binutils-gdb/ld
H.J. Lu f604c2a2a5 i386: Improve PLT generation and synthetic PLT symbols
On i386, 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.

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 i386 backend_data.
2. Add generic, lay and non-lazy PLT layout configurations to i386
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 i386 setup_gnu_properties, based
on PIC and target selection.  PLT section alignment is also set to PLT
entry size for non-NaCl/VxWorks target.
3. Remove elf_i386_create_dynamic_sections.  create_dynamic_sections
isn't always called, but GOT relocations need GOT relocations.  Instead,
create all i386 specific dynamic sections in i386 setup_gnu_properties,
which initializes elf.dynobj, so that i386 check_relocs can be simplified.
4. Rewrite elf_i386_get_synthetic_symtab to check PLT sections against
all dynamic relocations to support both lazy and non-lazy PLTs.

bfd/

	* elf32-i386.c (PLT_ENTRY_SIZE): Renamed to ...
	(LAZY_PLT_ENTRY_SIZE): This.
	(NON_LAZY_PLT_ENTRY_SIZE): New.
	(elf_i386_plt0_entry): Renamed to ...
	(elf_i386_lazy_plt0_entry): This.
	(elf_i386_plt_entry): Renamed to ...
	(elf_i386_lazy_plt_entry): This.
	(elf_i386_pic_plt0_entry): Renamed to ...
	(elf_i386_pic_lazy_plt0_entry): This.
	(elf_i386_pic_plt_entry): Renamed to ...
	(elf_i386_pic_lazy_plt_entry): This.
	(elf_i386_got_plt_entry): Renamed to ...
	(elf_i386_non_lazy_plt_entry): This.
	(elf_i386_pic_got_plt_entry): Renamed to ...
	(elf_i386_pic_non_lazy_plt_entry): This.
	(elf_i386_eh_frame_plt): Renamed to ...
	(elf_i386_eh_frame_lazy_plt): This.
	(elf_i386_eh_frame_plt_got): Renamed to ...
	(elf_i386_eh_frame_non_lazy_plt): This.
	(elf_i386_plt_layout): Renamed to ...
	(elf_i386_lazy_plt_layout): This.  Remove eh_frame_plt_got and
	eh_frame_plt_got_size.
	(elf_i386_non_lazy_plt_layout): New.
	(elf_i386_plt_layout): Likewise.
	(elf_i386_non_lazy_plt): Likewise.
	(GET_PLT_ENTRY_SIZE): Removed.
	(elf_i386_plt): Renamed to ...
	(elf_i386_lazy_plt): This.
	(elf_i386_backend_data): Remove plt.  Rename is_vxworks to os.
	(elf_i386_arch_bed): Updated.
	(elf_i386_link_hash_table): Add plt, lazy_plt and non_lazy_plt.
	(elf_i386_create_dynamic_sections): Removed.
	(elf_i386_check_relocs): Don't check elf.dynobj.  Don't call
	_bfd_elf_create_ifunc_sections nor _bfd_elf_create_got_section.
	(elf_i386_adjust_dynamic_symbol): Updated.
	(elf_i386_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.
	(elf_i386_size_dynamic_sections): Updated.  Check whether GOT
	output section is discarded only if GOT isn't empty.
	(elf_i386_relocate_section): Updated.  Properly get PLT index
	if there is no PLT0.
	(elf_i386_finish_dynamic_symbol): Updated.  Don't fill the
	second and third slots in the PLT entry if there is no PLT0.
	(elf_i386_finish_dynamic_sections): Updated.  Don't fill PLT0
	if there is no PLT0.  Set sh_entsize on the .plt.got section.
	(elf_i386_nacl_plt): Forward declaration.
	(elf_i386_get_plt_sym_val): Removed.
	(elf_i386_get_synthetic_symtab): Rewrite to check PLT sections
	against all dynamic relocations.
	(elf_i386_link_setup_gnu_properties): New function.
	(elf_backend_create_dynamic_sections): Updated.
	(elf_backend_setup_gnu_properties): New.
	(elf_i386_nacl_plt): Updated.
	(elf_i386_nacl_arch_bed): Likewise.
	(elf_i386_vxworks_arch_bed): Likewise.

ld/

	* testsuite/ld-i386/i386.exp: Add some -z now tests.
	* testsuite/ld-i386/plt-pic2.dd: New file.
	* testsuite/ld-i386/plt2.dd: Likewise.
	* testsuite/ld-i386/plt2.rd: Likewise.
	* testsuite/ld-i386/plt2.s: Likewise.
	* testsuite/ld-ifunc/ifunc-16-i386-now.d: Likewise.
	* testsuite/ld-ifunc/ifunc-2-i386-now.d: Likewise.
	* testsuite/ld-ifunc/ifunc-2-local-i386-now.d: Likewise.
	* testsuite/ld-ifunc/pr17154-i386-now.d: Likewise.
	* testsuite/ld-i386/pr20830.d: Update the .plt.got section
	with func@plt.
2017-05-08 10:11:32 -07:00
..
emulparams
emultempl
po
scripttempl
testsuite
.gitignore
aclocal.m4
ChangeLog
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-9197
ChangeLog-9899
config.in
configure
configure.ac
configure.host
configure.tgt
deffile.h
deffilep.y
dep-in.sed
elf-hints-local.h
fdl.texi
gen-doc.texi
genscrba.sh
genscripts.sh
h8-doc.texi
ld.h
ld.texinfo
ldbuildid.c
ldbuildid.h
ldcref.c
ldctor.c
ldctor.h
ldemul.c
ldemul.h
ldexp.c
ldexp.h
ldfile.c
ldfile.h
ldgram.y
ldint.texinfo
ldlang.c
ldlang.h
ldlex-wrapper.c
ldlex.h
ldlex.l
ldmain.c
ldmain.h
ldmisc.c
ldmisc.h
ldver.c
ldver.h
ldwrite.c
ldwrite.h
lexsup.c
MAINTAINERS
Makefile.am
Makefile.in
mri.c
mri.h
NEWS
pe-dll.c
pe-dll.h
pep-dll.c
pep-dll.h
plugin.c
plugin.h
README
stamp-h.in
sysdep.h
testplug2.c
testplug3.c
testplug4.c
testplug.c
TODO

This file contains invisible Unicode characters

This file contains invisible Unicode characters that are indistinguishable to humans but may be processed differently by a computer. If you think that this is intentional, you can safely ignore this warning. Use the Escape button to reveal them.

		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.