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.
39 template<int size
, bool big_endian
>
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 Section_ref::iterator p
= this->section_reloc_map_
.find(src_id
);
113 if (p
== this->section_reloc_map_
.end())
114 this->section_reloc_map_
[src_id
].insert(dst_id
);
116 p
->second
.insert(dst_id
);
121 Worklist_type work_list_
;
122 bool is_worklist_ready_
;
123 Section_ref section_reloc_map_
;
124 Sections_reachable referenced_list_
;
125 Cident_section_map cident_sections_
;
128 // Data to pass between successive invocations of do_layout
129 // in object.cc while garbage collecting. This data structure
130 // is filled by using the data from Read_symbols_data.
135 unsigned char* section_headers_data
;
137 unsigned char* section_names_data
;
138 // Size of section name data in bytes.
139 section_size_type section_names_size
;
141 unsigned char* symbols_data
;
142 // Size of symbol data in bytes.
143 section_size_type symbols_size
;
144 // Offset of external symbols within symbol data. This structure
145 // sometimes contains only external symbols, in which case this will
146 // be zero. Sometimes it contains all symbols.
147 section_offset_type external_symbols_offset
;
149 unsigned char* symbol_names_data
;
150 // Size of symbol name data in bytes.
151 section_size_type symbol_names_size
;
154 // This function implements the generic part of reloc
155 // processing to map a section to all the sections it
156 // references through relocs. It is called only during
157 // garbage collection (--gc-sections) and identical code
160 template<int size
, bool big_endian
, typename Target_type
, int sh_type
,
164 Symbol_table
* symtab
,
167 Sized_relobj
<size
, big_endian
>* src_obj
,
168 unsigned int src_indx
,
169 const unsigned char* prelocs
,
174 const unsigned char* plocal_syms
)
177 unsigned int dst_indx
;
180 typedef typename Reloc_types
<sh_type
, size
, big_endian
>::Reloc Reltype
;
181 const int reloc_size
= Reloc_types
<sh_type
, size
, big_endian
>::reloc_size
;
182 const int sym_size
= elfcpp::Elf_sizes
<size
>::sym_size
;
184 std::vector
<Section_id
>* secvec
= NULL
;
185 std::vector
<Symbol
*>* symvec
= NULL
;
186 std::vector
<std::pair
<long long, long long> >* addendvec
= NULL
;
187 bool is_icf_tracked
= false;
188 const char* cident_section_name
= NULL
;
190 std::string src_section_name
= (parameters
->options().icf_enabled()
191 ? src_obj
->section_name(src_indx
)
194 bool check_section_for_function_pointers
= false;
196 if (parameters
->options().icf_enabled()
197 && is_section_foldable_candidate(src_section_name
.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 check_section_for_function_pointers
=
207 symtab
->icf()->check_section_for_function_pointers(src_section_name
,
210 for (size_t i
= 0; i
< reloc_count
; ++i
, prelocs
+= reloc_size
)
212 Reltype
reloc(prelocs
);
213 typename
elfcpp::Elf_types
<size
>::Elf_WXword r_info
= reloc
.get_r_info();
214 unsigned int r_sym
= elfcpp::elf_r_sym
<size
>(r_info
);
215 unsigned int r_type
= elfcpp::elf_r_type
<size
>(r_info
);
216 typename
elfcpp::Elf_types
<size
>::Elf_Swxword addend
=
217 Reloc_types
<sh_type
, size
, big_endian
>::get_reloc_addend_noerror(&reloc
);
219 if (r_sym
< local_count
)
221 gold_assert(plocal_syms
!= NULL
);
222 typename
elfcpp::Sym
<size
, big_endian
> lsym(plocal_syms
224 unsigned int shndx
= lsym
.get_st_shndx();
226 shndx
= src_obj
->adjust_sym_shndx(r_sym
, shndx
, &is_ordinary
);
231 Section_id
dst_id(dst_obj
, dst_indx
);
234 (*secvec
).push_back(dst_id
);
235 (*symvec
).push_back(NULL
);
236 long long symvalue
= static_cast<long long>(lsym
.get_st_value());
237 (*addendvec
).push_back(std::make_pair(symvalue
,
238 static_cast<long long>(addend
)));
241 // When doing safe folding, check to see if this relocation is that
242 // of a function pointer being taken.
243 if (check_section_for_function_pointers
244 && lsym
.get_st_type() != elfcpp::STT_OBJECT
245 && scan
.local_reloc_may_be_function_pointer(symtab
, NULL
, NULL
,
249 symtab
->icf()->set_section_has_function_pointers(
250 src_obj
, lsym
.get_st_shndx());
252 if (shndx
== src_indx
)
257 Symbol
* gsym
= src_obj
->global_symbol(r_sym
);
258 gold_assert(gsym
!= NULL
);
259 if (gsym
->is_forwarder())
260 gsym
= symtab
->resolve_forwards(gsym
);
261 if (gsym
->source() != Symbol::FROM_OBJECT
)
264 dst_obj
= gsym
->object();
265 dst_indx
= gsym
->shndx(&is_ordinary
);
266 Section_id
dst_id(dst_obj
, dst_indx
);
268 // When doing safe folding, check to see if this relocation is that
269 // of a function pointer being taken.
270 if (check_section_for_function_pointers
271 && gsym
->type() != elfcpp::STT_OBJECT
273 || scan
.global_reloc_may_be_function_pointer(
274 symtab
, NULL
, NULL
, src_obj
, src_indx
, NULL
, reloc
,
276 symtab
->icf()->set_section_has_function_pointers(dst_obj
, dst_indx
);
281 // If the symbol name matches '__start_XXX' then the section with
282 // the C identifier like name 'XXX' should not be garbage collected.
283 // A similar treatment to symbols with the name '__stop_XXX'.
284 if (is_prefix_of(cident_section_start_prefix
, gsym
->name()))
286 cident_section_name
= (gsym
->name()
287 + strlen(cident_section_start_prefix
));
289 else if (is_prefix_of(cident_section_stop_prefix
, gsym
->name()))
291 cident_section_name
= (gsym
->name()
292 + strlen(cident_section_stop_prefix
));
296 (*secvec
).push_back(dst_id
);
297 (*symvec
).push_back(gsym
);
298 Sized_symbol
<size
>* sized_gsym
=
299 static_cast<Sized_symbol
<size
>* >(gsym
);
301 static_cast<long long>(sized_gsym
->value());
302 (*addendvec
).push_back(std::make_pair(symvalue
,
303 static_cast<long long>(addend
)));
306 if (parameters
->options().gc_sections())
308 symtab
->gc()->add_reference(src_obj
, src_indx
, dst_obj
, dst_indx
);
309 if (cident_section_name
!= NULL
)
311 Garbage_collection::Cident_section_map::iterator ele
=
312 symtab
->gc()->cident_sections()->find(std::string(cident_section_name
));
313 if (ele
== symtab
->gc()->cident_sections()->end())
315 Section_id
src_id(src_obj
, src_indx
);
316 Garbage_collection::Sections_reachable
&
317 v(symtab
->gc()->section_reloc_map()[src_id
]);
318 Garbage_collection::Sections_reachable
& cident_secn(ele
->second
);
319 for (Garbage_collection::Sections_reachable::iterator it_v
320 = cident_secn
.begin();
321 it_v
!= cident_secn
.end();
332 } // End of namespace gold.