// gc.h -- garbage collection of unused sections
// Copyright (C) 2009-2020 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;
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(Relobj* 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(Relobj* src_object, unsigned int src_shndx,
Relobj* 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 r_type, Relobj* obj)
{
if (Classify_reloc::sh_type == elfcpp::SHT_REL)
return Classify_reloc::get_size_for_reloc(r_type, obj);
return 0;
}
// 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,
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 Classify_reloc::Reltype Reltype;
const int reloc_size = Classify_reloc::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)
|| is_prefix_of(".eh_frame", 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);
unsigned int r_sym = Classify_reloc::get_r_sym(&reloc);
unsigned int r_type = Classify_reloc::get_r_type(&reloc);
typename elfcpp::Elf_types<size>::Elf_Swxword addend =
Classify_reloc::get_r_addend(&reloc);
Relobj* 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(src_obj, dst_indx));
else
(*secvec).push_back(Section_id(NULL, 0));
// If the target of the relocation is an STT_SECTION symbol,
// make a note of that by storing -1 in the symbol vector.
if (lsym.get_st_type() == elfcpp::STT_SECTION)
(*symvec).push_back(reinterpret_cast<Symbol*>(-1));
else
(*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>(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, target,
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
&& !gsym->object()->is_dynamic())
{
dst_obj = static_cast<Relobj*>(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
&& gsym->type() == elfcpp::STT_FUNC
&& check_section_for_function_pointers
&& dst_obj != NULL
&& (!is_ordinary
|| scan.global_reloc_may_be_function_pointer(
symtab, NULL, target, 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 && dst_obj != NULL)
(*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>(r_type, src_obj));
}
if (dst_obj == NULL)
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