From: "H. Peter Anvin" <hpa@zytor.com>
To: Nadav Amit <nadav.amit@gmail.com>, Marcelo Tosatti <mtosatti@redhat.com>
Cc: Gleb Natapov <gleb@kernel.org>,
Nadav Amit <namit@cs.technion.ac.il>,
pbonzini@redhat.com, tglx@linutronix.de, mingo@redhat.com,
x86@kernel.org, kvm@vger.kernel.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH 4/5] KVM: x86: RSI/RDI/RCX are zero-extended when affected by string ops
Date: Wed, 23 Apr 2014 14:01:26 -0700 [thread overview]
Message-ID: <53582A26.6040408@zytor.com> (raw)
In-Reply-To: <53582853.30009@gmail.com>
On 04/23/2014 01:53 PM, Nadav Amit wrote:
>>
>> Err, operand size is forced to 64-bits, not address size.
>>
>> "The following aspects of near branches are controlled by the effective
>> operand size:
>> • Truncation of the size of the instruction pointer"
>>
>> Still, "67h call" should not truncate EIP (which your patch does).
>>
> Yes, I missed it.
> But if I am not mistaken again, it means that the existing
> implementation of jmp_rel is broken as well when address-size override
> prefix is used. In this case, as I see it, the existing masking would
> cause the carry from the add operation to the lower half of the rip not
> to be added to the rip higher half.
>
> I guess another patch is needed for that as well.
>
Yes, on x86 JMP really should be thought of as "MOV ...,IP/EIP/RIP". On
some other architectures, e.g. m68k, JMP acts as if it was
"LEA ...,PC", which causes some serious confusion for people familiar
with that model. However, on x86 considering JMP as a MOV to the IP
register really is very consistent and will give you the right mental model.
-hpa
next prev parent reply other threads:[~2014-04-23 21:01 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-04-17 23:33 [PATCH 0/5] KVM: x86: Fix KVM behavior that does not follow spec Nadav Amit
2014-04-18 0:35 ` [PATCH 1/5] KVM: x86: Fix wrong/stuck PMU when guest does not use PMI Nadav Amit
2014-04-18 0:35 ` [PATCH 2/5] KVM: x86: Fix CR3 reserved bits Nadav Amit
2014-05-10 7:13 ` Jan Kiszka
2014-05-10 7:24 ` [PATCH] KVM: x86: Fix CR3 reserved bits check in long mode Jan Kiszka
2014-05-12 10:46 ` Paolo Bonzini
2014-04-18 0:35 ` [PATCH 3/5] KVM: x86: IN instruction emulation should ignore REP-prefix Nadav Amit
2014-04-18 4:11 ` [PATCH 4/5] KVM: x86: RSI/RDI/RCX are zero-extended when affected by string ops Nadav Amit
2014-04-18 4:11 ` [PATCH 5/5] KVM: x86: Processor mode may be determined incorrectly Nadav Amit
2014-04-20 9:26 ` [PATCH 4/5] KVM: x86: RSI/RDI/RCX are zero-extended when affected by string ops Gleb Natapov
2014-04-22 6:04 ` Nadav Amit
2014-04-23 19:58 ` Marcelo Tosatti
2014-04-23 20:11 ` Marcelo Tosatti
2014-04-23 20:53 ` Nadav Amit
2014-04-23 21:01 ` H. Peter Anvin [this message]
2014-04-23 20:47 ` [PATCH 0/5] KVM: x86: Fix KVM behavior that does not follow spec Marcelo Tosatti
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