[PATCH] x86emul: Fix AAM emulation AH output

[Teddy Astie <teddy.astie@xxxxxxxxxx>]

AAM is defined in APM as

AH = (AL/10d)
AL = (AL mod 10d)

However, due to the order of operations, we're incorrectly computing it as

AL = (AL mod 10d)
AH = (AL/10d) = ((originalAL mod 10d)/10d) = 0

Fix it by reordering the operations to match what's defined in APM
and avoid the unexpected dependency between the 2 operations.

Fixes: 8993572b9c16 ("x86emul: fold/eliminate some local variables")
Signed-off-by: Teddy Astie <teddy.astie@xxxxxxxxxx>
---
 xen/arch/x86/x86_emulate/x86_emulate.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/xen/arch/x86/x86_emulate/x86_emulate.c 
b/xen/arch/x86/x86_emulate/x86_emulate.c
index 89c37fea2c..f168f3ebcf 100644
--- a/xen/arch/x86/x86_emulate/x86_emulate.c
+++ b/xen/arch/x86/x86_emulate/x86_emulate.c
@@ -2511,8 +2511,8 @@ x86_emulate(
         else
         {
             generate_exception_if(!n, X86_EXC_DE);
-            _regs.al = _regs.al % n;
             _regs.ah = _regs.al / n;
+            _regs.al = _regs.al % n;
         }
         _regs.eflags &= ~(X86_EFLAGS_SF | X86_EFLAGS_ZF | X86_EFLAGS_PF);
         _regs.eflags |= !_regs.al ? X86_EFLAGS_ZF : 0;
-- 
2.55.0



--
Teddy Astie | Vates XCP-ng Developer

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