381 lines
13 KiB
C++
381 lines
13 KiB
C++
// gc.h -- garbage collection of unused sections
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// Copyright (C) 2009-2020 Free Software Foundation, Inc.
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// Written by Sriraman Tallam <tmsriram@google.com>.
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// This file is part of gold.
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// This program is free software; you can redistribute it and/or modify
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// it under the terms of the GNU General Public License as published by
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// the Free Software Foundation; either version 3 of the License, or
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// (at your option) any later version.
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// This program is distributed in the hope that it will be useful,
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// but WITHOUT ANY WARRANTY; without even the implied warranty of
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// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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// GNU General Public License for more details.
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// You should have received a copy of the GNU General Public License
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// along with this program; if not, write to the Free Software
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// Foundation, Inc., 51 Franklin Street - Fifth Floor, Boston,
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// MA 02110-1301, USA.
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#ifndef GOLD_GC_H
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#define GOLD_GC_H
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#include <vector>
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#include "elfcpp.h"
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#include "symtab.h"
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#include "object.h"
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#include "icf.h"
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namespace gold
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{
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class Object;
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template<int size, bool big_endian>
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class Sized_relobj_file;
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class Output_section;
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class General_options;
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class Layout;
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class Garbage_collection
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{
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public:
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typedef Unordered_set<Section_id, Section_id_hash> Sections_reachable;
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typedef std::map<Section_id, Sections_reachable> Section_ref;
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typedef std::vector<Section_id> Worklist_type;
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// This maps the name of the section which can be represented as a C
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// identifier (cident) to the list of sections that have that name.
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// Different object files can have cident sections with the same name.
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typedef std::map<std::string, Sections_reachable> Cident_section_map;
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Garbage_collection()
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: is_worklist_ready_(false)
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{ }
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// Accessor methods for the private members.
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Sections_reachable&
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referenced_list()
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{ return referenced_list_; }
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Section_ref&
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section_reloc_map()
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{ return this->section_reloc_map_; }
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Worklist_type&
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worklist()
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{ return this->work_list_; }
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bool
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is_worklist_ready()
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{ return this->is_worklist_ready_; }
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void
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worklist_ready()
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{ this->is_worklist_ready_ = true; }
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void
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do_transitive_closure();
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bool
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is_section_garbage(Relobj* obj, unsigned int shndx)
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{ return (this->referenced_list().find(Section_id(obj, shndx))
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== this->referenced_list().end()); }
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Cident_section_map*
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cident_sections()
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{ return &cident_sections_; }
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void
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add_cident_section(std::string section_name,
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Section_id secn)
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{ this->cident_sections_[section_name].insert(secn); }
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// Add a reference from the SRC_SHNDX-th section of SRC_OBJECT to
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// DST_SHNDX-th section of DST_OBJECT.
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void
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add_reference(Relobj* src_object, unsigned int src_shndx,
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Relobj* dst_object, unsigned int dst_shndx)
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{
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Section_id src_id(src_object, src_shndx);
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Section_id dst_id(dst_object, dst_shndx);
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Sections_reachable& reachable = this->section_reloc_map_[src_id];
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reachable.insert(dst_id);
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}
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private:
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Worklist_type work_list_;
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bool is_worklist_ready_;
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Section_ref section_reloc_map_;
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Sections_reachable referenced_list_;
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Cident_section_map cident_sections_;
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};
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// Data to pass between successive invocations of do_layout
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// in object.cc while garbage collecting. This data structure
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// is filled by using the data from Read_symbols_data.
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struct Symbols_data
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{
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// Section headers.
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unsigned char* section_headers_data;
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// Section names.
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unsigned char* section_names_data;
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// Size of section name data in bytes.
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section_size_type section_names_size;
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// Symbol data.
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unsigned char* symbols_data;
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// Size of symbol data in bytes.
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section_size_type symbols_size;
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// Offset of external symbols within symbol data. This structure
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// sometimes contains only external symbols, in which case this will
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// be zero. Sometimes it contains all symbols.
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section_offset_type external_symbols_offset;
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// Symbol names.
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unsigned char* symbol_names_data;
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// Size of symbol name data in bytes.
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section_size_type symbol_names_size;
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};
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// Relocations of type SHT_REL store the addend value in their bytes.
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// This function returns the size of the embedded addend which is
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// nothing but the size of the relocation.
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template<typename Classify_reloc>
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inline unsigned int
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get_embedded_addend_size(int r_type, Relobj* obj)
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{
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if (Classify_reloc::sh_type == elfcpp::SHT_REL)
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return Classify_reloc::get_size_for_reloc(r_type, obj);
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return 0;
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}
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// This function implements the generic part of reloc
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// processing to map a section to all the sections it
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// references through relocs. It is called only during
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// garbage collection (--gc-sections) and identical code
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// folding (--icf).
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template<int size, bool big_endian, typename Target_type,
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typename Scan, typename Classify_reloc>
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inline void
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gc_process_relocs(
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Symbol_table* symtab,
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Layout*,
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Target_type* target,
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Sized_relobj_file<size, big_endian>* src_obj,
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unsigned int src_indx,
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const unsigned char* prelocs,
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size_t reloc_count,
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Output_section*,
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bool,
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size_t local_count,
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const unsigned char* plocal_syms)
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{
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Scan scan;
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typedef typename Classify_reloc::Reltype Reltype;
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const int reloc_size = Classify_reloc::reloc_size;
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const int sym_size = elfcpp::Elf_sizes<size>::sym_size;
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Icf::Sections_reachable_info* secvec = NULL;
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Icf::Symbol_info* symvec = NULL;
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Icf::Addend_info* addendvec = NULL;
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Icf::Offset_info* offsetvec = NULL;
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Icf::Reloc_addend_size_info* reloc_addend_size_vec = NULL;
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bool is_icf_tracked = false;
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const char* cident_section_name = NULL;
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std::string src_section_name = (parameters->options().icf_enabled()
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? src_obj->section_name(src_indx)
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: "");
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bool check_section_for_function_pointers = false;
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if (parameters->options().icf_enabled()
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&& (is_section_foldable_candidate(src_section_name)
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|| is_prefix_of(".eh_frame", src_section_name.c_str())))
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{
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is_icf_tracked = true;
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Section_id src_id(src_obj, src_indx);
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Icf::Reloc_info* reloc_info =
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&symtab->icf()->reloc_info_list()[src_id];
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secvec = &reloc_info->section_info;
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symvec = &reloc_info->symbol_info;
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addendvec = &reloc_info->addend_info;
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offsetvec = &reloc_info->offset_info;
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reloc_addend_size_vec = &reloc_info->reloc_addend_size_info;
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}
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check_section_for_function_pointers =
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symtab->icf()->check_section_for_function_pointers(src_section_name,
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target);
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for (size_t i = 0; i < reloc_count; ++i, prelocs += reloc_size)
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{
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Reltype reloc(prelocs);
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unsigned int r_sym = Classify_reloc::get_r_sym(&reloc);
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unsigned int r_type = Classify_reloc::get_r_type(&reloc);
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typename elfcpp::Elf_types<size>::Elf_Swxword addend =
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Classify_reloc::get_r_addend(&reloc);
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Relobj* dst_obj;
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unsigned int dst_indx;
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typedef typename elfcpp::Elf_types<size>::Elf_Addr Address;
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Address dst_off;
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if (r_sym < local_count)
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{
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gold_assert(plocal_syms != NULL);
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typename elfcpp::Sym<size, big_endian> lsym(plocal_syms
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+ r_sym * sym_size);
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dst_indx = lsym.get_st_shndx();
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bool is_ordinary;
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dst_indx = src_obj->adjust_sym_shndx(r_sym, dst_indx, &is_ordinary);
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dst_obj = src_obj;
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dst_off = lsym.get_st_value() + addend;
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if (is_icf_tracked)
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{
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Address symvalue = dst_off - addend;
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if (is_ordinary)
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(*secvec).push_back(Section_id(src_obj, dst_indx));
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else
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(*secvec).push_back(Section_id(NULL, 0));
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// If the target of the relocation is an STT_SECTION symbol,
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// make a note of that by storing -1 in the symbol vector.
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if (lsym.get_st_type() == elfcpp::STT_SECTION)
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(*symvec).push_back(reinterpret_cast<Symbol*>(-1));
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else
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(*symvec).push_back(NULL);
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(*addendvec).push_back(std::make_pair(
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static_cast<long long>(symvalue),
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static_cast<long long>(addend)));
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uint64_t reloc_offset =
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convert_to_section_size_type(reloc.get_r_offset());
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(*offsetvec).push_back(reloc_offset);
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(*reloc_addend_size_vec).push_back(
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get_embedded_addend_size<Classify_reloc>(r_type, src_obj));
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}
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// When doing safe folding, check to see if this relocation is that
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// of a function pointer being taken.
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if (is_ordinary
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&& check_section_for_function_pointers
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&& lsym.get_st_type() != elfcpp::STT_OBJECT
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&& scan.local_reloc_may_be_function_pointer(symtab, NULL, target,
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src_obj, src_indx,
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NULL, reloc, r_type,
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lsym))
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symtab->icf()->set_section_has_function_pointers(
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src_obj, lsym.get_st_shndx());
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if (!is_ordinary || dst_indx == src_indx)
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continue;
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}
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else
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{
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Symbol* gsym = src_obj->global_symbol(r_sym);
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gold_assert(gsym != NULL);
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if (gsym->is_forwarder())
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gsym = symtab->resolve_forwards(gsym);
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dst_obj = NULL;
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dst_indx = 0;
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bool is_ordinary = false;
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if (gsym->source() == Symbol::FROM_OBJECT
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&& !gsym->object()->is_dynamic())
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{
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dst_obj = static_cast<Relobj*>(gsym->object());
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dst_indx = gsym->shndx(&is_ordinary);
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}
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dst_off = static_cast<const Sized_symbol<size>*>(gsym)->value();
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dst_off += addend;
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// When doing safe folding, check to see if this relocation is that
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// of a function pointer being taken.
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if (gsym->source() == Symbol::FROM_OBJECT
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&& gsym->type() == elfcpp::STT_FUNC
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&& check_section_for_function_pointers
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&& dst_obj != NULL
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&& (!is_ordinary
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|| scan.global_reloc_may_be_function_pointer(
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symtab, NULL, target, src_obj, src_indx, NULL, reloc,
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r_type, gsym)))
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symtab->icf()->set_section_has_function_pointers(dst_obj, dst_indx);
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// If the symbol name matches '__start_XXX' then the section with
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// the C identifier like name 'XXX' should not be garbage collected.
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// A similar treatment to symbols with the name '__stop_XXX'.
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if (is_prefix_of(cident_section_start_prefix, gsym->name()))
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{
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cident_section_name = (gsym->name()
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+ strlen(cident_section_start_prefix));
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}
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else if (is_prefix_of(cident_section_stop_prefix, gsym->name()))
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{
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cident_section_name = (gsym->name()
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+ strlen(cident_section_stop_prefix));
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}
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if (is_icf_tracked)
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{
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Address symvalue = dst_off - addend;
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if (is_ordinary && dst_obj != NULL)
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(*secvec).push_back(Section_id(dst_obj, dst_indx));
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else
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(*secvec).push_back(Section_id(NULL, 0));
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(*symvec).push_back(gsym);
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(*addendvec).push_back(std::make_pair(
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static_cast<long long>(symvalue),
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static_cast<long long>(addend)));
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uint64_t reloc_offset =
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convert_to_section_size_type(reloc.get_r_offset());
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(*offsetvec).push_back(reloc_offset);
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(*reloc_addend_size_vec).push_back(
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get_embedded_addend_size<Classify_reloc>(r_type, src_obj));
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}
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if (dst_obj == NULL)
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continue;
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if (!is_ordinary)
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continue;
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}
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if (parameters->options().gc_sections())
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{
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symtab->gc()->add_reference(src_obj, src_indx, dst_obj, dst_indx);
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parameters->sized_target<size, big_endian>()
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->gc_add_reference(symtab, src_obj, src_indx, dst_obj, dst_indx,
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dst_off);
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if (cident_section_name != NULL)
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{
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Garbage_collection::Cident_section_map::iterator ele =
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symtab->gc()->cident_sections()->find(std::string(cident_section_name));
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if (ele == symtab->gc()->cident_sections()->end())
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continue;
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Section_id src_id(src_obj, src_indx);
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Garbage_collection::Sections_reachable&
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v(symtab->gc()->section_reloc_map()[src_id]);
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Garbage_collection::Sections_reachable& cident_secn(ele->second);
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for (Garbage_collection::Sections_reachable::iterator it_v
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= cident_secn.begin();
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it_v != cident_secn.end();
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++it_v)
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{
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v.insert(*it_v);
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}
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}
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}
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}
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return;
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}
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} // End of namespace gold.
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#endif
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