Re: [PATCH 02/10] perf hisi-ptt: Fix PTT trace TLP Header parsing

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Medium] Relying on C bitfields without endianness macros breaks cross-platform decoding on big-endian hosts.
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commit acedfe06d43ba61d4515f85b3f80767187e8bcb7
Author: Sizhe Liu <liusizhe5@huawei.com>

perf hisi-ptt: Fix PTT trace TLP Header parsing

This commit fixes the DW0 bit field layout of the hisi_ptt_4dw union to
match the actual bit ordering after little-endian memory extraction. It
also changes the hex value printout to big-endian for readability, aligning
with the format diagram.

> diff --git a/tools/perf/util/hisi-ptt-decoder/hisi-ptt-pkt-decoder.c b/tools/perf/util/hisi-ptt-decoder/hisi-ptt-pkt-decoder.c
> index c48b2ce7c4a3d..67024f18ebbbc 100644
> --- a/tools/perf/util/hisi-ptt-decoder/hisi-ptt-pkt-decoder.c
> +++ b/tools/perf/util/hisi-ptt-decoder/hisi-ptt-pkt-decoder.c
> @@ -75,14 +76,14 @@ static const char * const hisi_ptt_4dw_pkt_field_name[] = {
>  
>  union hisi_ptt_4dw {
>  	struct {
> -		uint32_t format : 2;
> -		uint32_t type : 5;
> -		uint32_t t9 : 1;
> -		uint32_t t8 : 1;
> -		uint32_t th : 1;
> -		uint32_t so : 1;
> -		uint32_t len : 10;
>  		uint32_t time : 11;
> +		uint32_t len : 10;
> +		uint32_t so : 1;
> +		uint32_t th : 1;
> +		uint32_t t8 : 1;
> +		uint32_t t9 : 1;
> +		uint32_t type : 5;
> +		uint32_t format : 2;
>  	};
>  	uint32_t value;
>  };

[Severity: Medium]
Does this bitfield layout break on big-endian hosts?

In C, bitfield memory layout within a struct is implementation-defined. GCC
packs bitfields from LSB to MSB on little-endian architectures, but from MSB
to LSB on big-endian architectures.

By unconditionally reordering the bitfields, the time: 11 field extracts the
lowest bits on little-endian hosts. However, on big-endian hosts, it will
incorrectly fetch bits 31-21 of the 32-bit native integer instead of bits 10-0,
resulting in corrupted trace decoding.

Should this struct use endianness macros (e.g., #if defined(__LITTLE_ENDIAN_BITFIELD)) 
or bitwise shifts instead of relying on C bitfields to ensure cross-platform 
decoding works correctly?

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Sashiko AI review · https://sashiko.dev/#/patchset/20260604075005.2219785-1-liusizhe5@huawei.com?part=2