// gc.h -- garbage collection of unused sections
-// Copyright 2009 Free Software Foundation, Inc.
+// Copyright (C) 2009-2020 Free Software Foundation, Inc.
// Written by Sriraman Tallam <tmsriram@google.com>.
// This file is part of gold.
#ifndef GOLD_GC_H
#define GOLD_GC_H
-#include <queue>
+#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;
-
-template<int sh_type, int size, bool big_endian>
-class Reloc_types;
+class Sized_relobj_file;
class Output_section;
class General_options;
class Layout;
-typedef std::pair<Object *, unsigned int> Section_id;
-
class Garbage_collection
{
- struct Section_id_hash
- {
- size_t operator()(const Section_id& loc) const
- { return reinterpret_cast<uintptr_t>(loc.first) ^ loc.second; }
- };
+ public:
typedef Unordered_set<Section_id, Section_id_hash> Sections_reachable;
typedef std::map<Section_id, Sections_reachable> Section_ref;
- typedef std::queue<Section_id> Worklist_type;
-
- public :
- 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 section_reloc_map_; }
-
- Worklist_type&
- worklist()
- { return work_list_; }
-
- bool
- is_worklist_ready()
- { return is_worklist_ready_; }
-
- void
- worklist_ready()
- { is_worklist_ready_ = true; }
-
- void
- do_transitive_closure();
-
- private :
- Worklist_type work_list_;
- bool is_worklist_ready_;
- Section_ref section_reloc_map_;
- Sections_reachable referenced_list_;
+ 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
section_size_type symbol_names_size;
};
-// This function implements the the generic part of reloc
-// processing to map a section to all the sections it
-// references through relocs. It is used only during garbage
-// collection.
+// 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, int sh_type,
- typename Scan>
+template<int size, bool big_endian, typename Target_type,
+ typename Scan, typename Classify_reloc>
inline void
gc_process_relocs(
- const General_options& ,
Symbol_table* symtab,
Layout*,
- Target_type* ,
- Sized_relobj<size, big_endian>* object,
- unsigned int data_shndx,
+ 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 ,
+ bool,
size_t local_count,
const unsigned char* plocal_syms)
{
- Object *src_obj, *dst_obj;
- unsigned int src_indx, dst_indx;
-
- src_obj = object;
- src_indx = data_shndx;
-
- typedef typename Reloc_types<sh_type, size, big_endian>::Reloc Reltype;
- const int reloc_size = Reloc_types<sh_type, size, big_endian>::reloc_size;
+ 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);
- 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_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);
- unsigned int shndx = lsym.get_st_shndx();
+ dst_indx = lsym.get_st_shndx();
bool is_ordinary;
- shndx = object->adjust_sym_shndx(r_sym, shndx, &is_ordinary);
- if (!is_ordinary)
- continue;
+ dst_indx = src_obj->adjust_sym_shndx(r_sym, dst_indx, &is_ordinary);
dst_obj = src_obj;
- if (shndx == src_indx)
+ 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;
- dst_indx = shndx;
}
else
{
- Symbol* gsym = object->global_symbol(r_sym);
+ Symbol* gsym = src_obj->global_symbol(r_sym);
gold_assert(gsym != NULL);
if (gsym->is_forwarder())
gsym = symtab->resolve_forwards(gsym);
- if (gsym->source() != Symbol::FROM_OBJECT)
+
+ 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;
- bool is_ordinary;
- dst_obj = gsym->object();
- dst_indx = gsym->shndx(&is_ordinary);
if (!is_ordinary)
continue;
}
- Section_id p1(src_obj, src_indx);
- Section_id p2(dst_obj, dst_indx);
- Garbage_collection::Section_ref::iterator map_it;
- map_it = symtab->gc()->section_reloc_map().find(p1);
- if (map_it == symtab->gc()->section_reloc_map().end())
- {
- symtab->gc()->section_reloc_map()[p1].insert(p2);
- }
- else
+ if (parameters->options().gc_sections())
{
- Garbage_collection::Sections_reachable& v(map_it->second);
- v.insert(p2);
+ 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;
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