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authorSriraman Tallam <tmsriram@google.com>2010-02-13 02:04:21 +0000
committerSriraman Tallam <tmsriram@google.com>2010-02-13 02:04:21 +0000
commit21bb3914d64c5fb946423572fe895d2a08531030 (patch)
treee54ee31d83ccdcab0f5d392c6e1d1a683809b98d /gold/icf.cc
parent6076632b700e20fbb180fd582ed892ed3d0c2d91 (diff)
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2010-02-12 Sriraman Tallam <tmsriram@google.com>
* arm.cc (Scan::local_reloc_may_be_function_pointer): New function. (Scan::global_reloc_may_be_function_pointer): New function. * sparc.cc (Scan::local_reloc_may_be_function_pointer): New function. (Scan::global_reloc_may_be_function_pointer): New function. * powerpc.cc (Scan::local_reloc_may_be_function_pointer): New function. (Scan::global_reloc_may_be_function_pointer): New function. * i386.cc (Scan::local_reloc_may_be_function_pointer): New function. (Scan::global_reloc_may_be_function_pointer): New function. * x86_64.cc (Scan::local_reloc_may_be_function_pointer): New function. (Scan::global_reloc_may_be_function_pointer): New function. (Scan::possible_function_pointer_reloc): New function. (Target_x86_64::can_check_for_function_pointers): New function. * gc.h (gc_process_relocs): Scan relocation types to determine if function pointers were taken for targets that support it. * icf.cc (Icf::find_identical_sections): Include functions for folding in safe ICF whose pointer is not taken. * icf.h (Secn_fptr_taken_set): New typedef. (fptr_section_id_): New member. (section_has_function_pointers): New function. (set_section_has_function_pointers): New function. (check_section_for_function_pointers): New function. * options.h: Fix comment for safe ICF option. * target.h (can_check_for_function_pointers): New function. * testsuite/Makefile.am: Add icf_safe_so_test test case. Modify icf_safe_test for X86-64. * testsuite/Makefile.in: Regenerate. * testsuite/icf_safe_so_test.cc: New file. * testsuite/icf_safe_so_test.sh: New file. * testsuite/icf_safe_test.cc (kept_func_3): New function. (main): Change to take pointer to function kept_func_3. * testsuite/icf_safe_test.sh (arch_specific_safe_fold): Check if safe folding is done correctly for X86-64.
Diffstat (limited to 'gold/icf.cc')
-rw-r--r--gold/icf.cc43
1 files changed, 39 insertions, 4 deletions
diff --git a/gold/icf.cc b/gold/icf.cc
index 48cb9bf..ec3269c 100644
--- a/gold/icf.cc
+++ b/gold/icf.cc
@@ -101,6 +101,36 @@
// when folding takes place. This could lead to unexpected run-time
// behaviour.
//
+// Safe Folding :
+// ------------
+//
+// ICF in safe mode folds only ctors and dtors if their function pointers can
+// never be taken. Also, for X86-64, safe folding uses the relocation
+// type to determine if a function's pointer is taken or not and only folds
+// functions whose pointers are definitely not taken.
+//
+// Caveat with safe folding :
+// ------------------------
+//
+// This applies only to x86_64.
+//
+// Position independent executables are created from PIC objects (compiled
+// with -fPIC) and/or PIE objects (compiled with -fPIE). For PIE objects, the
+// relocation types for function pointer taken and a call are the same.
+// Now, it is not always possible to tell if an object used in the link of
+// a pie executable is a PIC object or a PIE object. Hence, for pie
+// executables, using relocation types to disambiguate function pointers is
+// currently disabled.
+//
+// Further, it is not correct to use safe folding to build non-pie
+// executables using PIC/PIE objects. PIC/PIE objects have different
+// relocation types for function pointers than non-PIC objects, and the
+// current implementation of safe folding does not handle those relocation
+// types. Hence, if used, functions whose pointers are taken could still be
+// folded causing unpredictable run-time behaviour if the pointers were used
+// in comparisons.
+//
+//
//
// How to run : --icf=[safe|all|none]
// Optional parameters : --icf-iterations <num> --print-icf-sections
@@ -560,6 +590,7 @@ Icf::find_identical_sections(const Input_objects* input_objects,
std::vector<unsigned int> num_tracked_relocs;
std::vector<bool> is_secn_or_group_unique;
std::vector<std::string> section_contents;
+ const Target& target = parameters->target();
// Decide which sections are possible candidates first.
@@ -577,14 +608,18 @@ Icf::find_identical_sections(const Input_objects* input_objects,
if (parameters->options().gc_sections()
&& symtab->gc()->is_section_garbage(*p, i))
continue;
+ const char* mangled_func_name = strrchr(section_name, '.');
+ gold_assert(mangled_func_name != NULL);
// With --icf=safe, check if the mangled function name is a ctor
// or a dtor. The mangled function name can be obtained from the
// section name by stripping the section prefix.
- const char* mangled_func_name = strrchr(section_name, '.');
- gold_assert(mangled_func_name != NULL);
if (parameters->options().icf_safe_folding()
- && !is_function_ctor_or_dtor(mangled_func_name + 1))
- continue;
+ && !is_function_ctor_or_dtor(mangled_func_name + 1)
+ && (!target.can_check_for_function_pointers()
+ || section_has_function_pointers(*p, i)))
+ {
+ continue;
+ }
this->id_section_.push_back(Section_id(*p, i));
this->section_id_[Section_id(*p, i)] = section_num;
this->kept_section_id_.push_back(section_num);