Re: [uml-devel] Am I doing something wrong with -skas0?

[Bodo Stroesser <bstroesser@fujitsu-siemens.com>]

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Bodo Stroesser wrote:
> stub_segv_handler misses the "push ebp" at the beginning. As you
> do the normally corresponding "pop eax" explicitly, I think stack
> pointer is wrong on call of sigreturn.
> 
> I have no idea, what makes happen this. Maybe it depends on compiler
> version?
> 

I hope, the attached patch fixes the problem. The patch is tested in
my 2.6.12-rc4 + skas0, where I didn't see the problem. It still works
fine for me.

Rob, could you please test whether the patch fixes the problem for you?

	Bodo

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# 
# From: Bodo Stroesser <bstroesser@fujitsu-siemens.com>
# 
# It's wrong to pop a fixed number of words from stack before
# calling sigreturn, as the number depends on what code is generated
# by the compiler for the start of stub_segv_handler().
# What we need is esp containing the address of sigcontext. So we
# explicitly load that pointer into esp.
# 
# Signed-off-by: Bodo Stroesser <bstroesser@fujitsu-siemens.com>

Index: linux-2.6.12-rc4/arch/um/sys-i386/stub_segv.c
===================================================================
--- linux-2.6.12-rc4.orig/arch/um/sys-i386/stub_segv.c	2005-07-14 13:15:53.364847980 +0200
+++ linux-2.6.12-rc4/arch/um/sys-i386/stub_segv.c	2005-07-14 13:36:02.980002269 +0200
@@ -22,10 +22,10 @@ stub_segv_handler(int sig)
 	__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));
-	/* Pop the frame pointer and return address since we need to leave
+	/* 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.
 	 */
-	__asm__("popl %%eax ; popl %%eax ; popl %%eax ; movl %0, %%eax ; "
-		"int $0x80" : : "g" (__NR_sigreturn));
+	__asm__("mov %0,%%esp ; movl %1, %%eax ; "
+		"int $0x80" : : "a" (sc), "g" (__NR_sigreturn));
 }