This implements a work-around for an icache bug on 476 that can cause
execution of stale instructions when control falls through from one
page to the next. The idea is to prevent such fall-through by
replacing the last instruction on a page with a branch to a patch
area containing the instruction, then branch to the next page.
The patch also fixes a number of bugs in the existing support for long
branch trampolines.
bfd/
* elf32-ppc.c (struct ppc_elf_link_hash_table): Add params.
Delete emit_stub_syms, no_tls_get_addr_opt. Update all uses.
(ppc_elf_link_params): New function.
(ppc_elf_create_glink): Align .glink to 64 bytes for ppc476
workaround.
(ppc_elf_select_plt_layout): Remove plt_style and emit_stub_syms
parameters. Use htab->params instead.
(ppc_elf_tls_setup): Remove no_tls_get_addr_opt parameter.
(ppc_elf_size_dynamic_sections): Align __glink_PLTresolve to
64 bytes for ppc476 workaround.
(struct ppc_elf_relax_info): New.
(ppc_elf_relax_section): Exclude linker created sections and
those too small to hold one instruction. Don't add another
branch around trampolines on later relax passes. Don't
generate trampolines for undefined symbols when !relocatable,
nor for plugin symbols. Allocate space for ppc476 workaround
patch area. Free fixups on error return path.
(ppc_elf_relocate_section): Handle ppc476 workaround patching.
* elf32-ppc.h (struct ppc_elf_params): New.
(ppc_elf_select_plt_layout, ppc_elf_tls_setup): Update prototype.
(ppc_elf_link_params): Declare.
* section.c (SEC_INFO_TYPE_TARGET): Define.
* bfd-in2.h: Regenerate.
ld/
* emultempl/ppc32elf.em (no_tls_get_addr_opt, emit_stub_syms)
plt_style): Delete. Adjust all refs to instead use..
(params): ..this. New variable.
(ppc_after_open_output): New function. Tweak params and pass to
ppc_elf_link_params.
(ppc_after_open): Adjust ppc_elf_select_plt_layout call.
(ppc_before_allocation): Adjust ppc_elf_tls_setup call. Enable
relaxation for ppc476 workaround.
(PARSE_AND_LIST_*): Add --{no-,}ppc476-workaround support.
(LDEMUL_CREATE_OUTPUT_SECTION_STATEMENTS): Define.
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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 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.
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