blob: df95a2fdff7319821a8c68a905ece1a1be98517b [file] [log] [blame]
/*
* This file is included twice from vdso2c.c. It generates code for 32-bit
* and 64-bit vDSOs. We need both for 64-bit builds, since 32-bit vDSOs
* 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 &&
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;
int i;
unsigned long j;
ELF(Shdr) *symtab_hdr = NULL, *strtab_hdr, *secstrings_hdr,
*alt_sec = NULL;
ELF(Dyn) *dyn = 0, *dyn_end = 0;
const char *secstrings;
uint64_t syms[NSYMS] = {};
struct BITSFUNC(fake_sections) fake_sections = {};
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++) {
if (GET_LE(&pt[i].p_type) == PT_LOAD) {
if (found_load)
fail("multiple PT_LOAD segs\n");
if (GET_LE(&pt[i].p_offset) != 0 ||
GET_LE(&pt[i].p_vaddr) != 0)
fail("PT_LOAD in wrong place\n");
if (GET_LE(&pt[i].p_memsz) != GET_LE(&pt[i].p_filesz))
fail("cannot handle memsz != filesz\n");
load_size = GET_LE(&pt[i].p_memsz);
found_load = 1;
} else if (GET_LE(&pt[i].p_type) == PT_DYNAMIC) {
dyn = addr + GET_LE(&pt[i].p_offset);
dyn_end = addr + GET_LE(&pt[i].p_offset) +
GET_LE(&pt[i].p_memsz);
}
}
if (!found_load)
fail("no PT_LOAD seg\n");
data_size = (load_size + 4095) / 4096 * 4096;
/* Walk the dynamic table */
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 || tag == DT_RELA ||
tag == DT_RELENT || tag == DT_TEXTREL)
fail("vdso image contains dynamic relocations\n");
}
/* Walk the section table */
secstrings_hdr = addr + GET_LE(&hdr->e_shoff) +
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) +
GET_LE(&hdr->e_shentsize) * i;
if (GET_LE(&sh->sh_type) == SHT_SYMTAB)
symtab_hdr = sh;
if (!strcmp(secstrings + GET_LE(&sh->sh_name),
".altinstructions"))
alt_sec = sh;
}
if (!symtab_hdr)
fail("no symbol table\n");
strtab_hdr = addr + GET_LE(&hdr->e_shoff) +
GET_LE(&hdr->e_shentsize) * GET_LE(&symtab_hdr->sh_link);
/* Walk the symbol table */
for (i = 0;
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) +
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].name)) {
if (syms[k]) {
fail("duplicate symbol %s\n",
required_syms[k].name);
}
syms[k] = GET_LE(&sym->st_value);
}
}
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])
continue; /* The mapping isn't used; ignore it. */
if (syms[i] % 4096)
fail("%s must be a multiple of 4096\n",
required_syms[i].name);
if (syms[i] < data_size)
fail("%s must be after the text mapping\n",
required_syms[i].name);
if (syms[sym_end_mapping] < syms[i] + 4096)
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");
if (!name) {
fwrite(addr, load_size, 1, outfile);
return;
}
fprintf(outfile, "/* AUTOMATICALLY GENERATED -- DO NOT EDIT */\n\n");
fprintf(outfile, "#include <linux/linkage.h>\n");
fprintf(outfile, "#include <asm/page_types.h>\n");
fprintf(outfile, "#include <asm/vdso.h>\n");
fprintf(outfile, "\n");
fprintf(outfile,
"static unsigned char raw_data[%lu] __page_aligned_data = {",
data_size);
for (j = 0; j < load_size; j++) {
if (j % 10 == 0)
fprintf(outfile, "\n\t");
fprintf(outfile, "0x%02X, ", (int)((unsigned char *)addr)[j]);
}
fprintf(outfile, "\n};\n\n");
fprintf(outfile, "static struct page *pages[%lu];\n\n",
data_size / 4096);
fprintf(outfile, "const struct vdso_image %s = {\n", name);
fprintf(outfile, "\t.data = raw_data,\n");
fprintf(outfile, "\t.size = %lu,\n", data_size);
fprintf(outfile, "\t.text_mapping = {\n");
fprintf(outfile, "\t\t.name = \"[vdso]\",\n");
fprintf(outfile, "\t\t.pages = pages,\n");
fprintf(outfile, "\t},\n");
if (alt_sec) {
fprintf(outfile, "\t.alt = %lu,\n",
(unsigned long)GET_LE(&alt_sec->sh_offset));
fprintf(outfile, "\t.alt_len = %lu,\n",
(unsigned long)GET_LE(&alt_sec->sh_size));
}
for (i = 0; i < NSYMS; i++) {
if (required_syms[i].export && syms[i])
fprintf(outfile, "\t.sym_%s = 0x%" PRIx64 ",\n",
required_syms[i].name, syms[i]);
}
fprintf(outfile, "};\n");
}