Re: [PATCH v2 1/2] perf alpha: Decode ProfileMe raw samples

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Low] perf alpha: missing -Wpacked suppression breaks build on 32-bit targets
--

commit 119dd432f8c77b285bd2a318dab7adc61639a02f
Author: Matt Turner <mattst88@gmail.com>

perf alpha: Decode ProfileMe raw samples

This commit decodes Alpha ProfileMe PERF_SAMPLE_RAW payloads in perf report
-D and perf script -D, and copies the UAPI header defining struct
alpha_profileme_sample into tools/arch.

> diff --git a/tools/arch/alpha/include/uapi/asm/perf_event.h b/tools/arch/alpha/include/uapi/asm/perf_event.h
> new file mode 100644
> index 0000000000000..aa0eff5a917cb
> --- /dev/null
> +++ b/tools/arch/alpha/include/uapi/asm/perf_event.h
> @@ -0,0 +1,31 @@

[ ... ]

> +#define ALPHA_PROFILEME_SAMPLE_VERSION	1
> +
> +struct alpha_profileme_sample {
> +	__u32 version;
> +	__u64 pmpc __attribute__((packed));
> +	__u64 i_stat __attribute__((packed));
> +	__u64 pctr_ctl __attribute__((packed));
> +};
> +
> +#endif /* _UAPI_ASM_ALPHA_PERF_EVENT_H */

[ ... ]

> diff --git a/tools/perf/util/alpha-sample-raw.c b/tools/perf/util/alpha-sample-raw.c
> new file mode 100644
> index 0000000000000..b4e336d8fc8f6
> --- /dev/null
> +++ b/tools/perf/util/alpha-sample-raw.c
> @@ -0,0 +1,145 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Alpha specific. Provide textual annotation for ProfileMe raw sample data.
> + */
> +
> +#include <stdio.h>
> +#include <string.h>
> +#include <linux/kernel.h>
> +#include <linux/perf_event.h>
> +
> +#include "../../arch/alpha/include/uapi/asm/perf_event.h"

[Severity: Low]
Will including this header without suppressing -Wpacked break the build on
32-bit architectures where the natural alignment of __u64 is 32 bits or less
(such as m68k, sh, arc, and microblaze)?

tools/perf/util/Build unconditionally compiles alpha-sample-raw.o on all
architectures with EXTRA_WARNINGS += -Wpacked (in
tools/scripts/Makefile.include) and CORE_CFLAGS += -Werror (in
tools/perf/Makefile.config).

In struct alpha_profileme_sample, the pmpc, i_stat, and pctr_ctl fields sit at
4-byte-aligned offsets after __u32 version and carry __attribute__((packed)),
which lowers their alignment to 1 byte. On targets where __u64 has 4-byte or
smaller alignment, those fields are already naturally aligned at offset 4, so
GCC emits a -Wpacked warning ("packed attribute causes inefficient alignment"),
failing the build under -Werror.

Should the header inclusion in tools/perf/util/alpha-sample-raw.c be wrapped in
diagnostic pragmas, similar to struct pai_data in
tools/perf/util/s390-sample-raw.c:

#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wpacked"
#pragma GCC diagnostic ignored "-Wattributes"
#include "../../arch/alpha/include/uapi/asm/perf_event.h"
#pragma GCC diagnostic pop

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20261030-perf-alpha-profileme-v2-0-9ce2f0b0e622@gmail.com?part=1