| 1 | // i386-signal.h - Catch runtime signals and turn them into exceptions
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| 2 | // on an i386 based Linux system.
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| 3 |
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| 4 | /* Copyright (C) 1998, 1999, 2001, 2002 Free Software Foundation
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| 5 |
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| 6 | This file is part of libgcj.
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| 7 |
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| 8 | This software is copyrighted work licensed under the terms of the
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| 9 | Libgcj License. Please consult the file "LIBGCJ_LICENSE" for
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| 10 | details. */
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| 11 |
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| 12 |
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| 13 | #ifndef JAVA_SIGNAL_H
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| 14 | #define JAVA_SIGNAL_H 1
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| 15 |
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| 16 | #include <signal.h>
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| 17 | #include <sys/syscall.h>
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| 18 |
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| 19 | #define HANDLE_SEGV 1
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| 20 | #define HANDLE_FPE 1
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| 21 |
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| 22 | #define SIGNAL_HANDLER(_name) \
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| 23 | static void _name (int _dummy)
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| 24 |
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| 25 | #define MAKE_THROW_FRAME(_exception) \
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| 26 | do \
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| 27 | { \
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| 28 | void **_p = (void **)&_dummy; \
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| 29 | struct sigcontext_struct *_regs = (struct sigcontext_struct *)++_p; \
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| 30 | \
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| 31 | /* Advance the program counter so that it is after the start of the \
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| 32 | instruction: the x86 exception handler expects \
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| 33 | the PC to point to the instruction after a call. */ \
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| 34 | _regs->eip += 2; \
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| 35 | \
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| 36 | } \
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| 37 | while (0)
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| 38 |
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| 39 | #define HANDLE_DIVIDE_OVERFLOW \
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| 40 | do \
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| 41 | { \
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| 42 | void **_p = (void **)&_dummy; \
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| 43 | struct sigcontext_struct *_regs = (struct sigcontext_struct *)++_p; \
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| 44 | \
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| 45 | register unsigned char *_eip = (unsigned char *)_regs->eip; \
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| 46 | \
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| 47 | /* According to the JVM spec, "if the dividend is the negative \
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| 48 | * integer of the smallest magnitude and the divisor is -1, then \
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| 49 | * overflow occurs and the result is equal to the dividend. Despite \
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| 50 | * the overflow, no exception occurs". \
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| 51 | \
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| 52 | * We handle this by inspecting the instruction which generated the \
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| 53 | * signal and advancing eip to point to the following instruction. \
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| 54 | * As the instructions are variable length it is necessary to do a \
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| 55 | * little calculation to figure out where the following instruction \
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| 56 | * actually is. \
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| 57 | \
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| 58 | */ \
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| 59 | \
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| 60 | if (_eip[0] == 0xf7) \
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| 61 | { \
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| 62 | unsigned char _modrm = _eip[1]; \
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| 63 | \
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| 64 | if (_regs->eax == 0x80000000 \
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| 65 | && ((_modrm >> 3) & 7) == 7) /* Signed divide */ \
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| 66 | { \
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| 67 | _regs->edx = 0; /* the remainder is zero */ \
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| 68 | switch (_modrm >> 6) \
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| 69 | { \
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| 70 | case 0: \
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| 71 | if ((_modrm & 7) == 5) \
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| 72 | _eip += 4; \
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| 73 | break; \
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| 74 | case 1: \
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| 75 | _eip += 1; \
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| 76 | break; \
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| 77 | case 2: \
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| 78 | _eip += 4; \
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| 79 | break; \
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| 80 | case 3: \
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| 81 | break; \
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| 82 | } \
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| 83 | _eip += 2; \
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| 84 | _regs->eip = (unsigned long)_eip; \
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| 85 | return; \
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| 86 | } \
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| 87 | else \
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| 88 | { \
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| 89 | /* Advance the program counter so that it is after the start \
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| 90 | of the instruction: this is because the x86 exception \
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| 91 | handler expects the PC to point to the instruction after a \
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| 92 | call. */ \
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| 93 | _regs->eip += 2; \
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| 94 | } \
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| 95 | } \
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| 96 | } \
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| 97 | while (0)
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| 98 |
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| 99 | /* We use old_kernel_sigaction here because we're calling the kernel
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| 100 | directly rather than via glibc. The sigaction structure that the
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| 101 | syscall uses is a different shape from the one in userland and not
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| 102 | visible to us in a header file so we define it here. */
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| 103 |
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| 104 | struct old_i386_kernel_sigaction {
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| 105 | void (*k_sa_handler) (int);
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| 106 | unsigned long k_sa_mask;
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| 107 | unsigned long k_sa_flags;
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| 108 | void (*sa_restorer) (void);
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| 109 | };
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| 110 |
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| 111 | #define RESTORE(name, syscall) RESTORE2 (name, syscall)
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| 112 | # define RESTORE2(name, syscall) \
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| 113 | asm \
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| 114 | ( \
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| 115 | ".text\n" \
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| 116 | ".byte 0 # Yes, this really is necessary\n" \
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| 117 | " .align 8\n" \
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| 118 | "__" #name ":\n" \
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| 119 | " popl %eax\n" \
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| 120 | " movl $" #syscall ", %eax\n" \
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| 121 | " int $0x80" \
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| 122 | );
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| 123 |
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| 124 | RESTORE (restore, __NR_sigreturn)
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| 125 | static void restore (void) asm ("__restore");
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| 126 |
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| 127 | #define INIT_SEGV \
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| 128 | do \
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| 129 | { \
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| 130 | nullp = new java::lang::NullPointerException (); \
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| 131 | struct old_i386_kernel_sigaction kact; \
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| 132 | kact.k_sa_handler = catch_segv; \
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| 133 | kact.k_sa_mask = 0; \
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| 134 | kact.k_sa_flags = 0x4000000; \
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| 135 | kact.sa_restorer = restore; \
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| 136 | syscall (SYS_sigaction, SIGSEGV, &kact, NULL); \
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| 137 | } \
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| 138 | while (0)
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| 139 |
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| 140 | #define INIT_FPE \
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| 141 | do \
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| 142 | { \
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| 143 | arithexception = new java::lang::ArithmeticException \
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| 144 | (JvNewStringLatin1 ("/ by zero")); \
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| 145 | struct old_i386_kernel_sigaction kact; \
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| 146 | kact.k_sa_handler = catch_fpe; \
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| 147 | kact.k_sa_mask = 0; \
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| 148 | kact.k_sa_flags = 0x4000000; \
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| 149 | kact.sa_restorer = restore; \
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| 150 | syscall (SYS_sigaction, SIGFPE, &kact, NULL); \
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| 151 | } \
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| 152 | while (0)
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| 153 |
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| 154 | /* You might wonder why we use syscall(SYS_sigaction) in INIT_FPE
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| 155 | * instead of the standard sigaction(). This is necessary because of
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| 156 | * the shenanigans above where we increment the PC saved in the
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| 157 | * context and then return. This trick will only work when we are
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| 158 | * called _directly_ by the kernel, because linuxthreads wraps signal
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| 159 | * handlers and its wrappers do not copy the sigcontext struct back
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| 160 | * when returning from a signal handler. If we return from our divide
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| 161 | * handler to a linuxthreads wrapper, we will lose the PC adjustment
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| 162 | * we made and return to the faulting instruction again. Using
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| 163 | * syscall(SYS_sigaction) causes our handler to be called directly
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| 164 | * by the kernel, bypassing any wrappers.
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| 165 |
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| 166 | * Also, there is at the present time no unwind info in the
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| 167 | * linuxthreads library's signal handlers and so we can't unwind
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| 168 | * through them anyway. */
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| 169 |
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| 170 | #endif /* JAVA_SIGNAL_H */
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| 171 |
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