2001-01-26 Andrew Haley <aph@redhat.com>

        (INIT_FPE): Use a direct system call to set the handler.


git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@39354 138bc75d-0d04-0410-961f-82ee72b054a4

1 files changed, 16 insertions, 2 deletions

diff --git a/libjava/include/i386-signal.h b/libjava/include/i386-signal.h
index 599edc940ad..de2e39cdbc2 100644
--- a/libjava/include/i386-signal.h
+++ b/libjava/include/i386-signal.h
@@ -1,6 +1,6 @@
 // i386-signal.h - Catch runtime signals and turn them into exceptions.
 
-/* Copyright (C) 1998, 1999  Free Software Foundation
+/* Copyright (C) 1998, 1999, 2001  Free Software Foundation
 
    This file is part of libgcj.
 
@@ -17,6 +17,7 @@ details.  */
 #define JAVA_SIGNAL_H 1
 
 #include <signal.h>
+#include <sys/syscall.h>
 
 #define HANDLE_SEGV 1
 #define HANDLE_FPE 1
@@ -140,9 +141,22 @@ do								\
     act.sa_handler = catch_fpe;					\
     sigemptyset (&act.sa_mask);					\
     act.sa_flags = 0;						\
-    __sigaction (SIGFPE, &act, NULL);				\
+    syscall (SYS_sigaction, SIGFPE, &act, 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.  This is a kludge, and a future
+ * version of this handler will do something better.  */
+
 #endif /* JAVA_SIGNAL_H */