linux-kernel - Re: [PATCH] arm64/cache: fix -Woverride-init compiler warnings

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Date:   Mon, 5 Aug 2019 07:47:37 -0400
From:   Qian Cai <cai@....pw>
To:     Will Deacon <will@...nel.org>
Cc:     Catalin Marinas <catalin.marinas@....com>,
        Mark Rutland <mark.rutland@....com>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] arm64/cache: fix -Woverride-init compiler warnings



> On Aug 5, 2019, at 5:52 AM, Will Deacon <will@...nel.org> wrote:
> 
> On Fri, Aug 02, 2019 at 11:32:24AM -0400, Qian Cai wrote:
>> The commit 155433cb365e ("arm64: cache: Remove support for ASID-tagged
>> VIVT I-caches") introduced some compiation warnings from GCC,
>> 
>> 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.
>> 
>> Fixes: 155433cb365e ("arm64: cache: Remove support for ASID-tagged VIVT I-caches")
>> Signed-off-by: Qian Cai <cai@....pw>
>> ---
>> arch/arm64/kernel/cpuinfo.c | 4 ++--
>> 1 file changed, 2 insertions(+), 2 deletions(-)
>> 
>> diff --git a/arch/arm64/kernel/cpuinfo.c b/arch/arm64/kernel/cpuinfo.c
>> index 876055e37352..193b38da8d96 100644
>> --- a/arch/arm64/kernel/cpuinfo.c
>> +++ b/arch/arm64/kernel/cpuinfo.c
>> @@ -34,10 +34,10 @@
>> static struct cpuinfo_arm64 boot_cpu_data;
>> 
>> static char *icache_policy_str[] = {
>> -	[0 ... ICACHE_POLICY_PIPT]	= "RESERVED/UNKNOWN",
>> +	[ICACHE_POLICY_VPIPT]		= "VPIPT",
>> +	[ICACHE_POLICY_VPIPT + 1]	= "RESERVED/UNKNOWN",
>> 	[ICACHE_POLICY_VIPT]		= "VIPT",
>> 	[ICACHE_POLICY_PIPT]		= "PIPT",
>> -	[ICACHE_POLICY_VPIPT]		= "VPIPT",
> 
> I really don't like this patch. Using "[0 ... MAXIDX] = <default>" is a
> useful idiom and I think the code is more error-prone the way you have
> restructured it.
> 
> Why are you passing -Woverride-init to the compiler anyway? There's only
> one Makefile that references that option, and it's specific to a pinctrl
> driver.

Those extra warnings can be enabled by “make W=1”. “-Woverride-init “ seems to be useful
to catch potential developer mistakes with unintented double-initializations. It is normal to
start to fix the most of false-positives first before globally enabling the flag by default just like
“-Wimplicit-fallthrough” mentioned in,

https://lwn.net/Articles/794944/