From: Bodo Stroesser <bstroesser@fujitsu-siemens.com>

This patch changes stub_segv_handler for i386 (and s390 later)
to simplify it and save some syscalls.
My previous patch already left SIGSEGV unmasked while stub_segv_handler
is running.
Now, we do no longer mask *any* signals if stub_segv_handler runs.
SIG(RT)ALRM already is handled by wait_stub_done(), the other
signals (SIGIO, SIGWINCH) must not happen.
stub_segv_handler for i386 (and s390) now stop *inside* stub_segv_handler
using "int3" and do no longer call sigreturn.

For this, SIGUSR1 no longer should be blocked. So i386 (and s390) set:
   #define ARCH_STUB_SEGV_MASK_SIGNAL -1
while x86_64 sets
   #define ARCH_STUB_SEGV_MASK_SIGNAL SIGUSR1
Thus, x86_64 further uses sigreturn at the end of its stub_segv_handler
to avoid the RCX problem. As soon as that problem is solved, x86_64 also
might stop using "int3".

Using the change, we no longer need to care about correct stack pointer
for sigreturn, which would cause some nasty code on s390.

Signed-off-by: Bodo Stroesser <bstroesser@fujitsu-siemens.com>
---


diff -puN arch/um/os-Linux/skas/process.c~tune-stub_segv_handler arch/um/os-Linux/skas/process.c
--- linux-2.6.12-rc4/arch/um/os-Linux/skas/process.c~tune-stub_segv_handler	2005-07-15 14:12:15.240075682 +0200
+++ linux-2.6.12-rc4-root/arch/um/os-Linux/skas/process.c	2005-07-15 14:12:15.252071977 +0200
@@ -183,8 +183,7 @@ static int userspace_tramp(void *stack)
 
 		set_sigstack((void *) UML_CONFIG_STUB_DATA, page_size());
 		set_handler(SIGSEGV, (void *) v, SA_ONSTACK | SA_NOMASK,
-			    SIGIO, SIGWINCH, SIGALRM, SIGVTALRM,
-			    SIGUSR1, -1);
+			    ARCH_STUB_SEGV_MASK_SIGNAL, -1);
 	}
 
 	os_stop_process(os_getpid());
diff -puN arch/um/sys-i386/stub_segv.c~tune-stub_segv_handler arch/um/sys-i386/stub_segv.c
--- linux-2.6.12-rc4/arch/um/sys-i386/stub_segv.c~tune-stub_segv_handler	2005-07-15 14:12:15.242075065 +0200
+++ linux-2.6.12-rc4-root/arch/um/sys-i386/stub_segv.c	2005-07-15 14:13:17.652802252 +0200
@@ -19,13 +19,8 @@ stub_segv_handler(int sig)
 	GET_FAULTINFO_FROM_SC(*((struct faultinfo *) UML_CONFIG_STUB_DATA), 
 			      sc);
 
-	__asm__("movl %0, %%eax ; int $0x80": : "g" (__NR_getpid));
-	__asm__("movl %%eax, %%ebx ; movl %0, %%eax ; movl %1, %%ecx ;"
-		"int $0x80": : "g" (__NR_kill), "g" (SIGUSR1));
-	/* Load pointer to sigcontext into esp, since we need to leave
-	 * the stack in its original form when we do the sigreturn here, by
-	 * hand.
+	/* Our work is done, just stop the handler.
+	 * Registers will be restored later, if userspace() restarts us.
 	 */
-	__asm__("mov %0,%%esp ; movl %1, %%eax ; "
-		"int $0x80" : : "a" (sc), "g" (__NR_sigreturn));
+	__asm__("int3");
 }
diff -puN arch/um/include/sysdep-i386/faultinfo.h~tune-stub_segv_handler arch/um/include/sysdep-i386/faultinfo.h
--- linux-2.6.12-rc4/arch/um/include/sysdep-i386/faultinfo.h~tune-stub_segv_handler	2005-07-15 14:12:15.245074138 +0200
+++ linux-2.6.12-rc4-root/arch/um/include/sysdep-i386/faultinfo.h	2005-07-15 14:12:15.253071669 +0200
@@ -26,4 +26,6 @@ struct faultinfo {
 
 #define PTRACE_FULL_FAULTINFO 0
 
+#define ARCH_STUB_SEGV_MASK_SIGNAL -1
+
 #endif
diff -puN arch/um/include/sysdep-x86_64/faultinfo.h~tune-stub_segv_handler arch/um/include/sysdep-x86_64/faultinfo.h
--- linux-2.6.12-rc4/arch/um/include/sysdep-x86_64/faultinfo.h~tune-stub_segv_handler	2005-07-15 14:12:15.247073521 +0200
+++ linux-2.6.12-rc4-root/arch/um/include/sysdep-x86_64/faultinfo.h	2005-07-15 14:12:15.253071669 +0200
@@ -26,4 +26,6 @@ struct faultinfo {
 
 #define PTRACE_FULL_FAULTINFO 1
 
+#define ARCH_STUB_SEGV_MASK_SIGNAL SIGUSR1
+
 #endif
_