From: Richard Henderson <rth@twiddle.net>
To: Sergey Fedorov <serge.fdrv@gmail.com>, qemu-devel@nongnu.org
Cc: Peter Maydell <peter.maydell@linaro.org>,
Eduardo Habkost <ehabkost@redhat.com>,
Anthony Green <green@moxielogic.com>,
Alexander Graf <agraf@suse.de>, Max Filippov <jcmvbkbc@gmail.com>,
Michael Walle <michael@walle.cc>,
qemu-arm@nongnu.org, qemu-ppc@nongnu.org,
Paolo Bonzini <pbonzini@redhat.com>,
Guan Xuetao <gxt@mprc.pku.edu.cn>,
Leon Alrae <leon.alrae@imgtec.com>,
Aurelien Jarno <aurelien@aurel32.net>, Jia Liu <proljc@gmail.com>
Subject: Re: [Qemu-arm] [Qemu-devel] [PATCH] target-*: Get rid of "PC advancement" trick
Date: Fri, 11 Dec 2015 15:39:10 -0800 [thread overview]
Message-ID: <566B5E9E.8040108@twiddle.net> (raw)
In-Reply-To: <1449773244-17078-1-git-send-email-serge.fdrv@gmail.com>
On 12/10/2015 10:47 AM, Sergey Fedorov wrote:
> The "PC advancement" trick was used just after recognizing that a
> breakpoint exception was going to be generated. This trick has had two
> points:
> 1. Guarantee that tb->size isn't zero: there are many places where it's
> expected to be non-zero. In fact, that is even stated in the comment
> for this field.
> 2. Try to satisfy disassembler's check for instruction length. To this
> end, PC advancement was done for estimated instruction length, but
> actually, didn't work properly in variable-instruction-length cases.
>
> Substitute this trick with checking for TB size at the end of
> translation. If we get an empty TB then just set tb->size to 1 and skip
> disassembling. Setting tb->size to 1 is enough to get correct behaviour,
> whereas an empty TB doesn't obviously need to be disassembled.
This doesn't help when the TB already has instructions, the TB would ordinarily
cross a page boundary, and the breakpoint is at the page boundary.
r~
WARNING: multiple messages have this Message-ID (diff)
From: Richard Henderson <rth@twiddle.net>
To: Sergey Fedorov <serge.fdrv@gmail.com>, qemu-devel@nongnu.org
Cc: Peter Maydell <peter.maydell@linaro.org>,
Eduardo Habkost <ehabkost@redhat.com>,
Anthony Green <green@moxielogic.com>,
Alexander Graf <agraf@suse.de>, Max Filippov <jcmvbkbc@gmail.com>,
Michael Walle <michael@walle.cc>,
qemu-arm@nongnu.org, qemu-ppc@nongnu.org,
Paolo Bonzini <pbonzini@redhat.com>,
"Edgar E. Iglesias" <edgar.iglesias@gmail.com>,
Guan Xuetao <gxt@mprc.pku.edu.cn>,
Leon Alrae <leon.alrae@imgtec.com>,
Aurelien Jarno <aurelien@aurel32.net>, Jia Liu <proljc@gmail.com>
Subject: Re: [Qemu-devel] [PATCH] target-*: Get rid of "PC advancement" trick
Date: Fri, 11 Dec 2015 15:39:10 -0800 [thread overview]
Message-ID: <566B5E9E.8040108@twiddle.net> (raw)
In-Reply-To: <1449773244-17078-1-git-send-email-serge.fdrv@gmail.com>
On 12/10/2015 10:47 AM, Sergey Fedorov wrote:
> The "PC advancement" trick was used just after recognizing that a
> breakpoint exception was going to be generated. This trick has had two
> points:
> 1. Guarantee that tb->size isn't zero: there are many places where it's
> expected to be non-zero. In fact, that is even stated in the comment
> for this field.
> 2. Try to satisfy disassembler's check for instruction length. To this
> end, PC advancement was done for estimated instruction length, but
> actually, didn't work properly in variable-instruction-length cases.
>
> Substitute this trick with checking for TB size at the end of
> translation. If we get an empty TB then just set tb->size to 1 and skip
> disassembling. Setting tb->size to 1 is enough to get correct behaviour,
> whereas an empty TB doesn't obviously need to be disassembled.
This doesn't help when the TB already has instructions, the TB would ordinarily
cross a page boundary, and the breakpoint is at the page boundary.
r~
next prev parent reply other threads:[~2015-12-11 23:39 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-12-10 18:47 [Qemu-devel] [PATCH] target-*: Get rid of "PC advancement" trick Sergey Fedorov
2015-12-11 23:39 ` Richard Henderson [this message]
2015-12-11 23:39 ` Richard Henderson
2015-12-12 20:02 ` [Qemu-arm] " Sergey Fedorov
2015-12-12 20:02 ` Sergey Fedorov
2015-12-14 16:19 ` [Qemu-arm] " Richard Henderson
2015-12-14 16:19 ` Richard Henderson
2015-12-15 21:02 ` [Qemu-arm] " Sergey Fedorov
2015-12-15 21:02 ` Sergey Fedorov
2015-12-16 17:03 ` [Qemu-arm] " Richard Henderson
2015-12-16 17:03 ` Richard Henderson
2015-12-16 21:13 ` [Qemu-arm] " Sergey Fedorov
2015-12-16 21:13 ` Sergey Fedorov
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