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.
38 template<int size
, bool big_endian
>
39 class Sized_relobj_file
;
41 template<int sh_type
, int size
, bool big_endian
>
45 class General_options
;
48 class Garbage_collection
52 typedef Unordered_set
<Section_id
, Section_id_hash
> Sections_reachable
;
53 typedef std::map
<Section_id
, Sections_reachable
> Section_ref
;
54 typedef std::vector
<Section_id
> Worklist_type
;
55 // This maps the name of the section which can be represented as a C
56 // identifier (cident) to the list of sections that have that name.
57 // Different object files can have cident sections with the same name.
58 typedef std::map
<std::string
, Sections_reachable
> Cident_section_map
;
61 : is_worklist_ready_(false)
64 // Accessor methods for the private members.
68 { return referenced_list_
; }
72 { return this->section_reloc_map_
; }
76 { return this->work_list_
; }
80 { return this->is_worklist_ready_
; }
84 { this->is_worklist_ready_
= true; }
87 do_transitive_closure();
90 is_section_garbage(Relobj
* obj
, unsigned int shndx
)
91 { return (this->referenced_list().find(Section_id(obj
, shndx
))
92 == this->referenced_list().end()); }
96 { return &cident_sections_
; }
99 add_cident_section(std::string section_name
,
101 { this->cident_sections_
[section_name
].insert(secn
); }
103 // Add a reference from the SRC_SHNDX-th section of SRC_OBJECT to
104 // DST_SHNDX-th section of DST_OBJECT.
106 add_reference(Relobj
* src_object
, unsigned int src_shndx
,
107 Relobj
* dst_object
, unsigned int dst_shndx
)
109 Section_id
src_id(src_object
, src_shndx
);
110 Section_id
dst_id(dst_object
, dst_shndx
);
111 Sections_reachable
& reachable
= this->section_reloc_map_
[src_id
];
112 reachable
.insert(dst_id
);
117 Worklist_type work_list_
;
118 bool is_worklist_ready_
;
119 Section_ref section_reloc_map_
;
120 Sections_reachable referenced_list_
;
121 Cident_section_map cident_sections_
;
124 // Data to pass between successive invocations of do_layout
125 // in object.cc while garbage collecting. This data structure
126 // is filled by using the data from Read_symbols_data.
131 unsigned char* section_headers_data
;
133 unsigned char* section_names_data
;
134 // Size of section name data in bytes.
135 section_size_type section_names_size
;
137 unsigned char* symbols_data
;
138 // Size of symbol data in bytes.
139 section_size_type symbols_size
;
140 // Offset of external symbols within symbol data. This structure
141 // sometimes contains only external symbols, in which case this will
142 // be zero. Sometimes it contains all symbols.
143 section_offset_type external_symbols_offset
;
145 unsigned char* symbol_names_data
;
146 // Size of symbol name data in bytes.
147 section_size_type symbol_names_size
;
150 // Relocations of type SHT_REL store the addend value in their bytes.
151 // This function returns the size of the embedded addend which is
152 // nothing but the size of the relocation.
154 template<typename Classify_reloc
>
156 get_embedded_addend_size(int sh_type
, int r_type
, Relobj
* obj
)
158 if (sh_type
!= elfcpp::SHT_REL
)
160 Classify_reloc classify_reloc
;
161 return classify_reloc
.get_size_for_reloc(r_type
, obj
);
164 // This function implements the generic part of reloc
165 // processing to map a section to all the sections it
166 // references through relocs. It is called only during
167 // garbage collection (--gc-sections) and identical code
170 template<int size
, bool big_endian
, typename Target_type
, int sh_type
,
171 typename Scan
, typename Classify_reloc
>
174 Symbol_table
* symtab
,
177 Sized_relobj_file
<size
, big_endian
>* src_obj
,
178 unsigned int src_indx
,
179 const unsigned char* prelocs
,
184 const unsigned char* plocal_syms
)
188 typedef typename Reloc_types
<sh_type
, size
, big_endian
>::Reloc Reltype
;
189 const int reloc_size
= Reloc_types
<sh_type
, size
, big_endian
>::reloc_size
;
190 const int sym_size
= elfcpp::Elf_sizes
<size
>::sym_size
;
192 Icf::Sections_reachable_info
* secvec
= NULL
;
193 Icf::Symbol_info
* symvec
= NULL
;
194 Icf::Addend_info
* addendvec
= NULL
;
195 Icf::Offset_info
* offsetvec
= NULL
;
196 Icf::Reloc_addend_size_info
* reloc_addend_size_vec
= NULL
;
197 bool is_icf_tracked
= false;
198 const char* cident_section_name
= NULL
;
200 std::string src_section_name
= (parameters
->options().icf_enabled()
201 ? src_obj
->section_name(src_indx
)
204 bool check_section_for_function_pointers
= false;
206 if (parameters
->options().icf_enabled()
207 && is_section_foldable_candidate(src_section_name
.c_str()))
209 is_icf_tracked
= true;
210 Section_id
src_id(src_obj
, src_indx
);
211 Icf::Reloc_info
* reloc_info
=
212 &symtab
->icf()->reloc_info_list()[src_id
];
213 secvec
= &reloc_info
->section_info
;
214 symvec
= &reloc_info
->symbol_info
;
215 addendvec
= &reloc_info
->addend_info
;
216 offsetvec
= &reloc_info
->offset_info
;
217 reloc_addend_size_vec
= &reloc_info
->reloc_addend_size_info
;
220 check_section_for_function_pointers
=
221 symtab
->icf()->check_section_for_function_pointers(src_section_name
,
224 for (size_t i
= 0; i
< reloc_count
; ++i
, prelocs
+= reloc_size
)
226 Reltype
reloc(prelocs
);
227 typename
elfcpp::Elf_types
<size
>::Elf_WXword r_info
= reloc
.get_r_info();
228 unsigned int r_sym
= elfcpp::elf_r_sym
<size
>(r_info
);
229 unsigned int r_type
= elfcpp::elf_r_type
<size
>(r_info
);
230 typename
elfcpp::Elf_types
<size
>::Elf_Swxword addend
=
231 Reloc_types
<sh_type
, size
, big_endian
>::get_reloc_addend_noerror(&reloc
);
233 unsigned int dst_indx
;
234 typedef typename
elfcpp::Elf_types
<size
>::Elf_Addr Address
;
237 if (r_sym
< local_count
)
239 gold_assert(plocal_syms
!= NULL
);
240 typename
elfcpp::Sym
<size
, big_endian
> lsym(plocal_syms
242 dst_indx
= lsym
.get_st_shndx();
244 dst_indx
= src_obj
->adjust_sym_shndx(r_sym
, dst_indx
, &is_ordinary
);
246 dst_off
= lsym
.get_st_value() + addend
;
250 Address symvalue
= dst_off
- addend
;
252 (*secvec
).push_back(Section_id(src_obj
, dst_indx
));
254 (*secvec
).push_back(Section_id(NULL
, 0));
255 (*symvec
).push_back(NULL
);
256 (*addendvec
).push_back(std::make_pair(
257 static_cast<long long>(symvalue
),
258 static_cast<long long>(addend
)));
259 uint64_t reloc_offset
=
260 convert_to_section_size_type(reloc
.get_r_offset());
261 (*offsetvec
).push_back(reloc_offset
);
262 (*reloc_addend_size_vec
).push_back(
263 get_embedded_addend_size
<Classify_reloc
>(sh_type
, r_type
,
267 // When doing safe folding, check to see if this relocation is that
268 // of a function pointer being taken.
270 && check_section_for_function_pointers
271 && lsym
.get_st_type() != elfcpp::STT_OBJECT
272 && scan
.local_reloc_may_be_function_pointer(symtab
, NULL
, NULL
,
276 symtab
->icf()->set_section_has_function_pointers(
277 src_obj
, lsym
.get_st_shndx());
279 if (!is_ordinary
|| dst_indx
== src_indx
)
284 Symbol
* gsym
= src_obj
->global_symbol(r_sym
);
285 gold_assert(gsym
!= NULL
);
286 if (gsym
->is_forwarder())
287 gsym
= symtab
->resolve_forwards(gsym
);
291 bool is_ordinary
= false;
292 if (gsym
->source() == Symbol::FROM_OBJECT
293 && !gsym
->object()->is_dynamic())
295 dst_obj
= static_cast<Relobj
*>(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
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
&& dst_obj
!= NULL
)
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
,
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
, dst_obj
, dst_indx
,
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.