bin/override.c

   1 /*****************************************************************************
   2  * override.c: overriden 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 #endif
  43 #ifdef NDEBUG
  44 # undef HAVE_BACKTRACE
  45 #endif
  46
  47 static bool override = false;
  48
  49 static void vlc_reset_override (void)
  50 {
  51     override = false;
  52 }
  53
  54 void vlc_enable_override (void)
  55 {
  56     override = true;
  57     pthread_atfork (NULL, NULL, vlc_reset_override);
  58 }
  59
  60 static void vlogbug (unsigned *pc, const char *level, const char *func,
  61                      const char *fmt, va_list ap)
  62 {
  63 #ifdef HAVE_BACKTRACE
  64     const size_t framec = 5;
  65     void *framev[framec];
  66
  67     backtrace (framev, framec);
  68 #endif
  69     flockfile (stderr);
  70     if (*pc < MAX_ERRORS)
  71     {
  72         (*pc)++;
  73         fprintf (stderr, "%s: call to %s(", level, func);
  74         vfprintf (stderr, fmt, ap);
  75         fputs (")\n", stderr);
  76         fflush (stderr);
  77 #ifdef HAVE_BACKTRACE
  78         backtrace_symbols_fd (framev + 2, framec - 2, fileno (stderr));
  79 #endif
  80     }
  81     funlockfile (stderr);
  82 }
  83
  84 static void logbug (unsigned *pc, const char *level, const char *func,
  85                     const char *fmt, ...)
  86 {
  87     va_list ap;
  88
  89     va_start (ap, fmt);
  90     vlogbug (pc, level, func, fmt, ap);
  91     va_end (ap);
  92 }
  93
  94 static void *getsym (const char *name)
  95 {
  96     void *sym = dlsym (RTLD_NEXT, name);
  97     if (sym == NULL)
  98     {
  99         fprintf (stderr, "Cannot resolve symbol %s: %s\n", name,
 100                  dlerror ());
 101         abort ();
 102     }
 103     return sym;
 104 }
 105
 106 #define LOG(level, ...) \
 107     do { \
 108         static unsigned counter = 0; \
 109         logbug(&counter, level, __func__, __VA_ARGS__); \
 110     } while (0)
 111
 112 /* Evil non-standard GNU C macro ;)
 113  *  typeof keyword,
 114  *  statement-expression,
 115  *  nested function...
 116  */
 117 #define CALL(func, ...) \
 118 ({ \
 119     static typeof (func) *sym = NULL; \
 120     static pthread_once_t once = PTHREAD_ONCE_INIT; \
 121     auto void getsym_once (void); \
 122     void getsym_once (void) \
 123     { \
 124         sym = getsym ( # func); \
 125     } \
 126     pthread_once (&once, getsym_once); \
 127     sym (__VA_ARGS__); \
 128 })
 129
 130
 131 /*** Environment ***
 132  *
 133  * "Conforming multi-threaded applications shall not use the environ variable
 134  *  to access or modify any environment variable while any other thread is
 135  *  concurrently modifying any environment variable." -- POSIX.
 136  *
 137  * Some evil libraries modify the environment. We currently ignore the calls as
 138  * they could crash the process. This may cause funny behaviour though. */
 139 int putenv (char *str)
 140 {
 141     if (override)
 142     {
 143         LOG("Blocked", "\"%s\"", str);
 144         return 0;
 145     }
 146     return CALL(putenv, str);
 147 }
 148
 149 int setenv (const char *name, const char *value, int overwrite)
 150 {
 151     if (override)
 152     {
 153         LOG("Blocked", "\"%s\", \"%s\", %d", name, value, overwrite);
 154         return 0;
 155     }
 156     return CALL(setenv, name, value, overwrite);
 157 }
 158
 159 int unsetenv (const char *name)
 160 {
 161     if (override)
 162     {
 163         LOG("Blocked", "\"%s\"", name);
 164         return 0;
 165     }
 166     return CALL(unsetenv, name);
 167 }
 168
 169
 170 /*** Pseudo random numbers ***
 171  *
 172  * The C PRNG is not thread-safe (and generally sucks, the POSIX 48-bits PRNG
 173  * is much better as a reproducible non-secure PRNG). To work around this, we
 174  * force evil callers to serialize. This makes the call safe, but fails to
 175  * preserve reproducibility of the number sequence (which usually does not
 176  * matter).
 177  **/
 178 static struct
 179 {
 180     pthread_mutex_t lock;
 181     unsigned int seed;
 182 } prng = { PTHREAD_MUTEX_INITIALIZER, 0, };
 183
 184 void srand (unsigned int seed)
 185 {
 186     pthread_mutex_lock (&prng.lock);
 187     LOG("Warning", "%d", seed);
 188     prng.seed = seed;
 189     pthread_mutex_unlock (&prng.lock);
 190 }
 191
 192 int rand (void)
 193 {
 194     int ret;
 195
 196     pthread_mutex_lock (&prng.lock);
 197     LOG("Warning", "");
 198     ret = rand_r (&prng.seed);
 199     pthread_mutex_unlock (&prng.lock);
 200     return ret;
 201 }
 202
 203
 204 #if 0
 205 /** Signals **/
 206 #include <signal.h>
 207
 208 static bool blocked_signal (int num)
 209 {
 210     switch (num)
 211     {
 212         case SIGINT:
 213         case SIGHUP:
 214         case SIGQUIT:
 215         case SIGTERM:
 216         case SIGPIPE:
 217         case SIGCHLD:
 218             return true;
 219     }
 220     return false;
 221 }
 222
 223 void (*signal (int signum, void (*handler) (int))) (int)
 224 {
 225     if (override)
 226     {
 227         if (handler != SIG_IGN && handler != SIG_DFL)
 228             goto error;
 229         if (!blocked_signal (signum))
 230             goto error;
 231         /* For our blocked signals, the handler won't matter much... */
 232         if (handler == SIG_DFL)
 233             LOG("Warning", "%d, SIG_DFL", signum, handler);
 234     }
 235     return CALL(signal, signum, handler);
 236 error:
 237     LOG("Blocked", "%d, %p", signum, handler);
 238     return SIG_DFL;
 239 }
 240
 241 int sigaction (int signum, const struct sigaction *act, struct sigaction *old)
 242 {
 243     if (override && act != NULL)
 244     {
 245         if ((act->sa_flags & SA_SIGINFO)
 246          || (act->sa_handler != SIG_IGN && act->sa_handler != SIG_DFL))
 247             goto error;
 248         if (act->sa_handler == SIG_DFL)
 249             LOG("Warning", "%d, %p, SIG_DFL", signum, act);
 250     }
 251     return CALL(sigaction, signum, act, old);
 252 error:
 253     LOG("Blocked", "%d, %p, %p", signum, act, old);
 254     return -1;
 255 }
 256 #endif
 257
 258
 259 /*** Locales ***
 260  * setlocale() is not thread-safe and has a tendency to crash other threads as
 261  * quite many libc and libintl calls depend on the locale.
 262  * Use uselocale() instead for thread-safety.
 263  */
 264 #include <locale.h>
 265
 266 char *setlocale (int cat, const char *locale)
 267 {
 268     if (override && locale != NULL)
 269     {
 270         LOG("Blocked", "%d, \"%s\"", cat, locale);
 271         return NULL;
 272     }
 273     return CALL(setlocale, cat, locale);
 274 }
 275
 276
 277 /* strerror() is not thread-safe in theory (POSIX), nor in practice (glibc).
 278  * This caused quite nasty crashes in the history of VLC/Linux. */
 279 char *strerror (int val)
 280 {
 281     if (override)
 282     {
 283         static const char msg[] =
 284             "Error message unavailable (use strerror_r instead of strerror)!";
 285         LOG("Blocked", "%d", val);
 286         return (char *)msg;
 287     }
 288     return CALL(strerror, val);
 289 }
 290
 291 /*** Xlib ****/
 292 #ifdef HAVE_X11_XLIB_H
 293 # include <X11/Xlib.h>
 294
 295 static pthread_mutex_t xlib_lock = PTHREAD_MUTEX_INITIALIZER;
 296
 297 int (*XSetErrorHandler (int (*handler) (Display *, XErrorEvent *)))
 298      (Display *, XErrorEvent *)
 299 {
 300     if (override)
 301     {
 302         int (*ret) (Display *, XErrorEvent *);
 303
 304         pthread_mutex_lock (&xlib_lock);
 305         LOG("Error", "%p", handler);
 306         ret = CALL(XSetErrorHandler, handler);
 307         pthread_mutex_unlock (&xlib_lock);
 308         return ret;
 309     }
 310     return CALL(XSetErrorHandler, handler);
 311 }
 312
 313 int (*XSetIOErrorHandler (int (*handler) (Display *))) (Display *)
 314 {
 315     if (override)
 316     {
 317         int (*ret) (Display *);
 318
 319         pthread_mutex_lock (&xlib_lock);
 320         LOG("Error", "%p", handler);
 321         ret = CALL(XSetIOErrorHandler, handler);
 322         pthread_mutex_unlock (&xlib_lock);
 323         return ret;
 324     }
 325     return CALL(XSetIOErrorHandler, handler);
 326 }
 327 #endif
 328 #else
 329 void vlc_enable_override (void)
 330 {
 331 }
 332 #endif