libjava/include/i386-signal.h

   1 // i386-signal.h - Catch runtime signals and turn them into exceptions.
   2
   3 /* Copyright (C) 1998, 1999, 2001  Free Software Foundation
   4
   5    This file is part of libgcj.
   6
   7 This software is copyrighted work licensed under the terms of the
   8 Libgcj License.  Please consult the file "LIBGCJ_LICENSE" for
   9 details.  */
  10
  11 /* This technique should work for all i386 based Unices which conform
  12  * to iBCS2.  This includes all versions of Linux more recent than 1.3
  13  */
  14
  15
  16 #ifndef JAVA_SIGNAL_H
  17 #define JAVA_SIGNAL_H 1
  18
  19 #include <signal.h>
  20 #include <sys/syscall.h>
  21
  22 #define HANDLE_SEGV 1
  23 #define HANDLE_FPE 1
  24
  25 #define SIGNAL_HANDLER(_name)   \
  26 static void _name (int _dummy)
  27
  28 #define MAKE_THROW_FRAME(_exception)                                    \
  29 do                                                                      \
  30 {                                                                       \
  31   void **_p = (void **)&_dummy;                                         \
  32   struct sigcontext_struct *_regs = (struct sigcontext_struct *)++_p;   \
  33                                                                         \
  34   /* Advance the program counter so that it is after the start of the   \
  35      instruction:  the x86 exception handler expects                    \
  36      the PC to point to the instruction after a call. */                \
  37   _regs->eip += 2;                                                      \
  38                                                                         \
  39 }                                                                       \
  40 while (0)
  41
  42 #define HANDLE_DIVIDE_OVERFLOW                                          \
  43 do                                                                      \
  44 {                                                                       \
  45   void **_p = (void **)&_dummy;                                         \
  46   struct sigcontext_struct *_regs = (struct sigcontext_struct *)++_p;   \
  47                                                                         \
  48   register unsigned char *_eip = (unsigned char *)_regs->eip;           \
  49                                                                         \
  50   /* According to the JVM spec, "if the dividend is the negative        \
  51    * integer of the smallest magnitude and the divisor is -1, then      \
  52    * overflow occurs and the result is equal to the dividend.  Despite  \
  53    * the overflow, no exception occurs".                                \
  54                                                                         \
  55    * We handle this by inspecting the instruction which generated the   \
  56    * signal and advancing eip to point to the following instruction.    \
  57    * As the instructions are variable length it is necessary to do a    \
  58    * little calculation to figure out where the following instruction   \
  59    * actually is.                                                       \
  60                                                                         \
  61    */                                                                   \
  62                                                                         \
  63   if (_eip[0] == 0xf7)                                                  \
  64     {                                                                   \
  65       unsigned char _modrm = _eip[1];                                   \
  66                                                                         \
  67       if (_regs->eax == 0x80000000                                      \
  68           && ((_modrm >> 3) & 7) == 7) /* Signed divide */              \
  69         {                                                               \
  70           _regs->edx = 0; /* the remainder is zero */                   \
  71           switch (_modrm >> 6)                                          \
  72             {                                                           \
  73             case 0:                                                     \
  74               if ((_modrm & 7) == 5)                                    \
  75                 _eip += 4;                                              \
  76               break;                                                    \
  77             case 1:                                                     \
  78               _eip += 1;                                                \
  79               break;                                                    \
  80             case 2:                                                     \
  81               _eip += 4;                                                \
  82               break;                                                    \
  83             case 3:                                                     \
  84               break;                                                    \
  85             }                                                           \
  86           _eip += 2;                                                    \
  87           _regs->eip = (unsigned long)_eip;                             \
  88           return;                                                       \
  89         }                                                               \
  90       else                                                              \
  91         {                                                               \
  92           /* Advance the program counter so that it is after the start  \
  93              of the instruction: this is because the x86 exception      \
  94              handler expects the PC to point to the instruction after a \
  95              call. */                                                   \
  96           _regs->eip += 2;                                              \
  97         }                                                               \
  98     }                                                                   \
  99 }                                                                       \
 100 while (0)
 101
 102 #define INIT_SEGV                                               \
 103 do                                                              \
 104   {                                                             \
 105     nullp = new java::lang::NullPointerException ();            \
 106     struct sigaction act;                                       \
 107     act.sa_handler = catch_segv;                                \
 108     sigemptyset (&act.sa_mask);                                 \
 109     act.sa_flags = 0;                                           \
 110     syscall (SYS_sigaction, SIGSEGV, &act, NULL);               \
 111   }                                                             \
 112 while (0)
 113
 114 #define INIT_FPE                                                \
 115 do                                                              \
 116   {                                                             \
 117     arithexception = new java::lang::ArithmeticException        \
 118       (JvNewStringLatin1 ("/ by zero"));                        \
 119     struct sigaction act;                                       \
 120     act.sa_handler = catch_fpe;                                 \
 121     sigemptyset (&act.sa_mask);                                 \
 122     act.sa_flags = 0;                                           \
 123     syscall (SYS_sigaction, SIGFPE, &act, NULL);                \
 124   }                                                             \
 125 while (0)
 126
 127 /* You might wonder why we use syscall(SYS_sigaction) in INIT_FPE
 128  * instead of the standard sigaction().  This is necessary because of
 129  * the shenanigans above where we increment the PC saved in the
 130  * context and then return.  This trick will only work when we are
 131  * called _directly_ by the kernel, because linuxthreads wraps signal
 132  * handlers and its wrappers do not copy the sigcontext struct back
 133  * when returning from a signal handler.  If we return from our divide
 134  * handler to a linuxthreads wrapper, we will lose the PC adjustment
 135  * we made and return to the faulting instruction again.  Using
 136  * syscall(SYS_sigaction) causes our handler to be called directly by
 137  * the kernel, bypassing any wrappers.  This is a kludge, and a future
 138  * version of this handler will do something better.  */
 139
 140 #endif /* JAVA_SIGNAL_H */
 141