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

This patch fixes ret_from_exception routine. Stack consistency is now preserved.

Signed-off-by: Grzegorz Milos <gm281@xxxxxxxxx>

Keir could you apply? Thanks.


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;           
        pushl $0                # no error code
@@ -101,10 +101,9 @@ do_exception:
     jmp 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
 # 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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