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

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Message-ID: <20190807115926.np7izmaq36kgxzdg@willie-the-truck>
Date:   Wed, 7 Aug 2019 12:59:27 +0100
From:   Will Deacon <will@...nel.org>
To:     Qian Cai <cai@....pw>
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 Wed, Aug 07, 2019 at 07:50:43AM -0400, Qian Cai wrote:
> 
> 
> > 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”)

None of these appear to use the range initialisers I was referring to, so I
don't see why this is relevant to the discussion at hand.

Will