diff options
Diffstat (limited to 'arch/x86/vdso/vdso2c.c')
| -rw-r--r-- | arch/x86/vdso/vdso2c.c | 128 |
1 files changed, 98 insertions, 30 deletions
diff --git a/arch/x86/vdso/vdso2c.c b/arch/x86/vdso/vdso2c.c index 238dbe82..8627db2 100644 --- a/arch/x86/vdso/vdso2c.c +++ b/arch/x86/vdso/vdso2c.c @@ -1,3 +1,53 @@ +/* + * vdso2c - A vdso image preparation tool + * Copyright (c) 2014 Andy Lutomirski and others + * Licensed under the GPL v2 + * + * vdso2c requires stripped and unstripped input. It would be trivial + * to fully strip the input in here, but, for reasons described below, + * we need to write a section table. Doing this is more or less + * equivalent to dropping all non-allocatable sections, but it's + * easier to let objcopy handle that instead of doing it ourselves. + * If we ever need to do something fancier than what objcopy provides, + * it would be straightforward to add here. + * + * We're keep 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. + */ + #include <inttypes.h> #include <stdint.h> #include <unistd.h> @@ -20,9 +70,9 @@ const char *outfilename; /* Symbols that we need in vdso2c. */ enum { + sym_vvar_start, sym_vvar_page, sym_hpet_page, - sym_end_mapping, sym_VDSO_FAKE_SECTION_TABLE_START, sym_VDSO_FAKE_SECTION_TABLE_END, }; @@ -38,9 +88,9 @@ struct vdso_sym { }; struct vdso_sym required_syms[] = { + [sym_vvar_start] = {"vvar_start", true}, [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 }, @@ -61,7 +111,8 @@ static void fail(const char *format, ...) va_start(ap, format); fprintf(stderr, "Error: "); vfprintf(stderr, format, ap); - unlink(outfilename); + if (outfilename) + unlink(outfilename); exit(1); va_end(ap); } @@ -96,9 +147,11 @@ extern void bad_put_le(void); #define NSYMS (sizeof(required_syms) / sizeof(required_syms[0])) -#define BITSFUNC3(name, bits) name##bits -#define BITSFUNC2(name, bits) BITSFUNC3(name, bits) -#define BITSFUNC(name) BITSFUNC2(name, ELF_BITS) +#define BITSFUNC3(name, bits, suffix) name##bits##suffix +#define BITSFUNC2(name, bits, suffix) BITSFUNC3(name, bits, suffix) +#define BITSFUNC(name) BITSFUNC2(name, ELF_BITS, ) + +#define INT_BITS BITSFUNC2(int, ELF_BITS, _t) #define ELF_BITS_XFORM2(bits, x) Elf##bits##_##x #define ELF_BITS_XFORM(bits, x) ELF_BITS_XFORM2(bits, x) @@ -112,30 +165,53 @@ extern void bad_put_le(void); #include "vdso2c.h" #undef ELF_BITS -static void go(void *addr, size_t len, FILE *outfile, const char *name) +static void go(void *raw_addr, size_t raw_len, + void *stripped_addr, size_t stripped_len, + FILE *outfile, const char *name) { - Elf64_Ehdr *hdr = (Elf64_Ehdr *)addr; + Elf64_Ehdr *hdr = (Elf64_Ehdr *)raw_addr; if (hdr->e_ident[EI_CLASS] == ELFCLASS64) { - go64(addr, len, outfile, name); + go64(raw_addr, raw_len, stripped_addr, stripped_len, + outfile, name); } else if (hdr->e_ident[EI_CLASS] == ELFCLASS32) { - go32(addr, len, outfile, name); + go32(raw_addr, raw_len, stripped_addr, stripped_len, + outfile, name); } else { fail("unknown ELF class\n"); } } +static void map_input(const char *name, void **addr, size_t *len, int prot) +{ + off_t tmp_len; + + int fd = open(name, O_RDONLY); + if (fd == -1) + err(1, "%s", name); + + tmp_len = lseek(fd, 0, SEEK_END); + if (tmp_len == (off_t)-1) + err(1, "lseek"); + *len = (size_t)tmp_len; + + *addr = mmap(NULL, tmp_len, prot, MAP_PRIVATE, fd, 0); + if (*addr == MAP_FAILED) + err(1, "mmap"); + + close(fd); +} + int main(int argc, char **argv) { - int fd; - off_t len; - void *addr; + size_t raw_len, stripped_len; + void *raw_addr, *stripped_addr; FILE *outfile; char *name, *tmp; int namelen; - if (argc != 3) { - printf("Usage: vdso2c INPUT OUTPUT\n"); + if (argc != 4) { + printf("Usage: vdso2c RAW_INPUT STRIPPED_INPUT OUTPUT\n"); return 1; } @@ -143,7 +219,7 @@ int main(int argc, char **argv) * Figure out the struct name. If we're writing to a .so file, * generate raw output insted. */ - name = strdup(argv[2]); + name = strdup(argv[3]); namelen = strlen(name); if (namelen >= 3 && !strcmp(name + namelen - 3, ".so")) { name = NULL; @@ -159,26 +235,18 @@ int main(int argc, char **argv) *tmp = '_'; } - fd = open(argv[1], O_RDONLY); - if (fd == -1) - err(1, "%s", argv[1]); - - len = lseek(fd, 0, SEEK_END); - if (len == (off_t)-1) - err(1, "lseek"); - - addr = mmap(NULL, len, PROT_READ | PROT_WRITE, MAP_PRIVATE, fd, 0); - if (addr == MAP_FAILED) - err(1, "mmap"); + map_input(argv[1], &raw_addr, &raw_len, PROT_READ); + map_input(argv[2], &stripped_addr, &stripped_len, PROT_READ); - outfilename = argv[2]; + outfilename = argv[3]; outfile = fopen(outfilename, "w"); if (!outfile) err(1, "%s", argv[2]); - go(addr, (size_t)len, outfile, name); + go(raw_addr, raw_len, stripped_addr, stripped_len, outfile, name); - munmap(addr, len); + munmap(raw_addr, raw_len); + munmap(stripped_addr, stripped_len); fclose(outfile); return 0; |
