mirror of
https://github.com/darlinghq/darling-gdb.git
synced 2024-12-05 10:57:57 +00:00
303 lines
10 KiB
Plaintext
303 lines
10 KiB
Plaintext
\input texinfo
|
|
@setfilename ldint.info
|
|
|
|
@ifinfo
|
|
@format
|
|
START-INFO-DIR-ENTRY
|
|
* Ld-Internals: (ldint). The GNU linker internals.
|
|
END-INFO-DIR-ENTRY
|
|
@end format
|
|
@end ifinfo
|
|
|
|
@ifinfo
|
|
This file documents the internals of the GNU linker ld.
|
|
|
|
Copyright (C) 1992 Free Software Foundation, Inc.
|
|
Contributed by Cygnus Support.
|
|
|
|
Permission is granted to make and distribute verbatim copies of
|
|
this manual provided the copyright notice and this permission notice
|
|
are preserved on all copies.
|
|
|
|
@ignore
|
|
Permission is granted to process this file through Tex and print the
|
|
results, provided the printed document carries copying permission
|
|
notice identical to this one except for the removal of this paragraph
|
|
(this paragraph not being relevant to the printed manual).
|
|
|
|
@end ignore
|
|
Permission is granted to copy or distribute modified versions of this
|
|
manual under the terms of the GPL (for which purpose this text may be
|
|
regarded as a program in the language TeX).
|
|
@end ifinfo
|
|
|
|
@iftex
|
|
@finalout
|
|
@setchapternewpage off
|
|
@settitle GNU Linker Internals
|
|
@titlepage
|
|
@title{A guide to the internals of the GNU linker}
|
|
@author Per Bothner, Steve Chamberlain
|
|
@author Cygnus Support
|
|
@page
|
|
@end iftex
|
|
@tex
|
|
\def\$#1${{#1}} % Kluge: collect RCS revision info without $...$
|
|
\xdef\manvers{\$Revision$} % For use in headers, footers too
|
|
{\parskip=0pt
|
|
\hfill Cygnus Support\par
|
|
\hfill \manvers\par
|
|
\hfill \TeX{}info \texinfoversion\par
|
|
}
|
|
@end tex
|
|
|
|
@vskip 0pt plus 1filll
|
|
Copyright @copyright{} 1992 Free Software Foundation, Inc.
|
|
|
|
Permission is granted to make and distribute verbatim copies of
|
|
this manual provided the copyright notice and this permission notice
|
|
are preserved on all copies.
|
|
|
|
@end titlepage
|
|
|
|
@node Top, README, (dir), (dir)
|
|
|
|
This file documents the internals of the GNU linker @code{ld}. It is a
|
|
collection of miscellaneous information with little form at this point.
|
|
Mostly, it is a repository into which you can put information about
|
|
GNU @code{ld} as you discover it (or as you design changes to @code{ld}).
|
|
|
|
@menu
|
|
* README:: The README File
|
|
* Emulations:: How linker emulations are generated
|
|
* Porting:: Porting the linker
|
|
@end menu
|
|
|
|
@node README, Emulations, Top, Top
|
|
@chapter The @file{README} File
|
|
|
|
Check the @file{README} file; it often has useful information that does not
|
|
appear anywhere else in the directory.
|
|
|
|
@node Emulations, Porting, README, Top
|
|
@chapter How linker emulations are generated
|
|
|
|
The linker is controlled by linker scripts written in a linker
|
|
control language. A linker emulation gives the personality of
|
|
the linker, and is mainly defined by certain linker scripts.
|
|
If you want to understand how these scripts are generated,
|
|
the main file to look at is the @file{genscripts.sh} shell script,
|
|
which is invoked by the @file{Makefile} for each ``emulation''
|
|
to generate a set of 5 linker scripts.
|
|
|
|
For example, for the sun3 emulation used by ld68k, @file{genscripts.sh}
|
|
sources the file @file{emulparams/sun3.sh}, which sets the emulation
|
|
parameters, and specifies that the format is a.out, and to use
|
|
@file{scripttempl/aout.sc} to generate the linker scripts.
|
|
|
|
@code{genscripts.sh} generates 5 different linker scripts, one for each
|
|
of the @code{ld} options @samp{-z} (default), @samp{-n}, @samp{-N},
|
|
@samp{-r} and @samp{-Ur}, where each script is slightly different and is
|
|
generated using the template in @file{scripttempl/aout.sc} (for the sun3).
|
|
|
|
@node Porting, , Emulations, Top
|
|
@chapter Porting the linker
|
|
|
|
Before porting @code{ld} itself, you will need to port the BFD library;
|
|
see @file{../bfd/PORTING}.
|
|
|
|
The @dfn{host} is the system a tool runs @emph{on}.
|
|
The @dfn{target} is the system a tool runs @emph{for}; i.e.,
|
|
a tool can read and write the binaries of the target.
|
|
Most often, host==target, but @code{ld} supports cross-linking
|
|
(and to some extent the same @code{ld} binary can be used a linker
|
|
for multiple target architectures).
|
|
|
|
@menu
|
|
* New host:: Porting to a new host
|
|
* New target:: Porting to a new target
|
|
* New emulation:: Porting to a new emulation target
|
|
* Emulation script:: Writing @var{emulation}.sh
|
|
* Linker scripts:: Writing a new @var{script}.sc
|
|
* -n and -N options:: Handling -n and -N style binaries in your linker script
|
|
@end menu
|
|
|
|
@node New host, New target, , Porting
|
|
@section Porting to a new host
|
|
|
|
Pick a name for your host. Call that @var{host-type}.
|
|
You need to create the file @file{config/@var{host-type}.mh}.
|
|
|
|
@node New target, New emulation, New host, Porting
|
|
@section Porting to a new target
|
|
|
|
Pick a name for your target. Call that @var{target}.
|
|
You need to create at least @file{config/@var{target}.mt}.
|
|
It should contain
|
|
|
|
@example
|
|
EMUL=@var{emulation}
|
|
@end example
|
|
|
|
An @dfn{emulation} controls the ``personality'' of @code{ld},
|
|
such as the default linker script. Usually, the
|
|
@var{emulation} will have the same name as the @var{target},
|
|
and you will need to create a new @var{emulation} (see below).
|
|
|
|
You also need to edit @file{Makefile.in} and possibly @file{configure.in}.
|
|
To see how to do that, search for existing examples (e.g., @code{sun3},
|
|
@code{sun4}, @code{hp300bsd}).
|
|
|
|
@node New emulation, Emulation script, New target, Porting
|
|
@section Porting to a new emulation target
|
|
|
|
Pick a name for your target. Call that @var{emulation}.
|
|
Usually, @var{emulation} and @var{target} are the same.
|
|
You need to create at least @file{emulparams/@var{emulation}.sh}.
|
|
You also need to edit @file{Makefile.in}.
|
|
To see how to do that, search for existing examples.
|
|
|
|
The file @file{emulparams/@var{emulation}.sh} defines a set of
|
|
parameters that are used to generate the emulation. Its syntax is that
|
|
of a Bourne shell script. It is ``sourced'' by @file{genscripts.sh}.
|
|
|
|
@node Emulation script, Linker scripts, New emulation, Porting
|
|
@section Writing @file{@var{emulation}.sh}
|
|
|
|
Usually, @file{@var{emulation}.sh} contains:
|
|
@example
|
|
EMULATION_NAME=@var{emulation}
|
|
SCRIPT_NAME=@var{script}
|
|
OUTPUT_FORMAT="@var{target-name}"
|
|
TEXT_START_ADDR=@var{text-start-addr}
|
|
PAGE_SIZE=@var{page-size}
|
|
SEGMENT_SIZE=@var{segment-size} # If different from PAGE_SIZE.
|
|
ARCH=@var{arch}
|
|
@end example
|
|
|
|
Here:
|
|
@table @code
|
|
@item @var{target-name}
|
|
Matches the @code{filename} field of the @code{bfd_target} you want
|
|
to use. (This is a string, and currently the first field.)
|
|
For an a.out target, @var{target-name} matches the @code{TARGETNAME}
|
|
defined in @file{../bfd/@var{target}.c}.
|
|
|
|
@item @var{arch}
|
|
The architecture: e.g., @code{m68k}, @code{sparc}, @dots{}.
|
|
|
|
@item @var{script}
|
|
The file @file{scripttempl/@var{script}.sc} is a shell script which,
|
|
when evaluated (by @file{genscripts.sh}), writes a linker script file to
|
|
standard output. You may need to write a new script. If you use the
|
|
a.out format or something similar, you can probably set
|
|
@example
|
|
SCRIPT_NAME=aout
|
|
@end example
|
|
|
|
@item @var{text-start-addr}
|
|
@itemx @var{page-size}
|
|
@itemx @var{segment-size}
|
|
These set the shell variables @code{TEXT_START_ADDR}, @code{PAGE_SIZE},
|
|
and @code{SEGMENT_SIZE} for use by @file{scripttempl/@var{script}.sc}.
|
|
If your script doesn't use these variables, you
|
|
don't have to define the variables,
|
|
For emulations using a.out files, you can get these
|
|
values from @file{../bfd/@var{target}.c}.
|
|
@end table
|
|
|
|
In some cases, you may need more more definitions.
|
|
For example, if you can't use @file{emultempl/generic.em},
|
|
you may need to add:
|
|
@example
|
|
TEMPLATE_NAME=@var{emulation}
|
|
@end example
|
|
and write your own @file{emultempl/@var{emulation}.em} file.
|
|
|
|
@node Linker scripts, -n and -N options, Emulation script, Porting
|
|
@section Writing a new linker script @file{scripttempl/@var{script}.sc}
|
|
|
|
You may need to write a new script file for your emulation.
|
|
|
|
Your script can use the shell variable @code{LD_FLAG}, which has the value:
|
|
@table @code
|
|
@item LD_FLAG=
|
|
when building a script to be used by default
|
|
@item LD_FLAG=n
|
|
when building a script to be used for @samp{ld -n}
|
|
@item LD_FLAG=N
|
|
when building a script to be used for @samp{ld -N}
|
|
@item LD_FLAG=r
|
|
when building a script to be used for @samp{ld -r}
|
|
@item LD_FLAG=u
|
|
when building a script to be used for @samp{ld -Ur}
|
|
@end table
|
|
|
|
The variable @code{RELOCATING} is only set if relocation is happening
|
|
(i.e., unless the linker is invoked with @samp{-r}).
|
|
Thus your script should has an action @code{@var{ACTION}}
|
|
that should only be done when relocating,
|
|
express that as:
|
|
@example
|
|
$@{RELOCATING+ ACTION@}
|
|
@end example
|
|
This is the case for most assignments, which should look like:
|
|
@example
|
|
$@{RELOCATING+ _end = .@}
|
|
@end example
|
|
|
|
Also, you should assign absolute addresses to sections only
|
|
when relocating, so:
|
|
@example
|
|
.text $@{RELOCATING+ $@{TEXT_START_ADDR@}@}:
|
|
@end example
|
|
|
|
The form:
|
|
@example
|
|
.section @{ ... @} > section
|
|
@end example
|
|
should be:
|
|
@example
|
|
.section @{ ... @} > $@{RELOCATING+ section@}
|
|
@end example
|
|
|
|
@code{RELOCATING} is set except when @code{LD_FLAG=r} or @code{LD_FLAG=u}.
|
|
@code{CONSTRUCTING} is set except when @code{LD_FLAG=u}.
|
|
|
|
Alignment of the data segments is controlled by the variables
|
|
@code{DATA_ALIGNMENT_} (note trailing underscore),
|
|
@code{DATA_ALIGNMENT_n}, @code{DATA_ALIGNMENT_N},
|
|
@code{DATA_ALIGNMENT_r}, or @code{DATA_ALIGNMENT_u} depending on the
|
|
value of @code{LD_FLAGS}. Normally, the default value works (this is
|
|
@code{"ALIGN($@{SEGMENT_SIZE@})"} for the @samp{_n}, and @samp{__}
|
|
(default) variants; @code{"."} for the @samp{_N}, variant; and @code{""}
|
|
for the @samp{_r} and @samp{_u} variants).
|
|
|
|
@node -n and -N options, , Linker scripts, Porting
|
|
@section Handling @samp{-n} and @samp{-N} style binaries in your linker script
|
|
|
|
The @samp{-n} linker option requests the linker to create a binary
|
|
with a write-protected text segment, but not demand-pagable (@code{NMAGIC}).
|
|
SunOS starts the text segment for demand-paged binaries at 0x2020
|
|
and other binaries at 0x2000, since the exec header (0x20 bytes)
|
|
is paged in with the text. Some other Unix variants do the same.
|
|
|
|
In that case, the @file{emulparams/@var{emulation}.sh} should define:
|
|
@table @code
|
|
@item NONPAGED_TEXT_START_ADDR
|
|
The text start address to use when linking with @samp{-n} or @samp{-N} options.
|
|
@end table
|
|
|
|
For example, on a sun4:
|
|
@example
|
|
TEXT_START_ADDR=0x2020
|
|
NONPAGED_TEXT_START_ADDR=0x2000
|
|
@end example
|
|
|
|
The @samp{-N} linker option creates a binary with a non-write-protected
|
|
text segment (@code{NMAGIC}). This is like @samp{-n}, except that the
|
|
data segment needs not be page-aligned.
|
|
|
|
@contents
|
|
@bye
|