From: David Gibson <david@gibson.dropbear.id.au>
To: Elena Afanasova <eafanasova@gmail.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>,
Thomas Huth <thuth@redhat.com>,
qemu-trivial@nongnu.org, jasowang@redhat.com,
qemu-ppc@nongnu.org, qemu-devel@nongnu.org
Subject: Re: [PATCH] hw/net: move allocation to the heap due to very large stack frame
Date: Fri, 16 Oct 2020 11:32:18 +1100 [thread overview]
Message-ID: <20201016003218.GF7078@yekko.fritz.box> (raw)
In-Reply-To: <96fa5d23ca57363e063b9b5006ad8f71e6b1b307.camel@gmail.com>
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On Wed, Oct 14, 2020 at 07:15:47AM -0700, Elena Afanasova wrote:
> On Tue, 2020-10-13 at 16:32 +1100, David Gibson wrote:
> > On Mon, Oct 12, 2020 at 03:45:02PM +0200, Paolo Bonzini wrote:
> > > On 12/10/20 12:44, Thomas Huth wrote:
> > > > I think this is one of the tasks from:
> > > >
> > > >
> > > > https://wiki.qemu.org/Contribute/BiteSizedTasks#Compiler-driven_cleanups
> > > >
> > > > It has been added by Paolo in 2016:
> > > >
> > > >
> > > > https://wiki.qemu.org/index.php?title=Contribute/BiteSizedTasks&diff=5368&oldid=5367
> > > >
> > > > ... so maybe Paolo can comment on the size that has been chosen
> > > > here...?
> > >
> > > I used 16K, mostly because it is a nice round number. 8k is too
> > > small
> > > due to PATH_MAX-sized variables. 16k seemed to be plenty and
> > > triggered
> > > in few-enough places that the cleanup is viable.
> >
> > Ok. Why are large stack frames bad in qemu?
> >
>
> I think that the main issue here is alloca() because it can lead to UB.
That's a fair point. I've applied the patch to ppc-for-5.2, with a
tweak to the commit message.
--
David Gibson | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_
| _way_ _around_!
http://www.ozlabs.org/~dgibson
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WARNING: multiple messages have this Message-ID (diff)
From: David Gibson <david@gibson.dropbear.id.au>
To: Elena Afanasova <eafanasova@gmail.com>
Cc: Thomas Huth <thuth@redhat.com>,
qemu-trivial@nongnu.org, jasowang@redhat.com,
qemu-devel@nongnu.org, qemu-ppc@nongnu.org,
Paolo Bonzini <pbonzini@redhat.com>
Subject: Re: [PATCH] hw/net: move allocation to the heap due to very large stack frame
Date: Fri, 16 Oct 2020 11:32:18 +1100 [thread overview]
Message-ID: <20201016003218.GF7078@yekko.fritz.box> (raw)
In-Reply-To: <96fa5d23ca57363e063b9b5006ad8f71e6b1b307.camel@gmail.com>
[-- Attachment #1: Type: text/plain, Size: 1332 bytes --]
On Wed, Oct 14, 2020 at 07:15:47AM -0700, Elena Afanasova wrote:
> On Tue, 2020-10-13 at 16:32 +1100, David Gibson wrote:
> > On Mon, Oct 12, 2020 at 03:45:02PM +0200, Paolo Bonzini wrote:
> > > On 12/10/20 12:44, Thomas Huth wrote:
> > > > I think this is one of the tasks from:
> > > >
> > > >
> > > > https://wiki.qemu.org/Contribute/BiteSizedTasks#Compiler-driven_cleanups
> > > >
> > > > It has been added by Paolo in 2016:
> > > >
> > > >
> > > > https://wiki.qemu.org/index.php?title=Contribute/BiteSizedTasks&diff=5368&oldid=5367
> > > >
> > > > ... so maybe Paolo can comment on the size that has been chosen
> > > > here...?
> > >
> > > I used 16K, mostly because it is a nice round number. 8k is too
> > > small
> > > due to PATH_MAX-sized variables. 16k seemed to be plenty and
> > > triggered
> > > in few-enough places that the cleanup is viable.
> >
> > Ok. Why are large stack frames bad in qemu?
> >
>
> I think that the main issue here is alloca() because it can lead to UB.
That's a fair point. I've applied the patch to ppc-for-5.2, with a
tweak to the commit message.
--
David Gibson | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_
| _way_ _around_!
http://www.ozlabs.org/~dgibson
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next prev parent reply other threads:[~2020-10-16 0:33 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-10-09 14:02 [PATCH] hw/net: move allocation to the heap due to very large stack frame Elena Afanasova
2020-10-09 14:14 ` Richard Henderson
2020-10-09 14:25 ` Philippe Mathieu-Daudé
2020-10-09 14:48 ` Greg Kurz
2020-10-09 14:48 ` Greg Kurz
2020-10-09 14:55 ` Li Qiang
2020-10-09 14:55 ` Li Qiang
2020-10-10 6:07 ` David Gibson
2020-10-10 6:07 ` David Gibson
2020-10-10 15:53 ` Elena Afanasova
2020-10-10 15:53 ` Elena Afanasova
2020-10-12 5:30 ` David Gibson
2020-10-12 5:30 ` David Gibson
2020-10-12 10:44 ` Thomas Huth
2020-10-12 10:44 ` Thomas Huth
2020-10-12 13:45 ` Paolo Bonzini
2020-10-13 5:32 ` David Gibson
2020-10-13 5:32 ` David Gibson
2020-10-14 14:15 ` Elena Afanasova
2020-10-14 14:15 ` Elena Afanasova
2020-10-16 0:32 ` David Gibson [this message]
2020-10-16 0:32 ` David Gibson
2020-10-11 2:23 ` Li Qiang
2020-10-12 5:28 ` David Gibson
2020-10-12 11:09 ` Philippe Mathieu-Daudé
2020-10-12 11:48 ` Philippe Mathieu-Daudé
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