1 // gc.h -- garbage collection of unused sections
3 // Copyright (C) 2009-2015 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.
39 template<int size
, bool big_endian
>
40 class Sized_relobj_file
;
42 template<int sh_type
, int size
, bool big_endian
>
46 class General_options
;
49 class Garbage_collection
53 typedef Unordered_set
<Section_id
, Section_id_hash
> Sections_reachable
;
54 typedef std::map
<Section_id
, Sections_reachable
> Section_ref
;
55 typedef std::queue
<Section_id
> Worklist_type
;
56 // This maps the name of the section which can be represented as a C
57 // identifier (cident) to the list of sections that have that name.
58 // Different object files can have cident sections with the same name.
59 typedef std::map
<std::string
, Sections_reachable
> Cident_section_map
;
62 : is_worklist_ready_(false)
65 // Accessor methods for the private members.
69 { return referenced_list_
; }
73 { return this->section_reloc_map_
; }
77 { return this->work_list_
; }
81 { return this->is_worklist_ready_
; }
85 { this->is_worklist_ready_
= true; }
88 do_transitive_closure();
91 is_section_garbage(Object
* obj
, unsigned int shndx
)
92 { return (this->referenced_list().find(Section_id(obj
, shndx
))
93 == this->referenced_list().end()); }
97 { return &cident_sections_
; }
100 add_cident_section(std::string section_name
,
102 { this->cident_sections_
[section_name
].insert(secn
); }
104 // Add a reference from the SRC_SHNDX-th section of SRC_OBJECT to
105 // DST_SHNDX-th section of DST_OBJECT.
107 add_reference(Object
* src_object
, unsigned int src_shndx
,
108 Object
* dst_object
, unsigned int dst_shndx
)
110 Section_id
src_id(src_object
, src_shndx
);
111 Section_id
dst_id(dst_object
, dst_shndx
);
112 Sections_reachable
& reachable
= this->section_reloc_map_
[src_id
];
113 reachable
.insert(dst_id
);
118 Worklist_type work_list_
;
119 bool is_worklist_ready_
;
120 Section_ref section_reloc_map_
;
121 Sections_reachable referenced_list_
;
122 Cident_section_map cident_sections_
;
125 // Data to pass between successive invocations of do_layout
126 // in object.cc while garbage collecting. This data structure
127 // is filled by using the data from Read_symbols_data.
132 unsigned char* section_headers_data
;
134 unsigned char* section_names_data
;
135 // Size of section name data in bytes.
136 section_size_type section_names_size
;
138 unsigned char* symbols_data
;
139 // Size of symbol data in bytes.
140 section_size_type symbols_size
;
141 // Offset of external symbols within symbol data. This structure
142 // sometimes contains only external symbols, in which case this will
143 // be zero. Sometimes it contains all symbols.
144 section_offset_type external_symbols_offset
;
146 unsigned char* symbol_names_data
;
147 // Size of symbol name data in bytes.
148 section_size_type symbol_names_size
;
151 // Relocations of type SHT_REL store the addend value in their bytes.
152 // This function returns the size of the embedded addend which is
153 // nothing but the size of the relocation.
155 template<typename Classify_reloc
>
157 get_embedded_addend_size(int sh_type
, int r_type
, Relobj
* obj
)
159 if (sh_type
!= elfcpp::SHT_REL
)
161 Classify_reloc classify_reloc
;
162 return classify_reloc
.get_size_for_reloc(r_type
, obj
);
165 // This function implements the generic part of reloc
166 // processing to map a section to all the sections it
167 // references through relocs. It is called only during
168 // garbage collection (--gc-sections) and identical code
171 template<int size
, bool big_endian
, typename Target_type
, int sh_type
,
172 typename Scan
, typename Classify_reloc
>
175 Symbol_table
* symtab
,
178 Sized_relobj_file
<size
, big_endian
>* src_obj
,
179 unsigned int src_indx
,
180 const unsigned char* prelocs
,
185 const unsigned char* plocal_syms
)
189 typedef typename Reloc_types
<sh_type
, size
, big_endian
>::Reloc Reltype
;
190 const int reloc_size
= Reloc_types
<sh_type
, size
, big_endian
>::reloc_size
;
191 const int sym_size
= elfcpp::Elf_sizes
<size
>::sym_size
;
193 Icf::Sections_reachable_info
* secvec
= NULL
;
194 Icf::Symbol_info
* symvec
= NULL
;
195 Icf::Addend_info
* addendvec
= NULL
;
196 Icf::Offset_info
* offsetvec
= NULL
;
197 Icf::Reloc_addend_size_info
* reloc_addend_size_vec
= NULL
;
198 bool is_icf_tracked
= false;
199 const char* cident_section_name
= NULL
;
201 std::string src_section_name
= (parameters
->options().icf_enabled()
202 ? src_obj
->section_name(src_indx
)
205 bool check_section_for_function_pointers
= false;
207 if (parameters
->options().icf_enabled()
208 && is_section_foldable_candidate(src_section_name
.c_str()))
210 is_icf_tracked
= true;
211 Section_id
src_id(src_obj
, src_indx
);
212 Icf::Reloc_info
* reloc_info
=
213 &symtab
->icf()->reloc_info_list()[src_id
];
214 secvec
= &reloc_info
->section_info
;
215 symvec
= &reloc_info
->symbol_info
;
216 addendvec
= &reloc_info
->addend_info
;
217 offsetvec
= &reloc_info
->offset_info
;
218 reloc_addend_size_vec
= &reloc_info
->reloc_addend_size_info
;
221 check_section_for_function_pointers
=
222 symtab
->icf()->check_section_for_function_pointers(src_section_name
,
225 for (size_t i
= 0; i
< reloc_count
; ++i
, prelocs
+= reloc_size
)
227 Reltype
reloc(prelocs
);
228 typename
elfcpp::Elf_types
<size
>::Elf_WXword r_info
= reloc
.get_r_info();
229 unsigned int r_sym
= elfcpp::elf_r_sym
<size
>(r_info
);
230 unsigned int r_type
= elfcpp::elf_r_type
<size
>(r_info
);
231 typename
elfcpp::Elf_types
<size
>::Elf_Swxword addend
=
232 Reloc_types
<sh_type
, size
, big_endian
>::get_reloc_addend_noerror(&reloc
);
234 unsigned int dst_indx
;
235 typedef typename
elfcpp::Elf_types
<size
>::Elf_Addr Address
;
238 if (r_sym
< local_count
)
240 gold_assert(plocal_syms
!= NULL
);
241 typename
elfcpp::Sym
<size
, big_endian
> lsym(plocal_syms
243 dst_indx
= lsym
.get_st_shndx();
245 dst_indx
= src_obj
->adjust_sym_shndx(r_sym
, dst_indx
, &is_ordinary
);
247 dst_off
= lsym
.get_st_value() + addend
;
251 Address symvalue
= dst_off
- addend
;
253 (*secvec
).push_back(Section_id(dst_obj
, dst_indx
));
255 (*secvec
).push_back(Section_id(NULL
, 0));
256 (*symvec
).push_back(NULL
);
257 (*addendvec
).push_back(std::make_pair(
258 static_cast<long long>(symvalue
),
259 static_cast<long long>(addend
)));
260 uint64_t reloc_offset
=
261 convert_to_section_size_type(reloc
.get_r_offset());
262 (*offsetvec
).push_back(reloc_offset
);
263 (*reloc_addend_size_vec
).push_back(
264 get_embedded_addend_size
<Classify_reloc
>(sh_type
, r_type
,
268 // When doing safe folding, check to see if this relocation is that
269 // of a function pointer being taken.
271 && check_section_for_function_pointers
272 && lsym
.get_st_type() != elfcpp::STT_OBJECT
273 && scan
.local_reloc_may_be_function_pointer(symtab
, NULL
, NULL
,
277 symtab
->icf()->set_section_has_function_pointers(
278 src_obj
, lsym
.get_st_shndx());
280 if (!is_ordinary
|| dst_indx
== src_indx
)
285 Symbol
* gsym
= src_obj
->global_symbol(r_sym
);
286 gold_assert(gsym
!= NULL
);
287 if (gsym
->is_forwarder())
288 gsym
= symtab
->resolve_forwards(gsym
);
292 bool is_ordinary
= false;
293 if (gsym
->source() == Symbol::FROM_OBJECT
)
295 dst_obj
= gsym
->object();
296 dst_indx
= gsym
->shndx(&is_ordinary
);
298 dst_off
= static_cast<const Sized_symbol
<size
>*>(gsym
)->value();
301 // When doing safe folding, check to see if this relocation is that
302 // of a function pointer being taken.
303 if (gsym
->source() == Symbol::FROM_OBJECT
304 && check_section_for_function_pointers
305 && gsym
->type() != elfcpp::STT_OBJECT
307 || scan
.global_reloc_may_be_function_pointer(
308 symtab
, NULL
, NULL
, src_obj
, src_indx
, NULL
, reloc
,
310 symtab
->icf()->set_section_has_function_pointers(dst_obj
, dst_indx
);
312 // If the symbol name matches '__start_XXX' then the section with
313 // the C identifier like name 'XXX' should not be garbage collected.
314 // A similar treatment to symbols with the name '__stop_XXX'.
315 if (is_prefix_of(cident_section_start_prefix
, gsym
->name()))
317 cident_section_name
= (gsym
->name()
318 + strlen(cident_section_start_prefix
));
320 else if (is_prefix_of(cident_section_stop_prefix
, gsym
->name()))
322 cident_section_name
= (gsym
->name()
323 + strlen(cident_section_stop_prefix
));
327 Address symvalue
= dst_off
- addend
;
328 if (is_ordinary
&& gsym
->source() == Symbol::FROM_OBJECT
)
329 (*secvec
).push_back(Section_id(dst_obj
, dst_indx
));
331 (*secvec
).push_back(Section_id(NULL
, 0));
332 (*symvec
).push_back(gsym
);
333 (*addendvec
).push_back(std::make_pair(
334 static_cast<long long>(symvalue
),
335 static_cast<long long>(addend
)));
336 uint64_t reloc_offset
=
337 convert_to_section_size_type(reloc
.get_r_offset());
338 (*offsetvec
).push_back(reloc_offset
);
339 (*reloc_addend_size_vec
).push_back(
340 get_embedded_addend_size
<Classify_reloc
>(sh_type
, r_type
,
344 if (gsym
->source() != Symbol::FROM_OBJECT
)
349 if (parameters
->options().gc_sections())
351 symtab
->gc()->add_reference(src_obj
, src_indx
, dst_obj
, dst_indx
);
352 parameters
->sized_target
<size
, big_endian
>()
353 ->gc_add_reference(symtab
, src_obj
, src_indx
,
354 dst_obj
, dst_indx
, dst_off
);
355 if (cident_section_name
!= NULL
)
357 Garbage_collection::Cident_section_map::iterator ele
=
358 symtab
->gc()->cident_sections()->find(std::string(cident_section_name
));
359 if (ele
== symtab
->gc()->cident_sections()->end())
361 Section_id
src_id(src_obj
, src_indx
);
362 Garbage_collection::Sections_reachable
&
363 v(symtab
->gc()->section_reloc_map()[src_id
]);
364 Garbage_collection::Sections_reachable
& cident_secn(ele
->second
);
365 for (Garbage_collection::Sections_reachable::iterator it_v
366 = cident_secn
.begin();
367 it_v
!= cident_secn
.end();
378 } // End of namespace gold.