cosmopolitan/libc/runtime/finddebugbinary.c

/*-*- mode:c;indent-tabs-mode:nil;c-basic-offset:2;tab-width:8;coding:utf-8 -*-│
│vi: set net ft=c ts=2 sts=2 sw=2 fenc=utf-8                                :vi│
╞══════════════════════════════════════════════════════════════════════════════╡
│ Copyright 2020 Justine Alexandra Roberts Tunney                              │
│                                                                              │
│ Permission to use, copy, modify, and/or distribute this software for         │
│ any purpose with or without fee is hereby granted, provided that the         │
│ above copyright notice and this permission notice appear in all copies.      │
│                                                                              │
│ THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL                │
│ WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED                │
│ WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE             │
│ AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL         │
│ DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR        │
│ PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER               │
│ TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR             │
│ PERFORMANCE OF THIS SOFTWARE.                                                │
╚─────────────────────────────────────────────────────────────────────────────*/
#include "ape/sections.internal.h"
#include "libc/calls/calls.h"
#include "libc/elf/def.h"
#include "libc/elf/elf.h"
#include "libc/elf/struct/ehdr.h"
#include "libc/elf/struct/sym.h"
#include "libc/errno.h"
#include "libc/intrin/bits.h"
#include "libc/macros.internal.h"
#include "libc/runtime/runtime.h"
#include "libc/runtime/symbols.internal.h"
#include "libc/str/str.h"
#include "libc/sysv/consts/map.h"
#include "libc/sysv/consts/o.h"
#include "libc/sysv/consts/prot.h"

static bool GetElfSymbolValue(const Elf64_Ehdr *ehdr, size_t esize,
                              const char *name, uint64_t *res) {
  Elf64_Xword i, n;
  const char *stab;
  const Elf64_Sym *st;
  if ((stab = GetElfStringTable(ehdr, esize)) &&
      (st = GetElfSymbolTable(ehdr, esize, &n))) {
    for (i = 0; i < n; ++i) {
      if (!strcmp(stab + st[i].st_name, name)) {
        *res = st[i].st_value;
        return true;
      }
    }
  }
  return false;
}

static bool IsMyDebugBinaryImpl(const char *path) {
  int fd;
  void *map;
  int64_t size;
  uintptr_t value;
  bool res = false;
  if ((fd = open(path, O_RDONLY | O_CLOEXEC, 0)) != -1) {
    // sanity test that this .com.dbg file (1) is an elf image, and (2)
    // contains the same number of bytes of code as our .com executable
    // which is currently running in memory.
    if ((size = lseek(fd, 0, SEEK_END)) != -1 &&
        (map = mmap(0, size, PROT_READ, MAP_SHARED, fd, 0)) != MAP_FAILED) {
      if (IsElf64Binary(map, size) &&
          GetElfSymbolValue(map, size, "_etext", &value)) {
        res = !_etext || value == (uintptr_t)_etext;
      }
      munmap(map, size);
    }
    close(fd);
  }
  return res;
}

static bool IsMyDebugBinary(const char *path) {
  int e;
  bool res;
  e = errno;
  res = IsMyDebugBinaryImpl(path);
  errno = e;
  return res;
}

/**
 * Returns path of binary with the debug information, or null.
 *
 * @return path to debug binary, or NULL
 */
const char *FindDebugBinary(void) {
  static bool once;
  static char *res;
  static char buf[PATH_MAX];
  char *p;
  size_t n;
  if (!once) {
    p = GetProgramExecutableName();
    n = strlen(p);
    if (n > 4 && READ32LE(p + n - 4) == READ32LE(".dbg") ||
        IsMyDebugBinary(p)) {
      res = p;
    } else if (n > 4 && READ32LE(p + n - 4) == READ32LE(".com") &&
               n + 4 < ARRAYLEN(buf)) {
      mempcpy(mempcpy(buf, p, n), ".dbg", 5);
      if (IsMyDebugBinary(buf)) {
        res = buf;
      }
    } else if (n + 8 < ARRAYLEN(buf)) {
      mempcpy(mempcpy(buf, p, n), ".com.dbg", 9);
      if (IsMyDebugBinary(buf)) {
        res = buf;
      }
    }
    if (!res) {
      res = getenv("COMDBG");
    }
    once = true;
  }
  return res;
}