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80070c0d34
binutils-gdb/ld
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Maciej W. Rozycki 80070c0d34 PR ld/21233: Avoid sweeping forced-undefined symbols in section GC 
Complement commit 902e9fc76a ("PR ld/20828: Move symbol version
processing ahead of GC symbol sweep"), commit b531344c34 ("PR
ld/20828: Reorder the symbol sweep stage of section GC") and commit
81ff47b3a5 ("PR ld/20828: Fix linker script symbols wrongly forced
local with section GC"), and prevent symbols forcibly entered in the
output file with the use of the `--undefined=' or `--require-defined='
linker command line options or the EXTERN linker script command from
being swept in section garbage collection and consequently recorded in
the dynamic symbol table as local entries.  This happens in certain
circumstances, where a symbol reference also exists in one of the static
input files, however only in a section which is garbage-collected and
does not make it to the output file, and the symbol is defined in a
dynamic object present in the link.

For example with the `i386-linux' target and the `pr21233.s' and
`pr21233-l.s' sources, and the `pr21233.ld' linker script included with
this change we get:

$ as -o pr21233-l.o pr21233-l.s
$ ld -shared -T pr21233.ld -o libpr21233.so pr21233-l.o
$ as -o pr21233.o pr21233.s
$ ld --gc-sections -e foo --require-defined=bar -T pr21233.ld -o pr21233 pr21233.o libpr21233.so
$ readelf --dyn-syms pr21233

Symbol table '.dynsym' contains 2 entries:
   Num:    Value  Size Type    Bind   Vis      Ndx Name
     0: 00000000     0 NOTYPE  LOCAL  DEFAULT  UND
     1: 00000000     0 OBJECT  LOCAL  DEFAULT  UND bar
$

which makes the run-time `bar' dependency of the `pr21233' executable
different from its corresponding link-time dependency, i.e. the presence
of `libpr21233.so' and its `bar' symbol is required at the link time,
however at the run time a copy of `libpr21233.so' without `bar' will do.
Similarly with `--undefined=' and EXTERN which do not actually require
the reference to the symbol requested to be satisfied with a definition
at the link time, however once the definition has been pulled at the
link time, so it should at the dynamic load time.

Additionally with the `mips-linux' target we get:

$ ld --gc-sections -e foo --require-defined=bar -T pr21233.ld -o pr21233 pr21233.o libpr21233.so
ld: BFD (GNU Binutils) 2.28.51.20170324 assertion fail .../bfd/elfxx-mips.c:3861
$

as the target is not prepared to handle such a local dynamic symbol.

With this change in effect we get:

$ readelf --dyn-syms pr21233

Symbol table '.dynsym' contains 2 entries:
   Num:    Value  Size Type    Bind   Vis      Ndx Name
     0: 00000000     0 NOTYPE  LOCAL  DEFAULT  UND
     1: 00000000     0 OBJECT  GLOBAL DEFAULT  UND bar
$

instead, for both targets.

	ld/
	PR ld/21233
	* ldlang.c (insert_undefined): Set `mark' for ELF symbols.
	* testsuite/ld-elf/pr21233.sd: New test.
	* testsuite/ld-elf/pr21233-l.sd: New test.
	* testsuite/ld-elf/pr21233.ld: New test linker script.
	* testsuite/ld-elf/pr21233-e.ld: New test linker script.
	* testsuite/ld-elf/pr21233.s: New test source.
	* testsuite/ld-elf/pr21233-l.s: New test source.
	* testsuite/ld-elf/shared.exp: Run the new tests.
2017-04-04 23:21:44 +01:00
..
emulparams PowerPC: incorrect library search order 2017-03-13 17:51:38 +10:30
emultempl Support ELF SHF_GNU_MBIND and PT_GNU_MBIND_XXX 2017-04-04 09:06:04 -07:00
po Add Serbian translation for the LD directory. 2017-01-27 11:27:50 +00:00
scripttempl Place read-only data in the text section on AVR Tiny targets. 2017-02-27 17:05:53 +00:00
testsuite PR ld/21233: Avoid sweeping forced-undefined symbols in section GC 2017-04-04 23:21:44 +01:00
.gitignore
aclocal.m4
ChangeLog PR ld/21233: Avoid sweeping forced-undefined symbols in section GC 2017-04-04 23:21:44 +01:00
ChangeLog-0001
ChangeLog-0203
ChangeLog-2004
ChangeLog-2005
ChangeLog-2006
ChangeLog-2007
ChangeLog-2008
ChangeLog-2009
ChangeLog-2010
ChangeLog-2011
ChangeLog-2012
ChangeLog-2013
ChangeLog-2014
ChangeLog-2015
ChangeLog-2016 ChangeLog rotation 2017-01-02 13:55:05 +10:30
ChangeLog-9197
ChangeLog-9899
config.in
configure Add Serbian translation for the LD directory. 2017-01-27 11:27:50 +00:00
configure.ac Add Serbian translation for the LD directory. 2017-01-27 11:27:50 +00:00
configure.host Run more ld tests when not native 2017-01-02 23:48:08 +10:30
configure.tgt IA16 support 2017-04-03 09:13:19 -07:00
deffile.h Update year range in copyright notice of all files. 2017-01-02 14:08:56 +10:30
deffilep.y Update year range in copyright notice of all files. 2017-01-02 14:08:56 +10:30
dep-in.sed
elf-hints-local.h
fdl.texi
gen-doc.texi Update year range in copyright notice of all files. 2017-01-02 14:08:56 +10:30
genscrba.sh
genscripts.sh Update year range in copyright notice of all files. 2017-01-02 14:08:56 +10:30
h8-doc.texi Update year range in copyright notice of all files. 2017-01-02 14:08:56 +10:30
ld.h Update year range in copyright notice of all files. 2017-01-02 14:08:56 +10:30
ld.texinfo Don't run new orphan tests on i860 and i960 2017-03-11 10:51:56 +10:30
ldbuildid.c Update year range in copyright notice of all files. 2017-01-02 14:08:56 +10:30
ldbuildid.h Update year range in copyright notice of all files. 2017-01-02 14:08:56 +10:30
ldcref.c Update year range in copyright notice of all files. 2017-01-02 14:08:56 +10:30
ldctor.c Update year range in copyright notice of all files. 2017-01-02 14:08:56 +10:30
ldctor.h Update year range in copyright notice of all files. 2017-01-02 14:08:56 +10:30
ldemul.c Update year range in copyright notice of all files. 2017-01-02 14:08:56 +10:30
ldemul.h Update year range in copyright notice of all files. 2017-01-02 14:08:56 +10:30
ldexp.c Update year range in copyright notice of all files. 2017-01-02 14:08:56 +10:30
ldexp.h Update year range in copyright notice of all files. 2017-01-02 14:08:56 +10:30
ldfile.c Update year range in copyright notice of all files. 2017-01-02 14:08:56 +10:30
ldfile.h Update year range in copyright notice of all files. 2017-01-02 14:08:56 +10:30
ldgram.y Update year range in copyright notice of all files. 2017-01-02 14:08:56 +10:30
ldint.texinfo Update year range in copyright notice of all files. 2017-01-02 14:08:56 +10:30
ldlang.c PR ld/21233: Avoid sweeping forced-undefined symbols in section GC 2017-04-04 23:21:44 +01:00
ldlang.h Update year range in copyright notice of all files. 2017-01-02 14:08:56 +10:30
ldlex-wrapper.c Update year range in copyright notice of all files. 2017-01-02 14:08:56 +10:30
ldlex.h Use noyywrap option in lex files. 2017-01-04 16:05:22 +00:00
ldlex.l Use noyywrap option in lex files. 2017-01-04 16:05:22 +00:00
ldmain.c Fix buffer overflows in ld when printing translated strings. 2017-01-31 12:07:04 +00:00
ldmain.h Update year range in copyright notice of all files. 2017-01-02 14:08:56 +10:30
ldmisc.c LD: vfinfo: Make clever formatters consistent WRT function name reporting 2017-02-15 13:41:51 +00:00
ldmisc.h Update year range in copyright notice of all files. 2017-01-02 14:08:56 +10:30
ldver.c Update year range in copyright notice of all files. 2017-01-02 14:08:56 +10:30
ldver.h Update year range in copyright notice of all files. 2017-01-02 14:08:56 +10:30
ldwrite.c Update year range in copyright notice of all files. 2017-01-02 14:08:56 +10:30
ldwrite.h Update year range in copyright notice of all files. 2017-01-02 14:08:56 +10:30
lexsup.c Update year range in copyright notice of all files. 2017-01-02 14:08:56 +10:30
MAINTAINERS Update year range in copyright notice of all files. 2017-01-02 14:08:56 +10:30
Makefile.am [ARC] Add new linker emulation for nps 2017-01-10 10:55:13 +00:00
Makefile.in [ARC] Add new linker emulation for nps 2017-01-10 10:55:13 +00:00
mri.c Update year range in copyright notice of all files. 2017-01-02 14:08:56 +10:30
mri.h Update year range in copyright notice of all files. 2017-01-02 14:08:56 +10:30
NEWS Support ELF SHF_GNU_MBIND and PT_GNU_MBIND_XXX 2017-04-04 09:06:04 -07:00
pe-dll.c Make the linker fail if asked to create more than 1^16 ordinal values for PE targets. 2017-03-03 11:35:03 +00:00
pe-dll.h Update year range in copyright notice of all files. 2017-01-02 14:08:56 +10:30
pep-dll.c Update year range in copyright notice of all files. 2017-01-02 14:08:56 +10:30
pep-dll.h Update year range in copyright notice of all files. 2017-01-02 14:08:56 +10:30
plugin.c Update year range in copyright notice of all files. 2017-01-02 14:08:56 +10:30
plugin.h Update year range in copyright notice of all files. 2017-01-02 14:08:56 +10:30
README Update year range in copyright notice of all files. 2017-01-02 14:08:56 +10:30
stamp-h.in
sysdep.h Update year range in copyright notice of all files. 2017-01-02 14:08:56 +10:30
testplug2.c Update year range in copyright notice of all files. 2017-01-02 14:08:56 +10:30
testplug3.c Update year range in copyright notice of all files. 2017-01-02 14:08:56 +10:30
testplug4.c Update year range in copyright notice of all files. 2017-01-02 14:08:56 +10:30
testplug.c Update year range in copyright notice of all files. 2017-01-02 14:08:56 +10:30
TODO

README

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		README for LD

This is the GNU linker.  It is distributed with other "binary
utilities" which should be in ../binutils.  See ../binutils/README for
more general notes, including where to send bug reports.

There are many features of the linker:

* The linker uses a Binary File Descriptor library (../bfd)
  that it uses to read and write object files.  This helps
  insulate the linker itself from the format of object files.

* The linker supports a number of different object file
  formats.  It can even handle multiple formats at once:
  Read two input formats and write a third.

* The linker can be configured for cross-linking.

* The linker supports a control language.

* There is a user manual (ld.texinfo), as well as the
  beginnings of an internals manual (ldint.texinfo).

Installation
============

See ../binutils/README.

If you want to make a cross-linker, you may want to specify
a different search path of -lfoo libraries than the default.
You can do this by setting the LIB_PATH variable in ./Makefile
or using the --with-lib-path configure switch.

To build just the linker, make the target all-ld from the top level
directory (one directory above this one).

Porting to a new target
=======================

See the ldint.texinfo manual.

Reporting bugs etc
===========================

See ../binutils/README.

Known problems
==============

The Solaris linker normally exports all dynamic symbols from an
executable.  The GNU linker does not do this by default.  This is
because the GNU linker tries to present the same interface for all
similar targets (in this case, all native ELF targets).  This does not
matter for normal programs, but it can make a difference for programs
which try to dlopen an executable, such as PERL or Tcl.  You can make
the GNU linker export all dynamic symbols with the -E or
--export-dynamic command line option.

HP/UX 9.01 has a shell bug that causes the linker scripts to be
generated incorrectly.  The symptom of this appears to be "fatal error
- scanner input buffer overflow" error messages.  There are various
workarounds to this:
  * Build and install bash, and build with "make SHELL=bash".
  * Update to a version of HP/UX with a working shell (e.g., 9.05).
  * Replace "(. ${srcdir}/scripttempl/${SCRIPT_NAME}.sc)" in
    genscripts.sh with "sh ${srcdir}..." (no parens) and make sure the
    emulparams script used exports any shell variables it sets.

Copyright (C) 2012-2017 Free Software Foundation, Inc.

Copying and distribution of this file, with or without modification,
are permitted in any medium without royalty provided the copyright
notice and this notice are preserved.