libjava/include/i386-signal.h

   1 // i386-signal.h - Catch runtime signals and turn them into exceptions
   2 // on an i386 based Linux system.
   3
   4 /* Copyright (C) 1998, 1999, 2001, 2002  Free Software Foundation
   5
   6    This file is part of libgcj.
   7
   8 This software is copyrighted work licensed under the terms of the
   9 Libgcj License.  Please consult the file "LIBGCJ_LICENSE" for
  10 details.  */
  11
  12
  13 #ifndef JAVA_SIGNAL_H
  14 #define JAVA_SIGNAL_H 1
  15
  16 #include <signal.h>
  17 #include <sys/syscall.h>
  18
  19 #define HANDLE_SEGV 1
  20 #define HANDLE_FPE 1
  21
  22 #define SIGNAL_HANDLER(_name)   \
  23 static void _name (int _dummy)
  24
  25 #define MAKE_THROW_FRAME(_exception)                                    \
  26 do                                                                      \
  27 {                                                                       \
  28   void **_p = (void **)&_dummy;                                         \
  29   volatile struct sigcontext_struct *_regs = (struct sigcontext_struct *)++_p;  \
  30                                                                         \
  31   /* Advance the program counter so that it is after the start of the   \
  32      instruction:  the x86 exception handler expects                    \
  33      the PC to point to the instruction after a call. */                \
  34   _regs->eip += 2;                                                      \
  35                                                                         \
  36 }                                                                       \
  37 while (0)
  38
  39 #define HANDLE_DIVIDE_OVERFLOW                                          \
  40 do                                                                      \
  41 {                                                                       \
  42   void **_p = (void **)&_dummy;                                         \
  43   volatile struct sigcontext_struct *_regs = (struct sigcontext_struct *)++_p;\
  44                                                                         \
  45   register unsigned char *_eip = (unsigned char *)_regs->eip;           \
  46                                                                         \
  47   /* According to the JVM spec, "if the dividend is the negative        \
  48    * integer of the smallest magnitude and the divisor is -1, then      \
  49    * overflow occurs and the result is equal to the dividend.  Despite  \
  50    * the overflow, no exception occurs".                                \
  51                                                                         \
  52    * We handle this by inspecting the instruction which generated the   \
  53    * signal and advancing eip to point to the following instruction.    \
  54    * As the instructions are variable length it is necessary to do a    \
  55    * little calculation to figure out where the following instruction   \
  56    * actually is.                                                       \
  57                                                                         \
  58    */                                                                   \
  59                                                                         \
  60   if (_eip[0] == 0xf7)                                                  \
  61     {                                                                   \
  62       unsigned char _modrm = _eip[1];                                   \
  63                                                                         \
  64       if (_regs->eax == 0x80000000                                      \
  65           && ((_modrm >> 3) & 7) == 7) /* Signed divide */              \
  66         {                                                               \
  67           _regs->edx = 0; /* the remainder is zero */                   \
  68           switch (_modrm >> 6)                                          \
  69             {                                                           \
  70             case 0:                                                     \
  71               if ((_modrm & 7) == 5)                                    \
  72                 _eip += 4;                                              \
  73               break;                                                    \
  74             case 1:                                                     \
  75               _eip += 1;                                                \
  76               break;                                                    \
  77             case 2:                                                     \
  78               _eip += 4;                                                \
  79               break;                                                    \
  80             case 3:                                                     \
  81               break;                                                    \
  82             }                                                           \
  83           _eip += 2;                                                    \
  84           _regs->eip = (unsigned long)_eip;                             \
  85           return;                                                       \
  86         }                                                               \
  87       else                                                              \
  88         {                                                               \
  89           /* Advance the program counter so that it is after the start  \
  90              of the instruction: this is because the x86 exception      \
  91              handler expects the PC to point to the instruction after a \
  92              call. */                                                   \
  93           _regs->eip += 2;                                              \
  94         }                                                               \
  95     }                                                                   \
  96 }                                                                       \
  97 while (0)
  98
  99 /* We use old_kernel_sigaction here because we're calling the kernel
 100    directly rather than via glibc.  The sigaction structure that the
 101    syscall uses is a different shape from the one in userland and not
 102    visible to us in a header file so we define it here.  */
 103
 104 struct old_i386_kernel_sigaction {
 105         void (*k_sa_handler) (int);
 106         unsigned long k_sa_mask;
 107         unsigned long k_sa_flags;
 108         void (*sa_restorer) (void);
 109 };
 110
 111 #define RESTORE(name, syscall) RESTORE2 (name, syscall)
 112 # define RESTORE2(name, syscall) \
 113 asm                                             \
 114   (                                             \
 115    ".text\n"                                    \
 116    ".byte 0  # Yes, this really is necessary\n" \
 117    "    .align 8\n"                             \
 118    "__" #name ":\n"                             \
 119    "    popl %eax\n"                            \
 120    "    movl $" #syscall ", %eax\n"             \
 121    "    int  $0x80"                             \
 122    );
 123
 124 RESTORE (restore, __NR_sigreturn)
 125 static void restore (void) asm ("__restore");
 126
 127 #define INIT_SEGV                                       \
 128 do                                                      \
 129   {                                                     \
 130     struct old_i386_kernel_sigaction kact;              \
 131     kact.k_sa_handler = catch_segv;                     \
 132     kact.k_sa_mask = 0;                                 \
 133     kact.k_sa_flags = 0x4000000;                        \
 134     kact.sa_restorer = restore;                         \
 135     syscall (SYS_sigaction, SIGSEGV, &kact, NULL);      \
 136   }                                                     \
 137 while (0)
 138
 139 #define INIT_FPE                                        \
 140 do                                                      \
 141   {                                                     \
 142     struct old_i386_kernel_sigaction kact;              \
 143     kact.k_sa_handler = catch_fpe;                      \
 144     kact.k_sa_mask = 0;                                 \
 145     kact.k_sa_flags = 0x4000000;                        \
 146     kact.sa_restorer = restore;                         \
 147     syscall (SYS_sigaction, SIGFPE, &kact, NULL);       \
 148   }                                                     \
 149 while (0)
 150
 151 /* You might wonder why we use syscall(SYS_sigaction) in INIT_FPE
 152  * instead of the standard sigaction().  This is necessary because of
 153  * the shenanigans above where we increment the PC saved in the
 154  * context and then return.  This trick will only work when we are
 155  * called _directly_ by the kernel, because linuxthreads wraps signal
 156  * handlers and its wrappers do not copy the sigcontext struct back
 157  * when returning from a signal handler.  If we return from our divide
 158  * handler to a linuxthreads wrapper, we will lose the PC adjustment
 159  * we made and return to the faulting instruction again.  Using
 160  * syscall(SYS_sigaction) causes our handler to be called directly
 161  * by the kernel, bypassing any wrappers.
 162
 163  * Also, there is at the present time no unwind info in the
 164  * linuxthreads library's signal handlers and so we can't unwind
 165  * through them anyway.  */
 166
 167 #endif /* JAVA_SIGNAL_H */
 168