https://sourceware.org/bugzilla/show_bug.cgi?id=21452
Bug ID: 21452
Summary: Enable safe ICF for shared object
Product: binutils
Version: 2.29 (HEAD)
Status: NEW
Severity: normal
Priority: P2
Component: gold
Assignee: ccoutant at gmail dot com
Reporter: hjl.tools at gmail dot com
CC: ian at airs dot com, rahulchaudhry at chromium dot org,
tmsriram at google dot com
Target Milestone: ---
Target: x86-64
x86-64.cc has
template<int size>
inline bool
Target_x86_64<size>::Scan::local_reloc_may_be_function_pointer(
Symbol_table* ,
Layout* ,
Target_x86_64<size>* ,
Sized_relobj_file<size, false>* src_obj,
unsigned int src_indx,
Output_section* ,
const elfcpp::Rela<size, false>& reloc,
unsigned int r_type,
const elfcpp::Sym<size, false>&)
{
// When building a shared library, do not fold any local symbols as it is
// not possible to distinguish pointer taken versus a call by looking at
// the relocation types.
if (parameters->options().shared())
return true;
return possible_function_pointer_reloc(src_obj, src_indx,
reloc.get_r_offset(), r_type);
}
// For safe ICF, scan a relocation for a global symbol to check if it
// corresponds to a function pointer being taken. In that case mark
// the function whose pointer was taken as not foldable.
template<int size>
inline bool
Target_x86_64<size>::Scan::global_reloc_may_be_function_pointer(
Symbol_table*,
Layout* ,
Target_x86_64<size>* ,
Sized_relobj_file<size, false>* src_obj,
unsigned int src_indx,
Output_section* ,
const elfcpp::Rela<size, false>& reloc,
unsigned int r_type,
Symbol* gsym
{
// When building a shared library, do not fold symbols whose visibility
// is hidden, internal or protected.
if (parameters->options().shared()
&& (gsym->visibility() == elfcpp::STV_INTERNAL
|| gsym->visibility() == elfcpp::STV_PROTECTED
|| gsym->visibility() == elfcpp::STV_HIDDEN))
return true;
return possible_function_pointer_reloc(src_obj, src_indx,
reloc.get_r_offset(), r_type);
}
With
commit 4aebb6312eb5dcd12f2f8420028547584b708907
Author: Rahul Chaudhry <rahulchaud...@google.com>
Date: Wed Feb 15 00:37:10 2017 -0800
Improved support for --icf=safe when used with -pie.
gold/
* x86_64.cc (Target_x86_64::do_can_check_for_function_pointers):
Return true even when building pie binaries.
(Target_x86_64::possible_function_pointer_reloc): Check opcode
for R_X86_64_PC32 relocations.
(Target_x86_64::local_reloc_may_be_function_pointer): Pass
extra arguments to local_reloc_may_be_function_pointer.
(Target_x86_64::global_reloc_may_be_function_pointer): Likewise.
* gc.h (gc_process_relocs): Add check for STT_FUNC.
* testsuite/Makefile.am (icf_safe_pie_test): New test case.
* testsuite/Makefile.in: Regenerate.
* testsuite/icf_safe_pie_test.sh: New shell script.
we now check opcode with R_X86_64_PC32 relocation, which tell branches from
function pointers. We should enable safe ICF for shared object on x86-64.
Also, global symbols with non-default visibility should be folded like local
symbols.
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