261 lines
7 KiB
C
261 lines
7 KiB
C
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/*
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* vdso2c - A vdso image preparation tool
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* Copyright (c) 2014 Andy Lutomirski and others
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* Licensed under the GPL v2
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*
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* vdso2c requires stripped and unstripped input. It would be trivial
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* to fully strip the input in here, but, for reasons described below,
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* we need to write a section table. Doing this is more or less
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* equivalent to dropping all non-allocatable sections, but it's
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* easier to let objcopy handle that instead of doing it ourselves.
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* If we ever need to do something fancier than what objcopy provides,
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* it would be straightforward to add here.
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*
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* We're keep 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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#include <inttypes.h>
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#include <stdint.h>
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#include <unistd.h>
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#include <stdarg.h>
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#include <stdlib.h>
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#include <stdio.h>
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#include <string.h>
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#include <fcntl.h>
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#include <err.h>
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#include <sys/mman.h>
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#include <sys/types.h>
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#include <tools/le_byteshift.h>
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#include <linux/elf.h>
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#include <linux/types.h>
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#include <linux/kernel.h>
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const char *outfilename;
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/* Symbols that we need in vdso2c. */
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enum {
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sym_vvar_start,
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sym_vvar_page,
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sym_hpet_page,
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sym_pvclock_page,
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sym_hvclock_page,
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sym_VDSO_FAKE_SECTION_TABLE_START,
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sym_VDSO_FAKE_SECTION_TABLE_END,
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};
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const int special_pages[] = {
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sym_vvar_page,
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sym_hpet_page,
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sym_pvclock_page,
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sym_hvclock_page,
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};
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struct vdso_sym {
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const char *name;
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bool export;
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};
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struct vdso_sym required_syms[] = {
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[sym_vvar_start] = {"vvar_start", true},
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[sym_vvar_page] = {"vvar_page", true},
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[sym_hpet_page] = {"hpet_page", true},
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[sym_pvclock_page] = {"pvclock_page", true},
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[sym_hvclock_page] = {"hvclock_page", true},
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[sym_VDSO_FAKE_SECTION_TABLE_START] = {
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"VDSO_FAKE_SECTION_TABLE_START", false
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},
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[sym_VDSO_FAKE_SECTION_TABLE_END] = {
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"VDSO_FAKE_SECTION_TABLE_END", false
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},
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{"VDSO32_NOTE_MASK", true},
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{"__kernel_vsyscall", true},
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{"__kernel_sigreturn", true},
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{"__kernel_rt_sigreturn", true},
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{"int80_landing_pad", true},
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};
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__attribute__((format(printf, 1, 2))) __attribute__((noreturn))
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static void fail(const char *format, ...)
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{
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va_list ap;
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va_start(ap, format);
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fprintf(stderr, "Error: ");
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vfprintf(stderr, format, ap);
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if (outfilename)
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unlink(outfilename);
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exit(1);
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va_end(ap);
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}
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/*
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* Evil macros for little-endian reads and writes
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*/
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#define GLE(x, bits, ifnot) \
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__builtin_choose_expr( \
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(sizeof(*(x)) == bits/8), \
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(__typeof__(*(x)))get_unaligned_le##bits(x), ifnot)
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extern void bad_get_le(void);
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#define LAST_GLE(x) \
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__builtin_choose_expr(sizeof(*(x)) == 1, *(x), bad_get_le())
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#define GET_LE(x) \
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GLE(x, 64, GLE(x, 32, GLE(x, 16, LAST_GLE(x))))
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#define PLE(x, val, bits, ifnot) \
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__builtin_choose_expr( \
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(sizeof(*(x)) == bits/8), \
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put_unaligned_le##bits((val), (x)), ifnot)
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extern void bad_put_le(void);
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#define LAST_PLE(x, val) \
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__builtin_choose_expr(sizeof(*(x)) == 1, *(x) = (val), bad_put_le())
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#define PUT_LE(x, val) \
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PLE(x, val, 64, PLE(x, val, 32, PLE(x, val, 16, LAST_PLE(x, val))))
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#define NSYMS ARRAY_SIZE(required_syms)
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#define BITSFUNC3(name, bits, suffix) name##bits##suffix
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#define BITSFUNC2(name, bits, suffix) BITSFUNC3(name, bits, suffix)
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#define BITSFUNC(name) BITSFUNC2(name, ELF_BITS, )
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#define INT_BITS BITSFUNC2(int, ELF_BITS, _t)
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#define ELF_BITS_XFORM2(bits, x) Elf##bits##_##x
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#define ELF_BITS_XFORM(bits, x) ELF_BITS_XFORM2(bits, x)
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#define ELF(x) ELF_BITS_XFORM(ELF_BITS, x)
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#define ELF_BITS 64
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#include "vdso2c.h"
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#undef ELF_BITS
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#define ELF_BITS 32
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#include "vdso2c.h"
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#undef ELF_BITS
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static void go(void *raw_addr, size_t raw_len,
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void *stripped_addr, size_t stripped_len,
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FILE *outfile, const char *name)
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{
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Elf64_Ehdr *hdr = (Elf64_Ehdr *)raw_addr;
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if (hdr->e_ident[EI_CLASS] == ELFCLASS64) {
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go64(raw_addr, raw_len, stripped_addr, stripped_len,
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outfile, name);
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} else if (hdr->e_ident[EI_CLASS] == ELFCLASS32) {
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go32(raw_addr, raw_len, stripped_addr, stripped_len,
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outfile, name);
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} else {
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fail("unknown ELF class\n");
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}
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}
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static void map_input(const char *name, void **addr, size_t *len, int prot)
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{
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off_t tmp_len;
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int fd = open(name, O_RDONLY);
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if (fd == -1)
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err(1, "%s", name);
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tmp_len = lseek(fd, 0, SEEK_END);
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if (tmp_len == (off_t)-1)
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err(1, "lseek");
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*len = (size_t)tmp_len;
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*addr = mmap(NULL, tmp_len, prot, MAP_PRIVATE, fd, 0);
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if (*addr == MAP_FAILED)
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err(1, "mmap");
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close(fd);
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}
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int main(int argc, char **argv)
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{
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size_t raw_len, stripped_len;
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void *raw_addr, *stripped_addr;
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FILE *outfile;
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char *name, *tmp;
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int namelen;
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if (argc != 4) {
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printf("Usage: vdso2c RAW_INPUT STRIPPED_INPUT OUTPUT\n");
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return 1;
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}
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/*
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* Figure out the struct name. If we're writing to a .so file,
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* generate raw output insted.
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*/
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name = strdup(argv[3]);
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namelen = strlen(name);
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if (namelen >= 3 && !strcmp(name + namelen - 3, ".so")) {
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name = NULL;
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} else {
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tmp = strrchr(name, '/');
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if (tmp)
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name = tmp + 1;
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tmp = strchr(name, '.');
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if (tmp)
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*tmp = '\0';
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for (tmp = name; *tmp; tmp++)
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if (*tmp == '-')
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*tmp = '_';
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}
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map_input(argv[1], &raw_addr, &raw_len, PROT_READ);
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map_input(argv[2], &stripped_addr, &stripped_len, PROT_READ);
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outfilename = argv[3];
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outfile = fopen(outfilename, "w");
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if (!outfile)
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err(1, "%s", argv[2]);
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go(raw_addr, raw_len, stripped_addr, stripped_len, outfile, name);
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munmap(raw_addr, raw_len);
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munmap(stripped_addr, stripped_len);
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fclose(outfile);
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return 0;
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}
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