Re: [Xen-devel] [PATCH] xen/arm: fix build after 2e35cdf

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Wed, 19 Jun 2019, Julien Grall wrote:
> Hi Stefano,
> 
> Title: You should at least mention this is for op-tee.
> 
> Also, mostly likely the sha1 is too small and likely to match multiple commit
> in the future. So you want to specify the title of the commit.
> 
> On 6/19/19 10:24 PM, Stefano Stabellini wrote:
> > Optee breaks the build with:
> > 
> > optee.c: In function ‘translate_noncontig.isra.4’:
> > optee.c:743:38: error: ‘xen_data’ may be used uninitialized in this function
> > [-Werror=maybe-uninitialized]
> >               xen_data->next_page_data = page_to_maddr(xen_pgs + 1);
> >                                        ^
> > optee.c:732:71: error: ‘guest_data’ may be used uninitialized in this
> > function [-Werror=maybe-uninitialized]
> >           page =
> > get_domain_ram_page(gaddr_to_gfn(guest_data->pages_list[idx]));
> >                                                                         ^
> > optee.c:750:21: error: ‘guest_pg’ may be used uninitialized in this function
> > [-Werror=maybe-uninitialized]
> >               put_page(guest_pg);
> >                       ^
> > cc1: all warnings being treated as errors
> > 
> > Fix it by initializing xen_data, guest_data, guest_pg to NULL. Also set
> > xen_pgs to NULL for consistency.
> 
> Without more explanation I think this is an unwise choice. If GCC thinks it is
> going to be used unitialized, then mostly likely you silent an error that
> could end up to dereference NULL.
> 
> Also, setting xen_pgs for consistency will only defeat the compiler. Leading
> to dereferencing NULL and crash Xen...
> 
> For xen_pgs, this should definitely not be NULL. For the two others, you need
> to explain why this is fine (if this is just because the compiler can't find
> the reason, then you should add a comment in the code to explain it).

I was only trying to unblock the build. I'll withdraw the patch and let
Volodmir fix it properly. 

Volodmir, FYI I reproduced the issue using Ubuntu Trusty gcc
4.8.4-2ubuntu1~14.04.3.

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