linux-kernel - Re: [PATCH v2] perf tool: fix endianness handling of u32 data in samples

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Date:	Fri, 2 Sep 2011 15:18:19 -0300
From:	Arnaldo Carvalho de Melo <acme@...stprotocols.net>
To:	David Ahern <dsahern@...il.com>
Cc:	linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org,
	mingo@...e.hu, peterz@...radead.org, fweisbec@...il.com,
	paulus@...ba.org, tglx@...utronix.de, anton@...ba.org
Subject: Re: [PATCH v2] perf tool: fix endianness handling of u32 data in
 samples

Em Fri, Sep 02, 2011 at 10:03:46AM -0600, David Ahern escreveu:
>  	if (type & PERF_SAMPLE_RAW) {
> -		u32 *p = (u32 *)array;
> +		u.val64 = *array;
> +		if (swapped) {
> +			static bool show_warn = true;
> +
> +			/* undo swap of u64, then swap on individual u32s */
> +			u.val64 = bswap_64(u.val64);
> +			u.val32[0] = bswap_32(u.val32[0]);
> +			u.val32[1] = bswap_32(u.val32[1]);
> +
> +			if (show_warn) {
> +				pr_warning("Endianness of raw data not corrected!\n");
> +				show_warn = false;
> +			}
> +		}

Can you use WARN_ONCE? Would become:
	
		if (WARN_ONCE(swapped, "Endianness of raw data not corrected!\n")) {
			/* undo swap of u64, then swap on individual u32s */
			u.val64 = bswap_64(u.val64);
			u.val32[0] = bswap_32(u.val32[0]);
			u.val32[1] = bswap_32(u.val32[1]);
		}

We have that and its the usual idiom in the kernel proper :-)

See tools/perf/util/include/asm/bug.h and net/can/af_can.c can_rcv for
an example.

Thanks,

- Arnaldo
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