x86: port to use common trampoline

arch/x86/defs.h

@@ -59,6 +59,9 @@
 
 #define MCONTEXT_GREGS	(20)
 
+#define FETCH_LINKPTR(dest) \
+	asm("movl (%%esp, %%ebx, 4), %0" : "=rm" ((dest)));
+
 #include "common-defs.h"
 
 #endif

arch/x86/startcontext.S

@@ -1,41 +0,0 @@
-/*
- * Copyright (c) 2018, 2020 Ariadne Conill <ariadne@dereferenced.org>
- *
- * Permission to use, copy, modify, and/or distribute this software for any
- * purpose with or without fee is hereby granted, provided that the above
- * copyright notice and this permission notice appear in all copies.
- *
- * This software is provided 'as is' and without any warranty, express or
- * implied.  In no event shall the authors be liable for any damages arising
- * from the use of this software.
- */
-
-#include "defs.h"
-
-FUNC(libucontext_trampoline)
-	/* get the proper context into position and test for NULL */
-	leal	(%esp,%ebx,4), %esp
-	cmpl	$0, (%esp)
-
-	/* restore global offset table, exit@plt and libucontext_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	libucontext_setcontext@plt
-	movl	%eax, (%esp)
-
-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
-END(libucontext_trampoline)

arch/x86/trampoline.c

@@ -0,0 +1,2 @@
+#include "defs.h"
+#include "common-trampoline.c"