Since there is no need to prepare for PLT branch on x86-64, generate
R_X86_64_PLT32, instead of R_X86_64_PC32, if possible, which can be
used as a marker for 32-bit PC-relative branches.
To compile Linux kernel, this patch:
From: "H.J. Lu" <hjl.tools@gmail.com>
Subject: [PATCH] x86: Treat R_X86_64_PLT32 as R_X86_64_PC32
On i386, there are 2 types of PLTs, PIC and non-PIC. PIE and shared
objects must use PIC PLT. To use PIC PLT, you need to load
_GLOBAL_OFFSET_TABLE_ into EBX first. There is no need for that on
x86-64 since x86-64 uses PC-relative PLT.
On x86-64, for 32-bit PC-relative branches, we can generate PLT32
relocation, instead of PC32 relocation, which can also be used as
a marker for 32-bit PC-relative branches. Linker can always reduce
PLT32 relocation to PC32 if function is defined locally. Local
functions should use PC32 relocation. As far as Linux kernel is
concerned, R_X86_64_PLT32 can be treated the same as R_X86_64_PC32
since Linux kernel doesn't use PLT.
is needed. It is available on hjl/plt32/master branch at
https://github.com/hjl-tools/linux
bfd/
PR gas/22791
* elf64-x86-64.c (is_32bit_relative_branch): Removed.
(elf_x86_64_relocate_section): Check PIC relocations in PIE.
Remove is_32bit_relative_branch usage. Disallow PC32 reloc
against protected function in shared object.
gas/
PR gas/22791
* config/tc-i386.c (need_plt32_p): New function.
(output_jump): Generate BFD_RELOC_X86_64_PLT32 if possible.
(md_estimate_size_before_relax): Likewise.
* testsuite/gas/i386/reloc64.d: Updated.
* testsuite/gas/i386/x86-64-jump.d: Likewise.
* testsuite/gas/i386/x86-64-mpx-branch-1.d: Likewise.
* testsuite/gas/i386/x86-64-mpx-branch-2.d: Likewise.
* testsuite/gas/i386/x86-64-relax-2.d: Likewise.
* testsuite/gas/i386/x86-64-relax-3.d: Likewise.
* testsuite/gas/i386/ilp32/reloc64.d: Likewise.
* testsuite/gas/i386/ilp32/x86-64-branch.d: Likewise.
ld/
PR gas/22791
* testsuite/ld-x86-64/mpx1c.rd: Updated.
* testsuite/ld-x86-64/pr22791-1.err: New file.
* testsuite/ld-x86-64/pr22791-1a.c: Likewise.
* testsuite/ld-x86-64/pr22791-1b.s: Likewise.
* testsuite/ld-x86-64/pr22791-2.rd: Likewise.
* testsuite/ld-x86-64/pr22791-2a.s: Likewise.
* testsuite/ld-x86-64/pr22791-2b.c: Likewise.
* testsuite/ld-x86-64/pr22791-2c.s: Likewise.
* testsuite/ld-x86-64/x86-64.exp: Run PR ld/22791 tests.
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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) 2012-2018 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.