From: Paolo Bonzini <pbonzini@redhat.com>
To: Stevie Lavern <stevie.lavern@gmail.com>, qemu-devel@nongnu.org
Subject: Re: [Bug] x86 EFLAGS refresh is not happening correctly
Date: Thu, 5 Aug 2021 13:33:50 +0200 [thread overview]
Message-ID: <380cef7a-fe5c-9252-e791-400c44486c2c@redhat.com> (raw)
In-Reply-To: <0d982751-7dfe-9a45-df5b-fbe57d36ccef@redhat.com>
On 05/08/21 13:24, Paolo Bonzini wrote:
> On 05/08/21 11:51, Stevie Lavern wrote:
>>
>> Shouldn't it be:
>> eflags = cpu_cc_compute_all(env, CC_OP) | (env->df & DF_MASK);
>> as eflags is entirely reevaluated by "cpu_cc_compute_all" ?
>
> No, both are wrong. env->eflags contains flags other than the
> arithmetic flags (OF/SF/ZF/AF/PF/CF) and those have to be preserved.
>
> The right code is in helper_read_eflags. You can move it into
> cpu_compute_eflags, and make helper_read_eflags use it.
Ah, actually the two are really the same, the TF/VM bits do not apply to
cpu_compute_eflags so it's correct.
What seems wrong is migration of the EFLAGS register. There should be
code in cpu_pre_save and cpu_post_load to special-case it and setup
CC_DST/CC_OP as done in cpu_load_eflags.
Also, cpu_load_eflags should assert that update_mask does not include
any of the arithmetic flags.
Paolo
next prev parent reply other threads:[~2021-08-05 11:35 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-08-05 9:51 [Bug] x86 EFLAGS refresh is not happening correctly Stevie Lavern
2021-08-05 11:24 ` Paolo Bonzini
2021-08-05 11:33 ` Paolo Bonzini [this message]
2021-08-05 12:47 ` Stevie Lavern
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