linux-kernel - Re: [PATCH v2] perf/x86/amd/uncore: Avoid a false positive warning about snprintf truncation in amd_uncore_umc_ctx

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Message-ID: <5907e4cf-d71f-4c5e-8504-a0177819ebb0@amd.com>
Date: Tue, 5 Nov 2024 15:04:02 +0530
From: Sandipan Das <sandipan.das@....com>
To: Jean Delvare <jdelvare@...e.de>
Cc: Peter Zijlstra <peterz@...radead.org>, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] perf/x86/amd/uncore: Avoid a false positive warning
 about snprintf truncation in amd_uncore_umc_ctx_init

On 11/5/2024 2:22 PM, Jean Delvare wrote:
> Fix the following warning:
>   CC [M]  arch/x86/events/amd/uncore.o
> arch/x86/events/amd/uncore.c: In function ‘amd_uncore_umc_ctx_init’:
> arch/x86/events/amd/uncore.c:951:52: warning: ‘%d’ directive output may be truncated writing between 1 and 10 bytes into a region of size 8 [-Wformat-truncation=]
>     snprintf(pmu->name, sizeof(pmu->name), "amd_umc_%d", index);
>                                                     ^~
> arch/x86/events/amd/uncore.c:951:43: note: directive argument in the range [0, 2147483647]
>     snprintf(pmu->name, sizeof(pmu->name), "amd_umc_%d", index);
>                                            ^~~~~~~~~~~~
> arch/x86/events/amd/uncore.c:951:4: note: ‘snprintf’ output between 10 and 19 bytes into a destination of size 16
>     snprintf(pmu->name, sizeof(pmu->name), "amd_umc_%d", index);
>     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> 
> As far as I can see, there can't be more than UNCORE_GROUP_MAX (256)
> groups and each group can't have more than 255 PMU, so the number
> printed by this %d can't exceed 65279, that's only 5 digits and would
> fit into the buffer. So it's a false positive warning. But we can
> make the compiler happy by declaring index as a 16-bit number.
> 
> Signed-off-by: Jean Delvare <jdelvare@...e.de>
> ---
> Changes in v2:
>  * Use the proper printf conversion specifier, to be on the safe side.
> 
> An alternative fix would be to extend UNCORE_NAME_LEN to 20, the
> downside being an increased memory consumption. Depends whether we
> expect UNCORE_GROUP_MAX to ever be increased, or groups to ever
> support more than 255 PMU.
> 

Its very unlikely for UNCORE_GROUP_MAX to change and the current
solution looks good to me.

Reviewed-by: Sandipan Das <sandipan.das@....com>