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 #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  */
 116 #define CALL(func, ...) \
 117 ({ typeof (func) *sym = getsym ( # func); sym (__VA_ARGS__); })
 118
 119 /*** Environment ***
 120  *
 121  * "Conforming multi-threaded applications shall not use the environ variable
 122  *  to access or modify any environment variable while any other thread is
 123  *  concurrently modifying any environment variable." -- POSIX.
 124  *
 125  * Some evil libraries modify the environment. We currently ignore the calls as
 126  * they could crash the process. This may cause funny behaviour though. */
 127 int putenv (char *str)
 128 {
 129     if (override)
 130     {
 131         LOG("Blocked", "\"%s\"", str);
 132         return 0;
 133     }
 134     return CALL(putenv, str);
 135 }
 136
 137 int setenv (const char *name, const char *value, int overwrite)
 138 {
 139     if (override)
 140     {
 141         LOG("Blocked", "\"%s\", \"%s\", %d", name, value, overwrite);
 142         return 0;
 143     }
 144     return CALL(setenv, name, value, overwrite);
 145 }
 146
 147 int unsetenv (const char *name)
 148 {
 149     if (override)
 150     {
 151         LOG("Blocked", "\"%s\"", name);
 152         return 0;
 153     }
 154     return CALL(unsetenv, name);
 155 }
 156
 157
 158 /*** Pseudo random numbers ***
 159  *
 160  * The C PRNG is not thread-safe (and generally sucks, the POSIX 48-bits PRNG
 161  * is much better as a reproducible non-secure PRNG). To work around this, we
 162  * force evil callers to serialize. This makes the call safe, but fails to
 163  * preserve reproducibility of the number sequence (which usually does not
 164  * matter).
 165  **/
 166 static struct
 167 {
 168     pthread_mutex_t lock;
 169     unsigned int seed;
 170 } prng = { PTHREAD_MUTEX_INITIALIZER, 0, };
 171
 172 void srand (unsigned int seed)
 173 {
 174     pthread_mutex_lock (&prng.lock);
 175     LOG("Warning", "%d", seed);
 176     prng.seed = seed;
 177     pthread_mutex_unlock (&prng.lock);
 178 }
 179
 180 int rand (void)
 181 {
 182     int ret;
 183
 184     pthread_mutex_lock (&prng.lock);
 185     LOG("Warning", "");
 186     ret = rand_r (&prng.seed);
 187     pthread_mutex_unlock (&prng.lock);
 188     return ret;
 189 }
 190
 191
 192 #if 0
 193 /** Signals **/
 194 #include <signal.h>
 195
 196 static bool blocked_signal (int num)
 197 {
 198     switch (num)
 199     {
 200         case SIGINT:
 201         case SIGHUP:
 202         case SIGQUIT:
 203         case SIGTERM:
 204         case SIGPIPE:
 205         case SIGCHLD:
 206             return true;
 207     }
 208     return false;
 209 }
 210
 211 void (*signal (int signum, void (*handler) (int))) (int)
 212 {
 213     if (override)
 214     {
 215         if (handler != SIG_IGN && handler != SIG_DFL)
 216             goto error;
 217         if (!blocked_signal (signum))
 218             goto error;
 219         /* For our blocked signals, the handler won't matter much... */
 220         if (handler == SIG_DFL)
 221             LOG("Warning", "%d, SIG_DFL", signum, handler);
 222     }
 223     return CALL(signal, signum, handler);
 224 error:
 225     LOG("Blocked", "%d, %p", signum, handler);
 226     return SIG_DFL;
 227 }
 228
 229 int sigaction (int signum, const struct sigaction *act, struct sigaction *old)
 230 {
 231     if (override && act != NULL)
 232     {
 233         if ((act->sa_flags & SA_SIGINFO)
 234          || (act->sa_handler != SIG_IGN && act->sa_handler != SIG_DFL))
 235             goto error;
 236         if (act->sa_handler == SIG_DFL)
 237             LOG("Warning", "%d, %p, SIG_DFL", signum, act);
 238     }
 239     return CALL(sigaction, signum, act, old);
 240 error:
 241     LOG("Blocked", "%d, %p, %p", signum, act, old);
 242     return -1;
 243 }
 244 #endif
 245
 246
 247 /*** Locales ***
 248  * setlocale() is not thread-safe and has a tendency to crash other threads as
 249  * quite many libc and libintl calls depend on the locale.
 250  * Use uselocale() instead for thread-safety.
 251  */
 252 #include <locale.h>
 253
 254 char *setlocale (int cat, const char *locale)
 255 {
 256     if (override && locale != NULL)
 257     {
 258         LOG("Blocked", "%d, \"%s\"", cat, locale);
 259         return NULL;
 260     }
 261     return CALL(setlocale, cat, locale);
 262 }
 263
 264
 265 /* strerror() is not thread-safe in theory (POSIX), nor in practice (glibc).
 266  * This caused quite nasty crashes in the history of VLC/Linux. */
 267 char *strerror (int val)
 268 {
 269     if (override)
 270     {
 271         static const char msg[] =
 272             "Error message unavailable (use strerror_r instead of strerror)!";
 273         LOG("Blocked", "%d", val);
 274         return (char *)msg;
 275     }
 276     return CALL(strerror, val);
 277 }
 278
 279 /*** Xlib ****/
 280 #ifdef HAVE_X11_XLIB_H
 281 # include <X11/Xlib.h>
 282
 283 static pthread_mutex_t xlib_lock = PTHREAD_MUTEX_INITIALIZER;
 284
 285 int (*XSetErrorHandler (int (*handler) (Display *, XErrorEvent *)))
 286      (Display *, XErrorEvent *)
 287 {
 288     if (override)
 289     {
 290         int (*ret) (Display *, XErrorEvent *);
 291
 292         pthread_mutex_lock (&xlib_lock);
 293         LOG("Error", "%p", handler);
 294         ret = CALL(XSetErrorHandler, handler);
 295         pthread_mutex_unlock (&xlib_lock);
 296         return ret;
 297     }
 298     return CALL(XSetErrorHandler, handler);
 299 }
 300
 301 int (*XSetIOErrorHandler (int (*handler) (Display *))) (Display *)
 302 {
 303     if (override)
 304     {
 305         int (*ret) (Display *);
 306
 307         pthread_mutex_lock (&xlib_lock);
 308         LOG("Error", "%p", handler);
 309         ret = CALL(XSetIOErrorHandler, handler);
 310         pthread_mutex_unlock (&xlib_lock);
 311         return ret;
 312     }
 313     return CALL(XSetIOErrorHandler, handler);
 314 }
 315 #endif
 316 #else
 317 void vlc_enable_override (void)
 318 {
 319 }
 320 #endif