Re: [PATCH] ArmPlatformPkg: eliminate Juno gcc build warning

[Laszlo Ersek <lersek@redhat.com>]

On 06/20/17 14:00, Leif Lindholm wrote:
> On Tue, Jun 20, 2017 at 01:28:38PM +0200, Ard Biesheuvel wrote:
>> (+ Laszlo)
>>
>> On 20 June 2017 at 13:00, Leif Lindholm <leif.lindholm@linaro.org> wrote:
>>> When building without LTO, gcc incorrectly resolves the hazards for
>>> 'PciRegBase’ when inlining, leading to "may be used uninitialized"
>>> warnings (and hence build failure with -Werror).
>>> Eliminate this warning by explicitly initializing the variable to 0.
>>>
>>> Contributed-under: TianoCore Contribution Agreement 1.0
>>> Signed-off-by: Leif Lindholm <leif.lindholm@linaro.org>
>>
>> Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
> 
> Thanks!
> 
>>> ---
>>>
>>> For those who have heard me mentioning this before but arguing against
>>> upstreaming this patch: I only just tweaked that this warning doesn't
>>> go away with more recent toolchains, but simply when switching to GCC5
>>> build profile, and hence LTO. Build failure still reproducible with
>>> gcc 6.3.1 and GCC49.
>>
>> /me annoyed
> 
> +1
> 
>> We keep hitting this with GCC, and I profoundly dislike having to add
>> redundant initialization sequences. Is there any other solution
>> possible, e.g., disable this warning for certain builds?
> 
> I would really like to not disable it.
> When it gets it right, that's usually a pretty horrific bug caught.
> And if we switch to LTO as the norm, I guess these will become less
> noticeable over time.
> But it does bug me too.

Perhaps we should introduce two macros to "MdePkg/Include/Base.h",

#define UNUSED_POINTER NULL
#define UNUSED_INTEGER 0

These could be used to suppress such warnings, without the risk of
misleading programmers (as to the real necessity of the variable
assignment at hand).

Thanks
Laszlo