trace.c

/**
 * Copyright © 2015 Saleem Abdulrasool <compnerd@compnerd.org>
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *
 * 1. Redistributions of source code must retain the above copyright notice,
 *    this list of conditions and the following disclaimer.
 *
 * 2. Redistributions in binary form must reproduce the above copyright notice,
 *    this list of conditions and the following disclaimer in the documentation
 *    and/or other materials provided with the distribution.
 *
 * 3. The name of the author may not be used to endorse or promote products
 *    derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR "AS IS" AND ANY EXPRESS OR IMPLIED
 * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO
 * EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS;
 * OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
 * WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR
 * OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
 * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 **/

/* x86_64-pc-linux-gnu-cc -std=c11 -fpic -shared -Wall -Werror %s -o libtrace.so -ldl */

#define _GNU_SOURCE

#include <assert.h>
#include <stdarg.h>
#include <stdbool.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#include <sys/auxv.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <dlfcn.h>
#include <dirent.h>
#include <execinfo.h>
#include <fcntl.h>
#include <regex.h>
#include <unistd.h>

#define COUNTOF(array) ((sizeof(array) / sizeof(*array)))

static const char *patterns[] = {
  "/usr/[^/]+/share",
};

static int fd = -1;
static bool initialised = false;
static regex_t paths[COUNTOF(patterns)];

void __attribute__ (( constructor )) constructor() {
  for (unsigned path = 0; path < COUNTOF(paths); ++path)
    if (regcomp(&paths[path], patterns[path], REG_EXTENDED | REG_NOSUB))
      return perror("unable to compile pattern");
  initialised = true;
}

void __attribute__ (( destructor )) destructor() {
  if (fd >= 0)
    close(fd);

  for (unsigned path = 0; path < COUNTOF(paths); ++path)
    regfree(&paths[path]);
}

static int get_fd() {
  char *buffer = NULL;

  if (fd >= 0)
    return fd;

  asprintf(&buffer, "%s/%u-%s-XXXXXX", getenv("TMPDIR") ?: "/tmp", getpid(),
           strrchr((char *)getauxval(AT_EXECFN), '/') + 1);
  fd = mkostemp(buffer, O_CLOEXEC | O_EXCL | O_SYNC | O_CREAT);
  if (fd < 0) {
    perror("unable to open log file");
    free(buffer);
    return 0;
  }
  free(buffer);

  return fd;
}

static bool match(const char *string) {
  if (!initialised)
    return false;

  for (unsigned path = 0; path < COUNTOF(paths); ++path)
    if (!regexec(&paths[path], string, 0, NULL, 0))
      return true;

  return false;
}

static void print_backtrace() {
  void *frame[128];
  size_t frames;

  frames = backtrace(frame, COUNTOF(frame));
  backtrace_symbols_fd(frame, frames, get_fd());
}

FILE *fopen(const char *path, const char *mode) {
  static FILE *(*real_fopen)(const char *, const char *) = NULL;

  if (real_fopen == NULL)
    real_fopen =
        (FILE *(*)(const char *, const char *))dlsym(RTLD_NEXT, "fopen");
  assert(real_fopen && "unable to find fopen(3)");

  if (match(path)) {
    dprintf(get_fd(), "fopen(%s, %s)\n", path, mode);
    print_backtrace();
    dprintf(get_fd(), "\r\n");
  }

  return real_fopen(path, mode);
}

int open(const char *pathname, int flags, ...) {
  static int (*real_open)(const char *, int, ...) = NULL;

  if (real_open == NULL)
    real_open = (int (*)(const char *, int, ...))dlsym(RTLD_NEXT, "open");
  assert(real_open && "unable to find open(2)");

  if (match(pathname)) {
    dprintf(get_fd(), "open(%s, %u, ...)\n", pathname, flags);
    print_backtrace();
    dprintf(get_fd(), "\r\n");
  }

  return real_open(pathname, flags);
}

int openat(int dirfd, const char *pathname, int flags, ...) {
  static int (*real_openat)(int, const char *, int, ...) = NULL;

  if (real_openat == NULL)
    real_openat =
        (int (*)(int, const char *, int, ...))dlsym(RTLD_NEXT, "openat");
  assert(real_openat && "unable to find openat(2)");

  if (match(pathname)) {
    dprintf(get_fd(), "openat(%u, %s, %u, ...)\n", dirfd, pathname, flags);
    print_backtrace();
    dprintf(get_fd(), "\r\n");
  }

  return real_openat(dirfd, pathname, flags);
}

DIR *opendir(const char *name) {
  static DIR *(*real_opendir)(const char *) = NULL;

  if (real_opendir == NULL)
    real_opendir = (DIR *(*)(const char *))dlsym(RTLD_NEXT, "opendir");
  assert(real_opendir && "unable to find opendir(3)");

  if (match(name)) {
    dprintf(get_fd(), "opendir(%s)\n", name);
    print_backtrace();
    dprintf(get_fd(), "\r\n");
  }

  return real_opendir(name);
}