linux-kernel - Re: [PATCH] x86/kernel: remove unneeded dead-store initialization

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Date:   Wed, 31 Mar 2021 10:49:05 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Yang Li <yang.lee@...ux.alibaba.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Nathan Chancellor <nathan@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        clang-built-linux <clang-built-linux@...glegroups.com>
Subject: Re: [PATCH] x86/kernel: remove unneeded dead-store initialization

On Wed, Mar 31, 2021 at 1:00 AM Yang Li <yang.lee@...ux.alibaba.com> wrote:
>
> make clang-analyzer on x86_64 defconfig caught my attention with:
>
> arch/x86/kernel/cpu/cacheinfo.c:880:24: warning: Value stored to
> 'this_cpu_ci' during its initialization is never read
> [clang-analyzer-deadcode.DeadStores]
> struct cpu_cacheinfo *this_cpu_ci = get_cpu_cacheinfo(cpu);
> ^
>
> So, simply remove this unneeded dead-store initialization to make
> clang-analyzer happy.
>
> As compilers will detect this unneeded assignment and optimize this anyway,
> the resulting object code is identical before and after this change.
>
> No functional change. No change to object code.

Reviewed-by: Nick Desaulniers <ndesaulniers@...gle.com>

Looks like this is from when this code was introduced in
commit 0d55ba46bfbe ("x86/cacheinfo: Move cacheinfo sysfs code to
generic infrastructure")
though this file was moved from arch/x86/kernel/cpu/intel_cacheinfo.c
to arch/x86/kernel/cpu/cacheinfo.c in
commit 1d200c078d0e ("x86/CPU: Rename intel_cacheinfo.c to cacheinfo.c")
(So I don't think a Fixes tag for 0d55ba46bfbe would be appropriate).

Thanks for the patch!

>
> Reported-by: Abaci Robot <abaci@...ux.alibaba.com>
> Signed-off-by: Yang Li <yang.lee@...ux.alibaba.com>
> ---
>  arch/x86/kernel/cpu/cacheinfo.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/x86/kernel/cpu/cacheinfo.c b/arch/x86/kernel/cpu/cacheinfo.c
> index 3ca9be4..d66af29 100644
> --- a/arch/x86/kernel/cpu/cacheinfo.c
> +++ b/arch/x86/kernel/cpu/cacheinfo.c
> @@ -877,7 +877,7 @@ void init_intel_cacheinfo(struct cpuinfo_x86 *c)
>  static int __cache_amd_cpumap_setup(unsigned int cpu, int index,
>                                     struct _cpuid4_info_regs *base)
>  {
> -       struct cpu_cacheinfo *this_cpu_ci = get_cpu_cacheinfo(cpu);
> +       struct cpu_cacheinfo *this_cpu_ci;
>         struct cacheinfo *this_leaf;
>         int i, sibling;
>
> --
> 1.8.3.1
>


-- 
Thanks,
~Nick Desaulniers