linux-kernel - Re: [PATCH] x86/xen: silence smatch warning in pmu_msr_chk

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Date:   Thu, 20 Oct 2022 15:16:02 +0200
From:   Jan Beulich <jbeulich@...e.com>
To:     Juergen Gross <jgross@...e.com>
Cc:     Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "H. Peter Anvin" <hpa@...or.com>, xen-devel@...ts.xenproject.org,
        Dan Carpenter <dan.carpenter@...cle.com>,
        linux-kernel@...r.kernel.org, x86@...nel.org
Subject: Re: [PATCH] x86/xen: silence smatch warning in pmu_msr_chk_emulated()

On 20.10.2022 13:37, Juergen Gross wrote:
> Commit 8714f7bcd3c2 ("xen/pv: add fault recovery control to pmu msr
> accesses") introduced code resulting in a warning issued by the smatch
> static checker, claiming to use an uninitialized variable.
> 
> This is a false positive, but work around the warning nevertheless.

The risk of introducing a problem might be quite low here, but in general
it exists: With the adjustment you remove any chance of the compiler
spotting a missing initialization before use. And I'm not convinced using
0 in such a case would actually be ending up sufficiently benign.

Jan

> --- a/arch/x86/xen/pmu.c
> +++ b/arch/x86/xen/pmu.c
> @@ -302,7 +302,7 @@ static bool xen_amd_pmu_emulate(unsigned int msr, u64 *val, bool is_read)
>  static bool pmu_msr_chk_emulated(unsigned int msr, uint64_t *val, bool is_read,
>  				 bool *emul)
>  {
> -	int type, index;
> +	int type = 0, index = 0;
>  
>  	if (is_amd_pmu_msr(msr))
>  		*emul = xen_amd_pmu_emulate(msr, val, is_read);