1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
|
// gc.h -- garbage collection of unused sections
// Copyright (C) 2009-2021 Free Software Foundation, Inc.
// Written by Sriraman Tallam <tmsriram@google.com>.
// This file is part of gold.
// This program is free software; you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation; either version 3 of the License, or
// (at your option) any later version.
// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU General Public License for more details.
// You should have received a copy of the GNU General Public License
// along with this program; if not, write to the Free Software
// Foundation, Inc., 51 Franklin Street - Fifth Floor, Boston,
// MA 02110-1301, USA.
#ifndef GOLD_GC_H
#define GOLD_GC_H
#include <vector>
#include "elfcpp.h"
#include "symtab.h"
#include "object.h"
#include "icf.h"
namespace gold
{
class Object;
template<int size, bool big_endian>
class Sized_relobj_file;
class Output_section;
class General_options;
class Layout;
class Garbage_collection
{
public:
typedef Unordered_set<Section_id, Section_id_hash> Sections_reachable;
typedef std::map<Section_id, Sections_reachable> Section_ref;
typedef std::vector<Section_id> Worklist_type;
// This maps the name of the section which can be represented as a C
// identifier (cident) to the list of sections that have that name.
// Different object files can have cident sections with the same name.
typedef std::map<std::string, Sections_reachable> Cident_section_map;
Garbage_collection()
: is_worklist_ready_(false)
{ }
// Accessor methods for the private members.
Sections_reachable&
referenced_list()
{ return referenced_list_; }
Section_ref&
section_reloc_map()
{ return this->section_reloc_map_; }
Worklist_type&
worklist()
{ return this->work_list_; }
bool
is_worklist_ready()
{ return this->is_worklist_ready_; }
void
worklist_ready()
{ this->is_worklist_ready_ = true; }
void
do_transitive_closure();
bool
is_section_garbage(Relobj* obj, unsigned int shndx)
{ return (this->referenced_list().find(Section_id(obj, shndx))
== this->referenced_list().end()); }
Cident_section_map*
cident_sections()
{ return &cident_sections_; }
void
add_cident_section(std::string section_name,
Section_id secn)
{ this->cident_sections_[section_name].insert(secn); }
// Add a reference from the SRC_SHNDX-th section of SRC_OBJECT to
// DST_SHNDX-th section of DST_OBJECT.
void
add_reference(Relobj* src_object, unsigned int src_shndx,
Relobj* dst_object, unsigned int dst_shndx)
{
Section_id src_id(src_object, src_shndx);
Section_id dst_id(dst_object, dst_shndx);
Sections_reachable& reachable = this->section_reloc_map_[src_id];
reachable.insert(dst_id);
}
private:
Worklist_type work_list_;
bool is_worklist_ready_;
Section_ref section_reloc_map_;
Sections_reachable referenced_list_;
Cident_section_map cident_sections_;
};
// Data to pass between successive invocations of do_layout
// in object.cc while garbage collecting. This data structure
// is filled by using the data from Read_symbols_data.
struct Symbols_data
{
// Section headers.
unsigned char* section_headers_data;
// Section names.
unsigned char* section_names_data;
// Size of section name data in bytes.
section_size_type section_names_size;
// Symbol data.
unsigned char* symbols_data;
// Size of symbol data in bytes.
section_size_type symbols_size;
// Offset of external symbols within symbol data. This structure
// sometimes contains only external symbols, in which case this will
// be zero. Sometimes it contains all symbols.
section_offset_type external_symbols_offset;
// Symbol names.
unsigned char* symbol_names_data;
// Size of symbol name data in bytes.
section_size_type symbol_names_size;
};
// Relocations of type SHT_REL store the addend value in their bytes.
// This function returns the size of the embedded addend which is
// nothing but the size of the relocation.
template<typename Classify_reloc>
inline unsigned int
get_embedded_addend_size(int r_type, Relobj* obj)
{
if (Classify_reloc::sh_type == elfcpp::SHT_REL)
return Classify_reloc::get_size_for_reloc(r_type, obj);
return 0;
}
// This function implements the generic part of reloc
// processing to map a section to all the sections it
// references through relocs. It is called only during
// garbage collection (--gc-sections) and identical code
// folding (--icf).
template<int size, bool big_endian, typename Target_type,
typename Scan, typename Classify_reloc>
inline void
gc_process_relocs(
Symbol_table* symtab,
Layout*,
Target_type* target,
Sized_relobj_file<size, big_endian>* src_obj,
unsigned int src_indx,
const unsigned char* prelocs,
size_t reloc_count,
Output_section*,
bool,
size_t local_count,
const unsigned char* plocal_syms)
{
Scan scan;
typedef typename Classify_reloc::Reltype Reltype;
const int reloc_size = Classify_reloc::reloc_size;
const int sym_size = elfcpp::Elf_sizes<size>::sym_size;
Icf::Sections_reachable_info* secvec = NULL;
Icf::Symbol_info* symvec = NULL;
Icf::Addend_info* addendvec = NULL;
Icf::Offset_info* offsetvec = NULL;
Icf::Reloc_addend_size_info* reloc_addend_size_vec = NULL;
bool is_icf_tracked = false;
const char* cident_section_name = NULL;
std::string src_section_name = (parameters->options().icf_enabled()
? src_obj->section_name(src_indx)
: "");
bool check_section_for_function_pointers = false;
if (parameters->options().icf_enabled()
&& (is_section_foldable_candidate(src_section_name)
|| is_prefix_of(".eh_frame", src_section_name.c_str())))
{
is_icf_tracked = true;
Section_id src_id(src_obj, src_indx);
Icf::Reloc_info* reloc_info =
&symtab->icf()->reloc_info_list()[src_id];
secvec = &reloc_info->section_info;
symvec = &reloc_info->symbol_info;
addendvec = &reloc_info->addend_info;
offsetvec = &reloc_info->offset_info;
reloc_addend_size_vec = &reloc_info->reloc_addend_size_info;
}
check_section_for_function_pointers =
symtab->icf()->check_section_for_function_pointers(src_section_name,
target);
for (size_t i = 0; i < reloc_count; ++i, prelocs += reloc_size)
{
Reltype reloc(prelocs);
unsigned int r_sym = Classify_reloc::get_r_sym(&reloc);
unsigned int r_type = Classify_reloc::get_r_type(&reloc);
typename elfcpp::Elf_types<size>::Elf_Swxword addend =
Classify_reloc::get_r_addend(&reloc);
Relobj* dst_obj;
unsigned int dst_indx;
typedef typename elfcpp::Elf_types<size>::Elf_Addr Address;
Address dst_off;
if (r_sym < local_count)
{
gold_assert(plocal_syms != NULL);
typename elfcpp::Sym<size, big_endian> lsym(plocal_syms
+ r_sym * sym_size);
dst_indx = lsym.get_st_shndx();
bool is_ordinary;
dst_indx = src_obj->adjust_sym_shndx(r_sym, dst_indx, &is_ordinary);
dst_obj = src_obj;
dst_off = lsym.get_st_value() + addend;
if (is_icf_tracked)
{
Address symvalue = dst_off - addend;
if (is_ordinary)
(*secvec).push_back(Section_id(src_obj, dst_indx));
else
(*secvec).push_back(Section_id(nullptr, 0));
// If the target of the relocation is an STT_SECTION symbol,
// make a note of that by storing -1 in the symbol vector.
if (lsym.get_st_type() == elfcpp::STT_SECTION)
(*symvec).push_back(reinterpret_cast<Symbol*>(-1));
else
(*symvec).push_back(NULL);
(*addendvec).push_back(std::make_pair(
static_cast<long long>(symvalue),
static_cast<long long>(addend)));
uint64_t reloc_offset =
convert_to_section_size_type(reloc.get_r_offset());
(*offsetvec).push_back(reloc_offset);
(*reloc_addend_size_vec).push_back(
get_embedded_addend_size<Classify_reloc>(r_type, src_obj));
}
// When doing safe folding, check to see if this relocation is that
// of a function pointer being taken.
if (is_ordinary
&& check_section_for_function_pointers
&& lsym.get_st_type() != elfcpp::STT_OBJECT
&& scan.local_reloc_may_be_function_pointer(symtab, NULL, target,
src_obj, src_indx,
NULL, reloc, r_type,
lsym))
symtab->icf()->set_section_has_function_pointers(
src_obj, lsym.get_st_shndx());
if (!is_ordinary || dst_indx == src_indx)
continue;
}
else
{
Symbol* gsym = src_obj->global_symbol(r_sym);
gold_assert(gsym != NULL);
if (gsym->is_forwarder())
gsym = symtab->resolve_forwards(gsym);
dst_obj = NULL;
dst_indx = 0;
bool is_ordinary = false;
if (gsym->source() == Symbol::FROM_OBJECT
&& !gsym->object()->is_dynamic())
{
dst_obj = static_cast<Relobj*>(gsym->object());
dst_indx = gsym->shndx(&is_ordinary);
}
dst_off = static_cast<const Sized_symbol<size>*>(gsym)->value();
dst_off += addend;
// When doing safe folding, check to see if this relocation is that
// of a function pointer being taken.
if (gsym->source() == Symbol::FROM_OBJECT
&& gsym->type() == elfcpp::STT_FUNC
&& check_section_for_function_pointers
&& dst_obj != NULL
&& (!is_ordinary
|| scan.global_reloc_may_be_function_pointer(
symtab, NULL, target, src_obj, src_indx, NULL, reloc,
r_type, gsym)))
symtab->icf()->set_section_has_function_pointers(dst_obj, dst_indx);
// If the symbol name matches '__start_XXX' then the section with
// the C identifier like name 'XXX' should not be garbage collected.
// A similar treatment to symbols with the name '__stop_XXX'.
if (is_prefix_of(cident_section_start_prefix, gsym->name()))
{
cident_section_name = (gsym->name()
+ strlen(cident_section_start_prefix));
}
else if (is_prefix_of(cident_section_stop_prefix, gsym->name()))
{
cident_section_name = (gsym->name()
+ strlen(cident_section_stop_prefix));
}
if (is_icf_tracked)
{
Address symvalue = dst_off - addend;
if (is_ordinary && dst_obj != NULL)
(*secvec).push_back(Section_id(dst_obj, dst_indx));
else
(*secvec).push_back(Section_id(nullptr, 0));
(*symvec).push_back(gsym);
(*addendvec).push_back(std::make_pair(
static_cast<long long>(symvalue),
static_cast<long long>(addend)));
uint64_t reloc_offset =
convert_to_section_size_type(reloc.get_r_offset());
(*offsetvec).push_back(reloc_offset);
(*reloc_addend_size_vec).push_back(
get_embedded_addend_size<Classify_reloc>(r_type, src_obj));
}
if (dst_obj == NULL)
continue;
if (!is_ordinary)
continue;
}
if (parameters->options().gc_sections())
{
symtab->gc()->add_reference(src_obj, src_indx, dst_obj, dst_indx);
parameters->sized_target<size, big_endian>()
->gc_add_reference(symtab, src_obj, src_indx, dst_obj, dst_indx,
dst_off);
if (cident_section_name != NULL)
{
Garbage_collection::Cident_section_map::iterator ele =
symtab->gc()->cident_sections()->find(std::string(cident_section_name));
if (ele == symtab->gc()->cident_sections()->end())
continue;
Section_id src_id(src_obj, src_indx);
Garbage_collection::Sections_reachable&
v(symtab->gc()->section_reloc_map()[src_id]);
Garbage_collection::Sections_reachable& cident_secn(ele->second);
for (Garbage_collection::Sections_reachable::iterator it_v
= cident_secn.begin();
it_v != cident_secn.end();
++it_v)
{
v.insert(*it_v);
}
}
}
}
return;
}
} // End of namespace gold.
#endif
|