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 __attribute__ ((__unused__)))
  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           unsigned char _rm = _modrm & 7;                               \
  68           _regs->edx = 0; /* the remainder is zero */                   \
  69           switch (_modrm >> 6)                                          \
  70             {                                                           \
  71             case 0:  /* register indirect */                            \
  72               if (_rm == 5)   /* 32-bit displacement */                 \
  73                 _eip += 4;                                              \
  74               if (_rm == 4)  /* A SIB byte follows the ModR/M byte */   \
  75                 _eip += 1;                                              \
  76               break;                                                    \
  77             case 1:  /* register indirect + 8-bit displacement */       \
  78               _eip += 1;                                                \
  79               if (_rm == 4)  /* A SIB byte follows the ModR/M byte */   \
  80                 _eip += 1;                                              \
  81               break;                                                    \
  82             case 2:  /* register indirect + 32-bit displacement */      \
  83               _eip += 4;                                                \
  84               if (_rm == 4)  /* A SIB byte follows the ModR/M byte */   \
  85                 _eip += 1;                                              \
  86               break;                                                    \
  87             case 3:                                                     \
  88               break;                                                    \
  89             }                                                           \
  90           _eip += 2;                                                    \
  91           _regs->eip = (unsigned long)_eip;                             \
  92           return;                                                       \
  93         }                                                               \
  94       else                                                              \
  95         {                                                               \
  96           /* Advance the program counter so that it is after the start  \
  97              of the instruction: this is because the x86 exception      \
  98              handler expects the PC to point to the instruction after a \
  99              call. */                                                   \
 100           _regs->eip += 2;                                              \
 101         }                                                               \
 102     }                                                                   \
 103 }                                                                       \
 104 while (0)
 105
 106 /* We use old_kernel_sigaction here because we're calling the kernel
 107    directly rather than via glibc.  The sigaction structure that the
 108    syscall uses is a different shape from the one in userland and not
 109    visible to us in a header file so we define it here.  */
 110
 111 struct old_i386_kernel_sigaction {
 112         void (*k_sa_handler) (int);
 113         unsigned long k_sa_mask;
 114         unsigned long k_sa_flags;
 115         void (*sa_restorer) (void);
 116 };
 117
 118 #define RESTORE(name, syscall) RESTORE2 (name, syscall)
 119 # define RESTORE2(name, syscall) \
 120 asm                                             \
 121   (                                             \
 122    ".text\n"                                    \
 123    ".byte 0  # Yes, this really is necessary\n" \
 124    "    .align 8\n"                             \
 125    "__" #name ":\n"                             \
 126    "    popl %eax\n"                            \
 127    "    movl $" #syscall ", %eax\n"             \
 128    "    int  $0x80"                             \
 129    );
 130
 131 RESTORE (restore, __NR_sigreturn)
 132 static void restore (void) asm ("__restore");
 133
 134 #define INIT_SEGV                                       \
 135 do                                                      \
 136   {                                                     \
 137     struct old_i386_kernel_sigaction kact;              \
 138     kact.k_sa_handler = catch_segv;                     \
 139     kact.k_sa_mask = 0;                                 \
 140     kact.k_sa_flags = 0x4000000;                        \
 141     kact.sa_restorer = restore;                         \
 142     syscall (SYS_sigaction, SIGSEGV, &kact, NULL);      \
 143   }                                                     \
 144 while (0)
 145
 146 #define INIT_FPE                                        \
 147 do                                                      \
 148   {                                                     \
 149     struct old_i386_kernel_sigaction kact;              \
 150     kact.k_sa_handler = catch_fpe;                      \
 151     kact.k_sa_mask = 0;                                 \
 152     kact.k_sa_flags = 0x4000000;                        \
 153     kact.sa_restorer = restore;                         \
 154     syscall (SYS_sigaction, SIGFPE, &kact, NULL);       \
 155   }                                                     \
 156 while (0)
 157
 158 /* You might wonder why we use syscall(SYS_sigaction) in INIT_FPE
 159  * instead of the standard sigaction().  This is necessary because of
 160  * the shenanigans above where we increment the PC saved in the
 161  * context and then return.  This trick will only work when we are
 162  * called _directly_ by the kernel, because linuxthreads wraps signal
 163  * handlers and its wrappers do not copy the sigcontext struct back
 164  * when returning from a signal handler.  If we return from our divide
 165  * handler to a linuxthreads wrapper, we will lose the PC adjustment
 166  * we made and return to the faulting instruction again.  Using
 167  * syscall(SYS_sigaction) causes our handler to be called directly
 168  * by the kernel, bypassing any wrappers.
 169
 170  * Also, there is at the present time no unwind info in the
 171  * linuxthreads library's signal handlers and so we can't unwind
 172  * through them anyway.  */
 173
 174 #endif /* JAVA_SIGNAL_H */
 175