Re: [PATCH] perf intel-pt: Fix undefined shift in intel_pt_bip()

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Low] The patch introduces a build failure by placing a variable declaration after a statement block, which violates the C90 compilation rules enforced in the perf tools build system.
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commit 8a68d39b58963034d86457f673e830e359365de8
Author: Liu Jing <liujing@cmss.chinamobile.com>

perf intel-pt: Fix undefined shift in intel_pt_bip()

This commit aims to fix an undefined shift behavior in intel_pt_bip() by
moving the bounds check before the shift and using an unsigned shift operation.

> diff --git a/tools/perf/util/intel-pt-decoder/intel-pt-decoder.c b/tools/perf/util/intel-pt-decoder/intel-pt-decoder.c
> index e733f6b1f7ac5..9abadd0d1c108 100644
> --- a/tools/perf/util/intel-pt-decoder/intel-pt-decoder.c
> +++ b/tools/perf/util/intel-pt-decoder/intel-pt-decoder.c
> @@ -2060,7 +2060,6 @@ static void intel_pt_bbp(struct intel_pt_decoder *decoder)
>  static void intel_pt_bip(struct intel_pt_decoder *decoder)
>  {
>  	uint32_t id = decoder->packet.count;
> -	uint32_t bit = 1 << id;
>  	int pos = decoder->blk_type_pos;
>  
>  	if (pos < 0 || id >= INTEL_PT_BLK_ITEM_ID_CNT) {
> @@ -2068,6 +2067,7 @@ static void intel_pt_bip(struct intel_pt_decoder *decoder)
>  			     id, decoder->blk_type);
>  		return;
>  	}
> +	uint32_t bit = 1U << id;

[Severity: Low]
Will this cause a build failure? It looks like the declaration of the bit
variable is now placed after an if statement block within intel_pt_bip().

The perf tools build system enables -Wdeclaration-after-statement and promotes
it to an error. Could this be fixed by separating the declaration and
initialization, like declaring uint32_t bit; at the top of the function and
then assigning it after the bounds check?

>  
>  	if (decoder->state.items.mask[pos] & bit) {
>  		intel_pt_log("WARNING: Duplicate block item %u type %d\n",

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Sashiko AI review · https://sashiko.dev/#/patchset/20260903082128.4972-2-liujing@cmss.chinamobile.com?part=1