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
  27 void vlc_enable_override (void);
  28
  29 #if defined (__GNUC__) \
  30  && (defined (__ELF__) && !defined (__sun__))
  31 /* Solaris crashes on printf("%s", NULL); which is legal, but annoying. */
  32
  33 #include <stdarg.h>
  34 #include <stdio.h>
  35 #include <stdlib.h>
  36 #include <string.h>
  37 #include <dlfcn.h>
  38 #include <pthread.h>
  39 #ifdef HAVE_EXECINFO_H
  40 # include <execinfo.h>
  41 #endif
  42 #ifdef NDEBUG
  43 # undef HAVE_BACKTRACE
  44 #endif
  45
  46 static bool override = false;
  47
  48 static void vlc_reset_override (void)
  49 {
  50     override = false;
  51 }
  52
  53 void vlc_enable_override (void)
  54 {
  55     override = true;
  56     pthread_atfork (NULL, NULL, vlc_reset_override);
  57 }
  58
  59 static void vlogbug (const char *level, const char *func, const char *fmt,
  60                      va_list ap)
  61 {
  62 #ifdef HAVE_BACKTRACE
  63     const size_t framec = 4;
  64     void *framev[framec];
  65
  66     backtrace (framev, framec);
  67 #endif
  68     flockfile (stderr);
  69     fprintf (stderr, "%s: call to %s(", level, func);
  70     vfprintf (stderr, fmt, ap);
  71     fputs (")\n", stderr);
  72     fflush (stderr);
  73 #ifdef HAVE_BACKTRACE
  74     backtrace_symbols_fd (framev + 2, framec - 2, fileno (stderr));
  75 #endif
  76     funlockfile (stderr);
  77 }
  78
  79 static void logbug (const char *level, const char *func, const char *fmt, ...)
  80 {
  81     va_list ap;
  82
  83     va_start (ap, fmt);
  84     vlogbug (level, func, fmt, ap);
  85     va_end (ap);
  86 }
  87
  88 static void *getsym (const char *name)
  89 {
  90     void *sym = dlsym (RTLD_NEXT, name);
  91     if (sym == NULL)
  92     {
  93         fprintf (stderr, "Cannot resolve symbol %s: %s\n", name,
  94                  dlerror ());
  95         abort ();
  96     }
  97     return sym;
  98 }
  99
 100 #define LOG(level, ...) logbug(level, __func__, __VA_ARGS__)
 101 /* Evil non-standard GNU C macro ;)
 102  *  typeof keyword,
 103  *  statement-expression,
 104  *  nested function...
 105  */
 106 #define CALL(func, ...) \
 107 ({ \
 108     static typeof (func) *sym = NULL; \
 109     static pthread_once_t once = PTHREAD_ONCE_INIT; \
 110     auto void getsym_once (void); \
 111     void getsym_once (void) \
 112     { \
 113         sym = getsym ( # func); \
 114     } \
 115     pthread_once (&once, getsym_once); \
 116     sym (__VA_ARGS__); \
 117 })
 118
 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 /** 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
 245
 246 /*** Locales ***
 247  * setlocale() is not thread-safe and has a tendency to crash other threads as
 248  * quite many libc and libintl calls depend on the locale.
 249  * Use uselocale() instead for thread-safety.
 250  */
 251 #include <locale.h>
 252
 253 char *setlocale (int cat, const char *locale)
 254 {
 255     if (override && locale != NULL)
 256     {
 257         LOG("Blocked", "%d, \"%s\"", cat, locale);
 258         return NULL;
 259     }
 260     return CALL(setlocale, cat, locale);
 261 }
 262
 263
 264 /* strerror() is not thread-safe in theory (POSIX), nor in practice (glibc).
 265  * This caused quite nasty crashes in the history of VLC/Linux. */
 266 char *strerror (int val)
 267 {
 268     if (override)
 269     {
 270         static const char msg[] =
 271             "Error message unavailable (use strerror_r instead of strerror)!";
 272         LOG("Blocked", "%d", val);
 273         return (char *)msg;
 274     }
 275     return CALL(strerror, val);
 276 }
 277
 278 /*** Xlib ****/
 279 #ifdef HAVE_X11_XLIB_H
 280 # include <X11/Xlib.h>
 281
 282 static pthread_mutex_t xlib_lock = PTHREAD_MUTEX_INITIALIZER;
 283
 284 int (*XSetErrorHandler (int (*handler) (Display *, XErrorEvent *)))
 285      (Display *, XErrorEvent *)
 286 {
 287     if (override)
 288     {
 289         int (*ret) (Display *, XErrorEvent *);
 290
 291         pthread_mutex_lock (&xlib_lock);
 292         LOG("Error", "%p", handler);
 293         ret = CALL(XSetErrorHandler, handler);
 294         pthread_mutex_unlock (&xlib_lock);
 295         return ret;
 296     }
 297     return CALL(XSetErrorHandler, handler);
 298 }
 299
 300 int (*XSetIOErrorHandler (int (*handler) (Display *))) (Display *)
 301 {
 302     if (override)
 303     {
 304         int (*ret) (Display *);
 305
 306         pthread_mutex_lock (&xlib_lock);
 307         LOG("Error", "%p", handler);
 308         ret = CALL(XSetIOErrorHandler, handler);
 309         pthread_mutex_unlock (&xlib_lock);
 310         return ret;
 311     }
 312     return CALL(XSetIOErrorHandler, handler);
 313 }
 314 #endif
 315 #else
 316 void vlc_enable_override (void)
 317 {
 318 }
 319 #endif