linux-kernel - Re: [PATCH] ARC: build: Turn off -Wmaybe-uninitialized for ARC gcc 4.8

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Message-ID: <56EBD65B.10109@synopsys.com>
Date:	Fri, 18 Mar 2016 15:50:11 +0530
From:	Vineet Gupta <Vineet.Gupta1@...opsys.com>
To:	Arnd Bergmann <arnd@...db.de>
CC:	<linux-snps-arc@...ts.infradead.org>,
	Claudiu Zissulescu <Claudiu.Zissulescu@...opsys.com>,
	Michal Marek <mmarek@...e.cz>,
	"Geert Uytterhoeven" <geert@...ux-m68k.org>,
	<linux-kbuild@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] ARC: build: Turn off -Wmaybe-uninitialized for ARC gcc
 4.8

On Friday 18 March 2016 03:22 PM, Arnd Bergmann wrote:
> On Friday 18 March 2016 14:16:23 Vineet Gupta wrote:
>> diff --git a/arch/arc/Makefile b/arch/arc/Makefile
>> index fed12f39d8ce..aeb101e8e674 100644
>> --- a/arch/arc/Makefile
>> +++ b/arch/arc/Makefile
>> @@ -48,9 +48,14 @@ endif
>>  upto_gcc44    :=  $(call cc-ifversion, -le, 0404, y)
>>  atleast_gcc44 :=  $(call cc-ifversion, -ge, 0404, y)
>>  atleast_gcc48 :=  $(call cc-ifversion, -ge, 0408, y)
>> +is_gcc48      :=  $(call cc-ifversion, -eq, 0408, y)
>>  
>>  cflags-$(atleast_gcc44)                        += -fsection-anchors
>>  
>> +# gcc 4.8 spits out false positives for default -O3
>> +# disable these for 4.8 and revisit when we upgrade to newer ver
>> +cflags-$(is_gcc48)                     += $(call cc-disable-warning,maybe-uninitialized,)
>> +
>>  cflags-$(CONFIG_ARC_HAS_LLSC)          += -mlock
>>  cflags-$(CONFIG_ARC_HAS_SWAPE)         += -mswape
> 
> Is this any better with gcc-4.9 or gcc-5? 

I don't think there's a production ARC toolchain with gcc 4.9 which we can use yet
- Claudiu is still in the the middle of upstreaming the new ARC HS port bits so
things are still in flight there. These tools are off of github !

Maybe it's better to add the flag to
> the line that adds -O3 for consistency. We do the same thing for -Os in the
> global Makefile, as that triggers a similar load of warnings.

Sure, but I prefer this to be only for gcc 4.8 as this warning seems to be
healthy in small doses :-) At least it keeps the door open for future discussion
with gcc guys !

The following nested construct actually works - does that look OK to you ?

ARCH_CFLAGS += -O3 $(call cc-ifversion, -lt, 0408, $(call
cc-disable-warning,maybe-uninitialized,))

Thx,
-Vineet
> 
> 	Arnd
> --
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