Re: [GIT PULL] Enable -Wstringop-overflow globally

[Thomas Hellström]

Hi,

On 1/27/24 20:53, Gustavo A. R. Silva wrote:
> On 1/27/24 09:11, David Laight wrote:
> > From: Linus Torvalds
> > > Sent: 26 January 2024 22:36
> > >
> > > On Fri, 26 Jan 2024 at 14:24, Kees Cook <keescook@xxxxxxxxxxxx> wrote:
> > > > I think xe has some other weird problems too. This may be related 
> > > > (under
> > > > allocating):
> > > >
> > > > ../drivers/gpu/drm/xe/xe_vm.c: In function 'xe_vma_create':
> > > > ../drivers/gpu/drm/xe/xe_vm.c:806:21: warning: allocation of 
> > > > insufficient size '224' for type
> > > 'struct xe_vma' with size '368' [-Walloc-size]
> > > >    806 |                 vma = kzalloc(sizeof(*vma) - sizeof(struct 
> > > > xe_userptr),
> > > >        |                     ^
> > >
> > > That code is indeed odd, but there's a comment in the xe_vma definition
> > >
> > >          /**
> > >           * @userptr: user pointer state, only allocated for VMAs 
> > > that are
> > >           * user pointers
> > >           */
> > >          struct xe_userptr userptr;
> > >
> > > although I agree that it should probably simply be made a final
> > > variably-sized array instead (and then you make that array size be
> > > 0/1).
> >
> > That entire code is odd.
> > It isn't obvious that the flag values that cause the short allocate
> > are the same ones that control whether the extra data is accessed.
> >
> > Never mind the oddities with the 'flags |= ' assignments int the
> > 'remap next' path.
> >
> > Anyone know how many of these actually get allocated (and their
> > lifetimes)?
> > How much difference would it make to allocate 368 (maybe 384?)
> > bytes instead of 224 (likely 256).
>
> [CC+ xen list and maintainers]
>
> Probably the xen maintainer can help us out here.

Unfortunately the number of these can be quite large, and with a long 
lifetime which I guess was the reason that size optimization was done in 
the first place.

Ideally IMO this should've been subclassed to an xe_userptr_vma, but 
until we have a chance to clean that up, We can look at the 
variable-sized array or simply allocate the full size until we get to that.

Thanks,

Thomas


> --
> Gustavo
>
> >     David
> >
> > -
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