1 // gc.h -- garbage collection of unused sections
3 // Copyright 2009, 2010 Free Software Foundation, Inc.
4 // Written by Sriraman Tallam <tmsriram@google.com>.
6 // This file is part of gold.
8 // This program is free software; you can redistribute it and/or modify
9 // it under the terms of the GNU General Public License as published by
10 // the Free Software Foundation; either version 3 of the License, or
11 // (at your option) any later version.
13 // This program is distributed in the hope that it will be useful,
14 // but WITHOUT ANY WARRANTY; without even the implied warranty of
15 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
16 // GNU General Public License for more details.
18 // You should have received a copy of the GNU General Public License
19 // along with this program; if not, write to the Free Software
20 // Foundation, Inc., 51 Franklin Street - Fifth Floor, Boston,
21 // MA 02110-1301, USA.
38 template<int size
, bool big_endian
>
41 template<int sh_type
, int size
, bool big_endian
>
45 class General_options
;
48 typedef std::pair
<Object
*, unsigned int> Section_id
;
50 class Garbage_collection
52 struct Section_id_hash
54 size_t operator()(const Section_id
& loc
) const
55 { return reinterpret_cast<uintptr_t>(loc
.first
) ^ loc
.second
; }
60 typedef Unordered_set
<Section_id
, Section_id_hash
> Sections_reachable
;
61 typedef std::map
<Section_id
, Sections_reachable
> Section_ref
;
62 typedef std::queue
<Section_id
> Worklist_type
;
63 // This maps the name of the section which can be represented as a C
64 // identifier (cident) to the list of sections that have that name.
65 // Different object files can have cident sections with the same name.
66 typedef std::map
<std::string
, Sections_reachable
> Cident_section_map
;
69 : is_worklist_ready_(false)
72 // Accessor methods for the private members.
76 { return referenced_list_
; }
80 { return this->section_reloc_map_
; }
84 { return this->work_list_
; }
88 { return this->is_worklist_ready_
; }
92 { this->is_worklist_ready_
= true; }
95 do_transitive_closure();
98 is_section_garbage(Object
* obj
, unsigned int shndx
)
99 { return (this->referenced_list().find(Section_id(obj
, shndx
))
100 == this->referenced_list().end()); }
104 { return &cident_sections_
; }
107 add_cident_section(std::string section_name
,
109 { this->cident_sections_
[section_name
].insert(secn
); }
111 // Add a reference from the SRC_SHNDX-th section of SRC_OBJECT to
112 // DST_SHNDX-th section of DST_OBJECT.
114 add_reference(Object
* src_object
, unsigned int src_shndx
,
115 Object
* dst_object
, unsigned int dst_shndx
)
117 Section_id
src_id(src_object
, src_shndx
);
118 Section_id
dst_id(dst_object
, dst_shndx
);
119 Section_ref::iterator p
= this->section_reloc_map_
.find(src_id
);
120 if (p
== this->section_reloc_map_
.end())
121 this->section_reloc_map_
[src_id
].insert(dst_id
);
123 p
->second
.insert(dst_id
);
128 Worklist_type work_list_
;
129 bool is_worklist_ready_
;
130 Section_ref section_reloc_map_
;
131 Sections_reachable referenced_list_
;
132 Cident_section_map cident_sections_
;
135 // Data to pass between successive invocations of do_layout
136 // in object.cc while garbage collecting. This data structure
137 // is filled by using the data from Read_symbols_data.
142 unsigned char* section_headers_data
;
144 unsigned char* section_names_data
;
145 // Size of section name data in bytes.
146 section_size_type section_names_size
;
148 unsigned char* symbols_data
;
149 // Size of symbol data in bytes.
150 section_size_type symbols_size
;
151 // Offset of external symbols within symbol data. This structure
152 // sometimes contains only external symbols, in which case this will
153 // be zero. Sometimes it contains all symbols.
154 section_offset_type external_symbols_offset
;
156 unsigned char* symbol_names_data
;
157 // Size of symbol name data in bytes.
158 section_size_type symbol_names_size
;
161 // This function implements the generic part of reloc
162 // processing to map a section to all the sections it
163 // references through relocs. It is called only during
164 // garbage collection (--gc-sections) and identical code
167 template<int size
, bool big_endian
, typename Target_type
, int sh_type
,
171 Symbol_table
* symtab
,
174 Sized_relobj
<size
, big_endian
>* src_obj
,
175 unsigned int src_indx
,
176 const unsigned char* prelocs
,
181 const unsigned char* plocal_syms
)
184 unsigned int dst_indx
;
186 typedef typename Reloc_types
<sh_type
, size
, big_endian
>::Reloc Reltype
;
187 const int reloc_size
= Reloc_types
<sh_type
, size
, big_endian
>::reloc_size
;
188 const int sym_size
= elfcpp::Elf_sizes
<size
>::sym_size
;
190 std::vector
<Section_id
>* secvec
= NULL
;
191 std::vector
<Symbol
*>* symvec
= NULL
;
192 std::vector
<std::pair
<long long, long long> >* addendvec
= NULL
;
193 bool is_icf_tracked
= false;
194 const char* cident_section_name
= NULL
;
196 if (parameters
->options().icf_enabled()
197 && is_section_foldable_candidate(src_obj
->section_name(src_indx
).c_str()))
199 is_icf_tracked
= true;
200 Section_id
src_id(src_obj
, src_indx
);
201 secvec
= &symtab
->icf()->section_reloc_list()[src_id
];
202 symvec
= &symtab
->icf()->symbol_reloc_list()[src_id
];
203 addendvec
= &symtab
->icf()->addend_reloc_list()[src_id
];
206 for (size_t i
= 0; i
< reloc_count
; ++i
, prelocs
+= reloc_size
)
208 Reltype
reloc(prelocs
);
209 typename
elfcpp::Elf_types
<size
>::Elf_WXword r_info
= reloc
.get_r_info();
210 unsigned int r_sym
= elfcpp::elf_r_sym
<size
>(r_info
);
211 typename
elfcpp::Elf_types
<size
>::Elf_Swxword addend
=
212 Reloc_types
<sh_type
, size
, big_endian
>::get_reloc_addend_noerror(&reloc
);
214 if (r_sym
< local_count
)
216 gold_assert(plocal_syms
!= NULL
);
217 typename
elfcpp::Sym
<size
, big_endian
> lsym(plocal_syms
219 unsigned int shndx
= lsym
.get_st_shndx();
221 shndx
= src_obj
->adjust_sym_shndx(r_sym
, shndx
, &is_ordinary
);
226 Section_id
dst_id(dst_obj
, dst_indx
);
229 (*secvec
).push_back(dst_id
);
230 (*symvec
).push_back(NULL
);
231 long long symvalue
= static_cast<long long>(lsym
.get_st_value());
232 (*addendvec
).push_back(std::make_pair(symvalue
,
233 static_cast<long long>(addend
)));
235 if (shndx
== src_indx
)
240 Symbol
* gsym
= src_obj
->global_symbol(r_sym
);
241 gold_assert(gsym
!= NULL
);
242 if (gsym
->is_forwarder())
243 gsym
= symtab
->resolve_forwards(gsym
);
244 if (gsym
->source() != Symbol::FROM_OBJECT
)
247 dst_obj
= gsym
->object();
248 dst_indx
= gsym
->shndx(&is_ordinary
);
251 Section_id
dst_id(dst_obj
, dst_indx
);
252 // If the symbol name matches '__start_XXX' then the section with
253 // the C identifier like name 'XXX' should not be garbage collected.
254 // A similar treatment to symbols with the name '__stop_XXX'.
255 if (is_prefix_of(cident_section_start_prefix
, gsym
->name()))
257 cident_section_name
= (gsym
->name()
258 + strlen(cident_section_start_prefix
));
260 else if (is_prefix_of(cident_section_stop_prefix
, gsym
->name()))
262 cident_section_name
= (gsym
->name()
263 + strlen(cident_section_stop_prefix
));
267 (*secvec
).push_back(dst_id
);
268 (*symvec
).push_back(gsym
);
269 Sized_symbol
<size
>* sized_gsym
=
270 static_cast<Sized_symbol
<size
>* >(gsym
);
272 static_cast<long long>(sized_gsym
->value());
273 (*addendvec
).push_back(std::make_pair(symvalue
,
274 static_cast<long long>(addend
)));
277 if (parameters
->options().gc_sections())
279 symtab
->gc()->add_reference(src_obj
, src_indx
, dst_obj
, dst_indx
);
280 if (cident_section_name
!= NULL
)
282 Garbage_collection::Cident_section_map::iterator ele
=
283 symtab
->gc()->cident_sections()->find(std::string(cident_section_name
));
284 if (ele
== symtab
->gc()->cident_sections()->end())
286 Section_id
src_id(src_obj
, src_indx
);
287 Garbage_collection::Sections_reachable
&
288 v(symtab
->gc()->section_reloc_map()[src_id
]);
289 Garbage_collection::Sections_reachable
& cident_secn(ele
->second
);
290 for (Garbage_collection::Sections_reachable::iterator it_v
291 = cident_secn
.begin();
292 it_v
!= cident_secn
.end();
303 } // End of namespace gold.