL FUNCTION
special_symbol_handling -- additional shared library symbol handling
SYNOPSIS
void special_symbol_handling ()
DESCRIPTION
Once the symbols from a shared object have been loaded in the usual
way, we are called to do any system specific symbol handling that
is needed.
For SunOS4, this consisted of grunging around in the dynamic
linkers structures to find symbol definitions for "common" symbols
and adding them to the minimal symbol table for the runtime common
objfile.
However, for SVR4, there's nothing to do.
*/
static void
svr4_special_symbol_handling (void)
{
}
/* Relocate the main executable. This function should be called upon
stopping the inferior process at the entry point to the program.
The entry point from BFD is compared to the PC and if they are
different, the main executable is relocated by the proper amount.
As written it will only attempt to relocate executables which
lack interpreter sections. It seems likely that only dynamic
linker executables will get relocated, though it should work
properly for a position-independent static executable as well. */
static void
svr4_relocate_main_executable (void)
{
asection *interp_sect;
CORE_ADDR pc = read_pc ();
/* Decide if the objfile needs to be relocated. As indicated above,
we will only be here when execution is stopped at the beginning
of the program. Relocation is necessary if the address at which
we are presently stopped differs from the start address stored in
the executable AND there's no interpreter section. The condition
regarding the interpreter section is very important because if
there *is* an interpreter section, execution will begin there
instead. When there is an interpreter section, the start address
is (presumably) used by the interpreter at some point to start
execution of the program.
If there is an interpreter, it is normal for it to be set to an
arbitrary address at the outset. The job of finding it is
handled in enable_break().
So, to summarize, relocations are necessary when there is no
interpreter section and the start address obtained from the
executable is different from the address at which GDB is
currently stopped.
[ The astute reader will note that we also test to make sure that
the executable in question has the DYNAMIC flag set. It is my
opinion that this test is unnecessary (undesirable even). It
was added to avoid inadvertent relocation of an executable
whose e_type member in the ELF header is not ET_DYN. There may
be a time in the future when it is desirable to do relocations
on other types of files as well in which case this condition
should either be removed or modified to accomodate the new file
type. (E.g, an ET_EXEC executable which has been built to be
position-independent could safely be relocated by the OS if
desired. It is true that this violates the ABI, but the ABI
has been known to be bent from time to time.) - Kevin, Nov 2000. ]
*/
interp_sect = bfd_get_section_by_name (exec_bfd, ".interp");
if (interp_sect == NULL
&& (bfd_get_file_flags (exec_bfd) & DYNAMIC) != 0
&& (exec_entry_point (exec_bfd, &exec_ops) != pc))
{
struct cleanup *old_chain;
struct section_offsets *new_offsets;
int i, changed;
CORE_ADDR displacement;
/* It is necessary to relocate the objfile. The amount to
relocate by is simply the address at which we are stopped
minus the starting address from the executable.
We relocate all of the sections by the same amount. This
behavior is mandated by recent editions of the System V ABI.
According to the System V Application Binary Interface,
Edition 4.1, page 5-5:
... Though the system chooses virtual addresses for
individual processes, it maintains the segments' relative
positions. Because position-independent code uses relative
addressesing between segments, the difference between
virtual addresses in memory must match the difference
between virtual addresses in the file. The difference
between the virtual address of any segment in memory and
the corresponding virtual address in the file is thus a
single constant value for any one executable or shared
object in a given process. This difference is the base
address. One use of the base address is to relocate the
memory image of the program during dynamic linking.
The same language also appears in Edition 4.0 of the System V
ABI and is left unspecified in some of the earlier editions. */
displacement = pc - exec_entry_point (exec_bfd, &exec_ops);
changed = 0;
new_offsets = xcalloc (symfile_objfile->num_sections,
sizeof (struct section_offsets));
old_chain = make_cleanup (xfree, new_offsets);
for (i = 0; i < symfile_objfile->num_sections; i++)
{
if (displacement != ANOFFSET (symfile_objfile->section_offsets, i))
changed = 1;
new_offsets->offsets[i] = displacement;
}
if (changed)
objfile_relocate (symfile_objfile, new_offsets);
do_cleanups (old_chain);
}
}
/*
GLOBAL FUNCTION
svr4_solib_create_inferior_hook -- shared library startup support
SYNOPSIS
void svr4_solib_create_inferior_hook()
DESCRIPTION
When gdb starts up the inferior, it nurses it along (through the
shell) until it is ready to execute it's first instruction. At this
point, this function gets called via expansion of the macro
SOLIB_CREATE_INFERIOR_HOOK.
For SunOS executables, this first instruction is typically the
one at "_start", or a similar text label, regardless of whether
the executable is statically or dynamically linked. The runtime
startup code takes care of dynamically linking in any shared
libraries, once gdb allows the inferior to continue.
For SVR4 executables, this first instruction is either the first
instruction in the dynamic linker (for dynamically linked
executables) or the instruction at "start" for statically linked
executables. For dynamically linked executables, the system
first exec's /lib/libc.so.N, which contains the dynamic linker,
and starts it running. The dynamic linker maps in any needed
shared libraries, maps in the actual user executable, and then
jumps to "start" in the user executable.
For both SunOS shared libraries, and SVR4 shared libraries, we
can arrange to cooperate with the dynamic linker to discover the
names of shared libraries that are dynamically linked, and the
base addresses to which they are linked.
This function is responsible for discovering those names and
addresses, and saving sufficient information about them to allow
their symbols to be read at a later time.
FIXME
Between enable_break() and disable_break(), this code does not
properly handle hitting breakpoints which the user might have
set in the startup code or in the dynamic linker itself. Proper
handling will probably have to wait until the implementation is
changed to use the "breakpoint handler function" method.
Also, what if child has exit()ed? Must exit loop somehow.
*/
static void
svr4_solib_create_inferior_hook (void)
{
/* Relocate the main executable if necessary. */
svr4_relocate_main_executable ();
if (!svr4_have_link_map_offsets ())
{
warning ("no shared library support for this OS / ABI");
return;
}
if (!enable_break ())
{
warning ("shared library handler failed to enable breakpoint");
return;
}
#if defined(_SCO_DS)
/* SCO needs the loop below, other systems should be using the
special shared library breakpoints and the shared library breakpoint
service routine.
Now run the target. It will eventually hit the breakpoint, at
which point all of the libraries will have been mapped in and we
can go groveling around in the dynamic linker structures to find
out what we need to know about them. */
clear_proceed_status ();
stop_soon = STOP_QUIETLY;
stop_signal = TARGET_SIGNAL_0;
do
{
target_resume (pid_to_ptid (-1), 0, stop_signal);
wait_for_inferior ();
}
while (stop_signal != TARGET_SIGNAL_TRAP);
stop_soon = NO_STOP_QUIETLY;
#endif /* defined(_SCO_DS) */
}
static void
svr4_clear_solib (void)
{
debug_base = 0;
}
static void
svr4_free_so (struct so_list *so)
{
xfree (so->lm_info->lm);
xfree (so->lm_info);
}
/* Clear any bits of ADDR that wouldn't fit in a target-format
data pointer. "Data pointer" here refers to whatever sort of
address the dynamic linker uses to manage its sections. At the
moment, we don't support shared libraries on any processors where
code and data pointers are different sizes.
This isn't really the right solution. What we really need here is
a way to do arithmetic on CORE_ADDR values that respects the
natural pointer/address correspondence. (For example, on the MIPS,
converting a 32-bit pointer to a 64-bit CORE_ADDR requires you to
sign-extend the value. There, simply truncating the bits above
TARGET_PTR_BIT, as we do below, is no good.) This should probably
be a new gdbarch method or something. */
static CORE_ADDR
svr4_truncate_ptr (CORE_ADDR addr)
{
if (TARGET_PTR_BIT == sizeof (CORE_ADDR) * 8)
/* We don't need to truncate anything, and the bit twiddling below
will fail due to overflow problems. */
return addr;
else
return addr & (((CORE_ADDR) 1 << TARGET_PTR_BIT) - 1);
}
static void
svr4_relocate_section_addresses (struct so_list *so,
struct section_table *sec)
{
sec->addr = svr4_truncate_ptr (sec->addr + LM_ADDR (so));
sec->endaddr = svr4_truncate_ptr (sec->endaddr + LM_ADDR (so));
}
/* Fetch a link_map_offsets structure for native targets using struct
definitions from link.h. See solib-legacy.c for the function
which does the actual work.
Note: For non-native targets (i.e. cross-debugging situations),
a target specific fetch_link_map_offsets() function should be
defined and registered via set_solib_svr4_fetch_link_map_offsets(). */
static struct link_map_offsets *
legacy_fetch_link_map_offsets (void)
{
if (legacy_svr4_fetch_link_map_offsets_hook)
return legacy_svr4_fetch_link_map_offsets_hook ();
else
{
internal_error (__FILE__, __LINE__,
"legacy_fetch_link_map_offsets called without legacy "
"link_map support enabled.");
return 0;
}
}
/* Fetch a link_map_offsets structure using the method registered in the
architecture vector. */
static struct link_map_offsets *
svr4_fetch_link_map_offsets (void)
{
struct link_map_offsets *(*flmo)(void) =
gdbarch_data (current_gdbarch, fetch_link_map_offsets_gdbarch_data);
if (flmo == NULL)
{
internal_error (__FILE__, __LINE__,
"svr4_fetch_link_map_offsets: fetch_link_map_offsets "
"method not defined for this architecture.");
return 0;
}
else
return (flmo ());
}
/* Return 1 if a link map offset fetcher has been defined, 0 otherwise. */
static int
svr4_have_link_map_offsets (void)
{
struct link_map_offsets *(*flmo)(void) =
gdbarch_data (current_gdbarch, fetch_link_map_offsets_gdbarch_data);
if (flmo == NULL
|| (flmo == legacy_fetch_link_map_offsets
&& legacy_svr4_fetch_link_map_offsets_hook == NULL))
return 0;
else
return 1;
}
/* set_solib_svr4_fetch_link_map_offsets() is intended to be called by
a <arch>_gdbarch_init() function. It is used to establish an
architecture specific link_map_offsets fetcher for the architecture
being defined. */
void
set_solib_svr4_fetch_link_map_offsets (struct gdbarch *gdbarch,
struct link_map_offsets *(*flmo) (void))
{
deprecated_set_gdbarch_data (gdbarch, fetch_link_map_offsets_gdbarch_data, flmo);
}
/* Initialize the architecture-specific link_map_offsets fetcher.
This is called after <arch>_gdbarch_init() has set up its `struct
gdbarch' for the new architecture, and is only called if the
link_map_offsets fetcher isn't already initialized (which is
usually done by calling set_solib_svr4_fetch_link_map_offsets()
above in <arch>_gdbarch_init()). Therefore we attempt to provide a
reasonable alternative (for native targets anyway) if the
<arch>_gdbarch_init() fails to call
set_solib_svr4_fetch_link_map_offsets(). */
static void *
init_fetch_link_map_offsets (struct gdbarch *gdbarch)
{
return legacy_fetch_link_map_offsets;
}
/* Most OS'es that have SVR4-style ELF dynamic libraries define a
`struct r_debug' and a `struct link_map' that are binary compatible
with the origional SVR4 implementation. */
/* Fetch (and possibly build) an appropriate `struct link_map_offsets'
for an ILP32 SVR4 system. */
struct link_map_offsets *
svr4_ilp32_fetch_link_map_offsets (void)
{
static struct link_map_offsets lmo;
static struct link_map_offsets *lmp = NULL;
if (lmp == NULL)
{
lmp = &lmo;
/* Everything we need is in the first 8 bytes. */
lmo.r_debug_size = 8;
lmo.r_map_offset = 4;
lmo.r_map_size = 4;
/* Everything we need is in the first 20 bytes. */
lmo.link_map_size = 20;
lmo.l_addr_offset = 0;
lmo.l_addr_size = 4;
lmo.l_name_offset = 4;
lmo.l_name_size = 4;
lmo.l_next_offset = 12;
lmo.l_next_size = 4;
lmo.l_prev_offset = 16;
lmo.l_prev_size = 4;
}
return lmp;
}
/* Fetch (and possibly build) an appropriate `struct link_map_offsets'
for an LP64 SVR4 system. */
struct link_map_offsets *
svr4_lp64_fetch_link_map_offsets (void)
{
static struct link_map_offsets lmo;
static struct link_map_offsets *lmp = NULL;
if (lmp == NULL)
{
lmp = &lmo;
/* Everything we need is in the first 16 bytes. */
lmo.r_debug_size = 16;
lmo.r_map_offset = 8;
lmo.r_map_size = 8;
/* Everything we need is in the first 40 bytes. */
lmo.link_map_size = 40;
lmo.l_addr_offset = 0;
lmo.l_addr_size = 8;
lmo.l_name_offset = 8;
lmo.l_name_size = 8;
lmo.l_next_offset = 24;
lmo.l_next_size = 8;
lmo.l_prev_offset = 32;
lmo.l_prev_size = 8;
}
return lmp;
}
static struct target_so_ops svr4_so_ops;
extern initialize_file_ftype _initialize_svr4_solib; /* -Wmissing-prototypes */
void
_initialize_svr4_solib (void)
{
fetch_link_map_offsets_gdbarch_data =
gdbarch_data_register_post_init (init_fetch_link_map_offsets);
svr4_so_ops.relocate_section_addresses = svr4_relocate_section_addresses;
svr4_so_ops.free_so = svr4_free_so;
svr4_so_ops.clear_solib = svr4_clear_solib;
svr4_so_ops.solib_create_inferior_hook = svr4_solib_create_inferior_hook;
svr4_so_ops.special_symbol_handling = svr4_special_symbol_handling;
svr4_so_ops.current_sos = svr4_current_sos;
svr4_so_ops.open_symbol_file_object = open_symbol_file_object;
svr4_so_ops.in_dynsym_resolve_code = svr4_in_dynsym_resolve_code;
/* FIXME: Don't do this here. *_gdbarch_init() should set so_ops. */
current_target_so_ops = &svr4_so_ops;
}
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