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. */
48 #ifdef HAVE_STRUCT__IO_FILE__FILENO
52 /* The following functions may be macros. Undefine them or they cause build
53 * failures when used in our hook macros below. */
55 /* In glibc, real fwrite_unlocked() is called in macro. */
56 #ifdef HAVE_FWRITE_UNLOCKED
57 # undef fwrite_unlocked
59 /* In Clang when compiling with hardening flags (fortify) on Debian Wheezy. */
62 /* On FreeBSD (9.1), __swbuf() is used instead of these macros. */
67 # undef putchar_unlocked
71 /* Used by various functions, including debug(). */
72 static ssize_t (*real_write)(int, void const *, size_t);
73 static int (*real_close)(int);
74 static size_t (*real_fwrite)(void const *, size_t, size_t, FILE *);
76 /* Did we already (try to) parse the environment and setup the necessary
78 static int initialized;
79 /* Force hooked writes even when not writing to a tty. Used for tests. */
80 static int force_write_to_non_tty;
83 #include "constants.h"
88 #include "hookmacros.h"
93 /* See hookmacros.h for the decision if a function call is colored. */
96 /* Prevent inlining into hook functions because it may increase the number of
97 * spilled registers unnecessarily. As it's not called very often accept the
99 static int isatty_noinline(int fd) noinline;
100 static int isatty_noinline(int fd) {
103 int saved_errno = errno;
104 int result = isatty(fd);
111 static void dup_fd(int oldfd, int newfd) {
113 debug("%3d -> %3d\t\t\t[%d]\n", oldfd, newfd, getpid());
116 assert(oldfd >= 0 && newfd >= 0);
118 if (unlikely(!initialized)) {
119 init_from_environment();
122 /* We are already tracking this file descriptor, add newfd to the list as
123 * it will reference the same descriptor. */
124 if (tracked_fds_find(oldfd)) {
125 if (!tracked_fds_find(newfd)) {
126 tracked_fds_add(newfd);
128 /* We are not tracking this file descriptor, remove newfd from the list
131 tracked_fds_remove(newfd);
135 static void close_fd(int fd) {
137 debug("%3d -> .\t\t\t[%d]\n", fd, getpid());
142 if (unlikely(!initialized)) {
143 init_from_environment();
146 tracked_fds_remove(fd);
150 /* "Action" handlers called when a file descriptor is matched. */
152 static char const *pre_string;
153 static size_t pre_string_size;
154 static char const *post_string;
155 static size_t post_string_size;
157 /* Load alternative pre/post strings from the environment if available, fall
158 * back to default values. */
159 static void init_pre_post_string(void) {
160 pre_string = getenv(ENV_NAME_PRE_STRING);
162 pre_string = DEFAULT_PRE_STRING;
164 pre_string_size = strlen(pre_string);
166 post_string = getenv(ENV_NAME_POST_STRING);
168 post_string = DEFAULT_POST_STRING;
170 post_string_size = strlen(post_string);
173 /* Don't inline any of the pre/post functions. Keep the hook function as small
174 * as possible for speed reasons. */
175 static void handle_fd_pre(int fd) noinline;
176 static void handle_fd_post(int fd) noinline;
177 static void handle_file_pre(FILE *stream) noinline;
178 static void handle_file_post(FILE *stream) noinline;
180 static void handle_fd_pre(int fd) {
181 int saved_errno = errno;
183 if (unlikely(!pre_string || !post_string)) {
184 init_pre_post_string();
187 DLSYM_FUNCTION(real_write, "write");
188 real_write(fd, pre_string, pre_string_size);
192 static void handle_fd_post(int fd) {
193 int saved_errno = errno;
195 /* write() already loaded above in handle_fd_pre(). */
196 real_write(fd, post_string, post_string_size);
201 static void handle_file_pre(FILE *stream) {
202 int saved_errno = errno;
204 if (unlikely(!pre_string || !post_string)) {
205 init_pre_post_string();
208 DLSYM_FUNCTION(real_fwrite, "fwrite");
209 real_fwrite(pre_string, pre_string_size, 1, stream);
213 static void handle_file_post(FILE *stream) {
214 int saved_errno = errno;
216 /* fwrite() already loaded above in handle_file_pre(). */
217 real_fwrite(post_string, post_string_size, 1, stream);
224 /* Hook all important output functions to manipulate their output. */
226 HOOK_FD3(ssize_t, write, fd,
227 int, fd, void const *, buf, size_t, count)
228 HOOK_FILE4(size_t, fwrite, stream,
229 void const *, ptr, size_t, size, size_t, nmemb, FILE *, stream)
232 HOOK_FILE2(int, fputs, stream,
233 char const *, s, FILE *, stream)
234 HOOK_FILE2(int, fputc, stream,
235 int, c, FILE *, stream)
236 HOOK_FILE2(int, putc, stream,
237 int, c, FILE *, stream)
238 HOOK_FILE1(int, putchar, stdout,
240 HOOK_FILE1(int, puts, stdout,
243 /* printf(3), excluding all s*() and vs*() functions (no output) */
244 HOOK_VAR_FILE1(int, printf, stdout, vprintf,
245 char const *, format)
246 HOOK_VAR_FILE2(int, fprintf, stream, vfprintf,
247 FILE *, stream, char const *, format)
248 HOOK_FILE2(int, vprintf, stdout,
249 char const *, format, va_list, ap)
250 HOOK_FILE3(int, vfprintf, stream,
251 FILE *, stream, char const *, format, va_list, ap)
252 /* Hardening functions (-D_FORTIFY_SOURCE=2), only functions from above */
253 HOOK_VAR_FILE2(int, __printf_chk, stdout, __vprintf_chk,
254 int, flag, char const *, format)
255 HOOK_VAR_FILE3(int, __fprintf_chk, fp, __vfprintf_chk,
256 FILE *, fp, int, flag, char const *, format)
257 HOOK_FILE3(int, __vprintf_chk, stdout,
258 int, flag, char const *, format, va_list, ap)
259 HOOK_FILE4(int, __vfprintf_chk, stream,
260 FILE *, stream, int, flag, char const *, format, va_list, ap)
262 /* unlocked_stdio(3), only functions from above are hooked */
263 #ifdef HAVE_FWRITE_UNLOCKED
264 HOOK_FILE4(size_t, fwrite_unlocked, stream,
265 void const *, ptr, size_t, size, size_t, nmemb, FILE *, stream)
267 #ifdef HAVE_FPUTS_UNLOCKED
268 HOOK_FILE2(int, fputs_unlocked, stream,
269 char const *, s, FILE *, stream)
271 #ifdef HAVE_FPUTC_UNLOCKED
272 HOOK_FILE2(int, fputc_unlocked, stream,
273 int, c, FILE *, stream)
275 HOOK_FILE2(int, putc_unlocked, stream,
276 int, c, FILE *, stream)
277 HOOK_FILE1(int, putchar_unlocked, stdout,
279 /* glibc defines (_IO_)putc_unlocked() to a macro which either updates the
280 * output buffer or calls __overflow(). As this code is inlined we can't
281 * handle the first case, but if __overflow() is called we can color that
282 * part. As writes to stderr are never buffered, __overflow() is always called
283 * and everything works fine. This is only a problem if stdout is dupped to
284 * stderr (which shouldn't be the case too often). */
285 #if defined(HAVE_STRUCT__IO_FILE__FILENO) && defined(HAVE___OVERFLOW)
286 /* _IO_FILE is glibc's representation of FILE. */
287 HOOK_FILE2(int, __overflow, f, _IO_FILE *, f, int, ch)
289 /* Same for FreeBSD's libc. However it's more aggressive: The inline writing
290 * and __swbuf() are also used for normal output (e.g. putc()). Writing to
291 * stderr is still fine; it always calls __swbuf() as stderr is always
294 HOOK_FILE2(int, __swbuf, f, int, c, FILE *, f)
298 HOOK_VOID1(void, perror, STDERR_FILENO,
301 /* err(3), non standard BSD extension */
303 HOOK_VAR_VOID2(void, err, STDERR_FILENO, verr,
304 int, eval, char const *, fmt)
305 HOOK_VAR_VOID2(void, errx, STDERR_FILENO, verrx,
306 int, eval, char const *, fmt)
307 HOOK_VAR_VOID1(void, warn, STDERR_FILENO, vwarn,
309 HOOK_VAR_VOID1(void, warnx, STDERR_FILENO, vwarnx,
311 HOOK_FUNC_SIMPLE3(void, verr, int, eval, const char *, fmt, va_list, args) {
312 /* Can't use verr() directly as it terminates the process which prevents
313 * the post string from being printed. */
317 HOOK_FUNC_SIMPLE3(void, verrx, int, eval, const char *, fmt, va_list, args) {
322 HOOK_VOID2(void, vwarn, STDERR_FILENO,
323 char const *, fmt, va_list, args)
324 HOOK_VOID2(void, vwarnx, STDERR_FILENO,
325 char const *, fmt, va_list, args)
328 /* error(3), non-standard GNU extension */
330 static void error_vararg(int status, int errnum,
331 char const *filename, unsigned int linenum,
332 char const *format, va_list ap) {
333 static char const *last_filename;
334 static unsigned int last_linenum;
336 /* Skip this error message if requested and if there was already an error
337 * in the same file/line. */
338 if (error_one_per_line
339 && filename != NULL && linenum != 0
340 && filename == last_filename && linenum == last_linenum) {
343 last_filename = filename;
344 last_linenum = linenum;
346 error_message_count++;
350 if (error_print_progname) {
351 error_print_progname();
353 fprintf(stderr, "%s:", program_invocation_name);
355 if (filename != NULL && linenum != 0) {
356 fprintf(stderr, "%s:%u:", filename, linenum);
357 if (error_print_progname) {
358 fprintf(stderr, " ");
361 if (!error_print_progname) {
362 fprintf(stderr, " ");
366 vfprintf(stderr, format, ap);
369 fprintf(stderr, ": %s", strerror(errnum));
372 fprintf(stderr, "\n");
378 void error_at_line(int status, int errnum,
379 char const *filename, unsigned int linenum,
380 char const *format, ...) {
383 va_start(ap, format);
384 error_vararg(status, errnum, filename, linenum, format, ap);
387 void error(int status, int errnum, char const *format, ...) {
390 va_start(ap, format);
391 error_vararg(status, errnum, NULL, 0, format, ap);
397 /* Hook functions which duplicate file descriptors to track them. */
400 HOOK_FUNC_DEF1(int, dup, int, oldfd) {
403 DLSYM_FUNCTION(real_dup, "dup");
405 newfd = real_dup(oldfd);
407 dup_fd(oldfd, newfd);
412 /* int dup2(int, int) */
413 HOOK_FUNC_DEF2(int, dup2, int, oldfd, int, newfd) {
414 DLSYM_FUNCTION(real_dup2, "dup2");
416 newfd = real_dup2(oldfd, newfd);
418 dup_fd(oldfd, newfd);
423 /* int dup3(int, int, int) */
424 HOOK_FUNC_DEF3(int, dup3, int, oldfd, int, newfd, int, flags) {
425 DLSYM_FUNCTION(real_dup3, "dup3");
427 newfd = real_dup3(oldfd, newfd, flags);
429 dup_fd(oldfd, newfd);
435 /* int fcntl(int, int, ...) */
436 HOOK_FUNC_VAR_DEF2(int, fcntl, int, fd, int, cmd /*, ... */) {
440 DLSYM_FUNCTION(real_fcntl, "fcntl");
442 /* fcntl() takes different types of arguments depending on the cmd type
443 * (int, void and pointers are used at the moment). Handling these
444 * arguments for different systems and with possible changes in the future
447 * Therefore always retrieve a void-pointer from our arguments (even if it
448 * wasn't there) and pass it to real_fcntl(). This shouldn't cause any
449 * problems because a void-pointer is most-likely bigger than an int
450 * (something which is not true in reverse) and shouldn't cause
451 * truncation. For register based calling conventions an invalid register
452 * content is passed, but ignored by real_fcntl(). Not perfect, but should
456 result = real_fcntl(fd, cmd, va_arg(ap, void *));
459 /* We only care about duping fds. */
460 if (cmd == F_DUPFD && result != -1) {
468 HOOK_FUNC_DEF1(int, close, int, fd) {
469 DLSYM_FUNCTION(real_close, "close");
474 return real_close(fd);
476 /* int fclose(FILE *) */
477 HOOK_FUNC_DEF1(int, fclose, FILE *, fp) {
480 DLSYM_FUNCTION(real_fclose, "fclose");
482 if (fp != NULL && (fd = fileno(fp)) >= 0) {
485 return real_fclose(fp);
489 /* Hook functions which are necessary for correct tracking. */
491 #if defined(HAVE_VFORK) && defined(HAVE_FORK)
493 /* vfork() is similar to fork() but the address space is shared between
494 * father and child. It's designed for fork()/exec() usage because it's
495 * faster than fork(). However according to the POSIX standard the "child"
496 * isn't allowed to perform any memory-modifications before the exec()
497 * (except the pid_t result variable of vfork()).
499 * As some programs don't adhere to the standard (e.g. the "child" closes
500 * or dups a descriptor before the exec()) and this breaks our tracking of
501 * file descriptors (e.g. it gets closed in the parent as well), we just
502 * fork() instead. This is in compliance with the POSIX standard and as
503 * most systems use copy-on-write anyway not a performance issue. */
509 /* Hook execve() and the other exec*() functions. Some shells use exec*() with
510 * a custom environment which doesn't necessarily contain our updates to
511 * ENV_NAME_FDS. It's also faster to update the environment only when
512 * necessary, right before the exec() to pass it to the new process. */
514 /* int execve(char const *, char * const [], char * const []) */
515 HOOK_FUNC_DEF3(int, execve, char const *, filename, char * const *, argv, char * const *, env) {
516 DLSYM_FUNCTION(real_execve, "execve");
521 /* Count arguments and search for existing ENV_NAME_FDS environment
524 char * const *x = env;
526 if (!strncmp(*x, ENV_NAME_FDS "=", strlen(ENV_NAME_FDS) + 1)) {
534 /* Terminating NULL. */
537 char *env_copy[count + 1 /* space for our new entry if necessary */];
538 memcpy(env_copy, env, count * sizeof(char *));
540 /* Make sure the information from the environment is loaded. We can't just
541 * do nothing (like update_environment()) because the caller might pass a
542 * different environment which doesn't include any of our settings. */
544 init_from_environment();
547 char fds_env[strlen(ENV_NAME_FDS) + 1 + update_environment_buffer_size()];
548 strcpy(fds_env, ENV_NAME_FDS "=");
549 update_environment_buffer(fds_env + strlen(ENV_NAME_FDS) + 1);
552 env_copy[index] = fds_env;
554 /* If the process removed ENV_NAME_FDS from the environment, re-add
556 env_copy[count-1] = fds_env;
557 env_copy[count] = NULL;
560 return real_execve(filename, argv, env_copy);
563 #define EXECL_COPY_VARARGS_START(args) \
567 /* Count arguments. */ \
568 size_t count = 1; /* arg */ \
570 while (va_arg(ap, char *)) { \
575 /* Copy varargs. */ \
576 char *args[count + 1 /* terminating NULL */]; \
577 args[0] = (char *)arg; /* there's no other way around the cast */ \
581 while ((x = va_arg(ap, char *))) { \
585 #define EXECL_COPY_VARARGS_END(args) \
587 #define EXECL_COPY_VARARGS(args) \
588 EXECL_COPY_VARARGS_START(args); \
589 EXECL_COPY_VARARGS_END(args);
591 int execl(char const *path, char const *arg, ...) {
592 EXECL_COPY_VARARGS(args);
594 /* execv() updates the environment. */
595 return execv(path, args);
597 int execlp(char const *file, char const *arg, ...) {
598 EXECL_COPY_VARARGS(args);
600 /* execvp() updates the environment. */
601 return execvp(file, args);
603 int execle(char const *path, char const *arg, ... /*, char * const envp[] */) {
606 EXECL_COPY_VARARGS_START(args);
607 /* Get envp[] located after arguments. */
608 envp = va_arg(ap, char * const *);
609 EXECL_COPY_VARARGS_END(args);
611 /* execve() updates the environment. */
612 return execve(path, args, envp);
615 /* int execv(char const *, char * const []) */
616 HOOK_FUNC_DEF2(int, execv, char const *, path, char * const *, argv) {
617 DLSYM_FUNCTION(real_execv, "execv");
619 update_environment();
620 return real_execv(path, argv);
623 /* int execvp(char const *, char * const []) */
624 HOOK_FUNC_DEF2(int, execvp, char const *, file, char * const *, argv) {
625 DLSYM_FUNCTION(real_execvp, "execvp");
627 update_environment();
628 return real_execvp(file, argv);
632 extern char **environ;
633 int execvpe(char const *file, char * const argv[], char * const envp[]) {
634 /* Fake the environment so we can reuse execvp(). */
635 environ = (char **)envp;
637 /* execvp() updates the environment. */
638 return execvp(file, argv);