bin/override.c

   1 /*****************************************************************************
   2  * override.c: overridden function calls for VLC media player
   3  *****************************************************************************
   4  * Copyright (C) 2010 Rémi Denis-Courmont
   5  *
   6  * This program is free software; you can redistribute it and/or modify
   7  * it under the terms of the GNU Lesser General Public License as published by
   8  * the Free Software Foundation; either version 2.1 of the License, or
   9  * (at your option) any later version.
  10  *
  11  * This program is distributed in the hope that it will be useful,
  12  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  13  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  14  * GNU Lesser General Public License for more details.
  15  *
  16  * You should have received a copy of the GNU Lesser General Public License
  17  * along with this program; if not, write to the Free Software
  18  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston MA 02110-1301, USA.
  19  *****************************************************************************/
  20
  21 #ifdef HAVE_CONFIG_H
  22 # include "config.h"
  23 #endif
  24
  25 #include <stdbool.h>
  26 #define MAX_ERRORS 5
  27
  28 void vlc_enable_override (void);
  29
  30 #if defined (__GNUC__) \
  31  && (defined (__ELF__) && !defined (__sun__))
  32 /* Solaris crashes on printf("%s", NULL); which is legal, but annoying. */
  33
  34 #include <stdarg.h>
  35 #include <stdio.h>
  36 #include <stdlib.h>
  37 #include <string.h>
  38 #include <dlfcn.h>
  39 #include <pthread.h>
  40 #ifdef HAVE_EXECINFO_H
  41 # include <execinfo.h>
  42 # include <unistd.h>
  43 #endif
  44 #ifdef NDEBUG
  45 # undef HAVE_BACKTRACE
  46 #endif
  47
  48 static bool override = false;
  49
  50 static void vlc_reset_override (void)
  51 {
  52     override = false;
  53 }
  54
  55 void vlc_enable_override (void)
  56 {
  57     override = true;
  58     pthread_atfork (NULL, NULL, vlc_reset_override);
  59 }
  60
  61 static void vlogbug (unsigned *pc, const char *level, const char *func,
  62                      const char *fmt, va_list ap)
  63 {
  64 #ifdef HAVE_BACKTRACE
  65     const size_t framec = 5;
  66     void *framev[framec];
  67
  68     backtrace (framev, framec);
  69 #endif
  70     flockfile (stderr);
  71     if (*pc < MAX_ERRORS)
  72     {
  73         (*pc)++;
  74         fprintf (stderr, "%s: call to %s(", level, func);
  75         vfprintf (stderr, fmt, ap);
  76         fputs (")\n", stderr);
  77         fflush (stderr);
  78 #ifdef HAVE_BACKTRACE
  79         backtrace_symbols_fd (framev + 2, framec - 2, STDERR_FILENO);
  80 #endif
  81     }
  82     funlockfile (stderr);
  83 }
  84
  85 static void logbug (unsigned *pc, const char *level, const char *func,
  86                     const char *fmt, ...)
  87 {
  88     va_list ap;
  89
  90     va_start (ap, fmt);
  91     vlogbug (pc, level, func, fmt, ap);
  92     va_end (ap);
  93 }
  94
  95 static void *getsym (const char *name)
  96 {
  97     void *sym = dlsym (RTLD_NEXT, name);
  98     if (sym == NULL)
  99     {
 100         fprintf (stderr, "Cannot resolve symbol %s: %s\n", name,
 101                  dlerror ());
 102         abort ();
 103     }
 104     return sym;
 105 }
 106
 107 #define LOG(level, ...) \
 108     do { \
 109         static unsigned counter = 0; \
 110         logbug(&counter, level, __func__, __VA_ARGS__); \
 111     } while (0)
 112
 113 /* Evil non-standard GNU C macro ;)
 114  *  typeof keyword,
 115  *  statement-expression
 116  */
 117 #define CALL(func, ...) \
 118 ({ typeof (func) *sym = getsym ( # func); sym (__VA_ARGS__); })
 119
 120 /*** Environment ***
 121  *
 122  * "Conforming multi-threaded applications shall not use the environ variable
 123  *  to access or modify any environment variable while any other thread is
 124  *  concurrently modifying any environment variable." -- POSIX.
 125  *
 126  * Some evil libraries modify the environment. We currently ignore the calls as
 127  * they could crash the process. This may cause funny behaviour though. */
 128 int putenv (char *str)
 129 {
 130     if (override)
 131     {
 132         LOG("Blocked", "\"%s\"", str);
 133         return 0;
 134     }
 135     return CALL(putenv, str);
 136 }
 137
 138 int setenv (const char *name, const char *value, int overwrite)
 139 {
 140     if (override)
 141     {
 142         LOG("Blocked", "\"%s\", \"%s\", %d", name, value, overwrite);
 143         return 0;
 144     }
 145     return CALL(setenv, name, value, overwrite);
 146 }
 147
 148 int unsetenv (const char *name)
 149 {
 150     if (override)
 151     {
 152         LOG("Blocked", "\"%s\"", name);
 153         return 0;
 154     }
 155     return CALL(unsetenv, name);
 156 }
 157
 158
 159 /*** Pseudo random numbers ***
 160  *
 161  * The C PRNG is not thread-safe (and generally sucks, the POSIX 48-bits PRNG
 162  * is much better as a reproducible non-secure PRNG). To work around this, we
 163  * force evil callers to serialize. This makes the call safe, but fails to
 164  * preserve reproducibility of the number sequence (which usually does not
 165  * matter).
 166  **/
 167 static struct
 168 {
 169     pthread_mutex_t lock;
 170     unsigned int seed;
 171 } prng = { PTHREAD_MUTEX_INITIALIZER, 0, };
 172
 173 void srand (unsigned int seed)
 174 {
 175     pthread_mutex_lock (&prng.lock);
 176     LOG("Warning", "%d", seed);
 177     prng.seed = seed;
 178     pthread_mutex_unlock (&prng.lock);
 179 }
 180
 181 int rand (void)
 182 {
 183     int ret;
 184
 185     pthread_mutex_lock (&prng.lock);
 186     LOG("Warning", "");
 187     ret = rand_r (&prng.seed);
 188     pthread_mutex_unlock (&prng.lock);
 189     return ret;
 190 }
 191
 192
 193 #if 0
 194 /** Signals **/
 195 #include <signal.h>
 196
 197 static bool blocked_signal (int num)
 198 {
 199     switch (num)
 200     {
 201         case SIGINT:
 202         case SIGHUP:
 203         case SIGQUIT:
 204         case SIGTERM:
 205         case SIGPIPE:
 206         case SIGCHLD:
 207             return true;
 208     }
 209     return false;
 210 }
 211
 212 void (*signal (int signum, void (*handler) (int))) (int)
 213 {
 214     if (override)
 215     {
 216         if (handler != SIG_IGN && handler != SIG_DFL)
 217             goto error;
 218         if (!blocked_signal (signum))
 219             goto error;
 220         /* For our blocked signals, the handler won't matter much... */
 221         if (handler == SIG_DFL)
 222             LOG("Warning", "%d, SIG_DFL", signum, handler);
 223     }
 224     return CALL(signal, signum, handler);
 225 error:
 226     LOG("Blocked", "%d, %p", signum, handler);
 227     return SIG_DFL;
 228 }
 229
 230 int sigaction (int signum, const struct sigaction *act, struct sigaction *old)
 231 {
 232     if (override && act != NULL)
 233     {
 234         if ((act->sa_flags & SA_SIGINFO)
 235          || (act->sa_handler != SIG_IGN && act->sa_handler != SIG_DFL))
 236             goto error;
 237         if (act->sa_handler == SIG_DFL)
 238             LOG("Warning", "%d, %p, SIG_DFL", signum, act);
 239     }
 240     return CALL(sigaction, signum, act, old);
 241 error:
 242     LOG("Blocked", "%d, %p, %p", signum, act, old);
 243     return -1;
 244 }
 245 #endif
 246
 247
 248 /*** Locales ***
 249  * setlocale() is not thread-safe and has a tendency to crash other threads as
 250  * quite many libc and libintl calls depend on the locale.
 251  * Use uselocale() instead for thread-safety.
 252  */
 253 #include <locale.h>
 254
 255 char *setlocale (int cat, const char *locale)
 256 {
 257     if (override && locale != NULL)
 258     {
 259         LOG("Blocked", "%d, \"%s\"", cat, locale);
 260         return NULL;
 261     }
 262     return CALL(setlocale, cat, locale);
 263 }
 264
 265
 266 /* strerror() is not thread-safe in theory (POSIX), nor in practice (glibc).
 267  * This caused quite nasty crashes in the history of VLC/Linux. */
 268 char *strerror (int val)
 269 {
 270     if (override)
 271     {
 272         static const char msg[] =
 273             "Error message unavailable (use strerror_r instead of strerror)!";
 274         LOG("Blocked", "%d", val);
 275         return (char *)msg;
 276     }
 277     return CALL(strerror, val);
 278 }
 279
 280 /*** Xlib ****/
 281 #ifdef HAVE_X11_XLIB_H
 282 # include <X11/Xlib.h>
 283
 284 static pthread_mutex_t xlib_lock = PTHREAD_MUTEX_INITIALIZER;
 285
 286 int (*XSetErrorHandler (int (*handler) (Display *, XErrorEvent *)))
 287      (Display *, XErrorEvent *)
 288 {
 289     if (override)
 290     {
 291         int (*ret) (Display *, XErrorEvent *);
 292
 293         pthread_mutex_lock (&xlib_lock);
 294         LOG("Error", "%p", handler);
 295         ret = CALL(XSetErrorHandler, handler);
 296         pthread_mutex_unlock (&xlib_lock);
 297         return ret;
 298     }
 299     return CALL(XSetErrorHandler, handler);
 300 }
 301
 302 int (*XSetIOErrorHandler (int (*handler) (Display *))) (Display *)
 303 {
 304     if (override)
 305     {
 306         int (*ret) (Display *);
 307
 308         pthread_mutex_lock (&xlib_lock);
 309         LOG("Error", "%p", handler);
 310         ret = CALL(XSetIOErrorHandler, handler);
 311         pthread_mutex_unlock (&xlib_lock);
 312         return ret;
 313     }
 314     return CALL(XSetIOErrorHandler, handler);
 315 }
 316 #endif
 317 #else
 318 void vlc_enable_override (void)
 319 {
 320 }
 321 #endif