2 * This file is included twice from vdso2c.c. It generates code for 32-bit
3 * and 64-bit vDSOs. We need both for 64-bit builds, since 32-bit vDSOs
4 * are built for 32-bit userspace.
8 * We're writing a section table for a few reasons:
10 * The Go runtime had a couple of bugs: it would read the section
11 * table to try to figure out how many dynamic symbols there were (it
12 * shouldn't have looked at the section table at all) and, if there
13 * were no SHT_SYNDYM section table entry, it would use an
14 * uninitialized value for the number of symbols. An empty DYNSYM
15 * table would work, but I see no reason not to write a valid one (and
16 * keep full performance for old Go programs). This hack is only
19 * The bug was introduced on 2012-08-31 by:
20 * https://code.google.com/p/go/source/detail?r=56ea40aac72b
21 * and was fixed on 2014-06-13 by:
22 * https://code.google.com/p/go/source/detail?r=fc1cd5e12595
24 * Binutils has issues debugging the vDSO: it reads the section table to
25 * find SHT_NOTE; it won't look at PT_NOTE for the in-memory vDSO, which
26 * would break build-id if we removed the section table. Binutils
27 * also requires that shstrndx != 0. See:
28 * https://sourceware.org/bugzilla/show_bug.cgi?id=17064
30 * elfutils might not look for PT_NOTE if there is a section table at
31 * all. I don't know whether this matters for any practical purpose.
33 * For simplicity, rather than hacking up a partial section table, we
34 * just write a mostly complete one. We omit non-dynamic symbols,
35 * though, since they're rather large.
37 * Once binutils gets fixed, we might be able to drop this for all but
38 * the 64-bit vdso, since build-id only works in kernel RPMs, and
39 * systems that update to new enough kernel RPMs will likely update
40 * binutils in sync. build-id has never worked for home-built kernel
41 * RPMs without manual symlinking, and I suspect that no one ever does
44 struct BITSFUNC(fake_sections)
47 unsigned long table_offset;
51 unsigned long shstr_offset;
58 static unsigned int BITSFUNC(find_shname)(struct BITSFUNC(fake_sections) *out,
61 const char *outname = out->shstrtab;
62 while (outname - out->shstrtab < out->shstrtab_len) {
63 if (!strcmp(name, outname))
64 return (outname - out->shstrtab) + out->shstr_offset;
65 outname += strlen(outname) + 1;
69 printf("Warning: could not find output name \"%s\"\n", name);
70 return out->shstr_offset + out->shstrtab_len - 1; /* Use a null. */
73 static void BITSFUNC(init_sections)(struct BITSFUNC(fake_sections) *out)
75 if (!out->in_shstrndx)
76 fail("didn't find the fake shstrndx\n");
78 memset(out->table, 0, out->max_count * sizeof(ELF(Shdr)));
80 if (out->max_count < 1)
81 fail("we need at least two fake output sections\n");
83 PUT_LE(&out->table[0].sh_type, SHT_NULL);
84 PUT_LE(&out->table[0].sh_name, BITSFUNC(find_shname)(out, ""));
89 static void BITSFUNC(copy_section)(struct BITSFUNC(fake_sections) *out,
90 int in_idx, const ELF(Shdr) *in,
93 uint64_t flags = GET_LE(&in->sh_flags);
95 bool copy = flags & SHF_ALLOC &&
96 strcmp(name, ".altinstructions") &&
97 strcmp(name, ".altinstr_replacement");
102 if (out->count >= out->max_count)
103 fail("too many copied sections (max = %d)\n", out->max_count);
105 if (in_idx == out->in_shstrndx)
106 out->out_shstrndx = out->count;
108 out->table[out->count] = *in;
109 PUT_LE(&out->table[out->count].sh_name,
110 BITSFUNC(find_shname)(out, name));
112 /* elfutils requires that a strtab have the correct type. */
113 if (!strcmp(name, ".fake_shstrtab"))
114 PUT_LE(&out->table[out->count].sh_type, SHT_STRTAB);
119 static void BITSFUNC(go)(void *addr, size_t len,
120 FILE *outfile, const char *name)
123 unsigned long load_size = -1; /* Work around bogus warning */
124 unsigned long data_size;
125 ELF(Ehdr) *hdr = (ELF(Ehdr) *)addr;
128 ELF(Shdr) *symtab_hdr = NULL, *strtab_hdr, *secstrings_hdr,
130 ELF(Dyn) *dyn = 0, *dyn_end = 0;
131 const char *secstrings;
132 uint64_t syms[NSYMS] = {};
134 struct BITSFUNC(fake_sections) fake_sections = {};
136 ELF(Phdr) *pt = (ELF(Phdr) *)(addr + GET_LE(&hdr->e_phoff));
138 /* Walk the segment table. */
139 for (i = 0; i < GET_LE(&hdr->e_phnum); i++) {
140 if (GET_LE(&pt[i].p_type) == PT_LOAD) {
142 fail("multiple PT_LOAD segs\n");
144 if (GET_LE(&pt[i].p_offset) != 0 ||
145 GET_LE(&pt[i].p_vaddr) != 0)
146 fail("PT_LOAD in wrong place\n");
148 if (GET_LE(&pt[i].p_memsz) != GET_LE(&pt[i].p_filesz))
149 fail("cannot handle memsz != filesz\n");
151 load_size = GET_LE(&pt[i].p_memsz);
153 } else if (GET_LE(&pt[i].p_type) == PT_DYNAMIC) {
154 dyn = addr + GET_LE(&pt[i].p_offset);
155 dyn_end = addr + GET_LE(&pt[i].p_offset) +
156 GET_LE(&pt[i].p_memsz);
160 fail("no PT_LOAD seg\n");
161 data_size = (load_size + 4095) / 4096 * 4096;
163 /* Walk the dynamic table */
164 for (i = 0; dyn + i < dyn_end &&
165 GET_LE(&dyn[i].d_tag) != DT_NULL; i++) {
166 typeof(dyn[i].d_tag) tag = GET_LE(&dyn[i].d_tag);
167 if (tag == DT_REL || tag == DT_RELSZ || tag == DT_RELA ||
168 tag == DT_RELENT || tag == DT_TEXTREL)
169 fail("vdso image contains dynamic relocations\n");
172 /* Walk the section table */
173 secstrings_hdr = addr + GET_LE(&hdr->e_shoff) +
174 GET_LE(&hdr->e_shentsize)*GET_LE(&hdr->e_shstrndx);
175 secstrings = addr + GET_LE(&secstrings_hdr->sh_offset);
176 for (i = 0; i < GET_LE(&hdr->e_shnum); i++) {
177 ELF(Shdr) *sh = addr + GET_LE(&hdr->e_shoff) +
178 GET_LE(&hdr->e_shentsize) * i;
179 if (GET_LE(&sh->sh_type) == SHT_SYMTAB)
182 if (!strcmp(secstrings + GET_LE(&sh->sh_name),
188 fail("no symbol table\n");
190 strtab_hdr = addr + GET_LE(&hdr->e_shoff) +
191 GET_LE(&hdr->e_shentsize) * GET_LE(&symtab_hdr->sh_link);
193 /* Walk the symbol table */
195 i < GET_LE(&symtab_hdr->sh_size) / GET_LE(&symtab_hdr->sh_entsize);
198 ELF(Sym) *sym = addr + GET_LE(&symtab_hdr->sh_offset) +
199 GET_LE(&symtab_hdr->sh_entsize) * i;
200 const char *name = addr + GET_LE(&strtab_hdr->sh_offset) +
201 GET_LE(&sym->st_name);
203 for (k = 0; k < NSYMS; k++) {
204 if (!strcmp(name, required_syms[k].name)) {
206 fail("duplicate symbol %s\n",
207 required_syms[k].name);
209 syms[k] = GET_LE(&sym->st_value);
213 if (!strcmp(name, "fake_shstrtab")) {
216 fake_sections.in_shstrndx = GET_LE(&sym->st_shndx);
217 fake_sections.shstrtab = addr + GET_LE(&sym->st_value);
218 fake_sections.shstrtab_len = GET_LE(&sym->st_size);
219 sh = addr + GET_LE(&hdr->e_shoff) +
220 GET_LE(&hdr->e_shentsize) *
221 fake_sections.in_shstrndx;
222 fake_sections.shstr_offset = GET_LE(&sym->st_value) -
223 GET_LE(&sh->sh_addr);
227 /* Build the output section table. */
228 if (!syms[sym_VDSO_FAKE_SECTION_TABLE_START] ||
229 !syms[sym_VDSO_FAKE_SECTION_TABLE_END])
230 fail("couldn't find fake section table\n");
231 if ((syms[sym_VDSO_FAKE_SECTION_TABLE_END] -
232 syms[sym_VDSO_FAKE_SECTION_TABLE_START]) % sizeof(ELF(Shdr)))
233 fail("fake section table size isn't a multiple of sizeof(Shdr)\n");
234 fake_sections.table = addr + syms[sym_VDSO_FAKE_SECTION_TABLE_START];
235 fake_sections.table_offset = syms[sym_VDSO_FAKE_SECTION_TABLE_START];
236 fake_sections.max_count = (syms[sym_VDSO_FAKE_SECTION_TABLE_END] -
237 syms[sym_VDSO_FAKE_SECTION_TABLE_START]) /
240 BITSFUNC(init_sections)(&fake_sections);
241 for (i = 0; i < GET_LE(&hdr->e_shnum); i++) {
242 ELF(Shdr) *sh = addr + GET_LE(&hdr->e_shoff) +
243 GET_LE(&hdr->e_shentsize) * i;
244 BITSFUNC(copy_section)(&fake_sections, i, sh,
245 secstrings + GET_LE(&sh->sh_name));
247 if (!fake_sections.out_shstrndx)
248 fail("didn't generate shstrndx?!?\n");
250 PUT_LE(&hdr->e_shoff, fake_sections.table_offset);
251 PUT_LE(&hdr->e_shentsize, sizeof(ELF(Shdr)));
252 PUT_LE(&hdr->e_shnum, fake_sections.count);
253 PUT_LE(&hdr->e_shstrndx, fake_sections.out_shstrndx);
255 /* Validate mapping addresses. */
256 for (i = 0; i < sizeof(special_pages) / sizeof(special_pages[0]); i++) {
258 continue; /* The mapping isn't used; ignore it. */
261 fail("%s must be a multiple of 4096\n",
262 required_syms[i].name);
263 if (syms[i] < data_size)
264 fail("%s must be after the text mapping\n",
265 required_syms[i].name);
266 if (syms[sym_end_mapping] < syms[i] + 4096)
267 fail("%s overruns end_mapping\n",
268 required_syms[i].name);
270 if (syms[sym_end_mapping] % 4096)
271 fail("end_mapping must be a multiple of 4096\n");
274 fwrite(addr, load_size, 1, outfile);
278 fprintf(outfile, "/* AUTOMATICALLY GENERATED -- DO NOT EDIT */\n\n");
279 fprintf(outfile, "#include <linux/linkage.h>\n");
280 fprintf(outfile, "#include <asm/page_types.h>\n");
281 fprintf(outfile, "#include <asm/vdso.h>\n");
282 fprintf(outfile, "\n");
284 "static unsigned char raw_data[%lu] __page_aligned_data = {",
286 for (j = 0; j < load_size; j++) {
288 fprintf(outfile, "\n\t");
289 fprintf(outfile, "0x%02X, ", (int)((unsigned char *)addr)[j]);
291 fprintf(outfile, "\n};\n\n");
293 fprintf(outfile, "static struct page *pages[%lu];\n\n",
296 fprintf(outfile, "const struct vdso_image %s = {\n", name);
297 fprintf(outfile, "\t.data = raw_data,\n");
298 fprintf(outfile, "\t.size = %lu,\n", data_size);
299 fprintf(outfile, "\t.text_mapping = {\n");
300 fprintf(outfile, "\t\t.name = \"[vdso]\",\n");
301 fprintf(outfile, "\t\t.pages = pages,\n");
302 fprintf(outfile, "\t},\n");
304 fprintf(outfile, "\t.alt = %lu,\n",
305 (unsigned long)GET_LE(&alt_sec->sh_offset));
306 fprintf(outfile, "\t.alt_len = %lu,\n",
307 (unsigned long)GET_LE(&alt_sec->sh_size));
309 for (i = 0; i < NSYMS; i++) {
310 if (required_syms[i].export && syms[i])
311 fprintf(outfile, "\t.sym_%s = 0x%" PRIx64 ",\n",
312 required_syms[i].name, syms[i]);
314 fprintf(outfile, "};\n");