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comparison: tools/footprint/foldelf.cpp

tools/footprint/foldelf.cpp

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1 /* -*- Mode: C++; indent-tabs-mode: nil; c-basic-offset: 4 -*-
2 *
3 * This Source Code Form is subject to the terms of the Mozilla Public
4 * License, v. 2.0. If a copy of the MPL was not distributed with this
5 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
6
7 /* This program reads an ELF file and computes information about
8 * redundancies.
9 */
10
11 #include <algorithm>
12 #include <fstream>
13 #include <string>
14 #include <vector>
15 #include <map>
16 #include <elf.h>
17 #include <sys/mman.h>
18 #include <sys/stat.h>
19 #include <fcntl.h>
20 #include <unistd.h>
21 #include <errno.h>
22 #include <getopt.h>
23
24 //----------------------------------------------------------------------
25
26 char* opt_type = "func";
27 char* opt_section = ".text";
28
29 //----------------------------------------------------------------------
30
31 static void
32 hexdump(ostream& out, const char* bytes, size_t count)
33 {
34 hex(out);
35
36 size_t off = 0;
37 while (off < count) {
38 out.form("%08lx: ", off);
39
40 const char* p = bytes + off;
41
42 int j = 0;
43 while (j < 16) {
44 out.form("%02x", p[j++] & 0xff);
45 if (j + off >= count)
46 break;
47
48 out.form("%02x ", p[j++] & 0xff);
49 if (j + off >= count)
50 break;
51 }
52
53 // Pad
54 for (; j < 16; ++j)
55 out << ((j%2) ? " " : " ");
56
57 for (j = 0; j < 16; ++j) {
58 if (j + off < count)
59 out.put(isprint(p[j]) ? p[j] : '.');
60 }
61
62 out << endl;
63 off += 16;
64 }
65 }
66
67 //----------------------------------------------------------------------
68
69 int
70 verify_elf_header(const Elf32_Ehdr* hdr)
71 {
72 if (hdr->e_ident[EI_MAG0] != ELFMAG0
73 || hdr->e_ident[EI_MAG1] != ELFMAG1
74 || hdr->e_ident[EI_MAG2] != ELFMAG2
75 || hdr->e_ident[EI_MAG3] != ELFMAG3) {
76 cerr << "not an elf file" << endl;
77 return -1;
78 }
79
80 if (hdr->e_ident[EI_CLASS] != ELFCLASS32) {
81 cerr << "not a 32-bit elf file" << endl;
82 return -1;
83 }
84
85 if (hdr->e_ident[EI_DATA] != ELFDATA2LSB) {
86 cerr << "not a little endian elf file" << endl;
87 return -1;
88 }
89
90 if (hdr->e_ident[EI_VERSION] != EV_CURRENT) {
91 cerr << "incompatible version" << endl;
92 return -1;
93 }
94
95 return 0;
96 }
97
98 //----------------------------------------------------------------------
99
100 class elf_symbol : public Elf32_Sym
101 {
102 public:
103 elf_symbol(const Elf32_Sym& sym)
104 { ::memcpy(static_cast<Elf32_Sym*>(this), &sym, sizeof(Elf32_Sym)); }
105
106 friend bool operator==(const elf_symbol& lhs, const elf_symbol& rhs) {
107 return 0 == ::memcmp(static_cast<const Elf32_Sym*>(&lhs),
108 static_cast<const Elf32_Sym*>(&rhs),
109 sizeof(Elf32_Sym)); }
110 };
111
112 //----------------------------------------------------------------------
113
114 static const char*
115 st_bind(unsigned char info)
116 {
117 switch (ELF32_ST_BIND(info)) {
118 case STB_LOCAL: return "local";
119 case STB_GLOBAL: return "global";
120 case STB_WEAK: return "weak";
121 default: return "unknown";
122 }
123 }
124
125 static const char*
126 st_type(unsigned char info)
127 {
128 switch (ELF32_ST_TYPE(info)) {
129 case STT_NOTYPE: return "none";
130 case STT_OBJECT: return "object";
131 case STT_FUNC: return "func";
132 case STT_SECTION: return "section";
133 case STT_FILE: return "file";
134 default: return "unknown";
135 }
136 }
137
138 static unsigned char
139 st_type(const char* type)
140 {
141 if (strcmp(type, "none") == 0) {
142 return STT_NOTYPE;
143 }
144 else if (strcmp(type, "object") == 0) {
145 return STT_OBJECT;
146 }
147 else if (strcmp(type, "func") == 0) {
148 return STT_FUNC;
149 }
150 else {
151 return 0;
152 }
153 }
154
155 //----------------------------------------------------------------------
156
157 typedef vector<elf_symbol> elf_symbol_table;
158 typedef map< basic_string<char>, elf_symbol_table > elf_text_map;
159
160 void
161 process_mapping(char* mapping, size_t size)
162 {
163 const Elf32_Ehdr* ehdr = reinterpret_cast<Elf32_Ehdr*>(mapping);
164 if (verify_elf_header(ehdr) < 0)
165 return;
166
167 // find the section headers
168 const Elf32_Shdr* shdrs = reinterpret_cast<Elf32_Shdr*>(mapping + ehdr->e_shoff);
169
170 // find the section header string table, .shstrtab
171 const Elf32_Shdr* shstrtabsh = shdrs + ehdr->e_shstrndx;
172 const char* shstrtab = mapping + shstrtabsh->sh_offset;
173
174 // find the sections we care about
175 const Elf32_Shdr *symtabsh, *strtabsh, *textsh;
176 int textndx;
177
178 for (int i = 0; i < ehdr->e_shnum; ++i) {
179 basic_string<char> name(shstrtab + shdrs[i].sh_name);
180 if (name == opt_section) {
181 textsh = shdrs + i;
182 textndx = i;
183 }
184 else if (name == ".symtab") {
185 symtabsh = shdrs + i;
186 }
187 else if (name == ".strtab") {
188 strtabsh = shdrs + i;
189 }
190 }
191
192 // find the .strtab
193 char* strtab = mapping + strtabsh->sh_offset;
194
195 // find the .text
196 char* text = mapping + textsh->sh_offset;
197 int textaddr = textsh->sh_addr;
198
199 // find the symbol table
200 int nentries = symtabsh->sh_size / sizeof(Elf32_Sym);
201 Elf32_Sym* symtab = reinterpret_cast<Elf32_Sym*>(mapping + symtabsh->sh_offset);
202
203 // look for symbols in the .text section
204 elf_text_map textmap;
205
206 for (int i = 0; i < nentries; ++i) {
207 const Elf32_Sym* sym = symtab + i;
208 if (sym->st_shndx == textndx &&
209 ELF32_ST_TYPE(sym->st_info) == st_type(opt_type) &&
210 sym->st_size) {
211 basic_string<char> functext(text + sym->st_value - textaddr, sym->st_size);
212
213 elf_symbol_table& syms = textmap[functext];
214 if (syms.end() == find(syms.begin(), syms.end(), elf_symbol(*sym)))
215 syms.insert(syms.end(), *sym);
216 }
217 }
218
219 int uniquebytes = 0, totalbytes = 0;
220 int uniquecount = 0, totalcount = 0;
221
222 for (elf_text_map::const_iterator entry = textmap.begin();
223 entry != textmap.end();
224 ++entry) {
225 const elf_symbol_table& syms = entry->second;
226
227 if (syms.size() <= 1)
228 continue;
229
230 int sz = syms.begin()->st_size;
231 uniquebytes += sz;
232 totalbytes += sz * syms.size();
233 uniquecount += 1;
234 totalcount += syms.size();
235
236 for (elf_symbol_table::const_iterator sym = syms.begin(); sym != syms.end(); ++sym)
237 cout << strtab + sym->st_name << endl;
238
239 dec(cout);
240 cout << syms.size() << " copies of " << sz << " bytes";
241 cout << " (" << ((syms.size() - 1) * sz) << " redundant bytes)" << endl;
242
243 hexdump(cout, entry->first.data(), entry->first.size());
244 cout << endl;
245 }
246
247 dec(cout);
248 cout << "bytes unique=" << uniquebytes << ", total=" << totalbytes << endl;
249 cout << "entries unique=" << uniquecount << ", total=" << totalcount << endl;
250 }
251
252 void
253 process_file(const char* name)
254 {
255 int fd = open(name, O_RDWR);
256 if (fd >= 0) {
257 struct stat statbuf;
258 if (fstat(fd, &statbuf) >= 0) {
259 size_t size = statbuf.st_size;
260
261 void* mapping = mmap(0, size, PROT_READ, MAP_SHARED, fd, 0);
262 if (mapping != MAP_FAILED) {
263 process_mapping(static_cast<char*>(mapping), size);
264 munmap(mapping, size);
265 }
266 }
267 close(fd);
268 }
269 }
270
271 static void
272 usage()
273 {
274 cerr << "foldelf [--section=<section>] [--type=<type>] [file ...]\n\
275 --section, -s the section of the ELF file to scan; defaults\n\
276 to ``.text''. Valid values include any section\n\
277 of the ELF file.\n\
278 --type, -t the type of object to examine in the section;\n\
279 defaults to ``func''. Valid values include\n\
280 ``none'', ``func'', or ``object''.\n";
281
282 }
283
284 static struct option opts[] = {
285 { "type", required_argument, 0, 't' },
286 { "section", required_argument, 0, 's' },
287 { "help", no_argument, 0, '?' },
288 { 0, 0, 0, 0 }
289 };
290
291 int
292 main(int argc, char* argv[])
293 {
294 while (1) {
295 int option_index = 0;
296 int c = getopt_long(argc, argv, "t:s:", opts, &option_index);
297
298 if (c < 0) break;
299
300 switch (c) {
301 case 't':
302 opt_type = optarg;
303 break;
304
305 case 's':
306 opt_section = optarg;
307 break;
308
309 case '?':
310 usage();
311 break;
312 }
313 }
314
315 for (int i = optind; i < argc; ++i)
316 process_file(argv[i]);
317
318 return 0;
319 }

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