linux-kernel - Re: [PATCH v2] arm64/cache: fix -Woverride-init compiler warnings

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Message-Id: <D11F0810-A6D0-4835-B71A-9DDDC120423B@lca.pw>
Date:   Wed, 7 Aug 2019 07:50:43 -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 v2] arm64/cache: fix -Woverride-init compiler warnings



> On Aug 7, 2019, at 6:56 AM, Will Deacon <will@...nel.org> wrote:
> 
> On Tue, Aug 06, 2019 at 03:34:34PM -0400, Qian Cai wrote:
>> diff --git a/arch/arm64/kernel/cpuinfo.c b/arch/arm64/kernel/cpuinfo.c
>> index 876055e37352..a0c495a3f4fd 100644
>> --- a/arch/arm64/kernel/cpuinfo.c
>> +++ b/arch/arm64/kernel/cpuinfo.c
>> @@ -34,10 +34,7 @@ DEFINE_PER_CPU(struct cpuinfo_arm64, cpu_data);
>> static struct cpuinfo_arm64 boot_cpu_data;
>> 
>> static char *icache_policy_str[] = {
>> -	[0 ... ICACHE_POLICY_PIPT]	= "RESERVED/UNKNOWN",
>> -	[ICACHE_POLICY_VIPT]		= "VIPT",
>> -	[ICACHE_POLICY_PIPT]		= "PIPT",
>> -	[ICACHE_POLICY_VPIPT]		= "VPIPT",
>> +	[0 ... ICACHE_POLICY_PIPT]	= "RESERVED/UNKNOWN"
>> };
>> 
>> unsigned long __icache_flags;
>> @@ -310,13 +307,16 @@ static void cpuinfo_detect_icache_policy(struct cpuinfo_arm64 *info)
>> 
>> 	switch (l1ip) {
>> 	case ICACHE_POLICY_PIPT:
>> +		icache_policy_str[ICACHE_POLICY_PIPT] = "PIPT";
>> 		break;
>> 	case ICACHE_POLICY_VPIPT:
>> +		icache_policy_str[ICACHE_POLICY_VPIPT] = "VPIPT";
>> 		set_bit(ICACHEF_VPIPT, &__icache_flags);
>> 		break;
>> 	default:
>> 		/* Fallthrough */
>> 	case ICACHE_POLICY_VIPT:
>> +		icache_policy_str[ICACHE_POLICY_VIPT] = "VIPT";
>> 		/* Assume aliasing */
>> 		set_bit(ICACHEF_ALIASING, &__icache_flags);
> 
> I still think this is worse than the code in mainline. I don't think
> -Woverride-init should warn when overriding a field from a GCC range
> designated initialiser, since it makes them considerably less useful
> imo.

Unfortunately, compiler people are moving into a different direction as
Clang would warn those kind of usage too.

It actually prove that those warnings are useful to find real issues. See,

Fae5e033d65a (“mfd: rk808: Fix RK818_IRQ_DISCHG_ILIM initializer”)
32df34d875bb (“[media] rc: img-ir: jvc: Remove unused no-leader timings”)

Especially, to find redundant initializations in large structures. e.g.,

e6ea0b917875 (“[media] dvb_frontend: Don't declare values twice at a table”)