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

[Elena Afanasova <eafanasova@gmail.com>]

On Sat, 2020-10-10 at 17:07 +1100, David Gibson wrote:
> On Fri, Oct 09, 2020 at 07:02:56AM -0700, Elena Afanasova wrote:
> > > From 09905773a00e417d3a37c12350d9e55466fdce8a Mon Sep 17 00:00:00
> > > 2001
> > From: Elena Afanasova <eafanasova@gmail.com>
> > Date: Fri, 9 Oct 2020 06:41:36 -0700
> > Subject: [PATCH] hw/net: move allocation to the heap due to very
> > large stack
> >  frame
> 
> Patch looks fine, but some more details of the motivation would be
> nice.  I wouldn't have thought that the size of a network packet
> counted as a "very large" stack frame by userspace standards.
> 

gcc with wstack-usage warns that stack frame size may be ~65Kbytes

> > Signed-off-by: Elena Afanasova <eafanasova@gmail.com>
> > ---
> >  hw/net/spapr_llan.c | 5 +++--
> >  1 file changed, 3 insertions(+), 2 deletions(-)
> > 
> > diff --git a/hw/net/spapr_llan.c b/hw/net/spapr_llan.c
> > index 2093f1bad0..581320a0e7 100644
> > --- a/hw/net/spapr_llan.c
> > +++ b/hw/net/spapr_llan.c
> > @@ -688,7 +688,8 @@ static target_ulong
> > h_send_logical_lan(PowerPCCPU *cpu,
> >      SpaprVioDevice *sdev = spapr_vio_find_by_reg(spapr->vio_bus,
> > reg);
> >      SpaprVioVlan *dev = VIO_SPAPR_VLAN_DEVICE(sdev);
> >      unsigned total_len;
> > -    uint8_t *lbuf, *p;
> > +    uint8_t *p;
> > +    g_autofree uint8_t *lbuf = NULL;
> >      int i, nbufs;
> >      int ret;
> >  
> > @@ -729,7 +730,7 @@ static target_ulong
> > h_send_logical_lan(PowerPCCPU *cpu,
> >          return H_RESOURCE;
> >      }
> >  
> > -    lbuf = alloca(total_len);
> > +    lbuf = g_malloc(total_len);
> >      p = lbuf;
> >      for (i = 0; i < nbufs; i++) {
> >          ret = spapr_vio_dma_read(sdev, VLAN_BD_ADDR(bufs[i]),