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// icf.h -- Identical Code Folding
// Copyright (C) 2009-2021 Free Software Foundation, Inc.
// Written by Sriraman Tallam <>.
// 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
// 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"
#include "object.h"
namespace gold
class Object;
class Input_objects;
class Symbol_table;
class Icf
typedef std::vector<Section_id> Sections_reachable_info;
typedef std::vector<Symbol*> Symbol_info;
typedef std::vector<std::pair<long long, long long> > Addend_info;
typedef std::vector<uint64_t> Offset_info;
typedef std::vector<unsigned int> Reloc_addend_size_info;
typedef Unordered_map<Section_id,
unsigned int,
Section_id_hash> Uniq_secn_id_map;
typedef Unordered_set<Section_id, Section_id_hash> Secn_fptr_taken_set;
typedef struct
// This stores the section corresponding to the reloc.
Sections_reachable_info section_info;
// This stores the symbol corresponding to the reloc.
Symbol_info symbol_info;
// This stores the symbol value and the addend for a reloc.
Addend_info addend_info;
Offset_info offset_info;
Reloc_addend_size_info reloc_addend_size_info;
} Reloc_info;
typedef Unordered_map<Section_id, Reloc_info,
Section_id_hash> Reloc_info_list;
// A region of some other section that should be considered part of
// a section for ICF purposes. This is used to avoid folding sections
// that have identical text and relocations but different .eh_frame
// information.
typedef struct
Section_id section;
section_offset_type offset;
section_size_type length;
} Extra_identity_info;
typedef std::multimap<Section_id, Extra_identity_info> Extra_identity_list;
: id_section_(), section_id_(), kept_section_id_(),
{ }
// Returns the kept folded identical section corresponding to
// dup_obj and dup_shndx.
get_folded_section(Relobj* dup_obj, unsigned int dup_shndx);
// Forms groups of identical sections where the first member
// of each group is the kept section during folding.
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.
{ this->icf_ready_ = true; }
// Returns true if ICF has been run.
{ return this->icf_ready_; }
// Unfolds the section denoted by OBJ and SHNDX if folded.
unfold_section(Relobj* obj, unsigned int shndx);
// Returns the kept section corresponding to the
// given section.
is_section_folded(Relobj* obj, unsigned int shndx);
// Given an object and a section index, this returns true if the
// pointer of the function defined in this section is taken.
section_has_function_pointers(Relobj* obj, unsigned int shndx)
return (this->fptr_section_id_.find(Section_id(obj, shndx))
!= this->fptr_section_id_.end());
// Records that a pointer of the function defined in this section
// is taken.
set_section_has_function_pointers(Relobj* obj, unsigned int shndx)
this->fptr_section_id_.insert(Section_id(obj, shndx));
// Checks if the section_name should be searched for relocs
// corresponding to taken function pointers. Ignores eh_frame
// and vtable sections.
inline bool
check_section_for_function_pointers(const std::string& section_name,
Target* target)
return (parameters->options().icf_safe_folding()
&& target->can_check_for_function_pointers()
&& target->section_may_have_icf_unsafe_pointers(
// Returns a map of a section to info (Reloc_info) about its relocations.
{ return this->reloc_info_list_; }
// Returns a map from section to region of a different section that should
// be considered part of the key section for ICF purposes.
{ return this->extra_identity_list_; }
// Returns a mapping of each section to a unique integer.
{ return this->section_id_; }
add_ehframe_links(Relobj* object, unsigned int ehframe_shndx,
Reloc_info& ehframe_relocs);
// 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_;
// Given a section id, this says if the pointer to this
// function is taken in which case it is dangerous to fold
// this function.
Secn_fptr_taken_set fptr_section_id_;
// Flag to indicate if ICF has been run.
bool icf_ready_;
// This list is populated by gc_process_relocs in gc.h.
Reloc_info_list reloc_info_list_;
// Regions of other sections that should be considered part of
// each section for ICF purposes.
Extra_identity_list extra_identity_list_;
// This function returns true if this section corresponds to a function that
// should be considered by icf as a possible candidate for folding. Some
// earlier gcc versions, like 4.0.3, put constructors and destructors in
// .gnu.linkonce.t sections and hence should be included too.
// The mechanism used to safely fold functions referenced by .eh_frame
// requires folding .gcc_except_table sections as well; see "Notes regarding
// C++ exception handling" at the top of for an explanation why.
inline bool
is_section_foldable_candidate(const std::string& section_name)
const char* section_name_cstr = section_name.c_str();
return (is_prefix_of(".text", section_name_cstr)
|| is_prefix_of(".gcc_except_table", section_name_cstr)
|| is_prefix_of(".gnu.linkonce.t", section_name_cstr));
} // End of namespace gold.