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This commit is contained in:
Sriraman Tallam 2009-08-05 20:51:56 +00:00
parent 9cc305ec20
commit ef15dade89
24 changed files with 1325 additions and 124 deletions
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46
gold/ChangeLog
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@ -1,3 +1,49 @@
2009-08-05 Sriraman Tallam <tmsriram@google.com>
* icf.cc: New file.
* icf.h: New file.
* Makefile.am (CCFILES): Add icf.cc.
(HFILES): Add icf.h
* Makefile.in: Regenerate.
* dynobj.h (Sized_dynobj::do_section_entsize): New function.
* gc.h (gc_process_relocs): Populate lists used by icf to contain
section, symbol and addend information for the relocs.
* gold.cc (queue_middle_tasks): Call identical code folding.
* gold.h: Add defines for multimap.
* layout.cc (Layout::create_symtab_sections): Add symtab as parameter
to the call of finalize_local_symbols.
* main.cc (main): Create object of class Icf.
* object.cc (Sized_relobj::do_layout): Allow this function to be
called twice during icf.
(Sized_relobj::do_finalize_local_symbols): Fold symbols corresponding
to sections marked as identical by icf.
(Sized_relobj::do_section_flags): Get section_flags from Symbols_data
when available.
(Sized_relobj::do_section_entsize): New function.
* object.h (Object::section_entsize): New function.
(Object::do_section_entsize): New pure virtual function.
(Relobj::finalize_local_symbols): Add new parameter.
(Relobj::do_section_entsize): New function.
* options.h (General_options::icf): New option.
(General_options::icf_iterations): New option.
(General_options::print_icf_sections): New option.
* plugin.cc (Sized_pluginobj::do_section_entsize): New function.
* plugin.h (Sized_pluginobj::do_section_entsize): New function.
* reloc.cc (Read_relocs::run): Delay scanning relocs when doing
icf.
* symtab.cc (Symbol_table::is_section_folded): New function.
(Symbol_table::sized_finalize_symbol): Fold symbols corresponding
to sections marked as identical by icf.
* symtab.h (Symbol_table::set_icf): New function.
(Symbol_table::icf): New function.
(Symbol_table::is_section_folded): New function.
(Symbol_table::icf_): New data member.
* target-reloc.h (relocate_section): Ignore sections folded by icf.
* testsuite/Makefile.am: Add commands to build icf_test.
* testsuite/Makefile.in: Regenerate.
* testsuite/icf_test.sh: New file.
* testsuite/icf_test.cc: New file.
2009-07-24 Chris Demetriou <cgd@google.com>
* layout.cc (is_compressible_debug_section): Fix incorrect

2
gold/Makefile.am
View File

@ -51,6 +51,7 @@ CCFILES = \
gc.cc \
gold.cc \
gold-threads.cc \
icf.cc \
incremental.cc \
layout.cc \
mapfile.cc \
@ -93,6 +94,7 @@ HFILES = \
gc.h \
gold.h \
gold-threads.h \
icf.h \
layout.h \
mapfile.h \
merge.h \

11
gold/Makefile.in
View File

@ -82,10 +82,10 @@ am__objects_1 = archive.$(OBJEXT) binary.$(OBJEXT) common.$(OBJEXT) \
dirsearch.$(OBJEXT) dynobj.$(OBJEXT) dwarf_reader.$(OBJEXT) \
ehframe.$(OBJEXT) errors.$(OBJEXT) expression.$(OBJEXT) \
fileread.$(OBJEXT) gc.$(OBJEXT) gold.$(OBJEXT) \
gold-threads.$(OBJEXT) incremental.$(OBJEXT) layout.$(OBJEXT) \
mapfile.$(OBJEXT) merge.$(OBJEXT) object.$(OBJEXT) \
options.$(OBJEXT) output.$(OBJEXT) parameters.$(OBJEXT) \
plugin.$(OBJEXT) readsyms.$(OBJEXT) \
gold-threads.$(OBJEXT) icf.$(OBJEXT) incremental.$(OBJEXT) \
layout.$(OBJEXT) mapfile.$(OBJEXT) merge.$(OBJEXT) \
object.$(OBJEXT) options.$(OBJEXT) output.$(OBJEXT) \
parameters.$(OBJEXT) plugin.$(OBJEXT) readsyms.$(OBJEXT) \
reduced_debug_output.$(OBJEXT) reloc.$(OBJEXT) \
resolve.$(OBJEXT) script-sections.$(OBJEXT) script.$(OBJEXT) \
stringpool.$(OBJEXT) symtab.$(OBJEXT) target.$(OBJEXT) \
@ -337,6 +337,7 @@ CCFILES = \
gc.cc \
gold.cc \
gold-threads.cc \
icf.cc \
incremental.cc \
layout.cc \
mapfile.cc \
@ -379,6 +380,7 @@ HFILES = \
gc.h \
gold.h \
gold-threads.h \
icf.h \
layout.h \
mapfile.h \
merge.h \
@ -565,6 +567,7 @@ distclean-compile:
@AMDEP_TRUE@@am__include@ @am__quote@./$(DEPDIR)/gold-threads.Po@am__quote@
@AMDEP_TRUE@@am__include@ @am__quote@./$(DEPDIR)/gold.Po@am__quote@
@AMDEP_TRUE@@am__include@ @am__quote@./$(DEPDIR)/i386.Po@am__quote@
@AMDEP_TRUE@@am__include@ @am__quote@./$(DEPDIR)/icf.Po@am__quote@
@AMDEP_TRUE@@am__include@ @am__quote@./$(DEPDIR)/incremental.Po@am__quote@
@AMDEP_TRUE@@am__include@ @am__quote@./$(DEPDIR)/layout.Po@am__quote@
@AMDEP_TRUE@@am__include@ @am__quote@./$(DEPDIR)/main.Po@am__quote@

5
gold/dynobj.h
View File

@ -198,6 +198,11 @@ class Sized_dynobj : public Dynobj
do_section_flags(unsigned int shndx)
{ return this->elf_file_.section_flags(shndx); }
// Not used for dynobj.
uint64_t
do_section_entsize(unsigned int )
{ gold_unreachable(); }
// Return section address.
uint64_t
do_section_address(unsigned int shndx)

158
gold/gc.h
View File

@ -24,6 +24,7 @@
#define GOLD_GC_H
#include <queue>
#include <vector>
#include "elfcpp.h"
#include "symtab.h"
@ -53,45 +54,51 @@ class Garbage_collection
{ return reinterpret_cast<uintptr_t>(loc.first) ^ loc.second; }
};
public:
typedef Unordered_set<Section_id, Section_id_hash> Sections_reachable;
typedef std::map<Section_id, Sections_reachable> Section_ref;
typedef std::queue<Section_id> Worklist_type;
public :
Garbage_collection()
:is_worklist_ready_(false)
{ }
Garbage_collection()
: is_worklist_ready_(false)
{ }
// Accessor methods for the private members.
// Accessor methods for the private members.
Sections_reachable&
referenced_list()
{ return referenced_list_; }
Sections_reachable&
referenced_list()
{ return referenced_list_; }
Section_ref&
section_reloc_map()
{ return section_reloc_map_; }
Section_ref&
section_reloc_map()
{ return this->section_reloc_map_; }
Worklist_type&
worklist()
{ return work_list_; }
bool
is_worklist_ready()
{ return is_worklist_ready_; }
Worklist_type&
worklist()
{ return this->work_list_; }
void
worklist_ready()
{ is_worklist_ready_ = true; }
bool
is_worklist_ready()
{ return this->is_worklist_ready_; }
void
do_transitive_closure();
void
worklist_ready()
{ this->is_worklist_ready_ = true; }
private :
Worklist_type work_list_;
bool is_worklist_ready_;
Section_ref section_reloc_map_;
Sections_reachable referenced_list_;
void
do_transitive_closure();
bool
is_section_garbage(Object* obj, unsigned int shndx)
{ return (this->referenced_list().find(Section_id(obj, shndx))
== this->referenced_list().end()); }
private:
Worklist_type work_list_;
bool is_worklist_ready_;
Section_ref section_reloc_map_;
Sections_reachable referenced_list_;
};
// Data to pass between successive invocations of do_layout
@ -120,10 +127,11 @@ struct Symbols_data
section_size_type symbol_names_size;
};
// This function implements the the generic part of reloc
// processing to map a section to all the sections it
// references through relocs. It is used only during garbage
// collection.
// This function implements the generic part of reloc
// processing to map a section to all the sections it
// references through relocs. It is called only during
// garbage collection (--gc-sections) and identical code
// folding (--icf).
template<int size, bool big_endian, typename Target_type, int sh_type,
typename Scan>
@ -133,8 +141,8 @@ gc_process_relocs(
Symbol_table* symtab,
Layout*,
Target_type* ,
Sized_relobj<size, big_endian>* object,
unsigned int data_shndx,
Sized_relobj<size, big_endian>* src_obj,
unsigned int src_indx,
const unsigned char* prelocs,
size_t reloc_count,
Output_section*,
@ -142,22 +150,36 @@ gc_process_relocs(
size_t local_count,
const unsigned char* plocal_syms)
{
Object *src_obj, *dst_obj;
unsigned int src_indx, dst_indx;
Object *dst_obj;
unsigned int dst_indx;
src_obj = object;
src_indx = data_shndx;
typedef typename Reloc_types<sh_type, size, big_endian>::Reloc Reltype;
const int reloc_size = Reloc_types<sh_type, size, big_endian>::reloc_size;
const int sym_size = elfcpp::Elf_sizes<size>::sym_size;
std::vector<Section_id>* secvec = NULL;
std::vector<Symbol*>* symvec = NULL;
std::vector<std::pair<long long, long long> >* addendvec = NULL;
bool is_icf_tracked = false;
if (parameters->options().icf()
&& is_prefix_of(".text.", (src_obj)->section_name(src_indx).c_str()))
{
is_icf_tracked = true;
Section_id src_id(src_obj, src_indx);
secvec = &symtab->icf()->section_reloc_list()[src_id];
symvec = &symtab->icf()->symbol_reloc_list()[src_id];
addendvec = &symtab->icf()->addend_reloc_list()[src_id];
}
for (size_t i = 0; i < reloc_count; ++i, prelocs += reloc_size)
{
Reltype reloc(prelocs);
typename elfcpp::Elf_types<size>::Elf_WXword r_info = reloc.get_r_info();
unsigned int r_sym = elfcpp::elf_r_sym<size>(r_info);
typename elfcpp::Elf_types<size>::Elf_Swxword addend =
Reloc_types<sh_type, size, big_endian>::get_reloc_addend_noerror(&reloc);
if (r_sym < local_count)
{
gold_assert(plocal_syms != NULL);
@ -165,17 +187,26 @@ gc_process_relocs(
+ r_sym * sym_size);
unsigned int shndx = lsym.get_st_shndx();
bool is_ordinary;
shndx = object->adjust_sym_shndx(r_sym, shndx, &is_ordinary);
if (!is_ordinary)
shndx = src_obj->adjust_sym_shndx(r_sym, shndx, &is_ordinary);
if (!is_ordinary)
continue;
dst_obj = src_obj;
if (shndx == src_indx)
continue;
dst_indx = shndx;
Section_id dst_id(dst_obj, dst_indx);
if (is_icf_tracked)
{
(*secvec).push_back(dst_id);
(*symvec).push_back(NULL);
long long symvalue = static_cast<long long>(lsym.get_st_value());
(*addendvec).push_back(std::make_pair(symvalue,
static_cast<long long>(addend)));
}
if (shndx == src_indx)
continue;
}
else
{
Symbol* gsym = object->global_symbol(r_sym);
Symbol* gsym = src_obj->global_symbol(r_sym);
gold_assert(gsym != NULL);
if (gsym->is_forwarder())
gsym = symtab->resolve_forwards(gsym);
@ -186,19 +217,34 @@ gc_process_relocs(
dst_indx = gsym->shndx(&is_ordinary);
if (!is_ordinary)
continue;
Section_id dst_id(dst_obj, dst_indx);
if (is_icf_tracked)
{
(*secvec).push_back(dst_id);
(*symvec).push_back(gsym);
Sized_symbol<size>* sized_gsym =
static_cast<Sized_symbol<size>* >(gsym);
long long symvalue =
static_cast<long long>(sized_gsym->value());
(*addendvec).push_back(std::make_pair(symvalue,
static_cast<long long>(addend)));
}
}
Section_id p1(src_obj, src_indx);
Section_id p2(dst_obj, dst_indx);
Garbage_collection::Section_ref::iterator map_it;
map_it = symtab->gc()->section_reloc_map().find(p1);
if (map_it == symtab->gc()->section_reloc_map().end())
if (parameters->options().gc_sections())
{
symtab->gc()->section_reloc_map()[p1].insert(p2);
}
else
{
Garbage_collection::Sections_reachable& v(map_it->second);
v.insert(p2);
Section_id src_id(src_obj, src_indx);
Section_id dst_id(dst_obj, dst_indx);
Garbage_collection::Section_ref::iterator map_it;
map_it = symtab->gc()->section_reloc_map().find(src_id);
if (map_it == symtab->gc()->section_reloc_map().end())
{
symtab->gc()->section_reloc_map()[src_id].insert(dst_id);
}
else
{
Garbage_collection::Sections_reachable& v(map_it->second);
v.insert(dst_id);
}
}
}
return;

32
gold/gold.cc
View File

@ -41,6 +41,7 @@
#include "reloc.h"
#include "defstd.h"
#include "plugin.h"
#include "icf.h"
namespace gold
{
@ -203,10 +204,10 @@ queue_initial_tasks(const General_options& options,
}
if (parameters->options().relocatable()
&& parameters->options().gc_sections())
gold_error(_("cannot mix -r with garbage collection"));
&& (parameters->options().gc_sections() || parameters->options().icf()))
gold_error(_("cannot mix -r with --gc-sections or --icf"));
if (parameters->options().gc_sections())
if (parameters->options().gc_sections() || parameters->options().icf())
{
workqueue->queue(new Task_function(new Gc_runner(options,
input_objects,
@ -309,8 +310,23 @@ queue_middle_tasks(const General_options& options,
gold_assert(symtab->gc() != NULL);
// Do a transitive closure on all references to determine the worklist.
symtab->gc()->do_transitive_closure();
// Call do_layout again to determine the output_sections for all
// referenced input sections.
}
// If identical code folding (--icf) is chosen it makes sense to do it
// only after garbage collection (--gc-sections) as we do not want to
// be folding sections that will be garbage.
if (parameters->options().icf())
{
symtab->icf()->find_identical_sections(input_objects, symtab);
}
// Call Object::layout for the second time to determine the
// output_sections for all referenced input sections. When
// --gc-sections or --icf is turned on, Object::layout is
// called twice. It is called the first time when the
// symbols are added.
if (parameters->options().gc_sections() || parameters->options().icf())
{
for (Input_objects::Relobj_iterator p = input_objects->relobj_begin();
p != input_objects->relobj_end();
++p)
@ -318,6 +334,7 @@ queue_middle_tasks(const General_options& options,
(*p)->layout(symtab, layout, NULL);
}
}
// Layout deferred objects due to plugins.
if (parameters->options().has_plugins())
{
@ -325,7 +342,8 @@ queue_middle_tasks(const General_options& options,
gold_assert(plugins != NULL);
plugins->layout_deferred_objects();
}
if (parameters->options().gc_sections())
if (parameters->options().gc_sections() || parameters->options().icf())
{
for (Input_objects::Relobj_iterator p = input_objects->relobj_begin();
p != input_objects->relobj_end();
@ -420,7 +438,7 @@ queue_middle_tasks(const General_options& options,
// If doing garbage collection, the relocations have already been read.
// Otherwise, read and scan the relocations.
if (parameters->options().gc_sections())
if (parameters->options().gc_sections() || parameters->options().icf())
{
for (Input_objects::Relobj_iterator p = input_objects->relobj_begin();
p != input_objects->relobj_end();

3
gold/gold.h
View File

@ -75,6 +75,7 @@
#define Unordered_set std::tr1::unordered_set
#define Unordered_map std::tr1::unordered_map
#define Unordered_multimap std::tr1::unordered_multimap
#define reserve_unordered_map(map, n) ((map)->rehash(n))
@ -86,6 +87,7 @@
#define Unordered_set __gnu_cxx::hash_set
#define Unordered_map __gnu_cxx::hash_map
#define Unordered_multimap __gnu_cxx::hash_multimap
namespace __gnu_cxx
{
@ -119,6 +121,7 @@ struct hash<T*>
#define Unordered_set std::set
#define Unordered_map std::map
#define Unordered_map std::multimap
#define reserve_unordered_map(map, n)

634
gold/icf.cc Normal file
View File

@ -0,0 +1,634 @@
// icf.cc -- Identical Code Folding.
//
// Copyright 2009 Free Software Foundation, Inc.
// Written by Sriraman Tallam <tmsriram@google.com>.
// This file is part of gold.
// This program is free software; you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation; either version 3 of the License, or
// (at your option) any later version.
// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU General Public License for more details.
// You should have received a copy of the GNU General Public License
// along with this program; if not, write to the Free Software
// Foundation, Inc., 51 Franklin Street - Fifth Floor, Boston,
// MA 02110-1301, USA.
// Identical Code Folding Algorithm
// ----------------------------------
// Detecting identical functions is done here and the basic algorithm
// is as follows. A checksum is computed on each .text section using
// its contents and relocations. If the symbol name corresponding to
// a relocation is known it is used to compute the checksum. If the
// symbol name is not known the stringified name of the object and the
// section number pointed to by the relocation is used. The checksums
// are stored as keys in a hash map and a section is identical to some
// other section if its checksum is already present in the hash map.
// Checksum collisions are handled by using a multimap and explicitly
// checking the contents when two sections have the same checksum.
//
// However, two functions A and B with identical text but with
// relocations pointing to different .text sections can be identical if
// the corresponding .text sections to which their relocations point to
// turn out to be identical. Hence, this checksumming process must be
// done repeatedly until convergence is obtained. Here is an example for
// the following case :
//
// int funcA () int funcB ()
// { {
// return foo(); return goo();
// } }
//
// The functions funcA and funcB are identical if functions foo() and
// goo() are identical.
//
// Hence, as described above, we repeatedly do the checksumming,
// assigning identical functions to the same group, until convergence is
// obtained. Now, we have two different ways to do this depending on how
// we initialize.
//
// Algorithm I :
// -----------
// We can start with marking all functions as different and repeatedly do
// the checksumming. This has the advantage that we do not need to wait
// for convergence. We can stop at any point and correctness will be
// guaranteed although not all cases would have been found. However, this
// has a problem that some cases can never be found even if it is run until
// convergence. Here is an example with mutually recursive functions :
//
// int funcA (int a) int funcB (int a)
// { {
// if (a == 1) if (a == 1)
// return 1; return 1;
// return 1 + funcB(a - 1); return 1 + funcA(a - 1);
// } }
//
// In this example funcA and funcB are identical and one of them could be
// folded into the other. However, if we start with assuming that funcA
// and funcB are not identical, the algorithm, even after it is run to
// convergence, cannot detect that they are identical. It should be noted
// that even if the functions were self-recursive, Algorithm I cannot catch
// that they are identical, at least as is.
//
// Algorithm II :
// ------------
// Here we start with marking all functions as identical and then repeat
// the checksumming until convergence. This can detect the above case
// mentioned above. It can detect all cases that Algorithm I can and more.
// However, the caveat is that it has to be run to convergence. It cannot
// be stopped arbitrarily like Algorithm I as correctness cannot be
// guaranteed. Algorithm II is not implemented.
//
// Algorithm I is used because experiments show that about three
// iterations are more than enough to achieve convergence. Algorithm I can
// handle recursive calls if it is changed to use a special common symbol
// for recursive relocs. This seems to be the most common case that
// Algorithm I could not catch as is. Mutually recursive calls are not
// frequent and Algorithm I wins because of its ability to be stopped
// arbitrarily.
//
// Caveat with using function pointers :
// ------------------------------------
//
// Programs using function pointer comparisons/checks should use function
// folding with caution as the result of such comparisons could be different
// when folding takes place. This could lead to unexpected run-time
// behaviour.
//
//
// How to run : --icf
// Optional parameters : --icf-iterations <num> --print-icf-sections
//
// Performance : Less than 20 % link-time overhead on industry strength
// applications. Up to 6 % text size reductions.
#include "gold.h"
#include "object.h"
#include "gc.h"
#include "icf.h"
#include "symtab.h"
#include "libiberty.h"
namespace gold
{
// This function determines if a section or a group of identical
// sections has unique contents. Such unique sections or groups can be
// declared final and need not be processed any further.
// Parameters :
// ID_SECTION : Vector mapping a section index to a Section_id pair.
// IS_SECN_OR_GROUP_UNIQUE : To check if a section or a group of identical
// sections is already known to be unique.
// SECTION_CONTENTS : Contains the section's text and relocs to sections
// that cannot be folded. SECTION_CONTENTS are NULL
// implies that this function is being called for the
// first time before the first iteration of icf.
static void
preprocess_for_unique_sections(const std::vector<Section_id>& id_section,
std::vector<bool>* is_secn_or_group_unique,
std::vector<std::string>* section_contents)
{
Unordered_map<uint32_t, unsigned int> uniq_map;
std::pair<Unordered_map<uint32_t, unsigned int>::iterator, bool>
uniq_map_insert;
for (unsigned int i = 0; i < id_section.size(); i++)
{
if ((*is_secn_or_group_unique)[i])
continue;
uint32_t cksum;
Section_id secn = id_section[i];
section_size_type plen;
if (section_contents == NULL)
{
const unsigned char* contents;
contents = secn.first->section_contents(secn.second,
&plen,
false);
cksum = xcrc32(contents, plen, 0xffffffff);
}
else
{
const unsigned char* contents_array = reinterpret_cast
<const unsigned char*>((*section_contents)[i].c_str());
cksum = xcrc32(contents_array, (*section_contents)[i].length(),
0xffffffff);
}
uniq_map_insert = uniq_map.insert(std::make_pair(cksum, i));
if (uniq_map_insert.second)
{
(*is_secn_or_group_unique)[i] = true;
}
else
{
(*is_secn_or_group_unique)[i] = false;
(*is_secn_or_group_unique)[uniq_map_insert.first->second] = false;
}
}
}
// This returns the buffer containing the section's contents, both
// text and relocs. Relocs are differentiated as those pointing to
// sections that could be folded and those that cannot. Only relocs
// pointing to sections that could be folded are recomputed on
// subsequent invocations of this function.
// Parameters :
// FIRST_ITERATION : true if it is the first invocation.
// SECN : Section for which contents are desired.
// SECTION_NUM : Unique section number of this section.
// NUM_TRACKED_RELOCS : Vector reference to store the number of relocs
// to ICF sections.
// KEPT_SECTION_ID : Vector which maps folded sections to kept sections.
// SECTION_CONTENTS : Store the section's text and relocs to non-ICF
// sections.
static std::string
get_section_contents(bool first_iteration,
const Section_id& secn,
unsigned int section_num,
unsigned int* num_tracked_relocs,
Symbol_table* symtab,
const std::vector<unsigned int>& kept_section_id,
std::vector<std::string>* section_contents)
{
section_size_type plen;
const unsigned char* contents = NULL;
if (first_iteration)
{
contents = secn.first->section_contents(secn.second,
&plen,
false);
}
// The buffer to hold all the contents including relocs. A checksum
// is then computed on this buffer.
std::string buffer;
std::string icf_reloc_buffer;
if (num_tracked_relocs)
*num_tracked_relocs = 0;
Icf::Section_list& seclist = symtab->icf()->section_reloc_list();
Icf::Symbol_list& symlist = symtab->icf()->symbol_reloc_list();
Icf::Addend_list& addendlist = symtab->icf()->addend_reloc_list();
Icf::Section_list::iterator it_seclist = seclist.find(secn);
Icf::Symbol_list::iterator it_symlist = symlist.find(secn);
Icf::Addend_list::iterator it_addendlist = addendlist.find(secn);
buffer.clear();
icf_reloc_buffer.clear();
// Process relocs and put them into the buffer.
if (it_seclist != seclist.end())
{
gold_assert(it_symlist != symlist.end());
gold_assert(it_addendlist != addendlist.end());
Icf::Sections_reachable_list v = it_seclist->second;
Icf::Symbol_info s = it_symlist->second;
Icf::Addend_info a = it_addendlist->second;
Icf::Sections_reachable_list::iterator it_v = v.begin();
Icf::Symbol_info::iterator it_s = s.begin();
Icf::Addend_info::iterator it_a = a.begin();
for (; it_v != v.end(); ++it_v, ++it_s, ++it_a)
{
// ADDEND_STR stores the symbol value and addend, each
// atmost 16 hex digits long. it_v points to a pair
// where first is the symbol value and second is the
// addend.
char addend_str[34];
snprintf(addend_str, sizeof(addend_str), "%llx %llx",
(*it_a).first, (*it_a).second);
Section_id reloc_secn(it_v->first, it_v->second);
// If this reloc turns back and points to the same section,
// like a recursive call, use a special symbol to mark this.
if (reloc_secn.first == secn.first
&& reloc_secn.second == secn.second)
{
if (first_iteration)
{
buffer.append("R");
buffer.append(addend_str);
buffer.append("@");
}
continue;
}
Icf::Uniq_secn_id_map& section_id_map =
symtab->icf()->section_to_int_map();
Icf::Uniq_secn_id_map::iterator section_id_map_it =
section_id_map.find(reloc_secn);
if (section_id_map_it != section_id_map.end())
{
// This is a reloc to a section that might be folded.
if (num_tracked_relocs)
(*num_tracked_relocs)++;
char kept_section_str[10];
unsigned int secn_id = section_id_map_it->second;
snprintf(kept_section_str, sizeof(kept_section_str), "%u",
kept_section_id[secn_id]);
if (first_iteration)
{
buffer.append("ICF_R");
buffer.append(addend_str);
}
icf_reloc_buffer.append(kept_section_str);
// Append the addend.
icf_reloc_buffer.append(addend_str);
icf_reloc_buffer.append("@");
}
else
{
// This is a reloc to a section that cannot be folded.
// Process it only in the first iteration.
if (!first_iteration)
continue;
uint64_t secn_flags = (it_v->first)->section_flags(it_v->second);
// This reloc points to a merge section. Hash the
// contents of this section.
if ((secn_flags & elfcpp::SHF_MERGE) != 0)
{
uint64_t entsize =
(it_v->first)->section_entsize(it_v->second);
long long offset = it_a->first + it_a->second;
section_size_type secn_len;
const unsigned char* str_contents =
(it_v->first)->section_contents(it_v->second,
&secn_len,
false) + offset;
if ((secn_flags & elfcpp::SHF_STRINGS) != 0)
{
// String merge section.
const char* str_char =
reinterpret_cast<const char*>(str_contents);
switch(entsize)
{
case 1:
{
buffer.append(str_char);
break;
}
case 2:
{
const uint16_t* ptr_16 =
reinterpret_cast<const uint16_t*>(str_char);
unsigned int strlen_16 = 0;
// Find the NULL character.
while(*(ptr_16 + strlen_16) != 0)
strlen_16++;
buffer.append(str_char, strlen_16 * 2);
}
break;
case 4:
{
const uint32_t* ptr_32 =
reinterpret_cast<const uint32_t*>(str_char);
unsigned int strlen_32 = 0;
// Find the NULL character.
while(*(ptr_32 + strlen_32) != 0)
strlen_32++;
buffer.append(str_char, strlen_32 * 4);
}
break;
default:
gold_unreachable();
}
}
else
{
// Use the entsize to determine the length.
buffer.append(reinterpret_cast<const
char*>(str_contents),
entsize);
}
}
else if ((*it_s) != NULL)
{
// If symbol name is available use that.
const char *sym_name = (*it_s)->name();
buffer.append(sym_name);
// Append the addend.
buffer.append(addend_str);
buffer.append("@");
}
else
{
// Symbol name is not available, like for a local symbol,
// use object and section id.
buffer.append(it_v->first->name());
char secn_id[10];
snprintf(secn_id, sizeof(secn_id), "%u",it_v->second);
buffer.append(secn_id);
// Append the addend.
buffer.append(addend_str);
buffer.append("@");
}
}
}
}
if (first_iteration)
{
buffer.append("Contents = ");
buffer.append(reinterpret_cast<const char*>(contents), plen);
// Store the section contents that dont change to avoid recomputing
// during the next call to this function.
(*section_contents)[section_num] = buffer;
}
else
{
gold_assert(buffer.empty());
// Reuse the contents computed in the previous iteration.
buffer.append((*section_contents)[section_num]);
}
buffer.append(icf_reloc_buffer);
return buffer;
}
// This function computes a checksum on each section to detect and form
// groups of identical sections. The first iteration does this for all
// sections.
// Further iterations do this only for the kept sections from each group to
// determine if larger groups of identical sections could be formed. The
// first section in each group is the kept section for that group.
//
// CRC32 is the checksumming algorithm and can have collisions. That is,
// two sections with different contents can have the same checksum. Hence,
// a multimap is used to maintain more than one group of checksum
// identical sections. A section is added to a group only after its
// contents are explicitly compared with the kept section of the group.
//
// Parameters :
// ITERATION_NUM : Invocation instance of this function.
// NUM_TRACKED_RELOCS : Vector reference to store the number of relocs
// to ICF sections.
// KEPT_SECTION_ID : Vector which maps folded sections to kept sections.
// ID_SECTION : Vector mapping a section to an unique integer.
// IS_SECN_OR_GROUP_UNIQUE : To check if a section or a group of identical
// sectionsis already known to be unique.
// SECTION_CONTENTS : Store the section's text and relocs to non-ICF
// sections.
static bool
match_sections(unsigned int iteration_num,
Symbol_table* symtab,
std::vector<unsigned int>* num_tracked_relocs,
std::vector<unsigned int>* kept_section_id,
const std::vector<Section_id>& id_section,
std::vector<bool>* is_secn_or_group_unique,
std::vector<std::string>* section_contents)
{
Unordered_multimap<uint32_t, unsigned int> section_cksum;
std::pair<Unordered_multimap<uint32_t, unsigned int>::iterator,
Unordered_multimap<uint32_t, unsigned int>::iterator> key_range;
bool converged = true;
if (iteration_num == 1)
preprocess_for_unique_sections(id_section,
is_secn_or_group_unique,
NULL);
else
preprocess_for_unique_sections(id_section,
is_secn_or_group_unique,
section_contents);
std::vector<std::string> full_section_contents;
for (unsigned int i = 0; i < id_section.size(); i++)
{
full_section_contents.push_back("");
if ((*is_secn_or_group_unique)[i])
continue;
Section_id secn = id_section[i];
std::string this_secn_contents;
uint32_t cksum;
if (iteration_num == 1)
{
unsigned int num_relocs = 0;
this_secn_contents = get_section_contents(true, secn, i, &num_relocs,
symtab, (*kept_section_id),
section_contents);
(*num_tracked_relocs)[i] = num_relocs;
}
else
{
if ((*kept_section_id)[i] != i)
{
// This section is already folded into something. See
// if it should point to a different kept section.
unsigned int kept_section = (*kept_section_id)[i];
if (kept_section != (*kept_section_id)[kept_section])
{
(*kept_section_id)[i] = (*kept_section_id)[kept_section];
}
continue;
}
this_secn_contents = get_section_contents(false, secn, i, NULL,
symtab, (*kept_section_id),
section_contents);
}
const unsigned char* this_secn_contents_array =
reinterpret_cast<const unsigned char*>(this_secn_contents.c_str());
cksum = xcrc32(this_secn_contents_array, this_secn_contents.length(),
0xffffffff);
size_t count = section_cksum.count(cksum);
if (count == 0)
{
// Start a group with this cksum.
section_cksum.insert(std::make_pair(cksum, i));
full_section_contents[i] = this_secn_contents;
}
else
{
key_range = section_cksum.equal_range(cksum);
Unordered_multimap<uint32_t, unsigned int>::iterator it;
// Search all the groups with this cksum for a match.
for (it = key_range.first; it != key_range.second; ++it)
{
unsigned int kept_section = it->second;
if (full_section_contents[kept_section].length()
!= this_secn_contents.length())
continue;
if (memcmp(full_section_contents[kept_section].c_str(),
this_secn_contents.c_str(),
this_secn_contents.length()) != 0)
continue;
(*kept_section_id)[i] = kept_section;
converged = false;
break;
}
if (it == key_range.second)
{
// Create a new group for this cksum.
section_cksum.insert(std::make_pair(cksum, i));
full_section_contents[i] = this_secn_contents;
}
}
// If there are no relocs to foldable sections do not process
// this section any further.
if (iteration_num == 1 && (*num_tracked_relocs)[i] == 0)
(*is_secn_or_group_unique)[i] = true;
}
return converged;
}
// This is the main ICF function called in gold.cc. This does the
// initialization and calls match_sections repeatedly (twice by default)
// which computes the crc checksums and detects identical functions.
void
Icf::find_identical_sections(const Input_objects* input_objects,
Symbol_table* symtab)
{
unsigned int section_num = 0;
std::vector<unsigned int> num_tracked_relocs;
std::vector<bool> is_secn_or_group_unique;
std::vector<std::string> section_contents;
// Decide which sections are possible candidates first.
for (Input_objects::Relobj_iterator p = input_objects->relobj_begin();
p != input_objects->relobj_end();
++p)
{
for (unsigned int i = 0;i < (*p)->shnum(); ++i)
{
// Only looking to fold functions, so just look at .text sections.
if (!is_prefix_of(".text.", (*p)->section_name(i).c_str()))
continue;
if (!(*p)->is_section_included(i))
continue;
if (parameters->options().gc_sections()
&& symtab->gc()->is_section_garbage(*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);
num_tracked_relocs.push_back(0);
is_secn_or_group_unique.push_back(false);
section_contents.push_back("");
section_num++;
}
}
unsigned int num_iterations = 0;
// Default number of iterations to run ICF is 2.
unsigned int max_iterations = (parameters->options().icf_iterations() > 0)
? parameters->options().icf_iterations()
: 2;
bool converged = false;
while (!converged && (num_iterations < max_iterations))
{
num_iterations++;
converged = match_sections(num_iterations, symtab,
&num_tracked_relocs, &this->kept_section_id_,
this->id_section_, &is_secn_or_group_unique,
&section_contents);
}
if (parameters->options().print_icf_sections())
{
if (converged)
gold_info(_("%s: ICF Converged after %u iteration(s)"),
program_name, num_iterations);
else
gold_info(_("%s: ICF stopped after %u iteration(s)"),
program_name, num_iterations);
}
this->icf_ready();
}
// This function determines if the section corresponding to the
// given object and index is folded based on if the kept section
// is different from this section.
bool
Icf::is_section_folded(Object* obj, unsigned int shndx)
{
Section_id secn(obj, shndx);
Uniq_secn_id_map::iterator it = this->section_id_.find(secn);
if (it == this->section_id_.end())
return false;
unsigned int section_num = it->second;
unsigned int kept_section_id = this->kept_section_id_[section_num];
return kept_section_id != section_num;
}
// This function returns the folded section for the given section.
Section_id
Icf::get_folded_section(Object* dup_obj, unsigned int dup_shndx)
{
Section_id dup_secn(dup_obj, dup_shndx);
Uniq_secn_id_map::iterator it = this->section_id_.find(dup_secn);
gold_assert(it != this->section_id_.end());
unsigned int section_num = it->second;
unsigned int kept_section_id = this->kept_section_id_[section_num];
Section_id folded_section = this->id_section_[kept_section_id];
return folded_section;
}
} // End of namespace gold.

140
gold/icf.h Normal file
View File

@ -0,0 +1,140 @@
// icf.h -- Identical Code Folding
// Copyright 2009 Free Software Foundation, Inc.
// Written by Sriraman Tallam <tmsriram@google.com>.
// This file is part of gold.
// This program is free software; you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation; either version 3 of the License, or
// (at your option) any later version.
// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU General Public License for more details.
// You should have received a copy of the GNU General Public License
// along with this program; if not, write to the Free Software
// Foundation, Inc., 51 Franklin Street - Fifth Floor, Boston,
// MA 02110-1301, USA.
#ifndef GOLD_ICF_H
#define GOLD_ICF_H
#include <vector>
#include "elfcpp.h"
#include "symtab.h"
namespace gold
{
class Object;
class Input_objects;
class Symbol_table;
typedef std::pair<Object*, unsigned int> Section_id;
class Icf
{
public:
struct Section_id_hash
{
size_t operator()(const Section_id& loc) const
{ return reinterpret_cast<uintptr_t>(loc.first) ^ loc.second; }
};
typedef std::vector<Section_id> Sections_reachable_list;
typedef std::vector<Symbol*> Symbol_info;
typedef std::vector<std::pair<long long, long long> > Addend_info;
typedef Unordered_map<Section_id,
Sections_reachable_list,
Section_id_hash> Section_list;
typedef Unordered_map<Section_id, Symbol_info, Section_id_hash> Symbol_list;
typedef Unordered_map<Section_id, Addend_info, Section_id_hash> Addend_list;
typedef Unordered_map<Section_id,
unsigned int,
Section_id_hash> Uniq_secn_id_map;
Icf()
: id_section_(), section_id_(), kept_section_id_(),
num_tracked_relocs(NULL), icf_ready_(false),
section_reloc_list_(), symbol_reloc_list_(),
addend_reloc_list_()
{ }
// Returns the kept folded identical section corresponding to
// dup_obj and dup_shndx.
Section_id
get_folded_section(Object* dup_obj, unsigned int dup_shndx);
// Forms groups of identical sections where the first member
// of each group is the kept section during folding.
void
find_identical_sections(const Input_objects* input_objects,
Symbol_table* symtab);
// This is set when ICF has been run and the groups of
// identical sections have been formed.
void
icf_ready()
{ this->icf_ready_ = true; }
// Returns true if ICF has been run.
bool
is_icf_ready()
{ return this->icf_ready_; }
// Returns the kept section corresponding to the
// given section.
bool
is_section_folded(Object* obj, unsigned int shndx);
// Returns a map of a section to a list of all sections referenced
// by its relocations.
Section_list&
section_reloc_list()
{ return this->section_reloc_list_; }
// Returns a map of a section to a list of all symbols referenced
// by its relocations.
Symbol_list&
symbol_reloc_list()
{ return this->symbol_reloc_list_; }
// Returns a maps of a section to a list of symbol values and addends
// of its relocations.
Addend_list&
addend_reloc_list()
{ return this->addend_reloc_list_; }
// Returns a mapping of each section to a unique integer.
Uniq_secn_id_map&
section_to_int_map()
{ return this->section_id_; }
private:
// Maps integers to sections.
std::vector<Section_id> id_section_;
// Does the reverse.
Uniq_secn_id_map section_id_;
// Given a section id, this maps it to the id of the kept
// section. If the id's are the same then this section is
// not folded.
std::vector<unsigned int> kept_section_id_;
unsigned int* num_tracked_relocs;
// Flag to indicate if ICF has been run.
bool icf_ready_;
// These lists are populated by gc_process_relocs in gc.h.
Section_list section_reloc_list_;
Symbol_list symbol_reloc_list_;
Addend_list addend_reloc_list_;
};
} // End of namespace gold.
#endif

2
gold/layout.cc
View File

@ -2253,7 +2253,7 @@ Layout::create_symtab_sections(const Input_objects* input_objects,
++p)
{
unsigned int index = (*p)->finalize_local_symbols(local_symbol_index,
off);
off, symtab);
off += (index - local_symbol_index) * symsize;
local_symbol_index = index;
}

9
gold/main.cc
View File

@ -44,6 +44,7 @@
#include "layout.h"
#include "plugin.h"
#include "gc.h"
#include "icf.h"
#include "incremental.h"
using namespace gold;
@ -203,9 +204,12 @@ main(int argc, char** argv)
// The list of input objects.
Input_objects input_objects;
// The Garbage Collection Object.
// The Garbage Collection (GC, --gc-sections) Object.
Garbage_collection gc;
// The Identical Code Folding (ICF, --icf) Object.
Icf icf;
// The symbol table. We're going to guess here how many symbols
// we're going to see based on the number of input files. Even when
// this is off, it means at worst we don't quite optimize hashtable
@ -216,6 +220,9 @@ main(int argc, char** argv)
if (parameters->options().gc_sections())
symtab.set_gc(&gc);
if (parameters->options().icf())
symtab.set_icf(&icf);
// The layout object.
Layout layout(command_line.number_of_input_files(),
&command_line.script_options());

158
gold/object.cc
View File

@ -914,14 +914,15 @@ Sized_relobj<size, big_endian>::layout_section(Layout* layout,
// whether they should be included in the link. If they should, we
// pass them to the Layout object, which will return an output section
// and an offset.
// During garbage collection (gc-sections), this function is called
// twice. When it is called the first time, it is for setting up some
// sections as roots to a work-list and to do comdat processing. Actual
// layout happens the second time around after all the relevant sections
// have been determined. The first time, is_worklist_ready is false.
// It is then set to true after the worklist is processed and the relevant
// sections are determined. Then, this function is called again to
// layout the sections.
// During garbage collection (--gc-sections) and identical code folding
// (--icf), this function is called twice. When it is called the first
// time, it is for setting up some sections as roots to a work-list for
// --gc-sections and to do comdat processing. Actual layout happens the
// second time around after all the relevant sections have been determined.
// The first time, is_worklist_ready or is_icf_ready is false. It is then
// set to true after the garbage collection worklist or identical code
// folding is processed and the relevant sections to be kept are
// determined. Then, this function is called again to layout the sections.
template<int size, bool big_endian>
void
@ -930,10 +931,22 @@ Sized_relobj<size, big_endian>::do_layout(Symbol_table* symtab,
Read_symbols_data* sd)
{
const unsigned int shnum = this->shnum();
bool is_gc_pass_one = (parameters->options().gc_sections()
&& !symtab->gc()->is_worklist_ready());
bool is_gc_pass_two = (parameters->options().gc_sections()
&& symtab->gc()->is_worklist_ready());
bool is_gc_pass_one = ((parameters->options().gc_sections()
&& !symtab->gc()->is_worklist_ready())
|| (parameters->options().icf()
&& !symtab->icf()->is_icf_ready()));
bool is_gc_pass_two = ((parameters->options().gc_sections()
&& symtab->gc()->is_worklist_ready())
|| (parameters->options().icf()
&& symtab->icf()->is_icf_ready()));
bool is_gc_or_icf = (parameters->options().gc_sections()
|| parameters->options().icf());
// Both is_gc_pass_one and is_gc_pass_two should not be true.
gold_assert(!(is_gc_pass_one && is_gc_pass_two));
if (shnum == 0)
return;
Symbols_data* gc_sd = NULL;
@ -958,7 +971,7 @@ Sized_relobj<size, big_endian>::do_layout(Symbol_table* symtab,
const unsigned char* symbol_names_data = NULL;
section_size_type symbol_names_size;
if (parameters->options().gc_sections())
if (is_gc_or_icf)
{
section_headers_data = gc_sd->section_headers_data;
section_names_size = gc_sd->section_names_size;
@ -986,9 +999,10 @@ Sized_relobj<size, big_endian>::do_layout(Symbol_table* symtab,
const unsigned char* pshdrs;
// Get the section names.
const unsigned char* pnamesu = parameters->options().gc_sections() ?
gc_sd->section_names_data :
sd->section_names->data();
const unsigned char* pnamesu = (is_gc_or_icf)
? gc_sd->section_names_data
: sd->section_names->data();
const char* pnames = reinterpret_cast<const char*>(pnamesu);
// If any input files have been claimed by plugins, we need to defer
@ -1141,7 +1155,7 @@ Sized_relobj<size, big_endian>::do_layout(Symbol_table* symtab,
}
}
if (is_gc_pass_one)
if (is_gc_pass_one && parameters->options().gc_sections())
{
if (is_section_name_included(name)
|| shdr.get_sh_type() == elfcpp::SHT_INIT_ARRAY
@ -1188,7 +1202,7 @@ Sized_relobj<size, big_endian>::do_layout(Symbol_table* symtab,
continue;
}
if (is_gc_pass_two)
if (is_gc_pass_two && parameters->options().gc_sections())
{
// This is executed during the second pass of garbage
// collection. do_layout has been called before and some
@ -1199,13 +1213,12 @@ Sized_relobj<size, big_endian>::do_layout(Symbol_table* symtab,
gold_assert(out_section_offsets[i] == invalid_address);
continue;
}
if ((shdr.get_sh_flags() & elfcpp::SHF_ALLOC) != 0)
if (symtab->gc()->referenced_list().find(Section_id(this,i))
== symtab->gc()->referenced_list().end())
if (((shdr.get_sh_flags() & elfcpp::SHF_ALLOC) != 0)
&& symtab->gc()->is_section_garbage(this, i))
{
if (parameters->options().print_gc_sections())
gold_info(_("%s: removing unused section from '%s'"
" in file '%s"),
" in file '%s'"),
program_name, this->section_name(i).c_str(),
this->name().c_str());
out_sections[i] = NULL;
@ -1213,6 +1226,36 @@ Sized_relobj<size, big_endian>::do_layout(Symbol_table* symtab,
continue;
}
}
if (is_gc_pass_two && parameters->options().icf())
{
if (out_sections[i] == NULL)
{
gold_assert(out_section_offsets[i] == invalid_address);
continue;
}
if (((shdr.get_sh_flags() & elfcpp::SHF_ALLOC) != 0)
&& symtab->icf()->is_section_folded(this, i))
{
if (parameters->options().print_icf_sections())
{
Section_id folded =
symtab->icf()->get_folded_section(this, i);
Relobj* folded_obj =
reinterpret_cast<Relobj*>(folded.first);
gold_info(_("%s: ICF folding section '%s' in file '%s'"
"into '%s' in file '%s'"),
program_name, this->section_name(i).c_str(),
this->name().c_str(),
folded_obj->section_name(folded.second).c_str(),
folded_obj->name().c_str());
}
out_sections[i] = NULL;
out_section_offsets[i] = invalid_address;
continue;
}
}
// Defer layout here if input files are claimed by plugins. When gc
// is turned on this function is called twice. For the second call
// should_defer_layout should be false.
@ -1228,7 +1271,8 @@ Sized_relobj<size, big_endian>::do_layout(Symbol_table* symtab,
out_sections[i] = reinterpret_cast<Output_section*>(2);
out_section_offsets[i] = invalid_address;
continue;
}
}
// During gc_pass_two if a section that was previously deferred is
// found, do not layout the section as layout_deferred_sections will
// do it later from gold.cc.
@ -1256,10 +1300,13 @@ Sized_relobj<size, big_endian>::do_layout(Symbol_table* symtab,
layout->layout_gnu_stack(seen_gnu_stack, gnu_stack_flags);
// When doing a relocatable link handle the reloc sections at the
// end. Garbage collection is not turned on for relocatable code.
// end. Garbage collection and Identical Code Folding is not
// turned on for relocatable code.
if (emit_relocs)
this->size_relocatable_relocs();
gold_assert(!parameters->options().gc_sections() || reloc_sections.empty());
gold_assert(!(is_gc_or_icf) || reloc_sections.empty());
for (std::vector<unsigned int>::const_iterator p = reloc_sections.begin();
p != reloc_sections.end();
++p)
@ -1342,6 +1389,7 @@ Sized_relobj<size, big_endian>::do_layout(Symbol_table* symtab,
delete[] gc_sd->section_names_data;
delete[] gc_sd->symbols_data;
delete[] gc_sd->symbol_names_data;
this->set_symbols_data(NULL);
}
else
{
@ -1554,7 +1602,8 @@ Sized_relobj<size, big_endian>::do_count_local_symbols(Stringpool* pool,
template<int size, bool big_endian>
unsigned int
Sized_relobj<size, big_endian>::do_finalize_local_symbols(unsigned int index,
off_t off)
off_t off,
Symbol_table* symtab)
{
gold_assert(off == static_cast<off_t>(align_address(off, size >> 3)));
@ -1596,6 +1645,21 @@ Sized_relobj<size, big_endian>::do_finalize_local_symbols(unsigned int index,
}
Output_section* os = out_sections[shndx];
Address secoffset = out_offsets[shndx];
if (symtab->is_section_folded(this, shndx))
{
gold_assert (os == NULL && secoffset == invalid_address);
// Get the os of the section it is folded onto.
Section_id folded = symtab->icf()->get_folded_section(this,
shndx);
gold_assert(folded.first != NULL);
Sized_relobj<size, big_endian>* folded_obj = reinterpret_cast
<Sized_relobj<size, big_endian>*>(folded.first);
os = folded_obj->output_section(folded.second);
gold_assert(os != NULL);
secoffset = folded_obj->get_output_section_offset(folded.second);
gold_assert(secoffset != invalid_address);
}
if (os == NULL)
{
@ -1605,7 +1669,7 @@ Sized_relobj<size, big_endian>::do_finalize_local_symbols(unsigned int index,
// so we leave the input value unchanged here.
continue;
}
else if (out_offsets[shndx] == invalid_address)
else if (secoffset == invalid_address)
{
uint64_t start;
@ -1647,11 +1711,11 @@ Sized_relobj<size, big_endian>::do_finalize_local_symbols(unsigned int index,
}
else if (lv.is_tls_symbol())
lv.set_output_value(os->tls_offset()
+ out_offsets[shndx]
+ secoffset
+ lv.input_value());
else
lv.set_output_value((relocatable ? 0 : os->address())
+ out_offsets[shndx]
+ secoffset
+ lv.input_value());
}
@ -1696,6 +1760,42 @@ Sized_relobj<size, big_endian>::do_set_local_dynsym_offset(off_t off)
return this->output_local_dynsym_count_;
}
// If Symbols_data is not NULL get the section flags from here otherwise
// get it from the file.
template<int size, bool big_endian>
uint64_t
Sized_relobj<size, big_endian>::do_section_flags(unsigned int shndx)
{
Symbols_data* sd = this->get_symbols_data();
if (sd != NULL)
{
const unsigned char* pshdrs = sd->section_headers_data
+ This::shdr_size * shndx;
typename This::Shdr shdr(pshdrs);
return shdr.get_sh_flags();
}
// If sd is NULL, read the section header from the file.
return this->elf_file_.section_flags(shndx);
}
// Get the section's ent size from Symbols_data. Called by get_section_contents
// in icf.cc
template<int size, bool big_endian>
uint64_t
Sized_relobj<size, big_endian>::do_section_entsize(unsigned int shndx)
{
Symbols_data* sd = this->get_symbols_data();
gold_assert (sd != NULL);
const unsigned char* pshdrs = sd->section_headers_data
+ This::shdr_size * shndx;
typename This::Shdr shdr(pshdrs);
return shdr.get_sh_entsize();
}
// Write out the local symbols.
template<int size, bool big_endian>

27
gold/object.h
View File

@ -321,6 +321,11 @@ class Object
section_flags(unsigned int shndx)
{ return this->do_section_flags(shndx); }
// Return the section entsize given a section index.
uint64_t
section_entsize(unsigned int shndx)
{ return this->do_section_entsize(shndx); }
// Return the section address given a section index.
uint64_t
section_address(unsigned int shndx)
@ -508,6 +513,10 @@ class Object
virtual uint64_t
do_section_flags(unsigned int shndx) = 0;
// Get section entsize--implemented by child class.
virtual uint64_t
do_section_entsize(unsigned int shndx) = 0;
// Get section address--implemented by child class.
virtual uint64_t
do_section_address(unsigned int shndx) = 0;
@ -617,7 +626,8 @@ class Relobj : public Object
output_sections_(),
map_to_relocatable_relocs_(NULL),
object_merge_map_(NULL),
relocs_must_follow_section_writes_(false)
relocs_must_follow_section_writes_(false),
sd_(NULL)
{ }
// During garbage collection, the Read_symbols_data pass for
@ -689,8 +699,8 @@ class Relobj : public Object
// indexes for the local variables, and set the offset where local
// symbol information will be stored. Returns the new local symbol index.
unsigned int
finalize_local_symbols(unsigned int index, off_t off)
{ return this->do_finalize_local_symbols(index, off); }
finalize_local_symbols(unsigned int index, off_t off, Symbol_table* symtab)
{ return this->do_finalize_local_symbols(index, off, symtab); }
// Set the output dynamic symbol table indexes for the local variables.
unsigned int
@ -814,7 +824,7 @@ class Relobj : public Object
// for the local variables, and set the offset where local symbol
// information will be stored.
virtual unsigned int
do_finalize_local_symbols(unsigned int, off_t) = 0;
do_finalize_local_symbols(unsigned int, off_t, Symbol_table*) = 0;
// Set the output dynamic symbol table indexes for the local variables.
virtual unsigned int
@ -1491,7 +1501,7 @@ class Sized_relobj : public Relobj
// Finalize the local symbols.
unsigned int
do_finalize_local_symbols(unsigned int, off_t);
do_finalize_local_symbols(unsigned int, off_t, Symbol_table*);
// Set the offset where local dynamic symbol information will be stored.
unsigned int
@ -1523,8 +1533,11 @@ class Sized_relobj : public Relobj
// Return section flags.
uint64_t
do_section_flags(unsigned int shndx)
{ return this->elf_file_.section_flags(shndx); }
do_section_flags(unsigned int shndx);
// Return section entsize.
uint64_t
do_section_entsize(unsigned int shndx);
// Return section address.
uint64_t

11
gold/options.h
View File

@ -813,6 +813,17 @@ class General_options
DEFINE_special(static, options::ONE_DASH, '\0',
N_("Do not link against shared libraries"), NULL);
DEFINE_bool(icf, options::TWO_DASHES, '\0', false,
N_("Fold identical functions"),
N_("Don't fold identical functions (default)"));
DEFINE_uint(icf_iterations, options::TWO_DASHES , '\0', 0,
N_("Number of iterations of ICF (default 2)"), N_("COUNT"));
DEFINE_bool(print_icf_sections, options::TWO_DASHES, '\0', false,
N_("List folded identical sections on stderr"),
N_("Do not list folded identical sections"));
DEFINE_bool(gc_sections, options::TWO_DASHES, '\0', false,
N_("Remove unused sections"),
N_("Don't remove unused sections (default)"));

10
gold/plugin.cc
View File

@ -684,6 +684,16 @@ Sized_pluginobj<size, big_endian>::do_section_flags(unsigned int)
return 0;
}
// Return section entsize. Not used for plugin objects.
template<int size, bool big_endian>
uint64_t
Sized_pluginobj<size, big_endian>::do_section_entsize(unsigned int)
{
gold_unreachable();
return 0;
}
// Return section address. Not used for plugin objects.
template<int size, bool big_endian>

4
gold/plugin.h
View File

@ -383,6 +383,10 @@ class Sized_pluginobj : public Pluginobj
uint64_t
do_section_flags(unsigned int shndx);
// Return section entsize.
uint64_t
do_section_entsize(unsigned int shndx);
// Return section address.
uint64_t
do_section_address(unsigned int shndx);

14
gold/reloc.cc
View File

@ -65,12 +65,12 @@ Read_relocs::run(Workqueue* workqueue)
this->object_->set_relocs_data(rd);
this->object_->release();
// If garbage collection is desired, we must process the relocs
// instead of scanning the relocs as reloc processing is necessary
// to determine unused sections.
if (parameters->options().gc_sections())
{
workqueue->queue_next(new Gc_process_relocs(this->options_,
// If garbage collection or identical comdat folding is desired, we
// process the relocs first before scanning them. Scanning of relocs is
// done only after garbage or identical sections is identified.
if (parameters->options().gc_sections() || parameters->options().icf())
{
workqueue->queue_next(new Gc_process_relocs(this->options_,
this->symtab_,
this->layout_,
this->object_, rd,
@ -418,7 +418,7 @@ Sized_relobj<size, big_endian>::do_scan_relocs(const General_options& options,
// When garbage collection is on, unreferenced sections are not included
// in the link that would have been included normally. This is known only
// after Read_relocs hence this check has to be done again.
if (parameters->options().gc_sections())
if (parameters->options().gc_sections() || parameters->options().icf())
{
if (p->output_section == NULL)
continue;

40
gold/symtab.cc
View File

@ -489,7 +489,7 @@ Symbol_table::Symbol_table(unsigned int count,
: saw_undefined_(0), offset_(0), table_(count), namepool_(),
forwarders_(), commons_(), tls_commons_(), small_commons_(),
large_commons_(), forced_locals_(), warnings_(),
version_script_(version_script), gc_(NULL)
version_script_(version_script), gc_(NULL), icf_(NULL)
{
namepool_.reserve(count);
}
@ -516,6 +516,13 @@ Symbol_table::Symbol_table_eq::operator()(const Symbol_table_key& k1,
return k1.first == k2.first && k1.second == k2.second;
}
bool
Symbol_table::is_section_folded(Object* obj, unsigned int shndx) const
{
return (parameters->options().icf()
&& this->icf_->is_section_folded(obj, shndx));
}
// For symbols that have been listed with -u option, add them to the
// work list to avoid gc'ing them.
@ -2417,8 +2424,22 @@ Symbol_table::sized_finalize_symbol(Symbol* unsized_sym)
{
Relobj* relobj = static_cast<Relobj*>(symobj);
Output_section* os = relobj->output_section(shndx);
uint64_t secoff64 = relobj->output_section_offset(shndx);
if (os == NULL)
if (this->is_section_folded(relobj, shndx))
{
gold_assert(os == NULL);
// Get the os of the section it is folded onto.
Section_id folded = this->icf_->get_folded_section(relobj,
shndx);
gold_assert(folded.first != NULL);
Relobj* folded_obj = reinterpret_cast<Relobj*>(folded.first);
os = folded_obj->output_section(folded.second);
gold_assert(os != NULL);
secoff64 = folded_obj->output_section_offset(folded.second);
}
if (os == NULL)
{
sym->set_symtab_index(-1U);
bool static_or_reloc = (parameters->doing_static_link() ||
@ -2428,10 +2449,10 @@ Symbol_table::sized_finalize_symbol(Symbol* unsized_sym)
return false;
}
uint64_t secoff64 = relobj->output_section_offset(shndx);
if (secoff64 == -1ULL)
{
// The section needs special handling (e.g., a merge section).
value = os->output_address(relobj, shndx, sym->value());
}
else
@ -2642,6 +2663,19 @@ Symbol_table::sized_write_globals(const Stringpool* sympool,
{
Relobj* relobj = static_cast<Relobj*>(symobj);
Output_section* os = relobj->output_section(in_shndx);
if (this->is_section_folded(relobj, in_shndx))
{
// This global symbol must be written out even though
// it is folded.
// Get the os of the section it is folded onto.
Section_id folded =
this->icf_->get_folded_section(relobj, in_shndx);
gold_assert(folded.first !=NULL);
Relobj* folded_obj =
reinterpret_cast<Relobj*>(folded.first);
os = folded_obj->output_section(folded.second);
gold_assert(os != NULL);
}
gold_assert(os != NULL);
shndx = os->out_shndx();

17
gold/symtab.h
View File

@ -28,6 +28,7 @@
#include <vector>
#include "gc.h"
#include "icf.h"
#include "elfcpp.h"
#include "parameters.h"
#include "stringpool.h"
@ -58,6 +59,7 @@ class Output_segment;
class Output_file;
class Output_symtab_xindex;
class Garbage_collection;
class Icf;
// The base class of an entry in the symbol table. The symbol table
// can have a lot of entries, so we don't want this class to big.
@ -1162,12 +1164,24 @@ class Symbol_table
~Symbol_table();
void
set_icf(Icf* icf)
{ this->icf_ = icf;}
Icf*
icf() const
{ return this->icf_; }
// Returns true if ICF determined that this is a duplicate section.
bool
is_section_folded(Object* obj, unsigned int shndx) const;
void
set_gc(Garbage_collection* gc)
{ this->gc_ = gc; }
Garbage_collection*
gc()
gc() const
{ return this->gc_; }
// During garbage collection, this keeps undefined symbols.
@ -1670,6 +1684,7 @@ class Symbol_table
// Information parsed from the version script, if any.
const Version_script_info& version_script_;
Garbage_collection* gc_;
Icf* icf_;
};
// We inline get_sized_symbol for efficiency.

6
gold/target-reloc.h
View File

@ -218,12 +218,14 @@ relocate_section(
// If the local symbol belongs to a section we are discarding,
// and that section is a debug section, try to find the
// corresponding kept section and map this symbol to its
// counterpart in the kept section.
// counterpart in the kept section. The symbol must not
// correspond to a section we are folding.
bool is_ordinary;
unsigned int shndx = psymval->input_shndx(&is_ordinary);
if (is_ordinary
&& shndx != elfcpp::SHN_UNDEF
&& !object->is_section_included(shndx))
&& !object->is_section_included(shndx)
&& !(relinfo->symtab->is_section_folded(object, shndx)))
{
if (comdat_behavior == CB_UNDETERMINED)
{

9
gold/testsuite/Makefile.am
View File

@ -115,6 +115,15 @@ gc_comdat_test: gc_comdat_test_1.o gc_comdat_test_2.o gcctestdir/ld
gc_comdat_test.stdout: gc_comdat_test
$(TEST_NM) -C gc_comdat_test > gc_comdat_test.stdout
check_SCRIPTS += icf_test.sh
check_DATA += icf_test.stdout
icf_test.o: icf_test.cc
$(CXXCOMPILE) -O0 -c -ffunction-sections -g -o $@ $<
icf_test: icf_test.o gcctestdir/ld
$(CXXLINK) -Bgcctestdir/ -Wl,--icf icf_test.o
icf_test.stdout: icf_test
$(TEST_NM) -C icf_test > icf_test.stdout
check_PROGRAMS += basic_test
check_PROGRAMS += basic_static_test

20
gold/testsuite/Makefile.in
View File

@ -57,11 +57,12 @@ check_PROGRAMS = object_unittest$(EXEEXT) binary_unittest$(EXEEXT) \
# Test --dynamic-list, --dynamic-list-data, --dynamic-list-cpp-new,
# and --dynamic-list-cpp-typeinfo
@GCC_TRUE@@NATIVE_LINKER_TRUE@am__append_1 = gc_comdat_test.sh \
@GCC_TRUE@@NATIVE_LINKER_TRUE@ two_file_shared.sh weak_plt.sh \
@GCC_TRUE@@NATIVE_LINKER_TRUE@ debug_msg.sh undef_symbol.sh \
@GCC_TRUE@@NATIVE_LINKER_TRUE@ ver_test_1.sh ver_test_2.sh \
@GCC_TRUE@@NATIVE_LINKER_TRUE@ ver_test_4.sh ver_test_5.sh \
@GCC_TRUE@@NATIVE_LINKER_TRUE@ ver_test_7.sh ver_test_10.sh \
@GCC_TRUE@@NATIVE_LINKER_TRUE@ icf_test.sh two_file_shared.sh \
@GCC_TRUE@@NATIVE_LINKER_TRUE@ weak_plt.sh debug_msg.sh \
@GCC_TRUE@@NATIVE_LINKER_TRUE@ undef_symbol.sh ver_test_1.sh \
@GCC_TRUE@@NATIVE_LINKER_TRUE@ ver_test_2.sh ver_test_4.sh \
@GCC_TRUE@@NATIVE_LINKER_TRUE@ ver_test_5.sh ver_test_7.sh \
@GCC_TRUE@@NATIVE_LINKER_TRUE@ ver_test_10.sh \
@GCC_TRUE@@NATIVE_LINKER_TRUE@ ver_matching_test.sh \
@GCC_TRUE@@NATIVE_LINKER_TRUE@ script_test_3.sh \
@GCC_TRUE@@NATIVE_LINKER_TRUE@ script_test_4.sh \
@ -74,6 +75,7 @@ check_PROGRAMS = object_unittest$(EXEEXT) binary_unittest$(EXEEXT) \
# We also want to make sure we do something reasonable when there's no
# debug info available. For the best test, we use .so's.
@GCC_TRUE@@NATIVE_LINKER_TRUE@am__append_2 = gc_comdat_test.stdout \
@GCC_TRUE@@NATIVE_LINKER_TRUE@ icf_test.stdout \
@GCC_TRUE@@NATIVE_LINKER_TRUE@ two_file_shared.dbg \
@GCC_TRUE@@NATIVE_LINKER_TRUE@ weak_plt_shared.so debug_msg.err \
@GCC_TRUE@@NATIVE_LINKER_TRUE@ debug_msg_so.err \
@ -345,7 +347,7 @@ check_PROGRAMS = object_unittest$(EXEEXT) binary_unittest$(EXEEXT) \
@NATIVE_LINKER_FALSE@ $(am__DEPENDENCIES_1) \
@NATIVE_LINKER_FALSE@ $(am__DEPENDENCIES_1)
subdir = testsuite
DIST_COMMON = $(srcdir)/Makefile.am $(srcdir)/Makefile.in
DIST_COMMON = $(srcdir)/Makefile.am $(srcdir)/Makefile.in ChangeLog
ACLOCAL_M4 = $(top_srcdir)/aclocal.m4
am__aclocal_m4_deps = $(top_srcdir)/../config/depstand.m4 \
$(top_srcdir)/../config/gettext-sister.m4 \
@ -2316,6 +2318,12 @@ uninstall-am: uninstall-info-am
@GCC_TRUE@@NATIVE_LINKER_TRUE@ $(CXXLINK) -Bgcctestdir/ -Wl,--gc-sections gc_comdat_test_1.o gc_comdat_test_2.o
@GCC_TRUE@@NATIVE_LINKER_TRUE@gc_comdat_test.stdout: gc_comdat_test
@GCC_TRUE@@NATIVE_LINKER_TRUE@ $(TEST_NM) -C gc_comdat_test > gc_comdat_test.stdout
@GCC_TRUE@@NATIVE_LINKER_TRUE@icf_test.o: icf_test.cc
@GCC_TRUE@@NATIVE_LINKER_TRUE@ $(CXXCOMPILE) -O0 -c -ffunction-sections -g -o $@ $<
@GCC_TRUE@@NATIVE_LINKER_TRUE@icf_test: icf_test.o gcctestdir/ld
@GCC_TRUE@@NATIVE_LINKER_TRUE@ $(CXXLINK) -Bgcctestdir/ -Wl,--icf icf_test.o
@GCC_TRUE@@NATIVE_LINKER_TRUE@icf_test.stdout: icf_test
@GCC_TRUE@@NATIVE_LINKER_TRUE@ $(TEST_NM) -C icf_test > icf_test.stdout
@GCC_TRUE@@NATIVE_LINKER_TRUE@basic_test.o: basic_test.cc
@GCC_TRUE@@NATIVE_LINKER_TRUE@ $(CXXCOMPILE) -O0 -c -o $@ $<
@GCC_TRUE@@NATIVE_LINKER_TRUE@basic_test: basic_test.o gcctestdir/ld

51
gold/testsuite/icf_test.cc Normal file
View File

@ -0,0 +1,51 @@
// icf_test.cc -- a test case for gold
// Copyright 2009 Free Software Foundation, Inc.
// Written by Sriraman Tallam <tmsriram@google.com>.
// This file is part of gold.
// This program is free software; you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation; either version 3 of the License, or
// (at your option) any later version.
// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU General Public License for more details.
// You should have received a copy of the GNU General Public License
// along with this program; if not, write to the Free Software
// Foundation, Inc., 51 Franklin Street - Fifth Floor, Boston,
// MA 02110-1301, USA.
// The goal of this program is to verify if identical code folding
// correctly identifies and folds functions. folded_func must be
// folded into kept_func.
int common()
{
return 1;
}
int kept_func()
{
common();
// Recursive call.
kept_func();
return 1;
}
int folded_func()
{
common();
// Recursive call.
folded_func();
return 1;
}
int main()
{
return 0;
}

40
gold/testsuite/icf_test.sh Executable file
View File

@ -0,0 +1,40 @@
#!/bin/sh
# icf_test.sh -- test --icf
# Copyright 2009 Free Software Foundation, Inc.
# Written by Sriraman Tallam <tmsriram@google.com>.
# This file is part of gold.
# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation; either version 3 of the License, or
# (at your option) any later version.
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU General Public License for more details.
# You should have received a copy of the GNU General Public License
# along with this program; if not, write to the Free Software
# Foundation, Inc., 51 Franklin Street - Fifth Floor, Boston,
# MA 02110-1301, USA.
# The goal of this program is to verify if icf works as expected.
# File icf_test.cc is in this test. This program checks if the
# identical sections are correctly folded.
check()
{
func_addr_1=`grep $2 $1 | awk '{print $1}'`
func_addr_2=`grep $3 $1 | awk '{print $1}'`
if [ $func_addr_1 != $func_addr_2 ]
then
echo "Identical Code Folding failed to fold" $2 "and" $3
exit 1
fi
}
check icf_test.stdout "folded_func" "kept_func"