x86: trampoline: fix GOT clobbering, pointed out by fabled

arch/x86/startcontext.S

@@ -15,15 +15,26 @@ __start_context:
 	/* get the proper context into position and test for NULL */
 	leal	(%esp,%ebx,4), %esp
 	cmpl	$0, (%esp)
-	je	hosed
+
+	/* restore global offset table, exit@plt and __setcontext@plt need this */
+	call	__i686.get_pc_thunk.bx
+	addl	$_GLOBAL_OFFSET_TABLE_, %ebx
+
+	/* if we have no linked context, lets get out of here */
+	je	no_linked_context
 
 	/* call setcontext to switch to the linked context */
 	call	__setcontext@plt
 	movl	%eax, (%esp)
 
-hosed:
+no_linked_context:
 	/* we are returning into a null context, it seems, so maybe we should exit */
 	call	exit@plt
 
 	/* something is really hosed, call hlt to force termination */
 	hlt
+
+
+__i686.get_pc_thunk.bx:
+	mov	(%esp), %ebx
+	ret