[Xen-devel] [PATCH] Mini-OS return from exception fix

[Grzegorz Milos <gm281@xxxxxxxxx>]

This patch fixes ret_from_exception routine. Stack consistency is now 
preserved.
Signed-off-by: Grzegorz Milos <gm281@xxxxxxxxx>

Keir could you apply? Thanks.

Gregor

> I've modified minios to do dynamic page fault handling rather than setup 
> all the page tables ahead of time (just to improve my understanding) but 
> it's crashing on return and looks like the stack may be wrong. Before I 
> dive in the assembler code, is the code in x86_32.S at page_fault and 
> ret_from_exception expected to work if the fault is fixed up?

diff -r 8690e3448971 -r 25619d57eaa5 extras/mini-os/arch/x86/x86_32.S
--- a/extras/mini-os/arch/x86/x86_32.S  Wed Jan 17 15:09:50 2007 +0000
+++ b/extras/mini-os/arch/x86/x86_32.S  Fri Feb 02 10:50:20 2007 +0000
@@ -69,7 +69,7 @@ CS            = 0x2C
        popl %ds;       \
        popl %es;       \
        addl $4,%esp;   \
-       iret;           \
+       iret;           
 
 ENTRY(divide_error)
        pushl $0                # no error code
@@ -101,10 +101,9 @@ do_exception:
     jmp ret_from_exception
     
 ret_from_exception:
-        movb CS(%esp),%cl
-       test $2,%cl          # slow return to ring 2 or 3
-       jne  safesti
-        RESTORE_ALL
+    movb CS(%esp),%cl
+    addl $8,%esp
+    RESTORE_ALL
 
 # A note on the "critical region" in our callback handler.
 # We want to avoid stacking callback handlers due to events occurring

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