[Qemu-devel] [PATCH] improve emulation correctness

[Dmitry Poletaev]

There is a set of test, that checks QEMU CPU for similar behavior with real 
hardware (http://roberto.greyhats.it/projects/pills.html). Test reg/pill2579.c 
can detect, that program is execute in emulated environment. It is related with 
behavior of rcl instruction. If the number of shifted bits more than 1, OF of 
eflags become undefined. Real CPUs does not change OF, if it is undefined. QEMU 
do it anyway.
Emulated program can execute that test and after that can understand 
environment not real.

Signed-off-by: Dmitry Poletaev <address@hidden>

diff --git a/target-i386/shift_helper_template.h 
b/target-i386/shift_helper_template.h
index cf91a2d..d5bd321 100644
--- a/target-i386/shift_helper_template.h
+++ b/target-i386/shift_helper_template.h
@@ -64,8 +64,10 @@ target_ulong glue(helper_rcl, SUFFIX)(CPUX86State *env, 
target_ulong t0,
         }
         t0 = res;
         env->cc_src = (eflags & ~(CC_C | CC_O)) |
-            (lshift(src ^ t0, 11 - (DATA_BITS - 1)) & CC_O) |
             ((src >> (DATA_BITS - count)) & CC_C);
+        if (count == 1) {
+            env->cc_src |= (lshift(src ^ t0, 11 - (DATA_BITS - 1)) & CC_O);
+        }
     }
     return t0;
}

This patch improve correctness of emulator behavior.