| // gc.h -- garbage collection of unused sections |
| |
| // Copyright (C) 2009-2021 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(static_cast<Relobj*>(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(static_cast<Relobj*>(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 |
