[PATCH] uml: skas0 stubs now check system call return values

Change syscall-stub's data to include a "expected retval".

Stub now checks syscalls retval and aborts execution of syscall list, if
retval != expected retval.

run_syscall_stub prints the data of the failed syscall, using the data pointer
and retval written by the stub to the beginning of the stack.

one_syscall_stub is removed, to simplify code, because only some instructions
are saved by one_syscall_stub, no host-syscall.

Using the stub with additional data (modify_ldt via stub)
is prepared also.

Signed-off-by: Bodo Stroesser <bstroesser@fujitsu-siemens.com>
Signed-off-by: Jeff Dike <jdike@addtoit.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

arch/um/sys-i386/stub.S

@@ -2,24 +2,50 @@
 
 	.globl syscall_stub
 .section .__syscall_stub, "x"
-syscall_stub:
-	int 	$0x80
-	mov	%eax, UML_CONFIG_STUB_DATA
-	int3
 
 	.globl batch_syscall_stub
 batch_syscall_stub:
-	mov	$UML_CONFIG_STUB_DATA, %esp
-again:	pop	%eax
+	/* load pointer to first operation */
+	mov	$(UML_CONFIG_STUB_DATA+8), %esp
+
+again:
+	/* load length of additional data */
+	mov	0x0(%esp), %eax
+
+	/* if(length == 0) : end of list */
+	/* write possible 0 to header */
+	mov	%eax, UML_CONFIG_STUB_DATA+4
 	cmpl	$0, %eax
 	jz	done
+
+	/* save current pointer */
+	mov	%esp, UML_CONFIG_STUB_DATA+4
+
+	/* skip additional data */
+	add	%eax, %esp
+
+	/* load syscall-# */
+	pop	%eax
+
+	/* load syscall params */
 	pop	%ebx
 	pop	%ecx
 	pop	%edx
 	pop	%esi
  	pop	%edi
 	pop	%ebp
+
+	/* execute syscall */
 	int	$0x80
+
+	/* check return value */
+	pop	%ebx
+	cmp	%ebx, %eax
+	je	again
+
+done:
+	/* save return value */
 	mov	%eax, UML_CONFIG_STUB_DATA
-	jmp	again
-done:	int3
+
+	/* stop */
+	int3