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Re: [Qemu-devel] [PATCH] Bug in AMD64 emulation Was: [AMD64] Possible pr

From: Jakub Jermar
Subject: Re: [Qemu-devel] [PATCH] Bug in AMD64 emulation Was: [AMD64] Possible problem with the DF flag during the SYSCALL instruction
Date: Thu, 27 Mar 2008 12:38:46 +0100
User-agent: Thunderbird (X11/20080227)

Alexander Graf wrote:

On Mar 25, 2008, at 8:45 PM, Jakub Jermar wrote:

as no one has picked my previous report up yet, I am resending my patch again. The patch fixes a bug in the way QEMU emulates AMD64 instruction called SYSCALL. The problem appears to be stale DF variable.

Sorry I didn't have a look at it before. Good catch though!
I believe you're searching for load_eflags(), which automatically updates the DF flag. Take a look at the SVM code for that issue as well (helper.c:helper_vmrun).

The included patch updates the DF flag in helper_syscall() using the load_eflags(). I thought of doing this as simply as possible and here's probably the result. When the first parameter of load_eflags() has the same value as env->eflags, the second argument doesn't matter, that's why it is 0.

Will you consider this for applying?


diff -ru qemu-0.9.1/target-i386/helper.c qemu-0.9.1-jj/target-i386/helper.c
--- qemu-0.9.1/target-i386/helper.c     2008-01-06 20:38:45.000000000 +0100
+++ qemu-0.9.1-jj/target-i386/helper.c  2008-03-27 12:27:37.000000000 +0100
@@ -1008,6 +1008,7 @@
                                DESC_S_MASK |
                                DESC_W_MASK | DESC_A_MASK);
         env->eflags &= ~env->fmask;
+        load_eflags(env->eflags, 0);
         if (code64)
             env->eip = env->lstar;

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