-// i386-signal.h - Catch runtime signals and turn them into exceptions.
+// i386-signal.h - Catch runtime signals and turn them into exceptions
+// on an i386 based Linux system.
-/* Copyright (C) 1998, 1999 Cygnus Solutions
+/* Copyright (C) 1998, 1999, 2001, 2002 Free Software Foundation
This file is part of libgcj.
Libgcj License. Please consult the file "LIBGCJ_LICENSE" for
details. */
-/* This technique should work for all i386 based Unices which conform
- to iBCS2. This includes all versions of Linux more recent than
- version 1.3 */
-
#ifndef JAVA_SIGNAL_H
#define JAVA_SIGNAL_H 1
#include <signal.h>
+#include <sys/syscall.h>
#define HANDLE_SEGV 1
#define HANDLE_FPE 1
+#define SIGNAL_HANDLER(_name) \
+static void _name (int _dummy __attribute__ ((__unused__)))
+
+#define MAKE_THROW_FRAME(_exception) \
+do \
+{ \
+ void **_p = (void **)&_dummy; \
+ volatile struct sigcontext_struct *_regs = (struct sigcontext_struct *)++_p; \
+ \
+ /* Advance the program counter so that it is after the start of the \
+ instruction: the x86 exception handler expects \
+ the PC to point to the instruction after a call. */ \
+ _regs->eip += 2; \
+ \
+} \
+while (0)
-#define MAKE_THROW_FRAME(_dummy) \
+#define HANDLE_DIVIDE_OVERFLOW \
+do \
{ \
void **_p = (void **)&_dummy; \
- struct sigcontext_struct *_regs = (struct sigcontext_struct *)++_p; \
- \
- register unsigned long _ebp = _regs->ebp; \
- register unsigned long _eip = _regs->eip; \
- \
- asm volatile ("mov %0, (%%ebp); mov %1, 4(%%ebp)" \
- : : "r"(_ebp), "r"(_eip)); \
-}
+ volatile struct sigcontext_struct *_regs = (struct sigcontext_struct *)++_p;\
+ \
+ register unsigned char *_eip = (unsigned char *)_regs->eip; \
+ \
+ /* According to the JVM spec, "if the dividend is the negative \
+ * integer of the smallest magnitude and the divisor is -1, then \
+ * overflow occurs and the result is equal to the dividend. Despite \
+ * the overflow, no exception occurs". \
+ \
+ * We handle this by inspecting the instruction which generated the \
+ * signal and advancing eip to point to the following instruction. \
+ * As the instructions are variable length it is necessary to do a \
+ * little calculation to figure out where the following instruction \
+ * actually is. \
+ \
+ */ \
+ \
+ if (_eip[0] == 0xf7) \
+ { \
+ unsigned char _modrm = _eip[1]; \
+ \
+ if (_regs->eax == 0x80000000 \
+ && ((_modrm >> 3) & 7) == 7) /* Signed divide */ \
+ { \
+ unsigned char _rm = _modrm & 7; \
+ _regs->edx = 0; /* the remainder is zero */ \
+ switch (_modrm >> 6) \
+ { \
+ case 0: /* register indirect */ \
+ if (_rm == 5) /* 32-bit displacement */ \
+ _eip += 4; \
+ if (_rm == 4) /* A SIB byte follows the ModR/M byte */ \
+ _eip += 1; \
+ break; \
+ case 1: /* register indirect + 8-bit displacement */ \
+ _eip += 1; \
+ if (_rm == 4) /* A SIB byte follows the ModR/M byte */ \
+ _eip += 1; \
+ break; \
+ case 2: /* register indirect + 32-bit displacement */ \
+ _eip += 4; \
+ if (_rm == 4) /* A SIB byte follows the ModR/M byte */ \
+ _eip += 1; \
+ break; \
+ case 3: \
+ break; \
+ } \
+ _eip += 2; \
+ _regs->eip = (unsigned long)_eip; \
+ return; \
+ } \
+ else \
+ { \
+ /* Advance the program counter so that it is after the start \
+ of the instruction: this is because the x86 exception \
+ handler expects the PC to point to the instruction after a \
+ call. */ \
+ _regs->eip += 2; \
+ } \
+ } \
+} \
+while (0)
+
+/* We use old_kernel_sigaction here because we're calling the kernel
+ directly rather than via glibc. The sigaction structure that the
+ syscall uses is a different shape from the one in userland and not
+ visible to us in a header file so we define it here. */
+
+struct old_i386_kernel_sigaction {
+ void (*k_sa_handler) (int);
+ unsigned long k_sa_mask;
+ unsigned long k_sa_flags;
+ void (*sa_restorer) (void);
+};
+
+#define RESTORE(name, syscall) RESTORE2 (name, syscall)
+# define RESTORE2(name, syscall) \
+asm \
+ ( \
+ ".text\n" \
+ ".byte 0 # Yes, this really is necessary\n" \
+ " .align 8\n" \
+ "__" #name ":\n" \
+ " popl %eax\n" \
+ " movl $" #syscall ", %eax\n" \
+ " int $0x80" \
+ );
+
+RESTORE (restore, __NR_sigreturn)
+static void restore (void) asm ("__restore");
+
+#define INIT_SEGV \
+do \
+ { \
+ struct old_i386_kernel_sigaction kact; \
+ kact.k_sa_handler = catch_segv; \
+ kact.k_sa_mask = 0; \
+ kact.k_sa_flags = 0x4000000; \
+ kact.sa_restorer = restore; \
+ syscall (SYS_sigaction, SIGSEGV, &kact, NULL); \
+ } \
+while (0)
+
+#define INIT_FPE \
+do \
+ { \
+ struct old_i386_kernel_sigaction kact; \
+ kact.k_sa_handler = catch_fpe; \
+ kact.k_sa_mask = 0; \
+ kact.k_sa_flags = 0x4000000; \
+ kact.sa_restorer = restore; \
+ syscall (SYS_sigaction, SIGFPE, &kact, NULL); \
+ } \
+while (0)
+
+/* You might wonder why we use syscall(SYS_sigaction) in INIT_FPE
+ * instead of the standard sigaction(). This is necessary because of
+ * the shenanigans above where we increment the PC saved in the
+ * context and then return. This trick will only work when we are
+ * called _directly_ by the kernel, because linuxthreads wraps signal
+ * handlers and its wrappers do not copy the sigcontext struct back
+ * when returning from a signal handler. If we return from our divide
+ * handler to a linuxthreads wrapper, we will lose the PC adjustment
+ * we made and return to the faulting instruction again. Using
+ * syscall(SYS_sigaction) causes our handler to be called directly
+ * by the kernel, bypassing any wrappers.
+
+ * Also, there is at the present time no unwind info in the
+ * linuxthreads library's signal handlers and so we can't unwind
+ * through them anyway. */
#endif /* JAVA_SIGNAL_H */
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