arch/x86/vdso/vdso2c.h

   1 /*
   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.
   5  */
   6
   7 /*
   8  * We're writing a section table for a few reasons:
   9  *
  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
  17  * needed on x86_64.
  18  *
  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
  23  *
  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
  29  *
  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.
  32  *
  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.
  36  *
  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
  42  * that.
  43  */
  44 struct BITSFUNC(fake_sections)
  45 {
  46         ELF(Shdr) *table;
  47         unsigned long table_offset;
  48         int count, max_count;
  49
  50         int in_shstrndx;
  51         unsigned long shstr_offset;
  52         const char *shstrtab;
  53         size_t shstrtab_len;
  54
  55         int out_shstrndx;
  56 };
  57
  58 static unsigned int BITSFUNC(find_shname)(struct BITSFUNC(fake_sections) *out,
  59                                           const char *name)
  60 {
  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;
  66         }
  67
  68         if (*name)
  69                 printf("Warning: could not find output name \"%s\"\n", name);
  70         return out->shstr_offset + out->shstrtab_len - 1;  /* Use a null. */
  71 }
  72
  73 static void BITSFUNC(init_sections)(struct BITSFUNC(fake_sections) *out)
  74 {
  75         if (!out->in_shstrndx)
  76                 fail("didn't find the fake shstrndx\n");
  77
  78         memset(out->table, 0, out->max_count * sizeof(ELF(Shdr)));
  79
  80         if (out->max_count < 1)
  81                 fail("we need at least two fake output sections\n");
  82
  83         PUT_LE(&out->table[0].sh_type, SHT_NULL);
  84         PUT_LE(&out->table[0].sh_name, BITSFUNC(find_shname)(out, ""));
  85
  86         out->count = 1;
  87 }
  88
  89 static void BITSFUNC(copy_section)(struct BITSFUNC(fake_sections) *out,
  90                                    int in_idx, const ELF(Shdr) *in,
  91                                    const char *name)
  92 {
  93         uint64_t flags = GET_LE(&in->sh_flags);
  94
  95         bool copy = flags & SHF_ALLOC &&
  96                 (GET_LE(&in->sh_size) ||
  97                  (GET_LE(&in->sh_type) != SHT_RELA &&
  98                   GET_LE(&in->sh_type) != SHT_REL)) &&
  99                 strcmp(name, ".altinstructions") &&
 100                 strcmp(name, ".altinstr_replacement");
 101
 102         if (!copy)
 103                 return;
 104
 105         if (out->count >= out->max_count)
 106                 fail("too many copied sections (max = %d)\n", out->max_count);
 107
 108         if (in_idx == out->in_shstrndx)
 109                 out->out_shstrndx = out->count;
 110
 111         out->table[out->count] = *in;
 112         PUT_LE(&out->table[out->count].sh_name,
 113                BITSFUNC(find_shname)(out, name));
 114
 115         /* elfutils requires that a strtab have the correct type. */
 116         if (!strcmp(name, ".fake_shstrtab"))
 117                 PUT_LE(&out->table[out->count].sh_type, SHT_STRTAB);
 118
 119         out->count++;
 120 }
 121
 122 static void BITSFUNC(go)(void *addr, size_t len,
 123                          FILE *outfile, const char *name)
 124 {
 125         int found_load = 0;
 126         unsigned long load_size = -1;  /* Work around bogus warning */
 127         unsigned long data_size;
 128         ELF(Ehdr) *hdr = (ELF(Ehdr) *)addr;
 129         int i;
 130         unsigned long j;
 131         ELF(Shdr) *symtab_hdr = NULL, *strtab_hdr, *secstrings_hdr,
 132                 *alt_sec = NULL;
 133         ELF(Dyn) *dyn = 0, *dyn_end = 0;
 134         const char *secstrings;
 135         uint64_t syms[NSYMS] = {};
 136
 137         struct BITSFUNC(fake_sections) fake_sections = {};
 138
 139         ELF(Phdr) *pt = (ELF(Phdr) *)(addr + GET_LE(&hdr->e_phoff));
 140
 141         /* Walk the segment table. */
 142         for (i = 0; i < GET_LE(&hdr->e_phnum); i++) {
 143                 if (GET_LE(&pt[i].p_type) == PT_LOAD) {
 144                         if (found_load)
 145                                 fail("multiple PT_LOAD segs\n");
 146
 147                         if (GET_LE(&pt[i].p_offset) != 0 ||
 148                             GET_LE(&pt[i].p_vaddr) != 0)
 149                                 fail("PT_LOAD in wrong place\n");
 150
 151                         if (GET_LE(&pt[i].p_memsz) != GET_LE(&pt[i].p_filesz))
 152                                 fail("cannot handle memsz != filesz\n");
 153
 154                         load_size = GET_LE(&pt[i].p_memsz);
 155                         found_load = 1;
 156                 } else if (GET_LE(&pt[i].p_type) == PT_DYNAMIC) {
 157                         dyn = addr + GET_LE(&pt[i].p_offset);
 158                         dyn_end = addr + GET_LE(&pt[i].p_offset) +
 159                                 GET_LE(&pt[i].p_memsz);
 160                 }
 161         }
 162         if (!found_load)
 163                 fail("no PT_LOAD seg\n");
 164         data_size = (load_size + 4095) / 4096 * 4096;
 165
 166         /* Walk the dynamic table */
 167         for (i = 0; dyn + i < dyn_end &&
 168                      GET_LE(&dyn[i].d_tag) != DT_NULL; i++) {
 169                 typeof(dyn[i].d_tag) tag = GET_LE(&dyn[i].d_tag);
 170                 if (tag == DT_REL || tag == DT_RELSZ || tag == DT_RELA ||
 171                     tag == DT_RELENT || tag == DT_TEXTREL)
 172                         fail("vdso image contains dynamic relocations\n");
 173         }
 174
 175         /* Walk the section table */
 176         secstrings_hdr = addr + GET_LE(&hdr->e_shoff) +
 177                 GET_LE(&hdr->e_shentsize)*GET_LE(&hdr->e_shstrndx);
 178         secstrings = addr + GET_LE(&secstrings_hdr->sh_offset);
 179         for (i = 0; i < GET_LE(&hdr->e_shnum); i++) {
 180                 ELF(Shdr) *sh = addr + GET_LE(&hdr->e_shoff) +
 181                         GET_LE(&hdr->e_shentsize) * i;
 182                 if (GET_LE(&sh->sh_type) == SHT_SYMTAB)
 183                         symtab_hdr = sh;
 184
 185                 if (!strcmp(secstrings + GET_LE(&sh->sh_name),
 186                             ".altinstructions"))
 187                         alt_sec = sh;
 188         }
 189
 190         if (!symtab_hdr)
 191                 fail("no symbol table\n");
 192
 193         strtab_hdr = addr + GET_LE(&hdr->e_shoff) +
 194                 GET_LE(&hdr->e_shentsize) * GET_LE(&symtab_hdr->sh_link);
 195
 196         /* Walk the symbol table */
 197         for (i = 0;
 198              i < GET_LE(&symtab_hdr->sh_size) / GET_LE(&symtab_hdr->sh_entsize);
 199              i++) {
 200                 int k;
 201                 ELF(Sym) *sym = addr + GET_LE(&symtab_hdr->sh_offset) +
 202                         GET_LE(&symtab_hdr->sh_entsize) * i;
 203                 const char *name = addr + GET_LE(&strtab_hdr->sh_offset) +
 204                         GET_LE(&sym->st_name);
 205
 206                 for (k = 0; k < NSYMS; k++) {
 207                         if (!strcmp(name, required_syms[k].name)) {
 208                                 if (syms[k]) {
 209                                         fail("duplicate symbol %s\n",
 210                                              required_syms[k].name);
 211                                 }
 212                                 syms[k] = GET_LE(&sym->st_value);
 213                         }
 214                 }
 215
 216                 if (!strcmp(name, "fake_shstrtab")) {
 217                         ELF(Shdr) *sh;
 218
 219                         fake_sections.in_shstrndx = GET_LE(&sym->st_shndx);
 220                         fake_sections.shstrtab = addr + GET_LE(&sym->st_value);
 221                         fake_sections.shstrtab_len = GET_LE(&sym->st_size);
 222                         sh = addr + GET_LE(&hdr->e_shoff) +
 223                                 GET_LE(&hdr->e_shentsize) *
 224                                 fake_sections.in_shstrndx;
 225                         fake_sections.shstr_offset = GET_LE(&sym->st_value) -
 226                                 GET_LE(&sh->sh_addr);
 227                 }
 228         }
 229
 230         /* Build the output section table. */
 231         if (!syms[sym_VDSO_FAKE_SECTION_TABLE_START] ||
 232             !syms[sym_VDSO_FAKE_SECTION_TABLE_END])
 233                 fail("couldn't find fake section table\n");
 234         if ((syms[sym_VDSO_FAKE_SECTION_TABLE_END] -
 235              syms[sym_VDSO_FAKE_SECTION_TABLE_START]) % sizeof(ELF(Shdr)))
 236                 fail("fake section table size isn't a multiple of sizeof(Shdr)\n");
 237         fake_sections.table = addr + syms[sym_VDSO_FAKE_SECTION_TABLE_START];
 238         fake_sections.table_offset = syms[sym_VDSO_FAKE_SECTION_TABLE_START];
 239         fake_sections.max_count = (syms[sym_VDSO_FAKE_SECTION_TABLE_END] -
 240                                    syms[sym_VDSO_FAKE_SECTION_TABLE_START]) /
 241                 sizeof(ELF(Shdr));
 242
 243         BITSFUNC(init_sections)(&fake_sections);
 244         for (i = 0; i < GET_LE(&hdr->e_shnum); i++) {
 245                 ELF(Shdr) *sh = addr + GET_LE(&hdr->e_shoff) +
 246                         GET_LE(&hdr->e_shentsize) * i;
 247                 BITSFUNC(copy_section)(&fake_sections, i, sh,
 248                                        secstrings + GET_LE(&sh->sh_name));
 249         }
 250         if (!fake_sections.out_shstrndx)
 251                 fail("didn't generate shstrndx?!?\n");
 252
 253         PUT_LE(&hdr->e_shoff, fake_sections.table_offset);
 254         PUT_LE(&hdr->e_shentsize, sizeof(ELF(Shdr)));
 255         PUT_LE(&hdr->e_shnum, fake_sections.count);
 256         PUT_LE(&hdr->e_shstrndx, fake_sections.out_shstrndx);
 257
 258         /* Validate mapping addresses. */
 259         for (i = 0; i < sizeof(special_pages) / sizeof(special_pages[0]); i++) {
 260                 if (!syms[i])
 261                         continue;  /* The mapping isn't used; ignore it. */
 262
 263                 if (syms[i] % 4096)
 264                         fail("%s must be a multiple of 4096\n",
 265                              required_syms[i].name);
 266                 if (syms[i] < data_size)
 267                         fail("%s must be after the text mapping\n",
 268                              required_syms[i].name);
 269                 if (syms[sym_end_mapping] < syms[i] + 4096)
 270                         fail("%s overruns end_mapping\n",
 271                              required_syms[i].name);
 272         }
 273         if (syms[sym_end_mapping] % 4096)
 274                 fail("end_mapping must be a multiple of 4096\n");
 275
 276         if (!name) {
 277                 fwrite(addr, load_size, 1, outfile);
 278                 return;
 279         }
 280
 281         fprintf(outfile, "/* AUTOMATICALLY GENERATED -- DO NOT EDIT */\n\n");
 282         fprintf(outfile, "#include <linux/linkage.h>\n");
 283         fprintf(outfile, "#include <asm/page_types.h>\n");
 284         fprintf(outfile, "#include <asm/vdso.h>\n");
 285         fprintf(outfile, "\n");
 286         fprintf(outfile,
 287                 "static unsigned char raw_data[%lu] __page_aligned_data = {",
 288                 data_size);
 289         for (j = 0; j < load_size; j++) {
 290                 if (j % 10 == 0)
 291                         fprintf(outfile, "\n\t");
 292                 fprintf(outfile, "0x%02X, ", (int)((unsigned char *)addr)[j]);
 293         }
 294         fprintf(outfile, "\n};\n\n");
 295
 296         fprintf(outfile, "static struct page *pages[%lu];\n\n",
 297                 data_size / 4096);
 298
 299         fprintf(outfile, "const struct vdso_image %s = {\n", name);
 300         fprintf(outfile, "\t.data = raw_data,\n");
 301         fprintf(outfile, "\t.size = %lu,\n", data_size);
 302         fprintf(outfile, "\t.text_mapping = {\n");
 303         fprintf(outfile, "\t\t.name = \"[vdso]\",\n");
 304         fprintf(outfile, "\t\t.pages = pages,\n");
 305         fprintf(outfile, "\t},\n");
 306         if (alt_sec) {
 307                 fprintf(outfile, "\t.alt = %lu,\n",
 308                         (unsigned long)GET_LE(&alt_sec->sh_offset));
 309                 fprintf(outfile, "\t.alt_len = %lu,\n",
 310                         (unsigned long)GET_LE(&alt_sec->sh_size));
 311         }
 312         for (i = 0; i < NSYMS; i++) {
 313                 if (required_syms[i].export && syms[i])
 314                         fprintf(outfile, "\t.sym_%s = 0x%" PRIx64 ",\n",
 315                                 required_syms[i].name, syms[i]);
 316         }
 317         fprintf(outfile, "};\n");
 318 }