2 * Hook output functions (like printf(3)) with LD_PRELOAD to color stderr (or
3 * other file descriptors).
5 * Copyright (C) 2013 Simon Ruderich
7 * This program is free software: you can redistribute it and/or modify
8 * it under the terms of the GNU General Public License as published by
9 * the Free Software Foundation, either version 3 of the License, or
10 * (at your option) any later version.
12 * This program is distributed in the hope that it will be useful,
13 * but WITHOUT ANY WARRANTY; without even the implied warranty of
14 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
15 * GNU General Public License for more details.
17 * You should have received a copy of the GNU General Public License
18 * along with this program. If not, see <http://www.gnu.org/licenses/>.
25 /* Must be loaded before the following headers. */
26 #include "ldpreload.h"
39 /* Conflicting declaration in glibc. */
40 #undef fwrite_unlocked
41 /* These functions may be macros when compiling with hardening flags (fortify)
42 * which cause build failures when used in our hook macros below. Observed
43 * with Clang on Debian Wheezy. */
48 /* Used by various functions, including debug(). */
49 static ssize_t (*real_write)(int, void const *, size_t);
50 static int (*real_close)(int);
51 static size_t (*real_fwrite)(void const *, size_t, size_t, FILE *);
53 /* Did we already (try to) parse the environment and setup the necessary
55 static int initialized;
56 /* Force hooked writes even when not writing to a tty. Used for tests. */
57 static int force_write_to_non_tty;
60 #include "constants.h"
65 #include "hookmacros.h"
70 /* See hookmacros.h for the decision if a function call is colored. */
73 /* Prevent inlining into hook functions because it may increase the number of
74 * spilled registers unnecessarily. As it's not called very often accept the
76 static int isatty_noinline(int fd) noinline;
77 static int isatty_noinline(int fd) {
78 int saved_errno = errno;
79 int result = isatty(fd);
86 static void dup_fd(int oldfd, int newfd) {
88 debug("%3d -> %3d\t\t\t[%d]\n", oldfd, newfd, getpid());
91 if (unlikely(!initialized)) {
92 init_from_environment();
95 /* We are already tracking this file descriptor, add newfd to the list as
96 * it will reference the same descriptor. */
97 if (tracked_fds_find(oldfd)) {
98 if (!tracked_fds_find(newfd)) {
99 tracked_fds_add(newfd);
101 /* We are not tracking this file descriptor, remove newfd from the list
104 tracked_fds_remove(newfd);
108 static void close_fd(int fd) {
110 debug("%3d -> .\t\t\t[%d]\n", fd, getpid());
113 if (unlikely(!initialized)) {
114 init_from_environment();
117 tracked_fds_remove(fd);
121 /* "Action" handlers called when a file descriptor is matched. */
123 static char const *pre_string;
124 static size_t pre_string_size;
125 static char const *post_string;
126 static size_t post_string_size;
128 /* Load alternative pre/post strings from the environment if available, fall
129 * back to default values. */
130 static void init_pre_post_string(void) {
131 pre_string = getenv(ENV_NAME_PRE_STRING);
133 pre_string = DEFAULT_PRE_STRING;
135 pre_string_size = strlen(pre_string);
137 post_string = getenv(ENV_NAME_POST_STRING);
139 post_string = DEFAULT_POST_STRING;
141 post_string_size = strlen(post_string);
144 /* Don't inline any of the pre/post functions. Keep the hook function as small
145 * as possible for speed reasons. */
146 static void handle_fd_pre(int fd) noinline;
147 static void handle_fd_post(int fd) noinline;
148 static void handle_file_pre(FILE *stream) noinline;
149 static void handle_file_post(FILE *stream) noinline;
151 static void handle_fd_pre(int fd) {
152 int saved_errno = errno;
154 if (unlikely(!pre_string || !post_string)) {
155 init_pre_post_string();
158 DLSYM_FUNCTION(real_write, "write");
159 real_write(fd, pre_string, pre_string_size);
163 static void handle_fd_post(int fd) {
164 int saved_errno = errno;
166 /* write() already loaded above in handle_fd_pre(). */
167 real_write(fd, post_string, post_string_size);
172 static void handle_file_pre(FILE *stream) {
173 int saved_errno = errno;
175 if (unlikely(!pre_string || !post_string)) {
176 init_pre_post_string();
179 DLSYM_FUNCTION(real_fwrite, "fwrite");
180 real_fwrite(pre_string, pre_string_size, 1, stream);
184 static void handle_file_post(FILE *stream) {
185 int saved_errno = errno;
187 /* fwrite() already loaded above in handle_file_pre(). */
188 real_fwrite(post_string, post_string_size, 1, stream);
195 /* Hook all important output functions to manipulate their output. */
197 HOOK_FD3(ssize_t, write, fd,
198 int, fd, void const *, buf, size_t, count)
199 HOOK_FILE4(size_t, fwrite, stream,
200 void const *, ptr, size_t, size, size_t, nmemb, FILE *, stream)
203 HOOK_FILE2(int, fputs, stream,
204 char const *, s, FILE *, stream)
205 HOOK_FILE2(int, fputc, stream,
206 int, c, FILE *, stream)
207 HOOK_FILE2(int, putc, stream,
208 int, c, FILE *, stream)
209 HOOK_FILE1(int, putchar, stdout,
211 HOOK_FILE1(int, puts, stdout,
214 /* printf(3), excluding all s*() and vs*() functions (no output) */
215 HOOK_VAR_FILE1(int, printf, stdout, vprintf,
216 char const *, format)
217 HOOK_VAR_FILE2(int, fprintf, stream, vfprintf,
218 FILE *, stream, char const *, format)
219 HOOK_FILE2(int, vprintf, stdout,
220 char const *, format, va_list, ap)
221 HOOK_FILE3(int, vfprintf, stream,
222 FILE *, stream, char const *, format, va_list, ap)
223 /* Hardening functions (-D_FORTIFY_SOURCE=2), only functions from above */
224 HOOK_VAR_FILE2(int, __printf_chk, stdout, __vprintf_chk,
225 int, flag, char const *, format)
226 HOOK_VAR_FILE3(int, __fprintf_chk, fp, __vfprintf_chk,
227 FILE *, fp, int, flag, char const *, format)
228 HOOK_FILE3(int, __vprintf_chk, stdout,
229 int, flag, char const *, format, va_list, ap)
230 HOOK_FILE4(int, __vfprintf_chk, stream,
231 FILE *, stream, int, flag, char const *, format, va_list, ap)
233 /* unlocked_stdio(3), only functions from above are hooked */
234 HOOK_FILE4(size_t, fwrite_unlocked, stream,
235 void const *, ptr, size_t, size, size_t, nmemb, FILE *, stream)
236 HOOK_FILE2(int, fputs_unlocked, stream,
237 char const *, s, FILE *, stream)
238 HOOK_FILE2(int, fputc_unlocked, stream,
239 int, c, FILE *, stream)
240 HOOK_FILE2(int, putc_unlocked, stream,
241 int, c, FILE *, stream)
242 HOOK_FILE1(int, putchar_unlocked, stdout,
246 HOOK_VOID1(void, perror, STDERR_FILENO,
251 static void error_vararg(int status, int errnum,
252 char const *filename, unsigned int linenum,
253 char const *format, va_list ap) {
254 static char const *last_filename;
255 static unsigned int last_linenum;
257 /* Skip this error message if requested and if there was already an error
258 * in the same file/line. */
259 if (error_one_per_line
260 && filename != NULL && linenum != 0
261 && filename == last_filename && linenum == last_linenum) {
264 last_filename = filename;
265 last_linenum = linenum;
267 error_message_count++;
271 if (error_print_progname) {
272 error_print_progname();
274 fprintf(stderr, "%s:", program_invocation_name);
276 if (filename != NULL && linenum != 0) {
277 fprintf(stderr, "%s:%u:", filename, linenum);
278 if (error_print_progname) {
279 fprintf(stderr, " ");
282 if (!error_print_progname) {
283 fprintf(stderr, " ");
287 vfprintf(stderr, format, ap);
290 fprintf(stderr, ": %s", strerror(errnum));
293 fprintf(stderr, "\n");
299 void error_at_line(int status, int errnum,
300 char const *filename, unsigned int linenum,
301 char const *format, ...) {
304 va_start(ap, format);
305 error_vararg(status, errnum, filename, linenum, format, ap);
308 void error(int status, int errnum, char const *format, ...) {
311 va_start(ap, format);
312 error_vararg(status, errnum, NULL, 0, format, ap);
318 /* Hook functions which duplicate file descriptors to track them. */
320 static int (*real_dup)(int);
321 static int (*real_dup2)(int, int);
322 static int (*real_dup3)(int, int, int);
326 DLSYM_FUNCTION(real_dup, "dup");
328 newfd = real_dup(oldfd);
330 dup_fd(oldfd, newfd);
335 int dup2(int oldfd, int newfd) {
336 DLSYM_FUNCTION(real_dup2, "dup2");
338 newfd = real_dup2(oldfd, newfd);
340 dup_fd(oldfd, newfd);
345 int dup3(int oldfd, int newfd, int flags) {
346 DLSYM_FUNCTION(real_dup3, "dup3");
348 newfd = real_dup3(oldfd, newfd, flags);
350 dup_fd(oldfd, newfd);
356 static int (*real_fcntl)(int, int, ...);
357 int fcntl(int fd, int cmd, ...) {
361 DLSYM_FUNCTION(real_fcntl, "fcntl");
363 /* fcntl() takes different types of arguments depending on the cmd type
364 * (int, void and pointers are used at the moment). Handling these
365 * arguments for different systems and with possible changes in the future
368 * Therefore always retrieve a void-pointer from our arguments (even if it
369 * wasn't there) and pass it to real_fcntl(). This shouldn't cause any
370 * problems because a void-pointer is most-likely bigger than an int
371 * (something which is not true in reverse) and shouldn't cause
372 * truncation. For register based calling conventions an invalid register
373 * content is passed, but ignored by real_fcntl(). Not perfect, but should
377 result = real_fcntl(fd, cmd, va_arg(ap, void *));
380 /* We only care about duping fds. */
381 if (cmd == F_DUPFD && result != -1) {
388 static int (*real_close)(int);
390 DLSYM_FUNCTION(real_close, "close");
393 return real_close(fd);
395 static int (*real_fclose)(FILE *);
396 int fclose(FILE *fp) {
397 DLSYM_FUNCTION(real_fclose, "fclose");
399 close_fd(fileno(fp));
400 return real_fclose(fp);
404 /* Hook functions which are necessary for correct tracking. */
406 #if defined(HAVE_VFORK) && defined(HAVE_FORK)
408 /* vfork() is similar to fork() but the address space is shared between
409 * father and child. It's designed for fork()/exec() usage because it's
410 * faster than fork(). However according to the POSIX standard the "child"
411 * isn't allowed to perform any memory-modifications before the exec()
412 * (except the pid_t result variable of vfork()).
414 * As some programs don't adhere to the standard (e.g. the "child" closes
415 * or dups a descriptor before the exec()) and this breaks our tracking of
416 * file descriptors (e.g. it gets closed in the parent as well), we just
417 * fork() instead. This is in compliance with the POSIX standard and as
418 * most systems use copy-on-write anyway not a performance issue. */
424 /* Hook execve() and the other exec*() functions. Some shells use exec*() with
425 * a custom environment which doesn't necessarily contain our updates to
426 * ENV_NAME_FDS. It's also faster to update the environment only when
427 * necessary, right before the exec() to pass it to the new process. */
429 static int (*real_execve)(char const *filename, char * const argv[], char * const env[]);
430 int execve(char const *filename, char * const argv[], char * const env[]) {
431 DLSYM_FUNCTION(real_execve, "execve");
436 /* Count arguments and search for existing ENV_NAME_FDS environment
439 char * const *x = env;
441 if (!strncmp(*x, ENV_NAME_FDS "=", strlen(ENV_NAME_FDS) + 1)) {
449 /* Terminating NULL. */
452 char *env_copy[count + 1 /* space for our new entry if necessary */];
453 memcpy(env_copy, env, count * sizeof(char *));
455 /* Make sure the information from the environment is loaded. We can't just
456 * do nothing (like update_environment()) because the caller might pass a
457 * different environment which doesn't include any of our settings. */
459 init_from_environment();
462 char fds_env[strlen(ENV_NAME_FDS) + 1 + update_environment_buffer_size()];
463 strcpy(fds_env, ENV_NAME_FDS "=");
464 update_environment_buffer(fds_env + strlen(ENV_NAME_FDS) + 1);
467 env_copy[index] = fds_env;
469 /* If the process removed ENV_NAME_FDS from the environment, re-add
471 env_copy[count-1] = fds_env;
472 env_copy[count] = NULL;
475 return real_execve(filename, argv, env_copy);
478 #define EXECL_COPY_VARARGS_START(args) \
482 /* Count arguments. */ \
483 size_t count = 1; /* arg */ \
485 while (va_arg(ap, char const *)) { \
490 /* Copy varargs. */ \
491 char *args[count + 1 /* terminating NULL */]; \
492 args[0] = (char *)arg; \
496 while ((x = va_arg(ap, char *))) { \
500 #define EXECL_COPY_VARARGS_END(args) \
502 #define EXECL_COPY_VARARGS(args) \
503 EXECL_COPY_VARARGS_START(args); \
504 EXECL_COPY_VARARGS_END(args);
506 int execl(char const *path, char const *arg, ...) {
507 EXECL_COPY_VARARGS(args);
509 update_environment();
510 return execv(path, args);
513 int execlp(char const *file, char const *arg, ...) {
514 EXECL_COPY_VARARGS(args);
516 update_environment();
517 return execvp(file, args);
520 int execle(char const *path, char const *arg, ... /*, char * const envp[] */) {
521 EXECL_COPY_VARARGS_START(args);
522 /* Get envp[] located after arguments. */
523 char * const *envp = va_arg(ap, char * const *);
524 EXECL_COPY_VARARGS_END(args);
526 return execve(path, args, envp);
529 static int (*real_execv)(char const *path, char * const argv[]);
530 int execv(char const *path, char * const argv[]) {
531 DLSYM_FUNCTION(real_execv, "execv");
533 update_environment();
534 return real_execv(path, argv);
537 static int (*real_execvp)(char const *path, char * const argv[]);
538 int execvp(char const *file, char * const argv[]) {
539 DLSYM_FUNCTION(real_execvp, "execvp");
541 update_environment();
542 return real_execvp(file, argv);
546 extern char **environ;
547 int execvpe(char const *file, char * const argv[], char * const envp[]) {
548 /* Fake the environment so we can reuse execvp(). */
549 environ = (char **)envp;
551 return execvp(file, argv);