binutils-gdb/ld
H.J. Lu 38b123494b x86-64: Improve PLT generation and synthetic PLT symbols
On x86-64, the procedure linkage table (PLT) is used to

1. Call external function.
2. Call internal IFUNC function.  The best implementation is selected
for the target processor at run-time.
3. Act as the canonical function address.
4. Support LD_AUDIT to audit external function calls.
5. Support LD_PROFILE to profile external function calls.

PLT looks like:

PLT0:  push  GOT[1]
       jmp   *GOT[2]
       nop
PLT1:  jmp   *GOT[name1_index]
       push  name1_reloc_index
       jmp   PLT0

GOT is an array of addresses.  Initially the GOT entry of name1 is
filled with the address of the "push name1_reloc_index" instruction.
The function, name1, is called via "jmp *GOT[name1]" in the PLT entry.
Even when lazy binding is disabled by "-z now", the PLT0 entry may
still be used with LD_AUDIT or LD_PROFILE if PLT entry is used for
canonical function address.

When linker is invoked with "-z bndplt", a different PLT layout in .plt
is used:

PLT0:  push     GOT[1]
       bnd jmp  *GOT[2]
       nop
PLT1:  push     name1_reloc_index
       bnd jmp  PLT0
       nop

together with a second PLT section, .pl.bnd:

PLT1:  bnd jmp  *GOT[name1_index]
       nop

where the GOT entry of name1 is filled with the address of the push
instruction of the corresponding entry in .plt.

1. With lazy binding, when the external function, name1, is called the
first time, dynamic linker is called via PLT0 to update GOT[name1_index]
with the actual address of name1 and transfers control to name1
afterwards.
2. PLT is also used to call a local IFUNC function, name1, run-time
loader updates GOT[name1_index] when loading the module.

This patch

1. Remove PLT layout configurations from x86-64 backend_data.
2. Add generic, lay and non-lazy PLT layout configurations to x86-64
link_hash_table.  Generic PLT layout includes the PLT entry templates,
information how to update the first instruction in PLT and PLT eh_frame
informaton, which are initialized in x86-64 setup_gnu_properties, based
on "-z bndplt" and target selection.  PLT section alignment is also set
to PLT entry size for non-NaCl target.
3. Remove elf_x86_64_create_dynamic_sections.  create_dynamic_sections
isn't always called, but GOT relocations need GOT relocations.  Instead,
create all x86-64 specific dynamic sections with alignment to their entry
size  in x86-64 setup_gnu_properties, which initializes elf.dynobj, so
that x86-64 check_relocs can be simplified.
4. Rewrite elf_x86_64_get_synthetic_symtab to check PLT sections against
all dynamic relocations to support both lazy and non-lazy PLTs.

There is no change in PLT.  The only externally visible change is the
improvement of synthetic PLT symbols for .plt.got.

bfd/

	* elf64-x86-64.c (PLT_ENTRY_SIZE): Renamed to ...
	(LAZY_PLT_ENTRY_SIZE): This.
	(NON_LAZY_PLT_ENTRY_SIZE): New.
	(elf_x86_64_plt0_entry): Renamed to ...
	(elf_x86_64_lazy_plt0_entry): This.
	(elf_x86_64_plt_entry): Renamed to ...
	(elf_x86_64_lazy_plt_entry): This.
	(elf_x86_64_bnd_plt0_entry): Renamed to ...
	(elf_x86_64_lazy_bnd_plt0_entry): This.
	(elf_x86_64_legacy_plt_entry): Removed.
	(elf_x86_64_bnd_plt_entry): Renamed to ...
	(elf_x86_64_lazy_bnd_plt_entry): This.
	(elf_x86_64_legacy_plt2_entry): Renamed to ...
	(elf_x86_64_non_lazy_plt_entry): This.
	(elf_x86_64_bnd_plt2_entry): Renamed to ...
	(elf_x86_64_non_lazy_bnd_plt_entry): This.
	(elf_x86_64_eh_frame_plt): Renamed to ...
	(elf_x86_64_eh_frame_lazy_plt): This.
	(elf_x86_64_eh_frame_bnd_plt): Renamed to ...
	(elf_x86_64_eh_frame_lazy_bnd_plt): This.
	(elf_x86_64_eh_frame_plt_got): Renamed to ...
	(elf_x86_64_eh_frame_non_lazy_plt): This.
	(elf_x86_64_lazy_plt_layout): New.
	(elf_x86_64_non_lazy_plt_layout): Likewise.
	(elf_x86_64_plt_layout): Likewise.
	(elf_x86_64_backend_data): Remove PLT layout information.  Add
	os for target system.
	(GET_PLT_ENTRY_SIZE): Removed.
	(elf_x86_64_lazy_plt): New.
	(elf_x86_64_non_lazy_plt): Likewise.
	(elf_x86_64_lazy_bnd_plt): Likewise.
	(elf_x86_64_non_lazy_bnd_plt): Likewise.
	(elf_x86-64_arch_bed): Updated.
	(elf_x86_64_link_hash_table): Add plt, lazy_plt and non_lazy_plt.
	(elf_x86_64_create_dynamic_sections): Removed.
	(elf_x86_64_check_relocs): Don't check elf.dynobj.  Don't call
	_bfd_elf_create_ifunc_sections nor _bfd_elf_create_got_section.
	(elf_x86-64_adjust_dynamic_symbol): Updated.
	(elf_x86_64_allocate_dynrelocs): Updated.  Pass 0 as PLT header
	size to _bfd_elf_allocate_ifunc_dyn_relocs and don't allocate
	size for PLT0 if there is no PLT0.  Get plt_entry_size from
	non_lazy_plt for non-lazy PLT entries.
	(elf_x86_64_size_dynamic_sections): Updated.  Get plt_entry_size
	from non_lazy_plt for non-lazy PLT entries.
	(elf_x86-64_relocate_section): Updated.  Properly get PLT index
	if there is no PLT0.
	(elf_x86_64_finish_dynamic_symbol): Updated.  Fill the first slot
	in the PLT entry with generic PLT layout.  Fill the non-lazy PLT
	entries with non-lazy PLT layout.  Don't fill the second and third
	slots in the PLT entry if there is no PLT0.
	(elf_x86_64_finish_dynamic_sections): Updated.  Don't fill PLT0
	if there is no PLT0.  Set sh_entsize on the .plt.got section.
	(compare_relocs): New.
	(elf_x86_64_plt_type): Likewise.
	(elf_x86_64_plt): Likewise.
	(elf_x86_64_nacl_plt): New. Forward declaration.
	(elf_x86_64_get_plt_sym_val): Removed.
	(elf_x86_64_get_synthetic_symtab): Rewrite to check PLT sections
	against all dynamic relocations.
	(elf_x86_64_link_setup_gnu_properties): New function.
	(elf_backend_create_dynamic_sections): Updated.
	(elf_backend_setup_gnu_properties): New.
	(elf_x86_64_nacl_plt): New.
	(elf_x86_64_nacl_arch_bed): Updated.

ld/

	* testsuite/ld-ifunc/ifunc-16-x86-64-now.d: New file.
	* testsuite/ld-ifunc/ifunc-2-local-x86-64-now.d: Likewise.
	* testsuite/ld-ifunc/ifunc-2-x86-64-now.d: Likewise.
	* testsuite/ld-ifunc/pr17154-x86-64-now.d: Likewise.
	* testsuite/ld-x86-64/bnd-branch-1-now.d: Likewise.
	* testsuite/ld-x86-64/bnd-ifunc-1-now.d: Likewise.
	* testsuite/ld-x86-64/bnd-ifunc-2-now.d: Likewise.
	* testsuite/ld-x86-64/bnd-plt-1-now.d: Likewise.
	* testsuite/ld-x86-64/mpx3n.dd: Likewise.
	* testsuite/ld-x86-64/mpx4n.dd: Likewise.
	* testsuite/ld-x86-64/plt-main-bnd-now.rd: Likewise.
	* testsuite/ld-x86-64/plt2.dd: Likewise.
	* testsuite/ld-x86-64/plt2.rd: Likewise.
	* testsuite/ld-x86-64/plt2.s: Likewise.
	* testsuite/ld-x86-64/pr20830a-now.d: Likewise.
	* testsuite/ld-x86-64/pr20830b-now.d: Likewise.
	* testsuite/ld-x86-64/pr21038a-now.d: Likewise.
	* testsuite/ld-x86-64/pr21038b-now.d: Likewise.
	* testsuite/ld-x86-64/pr21038c-now.d: Likewise.
	* testsuite/ld-x86-64/load1b-nacl.d: Updated.
	* testsuite/ld-x86-64/load1b.d: Likewise.
	* testsuite/ld-x86-64/plt-main-bnd.dd: Likewise.
	* testsuite/ld-x86-64/pr20253-1h.d: Likewise.
	* testsuite/ld-x86-64/pr20830a.d: Update the .plt.got section
	with func@plt.
	* testsuite/ld-x86-64/pr20830b.d: Likewise.
	* testsuite/ld-x86-64/pr21038a.d: Likewise.
	* testsuite/ld-x86-64/pr21038c.d: Likewise.
	* testsuite/ld-x86-64/mpx.exp: Add some -z now tests.
	* testsuite/ld-x86-64/x86-64.exp: Likewise.
2017-05-08 12:24:29 -07:00
..
emulparams Implement -z dynamic-undefined-weak 2017-04-19 20:39:52 +09:30
emultempl PR 21274, ld segfaults linking PE DLL 2017-04-11 19:49:13 +09:30
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 x86-64: Improve PLT generation and synthetic PLT symbols 2017-05-08 12:24:29 -07:00
.gitignore bfd/binutils/gas/gprof/ld/libiberty/opcodes: add .gitignore 2010-12-09 09:03:18 +00:00
aclocal.m4 Regenerate Makefile.in/aclocal.m4 automake 1.11.6 2016-04-15 16:20:55 -07:00
ChangeLog x86-64: Improve PLT generation and synthetic PLT symbols 2017-05-08 12:24:29 -07:00
ChangeLog-0001 Add copyright notices 2012-12-10 12:48:03 +00:00
ChangeLog-0203 Add copyright notices 2012-12-10 12:48:03 +00:00
ChangeLog-2004 Add copyright notices 2012-12-10 12:48:03 +00:00
ChangeLog-2005 Add copyright notices 2012-12-10 12:48:03 +00:00
ChangeLog-2006 Add copyright notices 2012-12-10 12:48:03 +00:00
ChangeLog-2007 Add copyright notices 2012-12-10 12:48:03 +00:00
ChangeLog-2008 strip off +x bits on non-executable/script files 2013-12-07 02:03:03 -05:00
ChangeLog-2009 Remove trailing spaces in ld 2015-08-12 04:46:43 -07:00
ChangeLog-2010 Add copyright notices 2012-12-10 12:48:03 +00:00
ChangeLog-2011 Add copyright notices 2012-12-10 12:48:03 +00:00
ChangeLog-2012 Rotate binutils ChangeLog for 2013 2013-01-02 17:06:32 +00:00
ChangeLog-2013 New Year - binutils ChangeLog rotation 2014-01-08 05:32:12 -08:00
ChangeLog-2014 ChangeLog rotatation and copyright year update 2015-01-02 00:53:45 +10:30
ChangeLog-2015 binutils ChangeLog rotation 2016-01-01 22:59:17 +10:30
ChangeLog-2016 ChangeLog rotation 2017-01-02 13:55:05 +10:30
ChangeLog-9197 Remove trailing spaces in ld 2015-08-12 04:46:43 -07:00
ChangeLog-9899 Add copyright notices 2012-12-10 12:48:03 +00:00
config.in Remove support for $PLATFORM in rpath search paths. 2016-11-04 13:57:40 +00:00
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 Remove trailing white spaces in ld 2013-01-10 20:08:03 +00:00
fdl.texi etc/ChangeLog 2010-06-08 10:30:56 +00:00
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 Implement -z dynamic-undefined-weak 2017-04-19 20:39:52 +09:30
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 Implement -z dynamic-undefined-weak 2017-04-19 20:39:52 +09:30
Makefile.in Implement -z dynamic-undefined-weak 2017-04-19 20:39:52 +09:30
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 PR 21274, ld segfaults linking PE DLL 2017-04-11 19:49:13 +09:30
pe-dll.h PR 21274, ld segfaults linking PE DLL 2017-04-11 19:49:13 +09:30
pep-dll.c Update year range in copyright notice of all files. 2017-01-02 14:08:56 +10:30
pep-dll.h PR 21274, ld segfaults linking PE DLL 2017-04-11 19:49:13 +09:30
plugin.c Handle symbol defined in IR and referenced in DSO 2017-04-20 07:48:35 -07:00
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

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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.