diff options
Diffstat (limited to 'arch/x86/vdso/vdso2c.h')
-rw-r--r-- | arch/x86/vdso/vdso2c.h | 202 |
1 files changed, 172 insertions, 30 deletions
diff --git a/arch/x86/vdso/vdso2c.h b/arch/x86/vdso/vdso2c.h index c6eefaf..11b65d4 100644 --- a/arch/x86/vdso/vdso2c.h +++ b/arch/x86/vdso/vdso2c.h @@ -4,23 +4,139 @@ * are built for 32-bit userspace. */ -static void GOFUNC(void *addr, size_t len, FILE *outfile, const char *name) +/* + * We're writing a section table for a few reasons: + * + * The Go runtime had a couple of bugs: it would read the section + * table to try to figure out how many dynamic symbols there were (it + * shouldn't have looked at the section table at all) and, if there + * were no SHT_SYNDYM section table entry, it would use an + * uninitialized value for the number of symbols. An empty DYNSYM + * table would work, but I see no reason not to write a valid one (and + * keep full performance for old Go programs). This hack is only + * needed on x86_64. + * + * The bug was introduced on 2012-08-31 by: + * https://code.google.com/p/go/source/detail?r=56ea40aac72b + * and was fixed on 2014-06-13 by: + * https://code.google.com/p/go/source/detail?r=fc1cd5e12595 + * + * Binutils has issues debugging the vDSO: it reads the section table to + * find SHT_NOTE; it won't look at PT_NOTE for the in-memory vDSO, which + * would break build-id if we removed the section table. Binutils + * also requires that shstrndx != 0. See: + * https://sourceware.org/bugzilla/show_bug.cgi?id=17064 + * + * elfutils might not look for PT_NOTE if there is a section table at + * all. I don't know whether this matters for any practical purpose. + * + * For simplicity, rather than hacking up a partial section table, we + * just write a mostly complete one. We omit non-dynamic symbols, + * though, since they're rather large. + * + * Once binutils gets fixed, we might be able to drop this for all but + * the 64-bit vdso, since build-id only works in kernel RPMs, and + * systems that update to new enough kernel RPMs will likely update + * binutils in sync. build-id has never worked for home-built kernel + * RPMs without manual symlinking, and I suspect that no one ever does + * that. + */ +struct BITSFUNC(fake_sections) +{ + ELF(Shdr) *table; + unsigned long table_offset; + int count, max_count; + + int in_shstrndx; + unsigned long shstr_offset; + const char *shstrtab; + size_t shstrtab_len; + + int out_shstrndx; +}; + +static unsigned int BITSFUNC(find_shname)(struct BITSFUNC(fake_sections) *out, + const char *name) +{ + const char *outname = out->shstrtab; + while (outname - out->shstrtab < out->shstrtab_len) { + if (!strcmp(name, outname)) + return (outname - out->shstrtab) + out->shstr_offset; + outname += strlen(outname) + 1; + } + + if (*name) + printf("Warning: could not find output name \"%s\"\n", name); + return out->shstr_offset + out->shstrtab_len - 1; /* Use a null. */ +} + +static void BITSFUNC(init_sections)(struct BITSFUNC(fake_sections) *out) +{ + if (!out->in_shstrndx) + fail("didn't find the fake shstrndx\n"); + + memset(out->table, 0, out->max_count * sizeof(ELF(Shdr))); + + if (out->max_count < 1) + fail("we need at least two fake output sections\n"); + + PUT_LE(&out->table[0].sh_type, SHT_NULL); + PUT_LE(&out->table[0].sh_name, BITSFUNC(find_shname)(out, "")); + + out->count = 1; +} + +static void BITSFUNC(copy_section)(struct BITSFUNC(fake_sections) *out, + int in_idx, const ELF(Shdr) *in, + const char *name) +{ + uint64_t flags = GET_LE(&in->sh_flags); + + bool copy = flags & SHF_ALLOC && + (GET_LE(&in->sh_size) || + (GET_LE(&in->sh_type) != SHT_RELA && + GET_LE(&in->sh_type) != SHT_REL)) && + strcmp(name, ".altinstructions") && + strcmp(name, ".altinstr_replacement"); + + if (!copy) + return; + + if (out->count >= out->max_count) + fail("too many copied sections (max = %d)\n", out->max_count); + + if (in_idx == out->in_shstrndx) + out->out_shstrndx = out->count; + + out->table[out->count] = *in; + PUT_LE(&out->table[out->count].sh_name, + BITSFUNC(find_shname)(out, name)); + + /* elfutils requires that a strtab have the correct type. */ + if (!strcmp(name, ".fake_shstrtab")) + PUT_LE(&out->table[out->count].sh_type, SHT_STRTAB); + + out->count++; +} + +static void BITSFUNC(go)(void *addr, size_t len, + FILE *outfile, const char *name) { int found_load = 0; unsigned long load_size = -1; /* Work around bogus warning */ unsigned long data_size; - Elf_Ehdr *hdr = (Elf_Ehdr *)addr; + ELF(Ehdr) *hdr = (ELF(Ehdr) *)addr; int i; unsigned long j; - Elf_Shdr *symtab_hdr = NULL, *strtab_hdr, *secstrings_hdr, + ELF(Shdr) *symtab_hdr = NULL, *strtab_hdr, *secstrings_hdr, *alt_sec = NULL; - Elf_Dyn *dyn = 0, *dyn_end = 0; + ELF(Dyn) *dyn = 0, *dyn_end = 0; const char *secstrings; uint64_t syms[NSYMS] = {}; - uint64_t fake_sections_value = 0, fake_sections_size = 0; + struct BITSFUNC(fake_sections) fake_sections = {}; - Elf_Phdr *pt = (Elf_Phdr *)(addr + GET_LE(&hdr->e_phoff)); + ELF(Phdr) *pt = (ELF(Phdr) *)(addr + GET_LE(&hdr->e_phoff)); /* Walk the segment table. */ for (i = 0; i < GET_LE(&hdr->e_phnum); i++) { @@ -51,7 +167,7 @@ static void GOFUNC(void *addr, size_t len, FILE *outfile, const char *name) for (i = 0; dyn + i < dyn_end && GET_LE(&dyn[i].d_tag) != DT_NULL; i++) { typeof(dyn[i].d_tag) tag = GET_LE(&dyn[i].d_tag); - if (tag == DT_REL || tag == DT_RELSZ || + if (tag == DT_REL || tag == DT_RELSZ || tag == DT_RELA || tag == DT_RELENT || tag == DT_TEXTREL) fail("vdso image contains dynamic relocations\n"); } @@ -61,7 +177,7 @@ static void GOFUNC(void *addr, size_t len, FILE *outfile, const char *name) GET_LE(&hdr->e_shentsize)*GET_LE(&hdr->e_shstrndx); secstrings = addr + GET_LE(&secstrings_hdr->sh_offset); for (i = 0; i < GET_LE(&hdr->e_shnum); i++) { - Elf_Shdr *sh = addr + GET_LE(&hdr->e_shoff) + + ELF(Shdr) *sh = addr + GET_LE(&hdr->e_shoff) + GET_LE(&hdr->e_shentsize) * i; if (GET_LE(&sh->sh_type) == SHT_SYMTAB) symtab_hdr = sh; @@ -82,29 +198,63 @@ static void GOFUNC(void *addr, size_t len, FILE *outfile, const char *name) i < GET_LE(&symtab_hdr->sh_size) / GET_LE(&symtab_hdr->sh_entsize); i++) { int k; - Elf_Sym *sym = addr + GET_LE(&symtab_hdr->sh_offset) + + ELF(Sym) *sym = addr + GET_LE(&symtab_hdr->sh_offset) + GET_LE(&symtab_hdr->sh_entsize) * i; const char *name = addr + GET_LE(&strtab_hdr->sh_offset) + GET_LE(&sym->st_name); for (k = 0; k < NSYMS; k++) { - if (!strcmp(name, required_syms[k])) { + if (!strcmp(name, required_syms[k].name)) { if (syms[k]) { fail("duplicate symbol %s\n", - required_syms[k]); + required_syms[k].name); } syms[k] = GET_LE(&sym->st_value); } } - if (!strcmp(name, "vdso_fake_sections")) { - if (fake_sections_value) - fail("duplicate vdso_fake_sections\n"); - fake_sections_value = GET_LE(&sym->st_value); - fake_sections_size = GET_LE(&sym->st_size); + if (!strcmp(name, "fake_shstrtab")) { + ELF(Shdr) *sh; + + fake_sections.in_shstrndx = GET_LE(&sym->st_shndx); + fake_sections.shstrtab = addr + GET_LE(&sym->st_value); + fake_sections.shstrtab_len = GET_LE(&sym->st_size); + sh = addr + GET_LE(&hdr->e_shoff) + + GET_LE(&hdr->e_shentsize) * + fake_sections.in_shstrndx; + fake_sections.shstr_offset = GET_LE(&sym->st_value) - + GET_LE(&sh->sh_addr); } } + /* Build the output section table. */ + if (!syms[sym_VDSO_FAKE_SECTION_TABLE_START] || + !syms[sym_VDSO_FAKE_SECTION_TABLE_END]) + fail("couldn't find fake section table\n"); + if ((syms[sym_VDSO_FAKE_SECTION_TABLE_END] - + syms[sym_VDSO_FAKE_SECTION_TABLE_START]) % sizeof(ELF(Shdr))) + fail("fake section table size isn't a multiple of sizeof(Shdr)\n"); + fake_sections.table = addr + syms[sym_VDSO_FAKE_SECTION_TABLE_START]; + fake_sections.table_offset = syms[sym_VDSO_FAKE_SECTION_TABLE_START]; + fake_sections.max_count = (syms[sym_VDSO_FAKE_SECTION_TABLE_END] - + syms[sym_VDSO_FAKE_SECTION_TABLE_START]) / + sizeof(ELF(Shdr)); + + BITSFUNC(init_sections)(&fake_sections); + for (i = 0; i < GET_LE(&hdr->e_shnum); i++) { + ELF(Shdr) *sh = addr + GET_LE(&hdr->e_shoff) + + GET_LE(&hdr->e_shentsize) * i; + BITSFUNC(copy_section)(&fake_sections, i, sh, + secstrings + GET_LE(&sh->sh_name)); + } + if (!fake_sections.out_shstrndx) + fail("didn't generate shstrndx?!?\n"); + + PUT_LE(&hdr->e_shoff, fake_sections.table_offset); + PUT_LE(&hdr->e_shentsize, sizeof(ELF(Shdr))); + PUT_LE(&hdr->e_shnum, fake_sections.count); + PUT_LE(&hdr->e_shstrndx, fake_sections.out_shstrndx); + /* Validate mapping addresses. */ for (i = 0; i < sizeof(special_pages) / sizeof(special_pages[0]); i++) { if (!syms[i]) @@ -112,25 +262,17 @@ static void GOFUNC(void *addr, size_t len, FILE *outfile, const char *name) if (syms[i] % 4096) fail("%s must be a multiple of 4096\n", - required_syms[i]); + required_syms[i].name); if (syms[i] < data_size) fail("%s must be after the text mapping\n", - required_syms[i]); + required_syms[i].name); if (syms[sym_end_mapping] < syms[i] + 4096) - fail("%s overruns end_mapping\n", required_syms[i]); + fail("%s overruns end_mapping\n", + required_syms[i].name); } if (syms[sym_end_mapping] % 4096) fail("end_mapping must be a multiple of 4096\n"); - /* Remove sections or use fakes */ - if (fake_sections_size % sizeof(Elf_Shdr)) - fail("vdso_fake_sections size is not a multiple of %ld\n", - (long)sizeof(Elf_Shdr)); - PUT_LE(&hdr->e_shoff, fake_sections_value); - PUT_LE(&hdr->e_shentsize, fake_sections_value ? sizeof(Elf_Shdr) : 0); - PUT_LE(&hdr->e_shnum, fake_sections_size / sizeof(Elf_Shdr)); - PUT_LE(&hdr->e_shstrndx, SHN_UNDEF); - if (!name) { fwrite(addr, load_size, 1, outfile); return; @@ -168,9 +310,9 @@ static void GOFUNC(void *addr, size_t len, FILE *outfile, const char *name) (unsigned long)GET_LE(&alt_sec->sh_size)); } for (i = 0; i < NSYMS; i++) { - if (syms[i]) + if (required_syms[i].export && syms[i]) fprintf(outfile, "\t.sym_%s = 0x%" PRIx64 ",\n", - required_syms[i], syms[i]); + required_syms[i].name, syms[i]); } fprintf(outfile, "};\n"); } |