Re: [PATCH] arm64/cache: silence -Woverride-init warnings

[Nathan Chancellor]

On Thu, Aug 08, 2019 at 11:38:08AM +0100, Mark Rutland wrote:
> On Wed, Aug 07, 2019 at 11:29:16PM -0400, Qian Cai wrote:
> > The commit 155433cb365e ("arm64: cache: Remove support for ASID-tagged
> > VIVT I-caches") introduced some compiation warnings from GCC (and
> > Clang) with -Winitializer-overrides),
> > 
> > arch/arm64/kernel/cpuinfo.c:38:26: warning: initialized field
> > overwritten [-Woverride-init]
> > [ICACHE_POLICY_VIPT]  = "VIPT",
> >                         ^~~~~~
> > arch/arm64/kernel/cpuinfo.c:38:26: note: (near initialization for
> > 'icache_policy_str[2]')
> > arch/arm64/kernel/cpuinfo.c:39:26: warning: initialized field
> > overwritten [-Woverride-init]
> > [ICACHE_POLICY_PIPT]  = "PIPT",
> >                         ^~~~~~
> > arch/arm64/kernel/cpuinfo.c:39:26: note: (near initialization for
> > 'icache_policy_str[3]')
> > arch/arm64/kernel/cpuinfo.c:40:27: warning: initialized field
> > overwritten [-Woverride-init]
> > [ICACHE_POLICY_VPIPT]  = "VPIPT",
> >                          ^~~~~~~
> > arch/arm64/kernel/cpuinfo.c:40:27: note: (near initialization for
> > 'icache_policy_str[0]')
> > 
> > because it initializes icache_policy_str[0 ... 3] twice. Since
> > arm64 developers are keen to keep the style of initializing a static
> > array with a non-zero pattern first, just disable those warnings for
> > both GCC and Clang of this file.
> > 
> > Fixes: 155433cb365e ("arm64: cache: Remove support for ASID-tagged VIVT I-caches")
> > Signed-off-by: Qian Cai <cai@xxxxxx>
> 
> This is _not_ a fix, and should not require backporting to stable trees.
> 
> What about all the other instances that we have in mainline?
> 
> I really don't think that we need to go down this road; we're just going
> to end up adding this to every file that happens to include a header
> using this scheme...
> 
> Please just turn this off by default for clang.
> 
> If we want to enable this, we need a mechanism to permit overridable
> assignments as we use range initializers for.
> 
> Thanks,
> Mark.
> 

For what it's worth, this is disabled by default for clang in the
kernel:

https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/scripts/Makefile.extrawarn?h=v5.3-rc3#n69

It only becomes visible with clang at W=1 because that section doesn't
get applied. It becomes visible with GCC at W=1 because of -Wextra.

Cheers,
Nathan