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, 2006, 2007  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 _Jv_##_name (int, siginfo_t *,                      \
  24                          void *_p __attribute__ ((__unused__)))
  25
  26 #define HANDLE_DIVIDE_OVERFLOW                                          \
  27 do                                                                      \
  28 {                                                                       \
  29   struct ucontext *_uc = (struct ucontext *)_p;                         \
  30   gregset_t &_gregs = _uc->uc_mcontext.gregs;                           \
  31   unsigned char *_eip = (unsigned char *)_gregs[REG_EIP];               \
  32                                                                         \
  33   /* According to the JVM spec, "if the dividend is the negative        \
  34    * integer of largest possible magnitude for the type and the         \
  35    * divisor is -1, then overflow occurs and the result is equal to     \
  36    * the dividend.  Despite the overflow, no exception occurs".         \
  37                                                                         \
  38    * We handle this by inspecting the instruction which generated the   \
  39    * signal and advancing ip to point to the following instruction.     \
  40    * As the instructions are variable length it is necessary to do a    \
  41    * little calculation to figure out where the following instruction   \
  42    * actually is.                                                       \
  43                                                                         \
  44   */                                                                    \
  45                                                                         \
  46   /* Detect a signed division of Integer.MIN_VALUE.  */                 \
  47   if (_eip[0] == 0xf7)                                                  \
  48     {                                                                   \
  49       bool _min_value_dividend = false;                                 \
  50       unsigned char _modrm = _eip[1];                                   \
  51                                                                         \
  52       if (((_modrm >> 3) & 7) == 7) /* Signed divide */                 \
  53         {                                                               \
  54           _min_value_dividend =                                         \
  55             _gregs[REG_EAX] == (greg_t)0x80000000UL;                    \
  56         }                                                               \
  57                                                                         \
  58       if (_min_value_dividend)                                          \
  59         {                                                               \
  60           unsigned char _rm = _modrm & 7;                               \
  61           _gregs[REG_EDX] = 0; /* the remainder is zero */              \
  62           switch (_modrm >> 6)                                          \
  63             {                                                           \
  64             case 0:  /* register indirect */                            \
  65               if (_rm == 5)   /* 32-bit displacement */                 \
  66                 _eip += 4;                                              \
  67               if (_rm == 4)  /* A SIB byte follows the ModR/M byte */   \
  68                 _eip += 1;                                              \
  69               break;                                                    \
  70             case 1:  /* register indirect + 8-bit displacement */       \
  71               _eip += 1;                                                \
  72               if (_rm == 4)  /* A SIB byte follows the ModR/M byte */   \
  73                 _eip += 1;                                              \
  74               break;                                                    \
  75             case 2:  /* register indirect + 32-bit displacement */      \
  76               _eip += 4;                                                \
  77               if (_rm == 4)  /* A SIB byte follows the ModR/M byte */   \
  78                 _eip += 1;                                              \
  79               break;                                                    \
  80             case 3:                                                     \
  81               break;                                                    \
  82             }                                                           \
  83           _eip += 2;                                                    \
  84           _gregs[REG_EIP] = (greg_t)_eip;                               \
  85           return;                                                       \
  86         }                                                               \
  87     }                                                                   \
  88 }                                                                       \
  89 while (0)
  90
  91 /* We use kernel_sigaction here because we're calling the kernel
  92    directly rather than via glibc.  The sigaction structure that the
  93    syscall uses is a different shape from the one in userland and not
  94    visible to us in a header file so we define it here.  */
  95
  96 extern "C"
  97 {
  98   struct kernel_sigaction
  99   {
 100     void (*k_sa_sigaction)(int,siginfo_t *,void *);
 101     unsigned long k_sa_flags;
 102     void (*k_sa_restorer) (void);
 103     sigset_t k_sa_mask;
 104   };
 105 }
 106
 107 #define MAKE_THROW_FRAME(_exception)
 108
 109 #define RESTORE(name, syscall) RESTORE2 (name, syscall)
 110 #define RESTORE2(name, syscall)                 \
 111 asm                                             \
 112   (                                             \
 113    ".text\n"                                    \
 114    ".byte 0  # Yes, this really is necessary\n" \
 115    "    .align 16\n"                            \
 116    "__" #name ":\n"                             \
 117    "    movl $" #syscall ", %eax\n"             \
 118    "    int  $0x80"                             \
 119    );
 120
 121 /* The return code for realtime-signals.  */
 122 RESTORE (restore_rt, __NR_rt_sigreturn)
 123 void restore_rt (void) asm ("__restore_rt")
 124   __attribute__ ((visibility ("hidden")));
 125
 126 #define INIT_SEGV                                               \
 127 do                                                              \
 128   {                                                             \
 129     struct kernel_sigaction act;                                \
 130     act.k_sa_sigaction = _Jv_catch_segv;                        \
 131     sigemptyset (&act.k_sa_mask);                               \
 132     act.k_sa_flags = SA_SIGINFO|0x4000000;                      \
 133     act.k_sa_restorer = restore_rt;                             \
 134     syscall (SYS_rt_sigaction, SIGSEGV, &act, NULL, _NSIG / 8); \
 135   }                                                             \
 136 while (0)
 137
 138 #define INIT_FPE                                                \
 139 do                                                              \
 140   {                                                             \
 141     struct kernel_sigaction act;                                \
 142     act.k_sa_sigaction = _Jv_catch_fpe;                         \
 143     sigemptyset (&act.k_sa_mask);                               \
 144     act.k_sa_flags = SA_SIGINFO|0x4000000;                      \
 145     act.k_sa_restorer = restore_rt;                             \
 146     syscall (SYS_rt_sigaction, SIGFPE, &act, NULL, _NSIG / 8);  \
 147   }                                                             \
 148 while (0)
 149
 150 /* You might wonder why we use syscall(SYS_sigaction) in INIT_FPE
 151  * instead of the standard sigaction().  This is necessary because of
 152  * the shenanigans above where we increment the PC saved in the
 153  * context and then return.  This trick will only work when we are
 154  * called _directly_ by the kernel, because linuxthreads wraps signal
 155  * handlers and its wrappers do not copy the sigcontext struct back
 156  * when returning from a signal handler.  If we return from our divide
 157  * handler to a linuxthreads wrapper, we will lose the PC adjustment
 158  * we made and return to the faulting instruction again.  Using
 159  * syscall(SYS_sigaction) causes our handler to be called directly
 160  * by the kernel, bypassing any wrappers.
 161
 162  * Also, there may not be any unwind info in the linuxthreads
 163  * library's signal handlers and so we can't unwind through them
 164  * anyway.  */
 165
 166 #endif /* JAVA_SIGNAL_H */
 167