X-Git-Url: https://codewiz.org/gitweb?a=blobdiff_plain;f=bertos%2Femul%2Fswitch_i386.S;h=f00d447c1467093ed74dedc8c5722099efe0566c;hb=e25abecb6a6ff52917d44d1331e5af831aeceb9c;hp=5032b31c2556d5fcb9bb60b0a7af8ad2d6a2ec59;hpb=2f1343e2774ac66a35c63ee90535265d67c78feb;p=bertos.git

diff --git a/bertos/emul/switch_i386.S b/bertos/emul/switch_i386.S
index 5032b31c..f00d447c 100644
--- a/bertos/emul/switch_i386.S
+++ b/bertos/emul/switch_i386.S
@@ -30,10 +30,22 @@
  * Copyright 1999, 2000, 2001 Bernie Innocenti <bernie@codewiz.org>
  * -->
  *
- * \version $Id$
  * \author Bernie Innocenti <bernie@codewiz.org>
  *
  * \brief i386 context switch
+ *
+ * x86 function calling convention:
+ * --------------------------------
+ *  arguments         | callee-saved        | extra caller-saved | return
+ * [callee-clobbered] |                     | [callee-clobbered] |
+ * -------------------------------------------------------------------------
+ * eax edx ecx        | ebx edi esi ebp [*] | <none>             | eax, edx
+ *
+ *  [*]  In the frame-pointers case rbp must hold a base address for the
+ *       current stack frame.
+ *
+ * asm_switch_context() can be considered as a normal function call, so we need
+ * to save all the callee-clobbered registers minus the return registers.
  */
 
 #ifdef __APPLE__
@@ -46,22 +58,12 @@
 /* void asm_switch_context(void ** new_sp [sp+4], void ** save_sp [sp+8]) */
 .globl SWITCH_CONTEXT
 SWITCH_CONTEXT:
-	pushl	%eax
-	pushl	%ebx
-	pushl	%ecx
-	pushl	%edx
-	pushl	%esi
-	pushl	%edi
 	pushl	%ebp
-	movl	0x24(%esp),%ebp         /* ebp = save_sp */
+	pushl	%ecx
+	movl	0x10(%esp),%ebp         /* ebp = save_sp */
 	movl	%esp,(%ebp)             /* *save_sp = esp */
-	movl	0x20(%esp),%ebp         /* ebp = new_sp */
+	movl	0x0c(%esp),%ebp         /* ebp = new_sp */
 	movl	(%ebp),%esp             /* esp = *new_sp */
-	popl	%ebp
-	popl	%edi
-	popl	%esi
-	popl	%edx
 	popl	%ecx
-	popl	%ebx
-	popl	%eax
+	popl	%ebp
 	ret