-// 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 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)
-#define MAKE_THROW_FRAME \
+#define MAKE_THROW_FRAME(_exception) \
do \
{ \
void **_p = (void **)&_dummy; \
struct sigcontext_struct *_regs = (struct sigcontext_struct *)++_p; \
\
- register unsigned long _ebp = _regs->ebp; \
- register unsigned char *_eip = (unsigned char *)_regs->eip; \
+ /* 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; \
\
- asm volatile ("mov %0, (%%ebp); mov %1, 4(%%ebp)" \
- : : "r"(_ebp), "r"(_eip)); \
} \
while (0)
void **_p = (void **)&_dummy; \
struct sigcontext_struct *_regs = (struct sigcontext_struct *)++_p; \
\
- register unsigned long *_ebp = (unsigned long *)_regs->ebp; \
register unsigned char *_eip = (unsigned char *)_regs->eip; \
\
/* According to the JVM spec, "if the dividend is the negative \
_regs->eip = (unsigned long)_eip; \
return; \
} \
- else if (((_modrm >> 3) & 7) == 6) /* Unsigned divide */ \
+ else \
{ \
- /* We assume that unsigned divisions are in library code, so \
- * we throw one level down the stack, which was hopefully \
- * the place that called the library routine. This will \
- * break if the library is ever compiled with \
- * -fomit-frame-pointer, but at least this way we've got a \
- * good chance of finding the exception handler. */ \
- \
- _eip = (unsigned char *)_ebp[1]; \
- _ebp = (unsigned long *)_ebp[0]; \
+ /* 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; \
} \
} \
- \
- asm volatile ("mov %0, (%%ebp); mov %1, 4(%%ebp)" \
- : : "r"(_ebp), "r"(_eip)); \
} \
while (0)
-#define INIT_SEGV \
-do \
- { \
- nullp = new java::lang::NullPointerException (); \
- struct sigaction act; \
- act.sa_handler = catch_segv; \
- sigemptyset (&act.sa_mask); \
- act.sa_flags = 0; \
- sigaction (SIGSEGV, &act, NULL); \
- } \
+/* 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 INIT_SEGV \
+do \
+ { \
+ nullp = new java::lang::NullPointerException (); \
+ struct old_i386_kernel_sigaction kact; \
+ kact.k_sa_handler = catch_segv; \
+ kact.k_sa_mask = 0; \
+ kact.k_sa_flags = 0; \
+ syscall (SYS_sigaction, SIGSEGV, &kact, NULL); \
+ } \
while (0)
-#define INIT_FPE \
+#define INIT_FPE \
do \
{ \
- arithexception = new java::lang::ArithmeticException \
+ arithexception = new java::lang::ArithmeticException \
(JvNewStringLatin1 ("/ by zero")); \
- struct sigaction act; \
- act.sa_handler = catch_fpe; \
- sigemptyset (&act.sa_mask); \
- act.sa_flags = 0; \
- sigaction (SIGFPE, &act, NULL); \
+ struct old_i386_kernel_sigaction kact; \
+ kact.k_sa_handler = catch_fpe; \
+ kact.k_sa_mask = 0; \
+ kact.k_sa_flags = 0; \
+ 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.
+
+ * Finally, the code that glibc uses to return from a signal handler
+ * is subject to change. */
+
#endif /* JAVA_SIGNAL_H */
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