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6d03d481 ST |
1 | // gc.h -- garbage collection of unused sections |
2 | ||
55a2bb35 | 3 | // Copyright 2009, 2010 Free Software Foundation, Inc. |
6d03d481 ST |
4 | // Written by Sriraman Tallam <tmsriram@google.com>. |
5 | ||
6 | // This file is part of gold. | |
7 | ||
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. | |
12 | ||
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. | |
17 | ||
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. | |
22 | ||
23 | #ifndef GOLD_GC_H | |
24 | #define GOLD_GC_H | |
25 | ||
26 | #include <queue> | |
ef15dade | 27 | #include <vector> |
6d03d481 ST |
28 | |
29 | #include "elfcpp.h" | |
30 | #include "symtab.h" | |
5ac169d4 | 31 | #include "object.h" |
f345227a | 32 | #include "icf.h" |
6d03d481 ST |
33 | |
34 | namespace gold | |
35 | { | |
36 | ||
37 | class Object; | |
38 | ||
39 | template<int size, bool big_endian> | |
40 | class Sized_relobj; | |
41 | ||
42 | template<int sh_type, int size, bool big_endian> | |
43 | class Reloc_types; | |
44 | ||
45 | class Output_section; | |
46 | class General_options; | |
47 | class Layout; | |
48 | ||
6d03d481 ST |
49 | class Garbage_collection |
50 | { | |
ef15dade ST |
51 | public: |
52 | ||
6d03d481 ST |
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; | |
f1ec9ded ST |
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; | |
6d03d481 | 60 | |
ef15dade ST |
61 | Garbage_collection() |
62 | : is_worklist_ready_(false) | |
63 | { } | |
64 | ||
65 | // Accessor methods for the private members. | |
66 | ||
67 | Sections_reachable& | |
68 | referenced_list() | |
69 | { return referenced_list_; } | |
70 | ||
71 | Section_ref& | |
72 | section_reloc_map() | |
73 | { return this->section_reloc_map_; } | |
74 | ||
75 | Worklist_type& | |
76 | worklist() | |
77 | { return this->work_list_; } | |
78 | ||
79 | bool | |
80 | is_worklist_ready() | |
81 | { return this->is_worklist_ready_; } | |
82 | ||
83 | void | |
84 | worklist_ready() | |
85 | { this->is_worklist_ready_ = true; } | |
86 | ||
87 | void | |
88 | do_transitive_closure(); | |
89 | ||
90 | bool | |
91 | is_section_garbage(Object* obj, unsigned int shndx) | |
92 | { return (this->referenced_list().find(Section_id(obj, shndx)) | |
93 | == this->referenced_list().end()); } | |
f1ec9ded ST |
94 | |
95 | Cident_section_map* | |
96 | cident_sections() | |
97 | { return &cident_sections_; } | |
98 | ||
99 | void | |
100 | add_cident_section(std::string section_name, | |
101 | Section_id secn) | |
102 | { this->cident_sections_[section_name].insert(secn); } | |
103 | ||
99e5bff2 DK |
104 | // Add a reference from the SRC_SHNDX-th section of SRC_OBJECT to |
105 | // DST_SHNDX-th section of DST_OBJECT. | |
106 | void | |
107 | add_reference(Object* src_object, unsigned int src_shndx, | |
108 | Object* dst_object, unsigned int dst_shndx) | |
109 | { | |
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); | |
115 | else | |
116 | p->second.insert(dst_id); | |
117 | } | |
118 | ||
ef15dade ST |
119 | private: |
120 | ||
121 | Worklist_type work_list_; | |
122 | bool is_worklist_ready_; | |
123 | Section_ref section_reloc_map_; | |
124 | Sections_reachable referenced_list_; | |
f1ec9ded | 125 | Cident_section_map cident_sections_; |
6d03d481 ST |
126 | }; |
127 | ||
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. | |
131 | ||
132 | struct Symbols_data | |
133 | { | |
134 | // Section headers. | |
135 | unsigned char* section_headers_data; | |
136 | // Section names. | |
137 | unsigned char* section_names_data; | |
138 | // Size of section name data in bytes. | |
139 | section_size_type section_names_size; | |
140 | // Symbol data. | |
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; | |
148 | // Symbol names. | |
149 | unsigned char* symbol_names_data; | |
150 | // Size of symbol name data in bytes. | |
151 | section_size_type symbol_names_size; | |
152 | }; | |
153 | ||
ef15dade ST |
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 | |
158 | // folding (--icf). | |
6d03d481 ST |
159 | |
160 | template<int size, bool big_endian, typename Target_type, int sh_type, | |
161 | typename Scan> | |
162 | inline void | |
163 | gc_process_relocs( | |
6d03d481 ST |
164 | Symbol_table* symtab, |
165 | Layout*, | |
21bb3914 | 166 | Target_type* target, |
ef15dade ST |
167 | Sized_relobj<size, big_endian>* src_obj, |
168 | unsigned int src_indx, | |
6d03d481 ST |
169 | const unsigned char* prelocs, |
170 | size_t reloc_count, | |
171 | Output_section*, | |
21bb3914 | 172 | bool, |
6d03d481 ST |
173 | size_t local_count, |
174 | const unsigned char* plocal_syms) | |
175 | { | |
ef15dade ST |
176 | Object *dst_obj; |
177 | unsigned int dst_indx; | |
21bb3914 | 178 | Scan scan; |
6d03d481 | 179 | |
6d03d481 ST |
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; | |
183 | ||
b487ad64 ST |
184 | Icf::Sections_reachable_info* secvec = NULL; |
185 | Icf::Symbol_info* symvec = NULL; | |
186 | Icf::Addend_info* addendvec = NULL; | |
187 | Icf::Offset_info* offsetvec = NULL; | |
ef15dade | 188 | bool is_icf_tracked = false; |
f1ec9ded | 189 | const char* cident_section_name = NULL; |
ef15dade | 190 | |
21bb3914 ST |
191 | std::string src_section_name = (parameters->options().icf_enabled() |
192 | ? src_obj->section_name(src_indx) | |
193 | : ""); | |
194 | ||
195 | bool check_section_for_function_pointers = false; | |
196 | ||
032ce4e9 | 197 | if (parameters->options().icf_enabled() |
21bb3914 | 198 | && is_section_foldable_candidate(src_section_name.c_str())) |
ef15dade ST |
199 | { |
200 | is_icf_tracked = true; | |
201 | Section_id src_id(src_obj, src_indx); | |
b487ad64 ST |
202 | Icf::Reloc_info* reloc_info = |
203 | &symtab->icf()->reloc_info_list()[src_id]; | |
204 | secvec = &reloc_info->section_info; | |
205 | symvec = &reloc_info->symbol_info; | |
206 | addendvec = &reloc_info->addend_info; | |
207 | offsetvec = &reloc_info->offset_info; | |
ef15dade ST |
208 | } |
209 | ||
21bb3914 ST |
210 | check_section_for_function_pointers = |
211 | symtab->icf()->check_section_for_function_pointers(src_section_name, | |
212 | target); | |
213 | ||
6d03d481 ST |
214 | for (size_t i = 0; i < reloc_count; ++i, prelocs += reloc_size) |
215 | { | |
216 | Reltype reloc(prelocs); | |
217 | typename elfcpp::Elf_types<size>::Elf_WXword r_info = reloc.get_r_info(); | |
218 | unsigned int r_sym = elfcpp::elf_r_sym<size>(r_info); | |
21bb3914 | 219 | unsigned int r_type = elfcpp::elf_r_type<size>(r_info); |
ef15dade ST |
220 | typename elfcpp::Elf_types<size>::Elf_Swxword addend = |
221 | Reloc_types<sh_type, size, big_endian>::get_reloc_addend_noerror(&reloc); | |
222 | ||
6d03d481 ST |
223 | if (r_sym < local_count) |
224 | { | |
225 | gold_assert(plocal_syms != NULL); | |
226 | typename elfcpp::Sym<size, big_endian> lsym(plocal_syms | |
227 | + r_sym * sym_size); | |
228 | unsigned int shndx = lsym.get_st_shndx(); | |
229 | bool is_ordinary; | |
ef15dade | 230 | shndx = src_obj->adjust_sym_shndx(r_sym, shndx, &is_ordinary); |
6d03d481 | 231 | dst_obj = src_obj; |
6d03d481 | 232 | dst_indx = shndx; |
ef15dade ST |
233 | if (is_icf_tracked) |
234 | { | |
ef38fd8a ST |
235 | if (is_ordinary) |
236 | (*secvec).push_back(Section_id(dst_obj, dst_indx)); | |
237 | else | |
238 | (*secvec).push_back(Section_id(NULL, 0)); | |
ef15dade ST |
239 | (*symvec).push_back(NULL); |
240 | long long symvalue = static_cast<long long>(lsym.get_st_value()); | |
241 | (*addendvec).push_back(std::make_pair(symvalue, | |
242 | static_cast<long long>(addend))); | |
b487ad64 ST |
243 | uint64_t reloc_offset = |
244 | convert_to_section_size_type(reloc.get_r_offset()); | |
245 | (*offsetvec).push_back(reloc_offset); | |
ef15dade | 246 | } |
21bb3914 ST |
247 | |
248 | // When doing safe folding, check to see if this relocation is that | |
249 | // of a function pointer being taken. | |
ef38fd8a ST |
250 | if (is_ordinary |
251 | && check_section_for_function_pointers | |
21bb3914 ST |
252 | && lsym.get_st_type() != elfcpp::STT_OBJECT |
253 | && scan.local_reloc_may_be_function_pointer(symtab, NULL, NULL, | |
254 | src_obj, src_indx, | |
255 | NULL, reloc, r_type, | |
256 | lsym)) | |
257 | symtab->icf()->set_section_has_function_pointers( | |
258 | src_obj, lsym.get_st_shndx()); | |
259 | ||
ef38fd8a | 260 | if (!is_ordinary || shndx == src_indx) |
ef15dade | 261 | continue; |
6d03d481 ST |
262 | } |
263 | else | |
264 | { | |
ef15dade | 265 | Symbol* gsym = src_obj->global_symbol(r_sym); |
6d03d481 ST |
266 | gold_assert(gsym != NULL); |
267 | if (gsym->is_forwarder()) | |
268 | gsym = symtab->resolve_forwards(gsym); | |
ef38fd8a ST |
269 | |
270 | dst_obj = NULL; | |
271 | dst_indx = 0; | |
272 | bool is_ordinary = false; | |
273 | if (gsym->source() == Symbol::FROM_OBJECT) | |
274 | { | |
275 | dst_obj = gsym->object(); | |
276 | dst_indx = gsym->shndx(&is_ordinary); | |
277 | } | |
21bb3914 ST |
278 | |
279 | // When doing safe folding, check to see if this relocation is that | |
280 | // of a function pointer being taken. | |
ef38fd8a ST |
281 | if (gsym->source() == Symbol::FROM_OBJECT |
282 | && check_section_for_function_pointers | |
21bb3914 ST |
283 | && gsym->type() != elfcpp::STT_OBJECT |
284 | && (!is_ordinary | |
285 | || scan.global_reloc_may_be_function_pointer( | |
286 | symtab, NULL, NULL, src_obj, src_indx, NULL, reloc, | |
287 | r_type, gsym))) | |
288 | symtab->icf()->set_section_has_function_pointers(dst_obj, dst_indx); | |
289 | ||
f1ec9ded ST |
290 | // If the symbol name matches '__start_XXX' then the section with |
291 | // the C identifier like name 'XXX' should not be garbage collected. | |
292 | // A similar treatment to symbols with the name '__stop_XXX'. | |
293 | if (is_prefix_of(cident_section_start_prefix, gsym->name())) | |
294 | { | |
295 | cident_section_name = (gsym->name() | |
296 | + strlen(cident_section_start_prefix)); | |
297 | } | |
298 | else if (is_prefix_of(cident_section_stop_prefix, gsym->name())) | |
299 | { | |
300 | cident_section_name = (gsym->name() | |
301 | + strlen(cident_section_stop_prefix)); | |
302 | } | |
ef15dade ST |
303 | if (is_icf_tracked) |
304 | { | |
ef38fd8a ST |
305 | if (is_ordinary && gsym->source() == Symbol::FROM_OBJECT) |
306 | (*secvec).push_back(Section_id(dst_obj, dst_indx)); | |
307 | else | |
308 | (*secvec).push_back(Section_id(NULL, 0)); | |
ef15dade ST |
309 | (*symvec).push_back(gsym); |
310 | Sized_symbol<size>* sized_gsym = | |
311 | static_cast<Sized_symbol<size>* >(gsym); | |
312 | long long symvalue = | |
313 | static_cast<long long>(sized_gsym->value()); | |
314 | (*addendvec).push_back(std::make_pair(symvalue, | |
315 | static_cast<long long>(addend))); | |
b487ad64 ST |
316 | uint64_t reloc_offset = |
317 | convert_to_section_size_type(reloc.get_r_offset()); | |
318 | (*offsetvec).push_back(reloc_offset); | |
21bb3914 | 319 | } |
ef38fd8a ST |
320 | |
321 | if (gsym->source() != Symbol::FROM_OBJECT) | |
322 | continue; | |
323 | if (!is_ordinary) | |
324 | continue; | |
6d03d481 | 325 | } |
ef15dade | 326 | if (parameters->options().gc_sections()) |
6d03d481 | 327 | { |
99e5bff2 | 328 | symtab->gc()->add_reference(src_obj, src_indx, dst_obj, dst_indx); |
f1ec9ded ST |
329 | if (cident_section_name != NULL) |
330 | { | |
331 | Garbage_collection::Cident_section_map::iterator ele = | |
332 | symtab->gc()->cident_sections()->find(std::string(cident_section_name)); | |
333 | if (ele == symtab->gc()->cident_sections()->end()) | |
334 | continue; | |
99e5bff2 | 335 | Section_id src_id(src_obj, src_indx); |
f1ec9ded ST |
336 | Garbage_collection::Sections_reachable& |
337 | v(symtab->gc()->section_reloc_map()[src_id]); | |
338 | Garbage_collection::Sections_reachable& cident_secn(ele->second); | |
339 | for (Garbage_collection::Sections_reachable::iterator it_v | |
340 | = cident_secn.begin(); | |
341 | it_v != cident_secn.end(); | |
342 | ++it_v) | |
343 | { | |
344 | v.insert(*it_v); | |
345 | } | |
346 | } | |
6d03d481 ST |
347 | } |
348 | } | |
349 | return; | |
350 | } | |
351 | ||
352 | } // End of namespace gold. | |
353 | ||
354 | #endif |