x86emul: Fix AAM emulation AH output

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: 8993572b9c ("x86emul: fold/eliminate some local variables")
Signed-off-by: Teddy Astie <teddy.astie@vates.tech>
Reviewed-by: Andrew Cooper <andrew.cooper3@citix.com>
master commit: 4c1aba82cf
master date: 2026-09-25 14:44:27 +0100

xen/arch/x86/x86_emulate/x86_emulate.c

@@ -2461,8 +2461,8 @@ 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;