sym_vvar_page,
sym_hpet_page,
sym_end_mapping,
+ sym_VDSO_FAKE_SECTION_TABLE_START,
+ sym_VDSO_FAKE_SECTION_TABLE_END,
};
const int special_pages[] = {
sym_hpet_page,
};
-char const * const required_syms[] = {
- [sym_vvar_page] = "vvar_page",
- [sym_hpet_page] = "hpet_page",
- [sym_end_mapping] = "end_mapping",
- "VDSO32_NOTE_MASK",
- "VDSO32_SYSENTER_RETURN",
- "__kernel_vsyscall",
- "__kernel_sigreturn",
- "__kernel_rt_sigreturn",
+struct vdso_sym {
+ const char *name;
+ bool export;
+};
+
+struct vdso_sym required_syms[] = {
+ [sym_vvar_page] = {"vvar_page", true},
+ [sym_hpet_page] = {"hpet_page", true},
+ [sym_end_mapping] = {"end_mapping", true},
+ [sym_VDSO_FAKE_SECTION_TABLE_START] = {
+ "VDSO_FAKE_SECTION_TABLE_START", false
+ },
+ [sym_VDSO_FAKE_SECTION_TABLE_END] = {
+ "VDSO_FAKE_SECTION_TABLE_END", false
+ },
+ {"VDSO32_NOTE_MASK", true},
+ {"VDSO32_SYSENTER_RETURN", true},
+ {"__kernel_vsyscall", true},
+ {"__kernel_sigreturn", true},
+ {"__kernel_rt_sigreturn", true},
};
__attribute__((format(printf, 1, 2))) __attribute__((noreturn))
* are built for 32-bit userspace.
*/
+/*
+ * 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;
+
+ 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)
{
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));
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])
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;
(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");
}
projects / GitHub / LineageOS / android_kernel_motorola_exynos9610.git / commitdiff