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"
28 /* Disable assert()s if not compiled with --enable-debug. */
47 #ifdef HAVE_STRUCT__IO_FILE__FILENO
51 /* Conflicting declaration in glibc. */
52 #undef fwrite_unlocked
53 /* These functions may be macros when compiling with hardening flags (fortify)
54 * which cause build failures when used in our hook macros below. Observed
55 * with Clang on Debian Wheezy. */
60 /* Used by various functions, including debug(). */
61 static ssize_t (*real_write)(int, void const *, size_t);
62 static int (*real_close)(int);
63 static size_t (*real_fwrite)(void const *, size_t, size_t, FILE *);
65 /* Did we already (try to) parse the environment and setup the necessary
67 static int initialized;
68 /* Force hooked writes even when not writing to a tty. Used for tests. */
69 static int force_write_to_non_tty;
72 #include "constants.h"
77 #include "hookmacros.h"
82 /* See hookmacros.h for the decision if a function call is colored. */
85 /* Prevent inlining into hook functions because it may increase the number of
86 * spilled registers unnecessarily. As it's not called very often accept the
88 static int isatty_noinline(int fd) noinline;
89 static int isatty_noinline(int fd) {
92 int saved_errno = errno;
93 int result = isatty(fd);
100 static void dup_fd(int oldfd, int newfd) {
102 debug("%3d -> %3d\t\t\t[%d]\n", oldfd, newfd, getpid());
105 assert(oldfd >= 0 && newfd >= 0);
107 if (unlikely(!initialized)) {
108 init_from_environment();
111 /* We are already tracking this file descriptor, add newfd to the list as
112 * it will reference the same descriptor. */
113 if (tracked_fds_find(oldfd)) {
114 if (!tracked_fds_find(newfd)) {
115 tracked_fds_add(newfd);
117 /* We are not tracking this file descriptor, remove newfd from the list
120 tracked_fds_remove(newfd);
124 static void close_fd(int fd) {
126 debug("%3d -> .\t\t\t[%d]\n", fd, getpid());
131 if (unlikely(!initialized)) {
132 init_from_environment();
135 tracked_fds_remove(fd);
139 /* "Action" handlers called when a file descriptor is matched. */
141 static char const *pre_string;
142 static size_t pre_string_size;
143 static char const *post_string;
144 static size_t post_string_size;
146 /* Load alternative pre/post strings from the environment if available, fall
147 * back to default values. */
148 static void init_pre_post_string(void) {
149 pre_string = getenv(ENV_NAME_PRE_STRING);
151 pre_string = DEFAULT_PRE_STRING;
153 pre_string_size = strlen(pre_string);
155 post_string = getenv(ENV_NAME_POST_STRING);
157 post_string = DEFAULT_POST_STRING;
159 post_string_size = strlen(post_string);
162 /* Don't inline any of the pre/post functions. Keep the hook function as small
163 * as possible for speed reasons. */
164 static void handle_fd_pre(int fd) noinline;
165 static void handle_fd_post(int fd) noinline;
166 static void handle_file_pre(FILE *stream) noinline;
167 static void handle_file_post(FILE *stream) noinline;
169 static void handle_fd_pre(int fd) {
170 int saved_errno = errno;
172 if (unlikely(!pre_string || !post_string)) {
173 init_pre_post_string();
176 DLSYM_FUNCTION(real_write, "write");
177 real_write(fd, pre_string, pre_string_size);
181 static void handle_fd_post(int fd) {
182 int saved_errno = errno;
184 /* write() already loaded above in handle_fd_pre(). */
185 real_write(fd, post_string, post_string_size);
190 static void handle_file_pre(FILE *stream) {
191 int saved_errno = errno;
193 if (unlikely(!pre_string || !post_string)) {
194 init_pre_post_string();
197 DLSYM_FUNCTION(real_fwrite, "fwrite");
198 real_fwrite(pre_string, pre_string_size, 1, stream);
202 static void handle_file_post(FILE *stream) {
203 int saved_errno = errno;
205 /* fwrite() already loaded above in handle_file_pre(). */
206 real_fwrite(post_string, post_string_size, 1, stream);
213 /* Hook all important output functions to manipulate their output. */
215 HOOK_FD3(ssize_t, write, fd,
216 int, fd, void const *, buf, size_t, count)
217 HOOK_FILE4(size_t, fwrite, stream,
218 void const *, ptr, size_t, size, size_t, nmemb, FILE *, stream)
221 HOOK_FILE2(int, fputs, stream,
222 char const *, s, FILE *, stream)
223 HOOK_FILE2(int, fputc, stream,
224 int, c, FILE *, stream)
225 HOOK_FILE2(int, putc, stream,
226 int, c, FILE *, stream)
227 HOOK_FILE1(int, putchar, stdout,
229 HOOK_FILE1(int, puts, stdout,
232 /* printf(3), excluding all s*() and vs*() functions (no output) */
233 HOOK_VAR_FILE1(int, printf, stdout, vprintf,
234 char const *, format)
235 HOOK_VAR_FILE2(int, fprintf, stream, vfprintf,
236 FILE *, stream, char const *, format)
237 HOOK_FILE2(int, vprintf, stdout,
238 char const *, format, va_list, ap)
239 HOOK_FILE3(int, vfprintf, stream,
240 FILE *, stream, char const *, format, va_list, ap)
241 /* Hardening functions (-D_FORTIFY_SOURCE=2), only functions from above */
242 HOOK_VAR_FILE2(int, __printf_chk, stdout, __vprintf_chk,
243 int, flag, char const *, format)
244 HOOK_VAR_FILE3(int, __fprintf_chk, fp, __vfprintf_chk,
245 FILE *, fp, int, flag, char const *, format)
246 HOOK_FILE3(int, __vprintf_chk, stdout,
247 int, flag, char const *, format, va_list, ap)
248 HOOK_FILE4(int, __vfprintf_chk, stream,
249 FILE *, stream, int, flag, char const *, format, va_list, ap)
251 /* unlocked_stdio(3), only functions from above are hooked */
252 HOOK_FILE4(size_t, fwrite_unlocked, stream,
253 void const *, ptr, size_t, size, size_t, nmemb, FILE *, stream)
254 HOOK_FILE2(int, fputs_unlocked, stream,
255 char const *, s, FILE *, stream)
256 HOOK_FILE2(int, fputc_unlocked, stream,
257 int, c, FILE *, stream)
258 HOOK_FILE2(int, putc_unlocked, stream,
259 int, c, FILE *, stream)
260 HOOK_FILE1(int, putchar_unlocked, stdout,
262 /* glibc defines (_IO_)putc_unlocked() to __overflow() in some cases. */
263 #ifdef HAVE_STRUCT__IO_FILE__FILENO
264 HOOK_FD2(int, __overflow, f->_fileno, _IO_FILE *, f, int, ch)
268 HOOK_VOID1(void, perror, STDERR_FILENO,
271 /* err(3), non standard BSD extension */
273 HOOK_VAR_VOID2(void, err, STDERR_FILENO, verr,
274 int, eval, char const *, fmt)
275 HOOK_VAR_VOID2(void, errx, STDERR_FILENO, verrx,
276 int, eval, char const *, fmt)
277 HOOK_VAR_VOID1(void, warn, STDERR_FILENO, vwarn,
279 HOOK_VAR_VOID1(void, warnx, STDERR_FILENO, vwarnx,
281 HOOK_FUNC_SIMPLE3(void, verr, int, eval, const char *, fmt, va_list, args) {
282 /* Can't use verr() directly as it terminates the process which prevents
283 * the post string from being printed. */
287 HOOK_FUNC_SIMPLE3(void, verrx, int, eval, const char *, fmt, va_list, args) {
292 HOOK_VOID2(void, vwarn, STDERR_FILENO,
293 char const *, fmt, va_list, args)
294 HOOK_VOID2(void, vwarnx, STDERR_FILENO,
295 char const *, fmt, va_list, args)
298 /* error(3), non-standard GNU extension */
300 static void error_vararg(int status, int errnum,
301 char const *filename, unsigned int linenum,
302 char const *format, va_list ap) {
303 static char const *last_filename;
304 static unsigned int last_linenum;
306 /* Skip this error message if requested and if there was already an error
307 * in the same file/line. */
308 if (error_one_per_line
309 && filename != NULL && linenum != 0
310 && filename == last_filename && linenum == last_linenum) {
313 last_filename = filename;
314 last_linenum = linenum;
316 error_message_count++;
320 if (error_print_progname) {
321 error_print_progname();
323 fprintf(stderr, "%s:", program_invocation_name);
325 if (filename != NULL && linenum != 0) {
326 fprintf(stderr, "%s:%u:", filename, linenum);
327 if (error_print_progname) {
328 fprintf(stderr, " ");
331 if (!error_print_progname) {
332 fprintf(stderr, " ");
336 vfprintf(stderr, format, ap);
339 fprintf(stderr, ": %s", strerror(errnum));
342 fprintf(stderr, "\n");
348 void error_at_line(int status, int errnum,
349 char const *filename, unsigned int linenum,
350 char const *format, ...) {
353 va_start(ap, format);
354 error_vararg(status, errnum, filename, linenum, format, ap);
357 void error(int status, int errnum, char const *format, ...) {
360 va_start(ap, format);
361 error_vararg(status, errnum, NULL, 0, format, ap);
367 /* Hook functions which duplicate file descriptors to track them. */
370 HOOK_FUNC_DEF1(int, dup, int, oldfd) {
373 DLSYM_FUNCTION(real_dup, "dup");
375 newfd = real_dup(oldfd);
377 dup_fd(oldfd, newfd);
382 /* int dup2(int, int) */
383 HOOK_FUNC_DEF2(int, dup2, int, oldfd, int, newfd) {
384 DLSYM_FUNCTION(real_dup2, "dup2");
386 newfd = real_dup2(oldfd, newfd);
388 dup_fd(oldfd, newfd);
393 /* int dup3(int, int, int) */
394 HOOK_FUNC_DEF3(int, dup3, int, oldfd, int, newfd, int, flags) {
395 DLSYM_FUNCTION(real_dup3, "dup3");
397 newfd = real_dup3(oldfd, newfd, flags);
399 dup_fd(oldfd, newfd);
405 /* int fcntl(int, int, ...) */
406 HOOK_FUNC_VAR_DEF2(int, fcntl, int, fd, int, cmd /*, ... */) {
410 DLSYM_FUNCTION(real_fcntl, "fcntl");
412 /* fcntl() takes different types of arguments depending on the cmd type
413 * (int, void and pointers are used at the moment). Handling these
414 * arguments for different systems and with possible changes in the future
417 * Therefore always retrieve a void-pointer from our arguments (even if it
418 * wasn't there) and pass it to real_fcntl(). This shouldn't cause any
419 * problems because a void-pointer is most-likely bigger than an int
420 * (something which is not true in reverse) and shouldn't cause
421 * truncation. For register based calling conventions an invalid register
422 * content is passed, but ignored by real_fcntl(). Not perfect, but should
426 result = real_fcntl(fd, cmd, va_arg(ap, void *));
429 /* We only care about duping fds. */
430 if (cmd == F_DUPFD && result != -1) {
438 HOOK_FUNC_DEF1(int, close, int, fd) {
439 DLSYM_FUNCTION(real_close, "close");
444 return real_close(fd);
446 /* int fclose(FILE *) */
447 HOOK_FUNC_DEF1(int, fclose, FILE *, fp) {
450 DLSYM_FUNCTION(real_fclose, "fclose");
452 if (fp != NULL && (fd = fileno(fp)) >= 0) {
455 return real_fclose(fp);
459 /* Hook functions which are necessary for correct tracking. */
461 #if defined(HAVE_VFORK) && defined(HAVE_FORK)
463 /* vfork() is similar to fork() but the address space is shared between
464 * father and child. It's designed for fork()/exec() usage because it's
465 * faster than fork(). However according to the POSIX standard the "child"
466 * isn't allowed to perform any memory-modifications before the exec()
467 * (except the pid_t result variable of vfork()).
469 * As some programs don't adhere to the standard (e.g. the "child" closes
470 * or dups a descriptor before the exec()) and this breaks our tracking of
471 * file descriptors (e.g. it gets closed in the parent as well), we just
472 * fork() instead. This is in compliance with the POSIX standard and as
473 * most systems use copy-on-write anyway not a performance issue. */
479 /* Hook execve() and the other exec*() functions. Some shells use exec*() with
480 * a custom environment which doesn't necessarily contain our updates to
481 * ENV_NAME_FDS. It's also faster to update the environment only when
482 * necessary, right before the exec() to pass it to the new process. */
484 /* int execve(char const *, char * const [], char * const []) */
485 HOOK_FUNC_DEF3(int, execve, char const *, filename, char * const *, argv, char * const *, env) {
486 DLSYM_FUNCTION(real_execve, "execve");
491 /* Count arguments and search for existing ENV_NAME_FDS environment
494 char * const *x = env;
496 if (!strncmp(*x, ENV_NAME_FDS "=", strlen(ENV_NAME_FDS) + 1)) {
504 /* Terminating NULL. */
507 char *env_copy[count + 1 /* space for our new entry if necessary */];
508 memcpy(env_copy, env, count * sizeof(char *));
510 /* Make sure the information from the environment is loaded. We can't just
511 * do nothing (like update_environment()) because the caller might pass a
512 * different environment which doesn't include any of our settings. */
514 init_from_environment();
517 char fds_env[strlen(ENV_NAME_FDS) + 1 + update_environment_buffer_size()];
518 strcpy(fds_env, ENV_NAME_FDS "=");
519 update_environment_buffer(fds_env + strlen(ENV_NAME_FDS) + 1);
522 env_copy[index] = fds_env;
524 /* If the process removed ENV_NAME_FDS from the environment, re-add
526 env_copy[count-1] = fds_env;
527 env_copy[count] = NULL;
530 return real_execve(filename, argv, env_copy);
533 #define EXECL_COPY_VARARGS_START(args) \
537 /* Count arguments. */ \
538 size_t count = 1; /* arg */ \
540 while (va_arg(ap, char *)) { \
545 /* Copy varargs. */ \
546 char *args[count + 1 /* terminating NULL */]; \
547 args[0] = (char *)arg; /* there's no other way around the cast */ \
551 while ((x = va_arg(ap, char *))) { \
555 #define EXECL_COPY_VARARGS_END(args) \
557 #define EXECL_COPY_VARARGS(args) \
558 EXECL_COPY_VARARGS_START(args); \
559 EXECL_COPY_VARARGS_END(args);
561 int execl(char const *path, char const *arg, ...) {
562 EXECL_COPY_VARARGS(args);
564 /* execv() updates the environment. */
565 return execv(path, args);
567 int execlp(char const *file, char const *arg, ...) {
568 EXECL_COPY_VARARGS(args);
570 /* execvp() updates the environment. */
571 return execvp(file, args);
573 int execle(char const *path, char const *arg, ... /*, char * const envp[] */) {
576 EXECL_COPY_VARARGS_START(args);
577 /* Get envp[] located after arguments. */
578 envp = va_arg(ap, char * const *);
579 EXECL_COPY_VARARGS_END(args);
581 /* execve() updates the environment. */
582 return execve(path, args, envp);
585 /* int execv(char const *, char * const []) */
586 HOOK_FUNC_DEF2(int, execv, char const *, path, char * const *, argv) {
587 DLSYM_FUNCTION(real_execv, "execv");
589 update_environment();
590 return real_execv(path, argv);
593 /* int execvp(char const *, char * const []) */
594 HOOK_FUNC_DEF2(int, execvp, char const *, file, char * const *, argv) {
595 DLSYM_FUNCTION(real_execvp, "execvp");
597 update_environment();
598 return real_execvp(file, argv);
602 extern char **environ;
603 int execvpe(char const *file, char * const argv[], char * const envp[]) {
604 /* Fake the environment so we can reuse execvp(). */
605 environ = (char **)envp;
607 /* execvp() updates the environment. */
608 return execvp(file, argv);