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4277535cdc
binutils-gdb/gold/gc.h
Rafael Ávila de Espíndola 4277535cdc Use LIFO instead of FIFO to implement gc's transitive closure. 
FIFO is harder to implement and has less locality than LIFO. It is
also not necessary to implement a transitive closure, a LIFO works
just as well.
2015-04-17 11:51:36 -04:00

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// gc.h -- garbage collection of unused sections
// Copyright (C) 2009-2015 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_GC_H
#define GOLD_GC_H
#include <vector>
#include "elfcpp.h"
#include "symtab.h"
#include "object.h"
#include "icf.h"
namespace gold
{
class Object;
template<int size, bool big_endian>
class Sized_relobj_file;
template<int sh_type, int size, bool big_endian>
struct Reloc_types;
class Output_section;
class General_options;
class Layout;
class Garbage_collection
{
public:
typedef Unordered_set<Section_id, Section_id_hash> Sections_reachable;
typedef std::map<Section_id, Sections_reachable> Section_ref;
typedef std::vector<Section_id> Worklist_type;
// This maps the name of the section which can be represented as a C
// identifier (cident) to the list of sections that have that name.
// Different object files can have cident sections with the same name.
typedef std::map<std::string, Sections_reachable> Cident_section_map;
Garbage_collection()
: is_worklist_ready_(false)
{ }
// Accessor methods for the private members.
Sections_reachable&
referenced_list()
{ return referenced_list_; }
Section_ref&
section_reloc_map()
{ return this->section_reloc_map_; }
Worklist_type&
worklist()
{ return this->work_list_; }
bool
is_worklist_ready()
{ return this->is_worklist_ready_; }
void
worklist_ready()
{ this->is_worklist_ready_ = true; }
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()); }
Cident_section_map*
cident_sections()
{ return &cident_sections_; }
void
add_cident_section(std::string section_name,
Section_id secn)
{ this->cident_sections_[section_name].insert(secn); }
// Add a reference from the SRC_SHNDX-th section of SRC_OBJECT to
// DST_SHNDX-th section of DST_OBJECT.
void
add_reference(Object* src_object, unsigned int src_shndx,
Object* dst_object, unsigned int dst_shndx)
{
Section_id src_id(src_object, src_shndx);
Section_id dst_id(dst_object, dst_shndx);
Sections_reachable& reachable = this->section_reloc_map_[src_id];
reachable.insert(dst_id);
}
private:
Worklist_type work_list_;
bool is_worklist_ready_;
Section_ref section_reloc_map_;
Sections_reachable referenced_list_;
Cident_section_map cident_sections_;
};
// Data to pass between successive invocations of do_layout
// in object.cc while garbage collecting. This data structure
// is filled by using the data from Read_symbols_data.
struct Symbols_data
{
// Section headers.
unsigned char* section_headers_data;
// Section names.
unsigned char* section_names_data;
// Size of section name data in bytes.
section_size_type section_names_size;
// Symbol data.
unsigned char* symbols_data;
// Size of symbol data in bytes.
section_size_type symbols_size;
// Offset of external symbols within symbol data. This structure
// sometimes contains only external symbols, in which case this will
// be zero. Sometimes it contains all symbols.
section_offset_type external_symbols_offset;
// Symbol names.
unsigned char* symbol_names_data;
// Size of symbol name data in bytes.
section_size_type symbol_names_size;
};
// Relocations of type SHT_REL store the addend value in their bytes.
// This function returns the size of the embedded addend which is
// nothing but the size of the relocation.
template<typename Classify_reloc>
inline unsigned int
get_embedded_addend_size(int sh_type, int r_type, Relobj* obj)
{
if (sh_type != elfcpp::SHT_REL)
return 0;
Classify_reloc classify_reloc;
return classify_reloc.get_size_for_reloc(r_type, obj);
}
// 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, typename Classify_reloc>
inline void
gc_process_relocs(
Symbol_table* symtab,
Layout*,
Target_type* target,
Sized_relobj_file<size, big_endian>* src_obj,
unsigned int src_indx,
const unsigned char* prelocs,
size_t reloc_count,
Output_section*,
bool,
size_t local_count,
const unsigned char* plocal_syms)
{
Scan scan;
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;
Icf::Sections_reachable_info* secvec = NULL;
Icf::Symbol_info* symvec = NULL;
Icf::Addend_info* addendvec = NULL;
Icf::Offset_info* offsetvec = NULL;
Icf::Reloc_addend_size_info* reloc_addend_size_vec = NULL;
bool is_icf_tracked = false;
const char* cident_section_name = NULL;
std::string src_section_name = (parameters->options().icf_enabled()
? src_obj->section_name(src_indx)
: "");
bool check_section_for_function_pointers = false;
if (parameters->options().icf_enabled()
&& is_section_foldable_candidate(src_section_name.c_str()))
{
is_icf_tracked = true;
Section_id src_id(src_obj, src_indx);
Icf::Reloc_info* reloc_info =
&symtab->icf()->reloc_info_list()[src_id];
secvec = &reloc_info->section_info;
symvec = &reloc_info->symbol_info;
addendvec = &reloc_info->addend_info;
offsetvec = &reloc_info->offset_info;
reloc_addend_size_vec = &reloc_info->reloc_addend_size_info;
}
check_section_for_function_pointers =
symtab->icf()->check_section_for_function_pointers(src_section_name,
target);
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);
unsigned int r_type = elfcpp::elf_r_type<size>(r_info);
typename elfcpp::Elf_types<size>::Elf_Swxword addend =
Reloc_types<sh_type, size, big_endian>::get_reloc_addend_noerror(&reloc);
Object* dst_obj;
unsigned int dst_indx;
typedef typename elfcpp::Elf_types<size>::Elf_Addr Address;
Address dst_off;
if (r_sym < local_count)
{
gold_assert(plocal_syms != NULL);
typename elfcpp::Sym<size, big_endian> lsym(plocal_syms
+ r_sym * sym_size);
dst_indx = lsym.get_st_shndx();
bool is_ordinary;
dst_indx = src_obj->adjust_sym_shndx(r_sym, dst_indx, &is_ordinary);
dst_obj = src_obj;
dst_off = lsym.get_st_value() + addend;
if (is_icf_tracked)
{
Address symvalue = dst_off - addend;
if (is_ordinary)
(*secvec).push_back(Section_id(dst_obj, dst_indx));
else
(*secvec).push_back(Section_id(NULL, 0));
(*symvec).push_back(NULL);
(*addendvec).push_back(std::make_pair(
static_cast<long long>(symvalue),
static_cast<long long>(addend)));
uint64_t reloc_offset =
convert_to_section_size_type(reloc.get_r_offset());
(*offsetvec).push_back(reloc_offset);
(*reloc_addend_size_vec).push_back(
get_embedded_addend_size<Classify_reloc>(sh_type, r_type,
src_obj));
}
// When doing safe folding, check to see if this relocation is that
// of a function pointer being taken.
if (is_ordinary
&& check_section_for_function_pointers
&& lsym.get_st_type() != elfcpp::STT_OBJECT
&& scan.local_reloc_may_be_function_pointer(symtab, NULL, NULL,
src_obj, src_indx,
NULL, reloc, r_type,
lsym))
symtab->icf()->set_section_has_function_pointers(
src_obj, lsym.get_st_shndx());
if (!is_ordinary || dst_indx == src_indx)
continue;
}
else
{
Symbol* gsym = src_obj->global_symbol(r_sym);
gold_assert(gsym != NULL);
if (gsym->is_forwarder())
gsym = symtab->resolve_forwards(gsym);
dst_obj = NULL;
dst_indx = 0;
bool is_ordinary = false;
if (gsym->source() == Symbol::FROM_OBJECT)
{
dst_obj = gsym->object();
dst_indx = gsym->shndx(&is_ordinary);
}
dst_off = static_cast<const Sized_symbol<size>*>(gsym)->value();
dst_off += addend;
// When doing safe folding, check to see if this relocation is that
// of a function pointer being taken.
if (gsym->source() == Symbol::FROM_OBJECT
&& check_section_for_function_pointers
&& gsym->type() != elfcpp::STT_OBJECT
&& (!is_ordinary
|| scan.global_reloc_may_be_function_pointer(
symtab, NULL, NULL, src_obj, src_indx, NULL, reloc,
r_type, gsym)))
symtab->icf()->set_section_has_function_pointers(dst_obj, dst_indx);
// If the symbol name matches '__start_XXX' then the section with
// the C identifier like name 'XXX' should not be garbage collected.
// A similar treatment to symbols with the name '__stop_XXX'.
if (is_prefix_of(cident_section_start_prefix, gsym->name()))
{
cident_section_name = (gsym->name()
+ strlen(cident_section_start_prefix));
}
else if (is_prefix_of(cident_section_stop_prefix, gsym->name()))
{
cident_section_name = (gsym->name()
+ strlen(cident_section_stop_prefix));
}
if (is_icf_tracked)
{
Address symvalue = dst_off - addend;
if (is_ordinary && gsym->source() == Symbol::FROM_OBJECT)
(*secvec).push_back(Section_id(dst_obj, dst_indx));
else
(*secvec).push_back(Section_id(NULL, 0));
(*symvec).push_back(gsym);
(*addendvec).push_back(std::make_pair(
static_cast<long long>(symvalue),
static_cast<long long>(addend)));
uint64_t reloc_offset =
convert_to_section_size_type(reloc.get_r_offset());
(*offsetvec).push_back(reloc_offset);
(*reloc_addend_size_vec).push_back(
get_embedded_addend_size<Classify_reloc>(sh_type, r_type,
src_obj));
}
if (gsym->source() != Symbol::FROM_OBJECT)
continue;
if (!is_ordinary)
continue;
}
if (parameters->options().gc_sections())
{
symtab->gc()->add_reference(src_obj, src_indx, dst_obj, dst_indx);
parameters->sized_target<size, big_endian>()
->gc_add_reference(symtab, src_obj, src_indx,
dst_obj, dst_indx, dst_off);
if (cident_section_name != NULL)
{
Garbage_collection::Cident_section_map::iterator ele =
symtab->gc()->cident_sections()->find(std::string(cident_section_name));
if (ele == symtab->gc()->cident_sections()->end())
continue;
Section_id src_id(src_obj, src_indx);
Garbage_collection::Sections_reachable&
v(symtab->gc()->section_reloc_map()[src_id]);
Garbage_collection::Sections_reachable& cident_secn(ele->second);
for (Garbage_collection::Sections_reachable::iterator it_v
= cident_secn.begin();
it_v != cident_secn.end();
++it_v)
{
v.insert(*it_v);
}
}
}
}
return;
}
} // End of namespace gold.
#endif
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