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@@ -4,23 +4,136 @@
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* are built for 32-bit userspace.
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*/
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-static void GOFUNC(void *addr, size_t len, FILE *outfile, const char *name)
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+/*
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+ * We're writing a section table for a few reasons:
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+ *
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+ * The Go runtime had a couple of bugs: it would read the section
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+ * table to try to figure out how many dynamic symbols there were (it
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+ * shouldn't have looked at the section table at all) and, if there
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+ * were no SHT_SYNDYM section table entry, it would use an
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+ * uninitialized value for the number of symbols. An empty DYNSYM
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+ * table would work, but I see no reason not to write a valid one (and
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+ * keep full performance for old Go programs). This hack is only
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+ * needed on x86_64.
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+ *
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+ * The bug was introduced on 2012-08-31 by:
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+ * https://code.google.com/p/go/source/detail?r=56ea40aac72b
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+ * and was fixed on 2014-06-13 by:
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+ * https://code.google.com/p/go/source/detail?r=fc1cd5e12595
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+ *
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+ * Binutils has issues debugging the vDSO: it reads the section table to
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+ * find SHT_NOTE; it won't look at PT_NOTE for the in-memory vDSO, which
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+ * would break build-id if we removed the section table. Binutils
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+ * also requires that shstrndx != 0. See:
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+ * https://sourceware.org/bugzilla/show_bug.cgi?id=17064
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+ *
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+ * elfutils might not look for PT_NOTE if there is a section table at
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+ * all. I don't know whether this matters for any practical purpose.
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+ *
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+ * For simplicity, rather than hacking up a partial section table, we
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+ * just write a mostly complete one. We omit non-dynamic symbols,
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+ * though, since they're rather large.
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+ *
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+ * Once binutils gets fixed, we might be able to drop this for all but
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+ * the 64-bit vdso, since build-id only works in kernel RPMs, and
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+ * systems that update to new enough kernel RPMs will likely update
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+ * binutils in sync. build-id has never worked for home-built kernel
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+ * RPMs without manual symlinking, and I suspect that no one ever does
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+ * that.
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+ */
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+struct BITSFUNC(fake_sections)
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+{
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+ ELF(Shdr) *table;
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+ unsigned long table_offset;
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+ int count, max_count;
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+
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+ int in_shstrndx;
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+ unsigned long shstr_offset;
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+ const char *shstrtab;
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+ size_t shstrtab_len;
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+
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+ int out_shstrndx;
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+};
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+
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+static unsigned int BITSFUNC(find_shname)(struct BITSFUNC(fake_sections) *out,
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+ const char *name)
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+{
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+ const char *outname = out->shstrtab;
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+ while (outname - out->shstrtab < out->shstrtab_len) {
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+ if (!strcmp(name, outname))
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+ return (outname - out->shstrtab) + out->shstr_offset;
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+ outname += strlen(outname) + 1;
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+ }
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+
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+ if (*name)
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+ printf("Warning: could not find output name \"%s\"\n", name);
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+ return out->shstr_offset + out->shstrtab_len - 1; /* Use a null. */
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+}
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+
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+static void BITSFUNC(init_sections)(struct BITSFUNC(fake_sections) *out)
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+{
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+ if (!out->in_shstrndx)
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+ fail("didn't find the fake shstrndx\n");
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+
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+ memset(out->table, 0, out->max_count * sizeof(ELF(Shdr)));
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+
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+ if (out->max_count < 1)
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+ fail("we need at least two fake output sections\n");
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+
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+ PUT_LE(&out->table[0].sh_type, SHT_NULL);
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+ PUT_LE(&out->table[0].sh_name, BITSFUNC(find_shname)(out, ""));
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+
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+ out->count = 1;
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+}
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+
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+static void BITSFUNC(copy_section)(struct BITSFUNC(fake_sections) *out,
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+ int in_idx, const ELF(Shdr) *in,
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+ const char *name)
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+{
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+ uint64_t flags = GET_LE(&in->sh_flags);
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+
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+ bool copy = flags & SHF_ALLOC &&
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+ strcmp(name, ".altinstructions") &&
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+ strcmp(name, ".altinstr_replacement");
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+
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+ if (!copy)
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+ return;
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+
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+ if (out->count >= out->max_count)
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+ fail("too many copied sections (max = %d)\n", out->max_count);
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+
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+ if (in_idx == out->in_shstrndx)
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+ out->out_shstrndx = out->count;
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+
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+ out->table[out->count] = *in;
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+ PUT_LE(&out->table[out->count].sh_name,
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+ BITSFUNC(find_shname)(out, name));
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+
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+ /* elfutils requires that a strtab have the correct type. */
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+ if (!strcmp(name, ".fake_shstrtab"))
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+ PUT_LE(&out->table[out->count].sh_type, SHT_STRTAB);
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+
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+ out->count++;
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+}
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+
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+static void BITSFUNC(go)(void *addr, size_t len,
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+ FILE *outfile, const char *name)
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{
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int found_load = 0;
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unsigned long load_size = -1; /* Work around bogus warning */
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unsigned long data_size;
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- Elf_Ehdr *hdr = (Elf_Ehdr *)addr;
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+ ELF(Ehdr) *hdr = (ELF(Ehdr) *)addr;
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int i;
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unsigned long j;
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- Elf_Shdr *symtab_hdr = NULL, *strtab_hdr, *secstrings_hdr,
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+ ELF(Shdr) *symtab_hdr = NULL, *strtab_hdr, *secstrings_hdr,
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*alt_sec = NULL;
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- Elf_Dyn *dyn = 0, *dyn_end = 0;
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+ ELF(Dyn) *dyn = 0, *dyn_end = 0;
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const char *secstrings;
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uint64_t syms[NSYMS] = {};
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- uint64_t fake_sections_value = 0, fake_sections_size = 0;
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+ struct BITSFUNC(fake_sections) fake_sections = {};
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- Elf_Phdr *pt = (Elf_Phdr *)(addr + GET_LE(&hdr->e_phoff));
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+ ELF(Phdr) *pt = (ELF(Phdr) *)(addr + GET_LE(&hdr->e_phoff));
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/* Walk the segment table. */
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for (i = 0; i < GET_LE(&hdr->e_phnum); i++) {
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@@ -51,7 +164,7 @@ static void GOFUNC(void *addr, size_t len, FILE *outfile, const char *name)
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for (i = 0; dyn + i < dyn_end &&
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GET_LE(&dyn[i].d_tag) != DT_NULL; i++) {
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typeof(dyn[i].d_tag) tag = GET_LE(&dyn[i].d_tag);
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- if (tag == DT_REL || tag == DT_RELSZ ||
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+ if (tag == DT_REL || tag == DT_RELSZ || tag == DT_RELA ||
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tag == DT_RELENT || tag == DT_TEXTREL)
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fail("vdso image contains dynamic relocations\n");
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}
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@@ -61,7 +174,7 @@ static void GOFUNC(void *addr, size_t len, FILE *outfile, const char *name)
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GET_LE(&hdr->e_shentsize)*GET_LE(&hdr->e_shstrndx);
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secstrings = addr + GET_LE(&secstrings_hdr->sh_offset);
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for (i = 0; i < GET_LE(&hdr->e_shnum); i++) {
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- Elf_Shdr *sh = addr + GET_LE(&hdr->e_shoff) +
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+ ELF(Shdr) *sh = addr + GET_LE(&hdr->e_shoff) +
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GET_LE(&hdr->e_shentsize) * i;
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if (GET_LE(&sh->sh_type) == SHT_SYMTAB)
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symtab_hdr = sh;
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@@ -82,29 +195,63 @@ static void GOFUNC(void *addr, size_t len, FILE *outfile, const char *name)
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i < GET_LE(&symtab_hdr->sh_size) / GET_LE(&symtab_hdr->sh_entsize);
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i++) {
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int k;
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- Elf_Sym *sym = addr + GET_LE(&symtab_hdr->sh_offset) +
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+ ELF(Sym) *sym = addr + GET_LE(&symtab_hdr->sh_offset) +
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GET_LE(&symtab_hdr->sh_entsize) * i;
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const char *name = addr + GET_LE(&strtab_hdr->sh_offset) +
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GET_LE(&sym->st_name);
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for (k = 0; k < NSYMS; k++) {
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- if (!strcmp(name, required_syms[k])) {
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+ if (!strcmp(name, required_syms[k].name)) {
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if (syms[k]) {
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fail("duplicate symbol %s\n",
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- required_syms[k]);
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+ required_syms[k].name);
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}
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syms[k] = GET_LE(&sym->st_value);
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}
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}
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- if (!strcmp(name, "vdso_fake_sections")) {
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- if (fake_sections_value)
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- fail("duplicate vdso_fake_sections\n");
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- fake_sections_value = GET_LE(&sym->st_value);
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- fake_sections_size = GET_LE(&sym->st_size);
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+ if (!strcmp(name, "fake_shstrtab")) {
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+ ELF(Shdr) *sh;
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+
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+ fake_sections.in_shstrndx = GET_LE(&sym->st_shndx);
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+ fake_sections.shstrtab = addr + GET_LE(&sym->st_value);
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+ fake_sections.shstrtab_len = GET_LE(&sym->st_size);
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+ sh = addr + GET_LE(&hdr->e_shoff) +
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+ GET_LE(&hdr->e_shentsize) *
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+ fake_sections.in_shstrndx;
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+ fake_sections.shstr_offset = GET_LE(&sym->st_value) -
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+ GET_LE(&sh->sh_addr);
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}
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}
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+ /* Build the output section table. */
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+ if (!syms[sym_VDSO_FAKE_SECTION_TABLE_START] ||
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+ !syms[sym_VDSO_FAKE_SECTION_TABLE_END])
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+ fail("couldn't find fake section table\n");
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+ if ((syms[sym_VDSO_FAKE_SECTION_TABLE_END] -
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+ syms[sym_VDSO_FAKE_SECTION_TABLE_START]) % sizeof(ELF(Shdr)))
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+ fail("fake section table size isn't a multiple of sizeof(Shdr)\n");
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+ fake_sections.table = addr + syms[sym_VDSO_FAKE_SECTION_TABLE_START];
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+ fake_sections.table_offset = syms[sym_VDSO_FAKE_SECTION_TABLE_START];
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+ fake_sections.max_count = (syms[sym_VDSO_FAKE_SECTION_TABLE_END] -
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+ syms[sym_VDSO_FAKE_SECTION_TABLE_START]) /
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+ sizeof(ELF(Shdr));
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+
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+ BITSFUNC(init_sections)(&fake_sections);
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+ for (i = 0; i < GET_LE(&hdr->e_shnum); i++) {
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+ ELF(Shdr) *sh = addr + GET_LE(&hdr->e_shoff) +
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+ GET_LE(&hdr->e_shentsize) * i;
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+ BITSFUNC(copy_section)(&fake_sections, i, sh,
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+ secstrings + GET_LE(&sh->sh_name));
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+ }
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+ if (!fake_sections.out_shstrndx)
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+ fail("didn't generate shstrndx?!?\n");
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+
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+ PUT_LE(&hdr->e_shoff, fake_sections.table_offset);
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+ PUT_LE(&hdr->e_shentsize, sizeof(ELF(Shdr)));
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+ PUT_LE(&hdr->e_shnum, fake_sections.count);
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+ PUT_LE(&hdr->e_shstrndx, fake_sections.out_shstrndx);
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+
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/* Validate mapping addresses. */
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for (i = 0; i < sizeof(special_pages) / sizeof(special_pages[0]); i++) {
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if (!syms[i])
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@@ -112,25 +259,17 @@ static void GOFUNC(void *addr, size_t len, FILE *outfile, const char *name)
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if (syms[i] % 4096)
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fail("%s must be a multiple of 4096\n",
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- required_syms[i]);
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+ required_syms[i].name);
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if (syms[i] < data_size)
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fail("%s must be after the text mapping\n",
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- required_syms[i]);
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+ required_syms[i].name);
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if (syms[sym_end_mapping] < syms[i] + 4096)
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- fail("%s overruns end_mapping\n", required_syms[i]);
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+ fail("%s overruns end_mapping\n",
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+ required_syms[i].name);
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}
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if (syms[sym_end_mapping] % 4096)
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fail("end_mapping must be a multiple of 4096\n");
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- /* Remove sections or use fakes */
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- if (fake_sections_size % sizeof(Elf_Shdr))
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- fail("vdso_fake_sections size is not a multiple of %ld\n",
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- (long)sizeof(Elf_Shdr));
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- PUT_LE(&hdr->e_shoff, fake_sections_value);
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- PUT_LE(&hdr->e_shentsize, fake_sections_value ? sizeof(Elf_Shdr) : 0);
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- PUT_LE(&hdr->e_shnum, fake_sections_size / sizeof(Elf_Shdr));
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- PUT_LE(&hdr->e_shstrndx, SHN_UNDEF);
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-
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if (!name) {
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fwrite(addr, load_size, 1, outfile);
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return;
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@@ -168,9 +307,9 @@ static void GOFUNC(void *addr, size_t len, FILE *outfile, const char *name)
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(unsigned long)GET_LE(&alt_sec->sh_size));
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}
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for (i = 0; i < NSYMS; i++) {
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- if (syms[i])
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+ if (required_syms[i].export && syms[i])
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fprintf(outfile, "\t.sym_%s = 0x%" PRIx64 ",\n",
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- required_syms[i], syms[i]);
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+ required_syms[i].name, syms[i]);
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}
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fprintf(outfile, "};\n");
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}
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Linus Torvalds