Re: [kvm-unit-tests PATCH] s390x: Ignore gcc 12 warnings for low addresses

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On Tue, 17 May 2022 18:09:54 +0200
Thomas Huth <thuth@xxxxxxxxxx> wrote:

> On 17/05/2022 14.02, Claudio Imbrenda wrote:
> > On Mon, 16 May 2022 16:43:32 +0200
> > Janis Schoetterl-Glausch <scgl@xxxxxxxxxxxxx> wrote:
> >   
> >> gcc 12 warns if a memory operand to inline asm points to memory in the
> >> first 4k bytes. However, in our case, these operands are fine, either
> >> because we actually want to use that memory, or expect and handle the
> >> resulting exception.
> >> Therefore, silence the warning.  
> > 
> > I really dislike this  
> 
> I agree the pragmas are ugly. But maybe we should mimic what the kernel
> is doing here?
> 
> $ git show 8b202ee218395
> commit 8b202ee218395319aec1ef44f72043e1fbaccdd6
> Author: Sven Schnelle <svens@xxxxxxxxxxxxx>
> Date:   Mon Apr 25 14:17:42 2022 +0200
> 
>      s390: disable -Warray-bounds
>      
>      gcc-12 shows a lot of array bound warnings on s390. This is caused
>      by the S390_lowcore macro which uses a hardcoded address of 0.
>      
>      Wrapping that with absolute_pointer() works, but gcc no longer knows
>      that a 12 bit displacement is sufficient to access lowcore. So it
>      emits instructions like 'lghi %r1,0; l %rx,xxx(%r1)' instead of a
>      single load/store instruction. As s390 stores variables often
>      read/written in lowcore, this is considered problematic. Therefore
>      disable -Warray-bounds on s390 for gcc-12 for the time being, until
>      there is a better solution.
> 
> ... so we should maybe disable it in the Makefile, too, until the
> kernel folks found a nicer solution?

it's a bit extreme, but if it's good enough for the kernel, it's good
enough for us

> 
>   Thomas
> 




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