Some linker code editing needs to change multiple insns. In some
cases multiple relocations are involved and it is not sufficient to
make the changes independently as relocations are processed, because
doing so might lead to a partial edit. So in order to safely edit we
need all the relocations available in relocate(). Also, to emit
edited relocs corresponding to the edited code sequence we need some
way to pass information from relocate() to relocate_relocs(),
particularly if the edit depends on insns. We can't modify input
relocs in relocate() as they are mmapped PROT_READ, nor it is
particularly clean to write relocs to the output at that stage. So
add a Relocatable_relocs* field to relinfo to mark edited relocs.
Given that relocate is passed the raw reloc pointer, it makes sense to
remove the rel/rela parameter and r_type too. However, that means the
mips relocate() needs to know whether SHT_REL or SHT_RELA relocs are
being processed. So add a rel_type for mips, which also has the
benefit of removing relocate() overloading there.
This patch adds the infrastructure without making use of it.
Note that relinfo->rr will be NULL if not outputting relocations.
* object.h (struct Relocate_info): Add "rr".
* reloc.h (Relocatable_relocs::set_strategy): New accessor.
* reloc.cc (Sized_relobj_file::do_relocate_sections): Init
relinfo.rr for relocate_section and relocate_relocs.
* powerpc.cc (relocate): Add rel_type and preloc parameters.
Delete rela and r_type params, instead recalculate these from
preloc.
(relocate_relocs): Delete Relocatable_relocs* param, instead
use relinfo->rr.
* aarch64.cc: Likewise.
* arm.cc: Likewise.
* i386.cc: Likewise.
* mips.cc: Likewise.
* s390.cc: Likewise.
* sparc.cc: Likewise.
* target.h: Likewise.
* tilegx.cc: Likewise.
* x86_64.cc: Likewise.
* testsuite/testfile.cc: Likewise.
* target-reloc.h (relocate_section): Adjust to suit.
(apply_relocation, relocate_relocs): Likewise.
to access a global as it expects a GOTPCREL relocation. This is really not
necessary as the linker could use a copy relocation to get around it. This
patch enables copy relocations with pie.
Context:
This is useful because currently the GCC compiler with option -fpie makes
every extern global access go through the GOT. That is because the compiler
cannot tell if a global will end up being defined in the executable or not
and is conservative. This ends up hurting performance when the binary is linked
as mostly static where most of the globals do end up being defined in the
executable. By allowing copy relocs with fPIE, the compiler need not generate
a GOTPCREL(GOT access) for any global access. It can safely assume that all
globals will be defined in the executable and generate a PC-relative access
instead. Gold can then create a copy reloc for only the undefined globals.
gold/
* symtab.h (may_need_copy_reloc): Remove check for position independent
code.
* x86_64.cc (Target_x86_64<size>::Scan::global): Add check for no
position independence before pc absolute may_need_copy_reloc call.
Add check for executable output befor pc relative may_need_copy_reloc
call.
* i386.cc: Ditto.
* arm.cc: Ditto.
* sparc.cc: Ditto.
* tilegx.cc: Ditto.
* powerpc.cc: Add check for no position independence before
may_need_copy_reloc calls.
* testsuite/pie_copyrelocs_test.cc: New file.
* testsuite/pie_copyrelocs_shared_test.cc: New file.
* Makefile.am (pie_copyrelocs_test): New test.
* Makefile.in: Regenerate.
bytes, so that the 16 bit relocations have a greater chance of
working.
* tilegx.cc (Target_tilegx::do_finalize_sections): Adjust
global_offset_table_ value for larget got.
(Target_tilegx::Relocate::relocate): Handle adjusted got value.
Alan Modra
Cary Coutant
Marcin Kościelnicki
Sriraman Tallam
Roland McGrath
Cary Coutant
Ian Lance Taylor
Walter Lee