Re: [PATCH] hw/net: move allocation to the heap due to very large stack frame

[David Gibson]

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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