linux-kernel - Re: [PATCH v6 6/9] kselftest/arm64/mte: add address tag related macro and function

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Message-ID: <5e937cf0-3b71-4c17-838e-8b38595c153c@sirena.org.uk>
Date: Wed, 11 Jun 2025 12:58:04 +0100
From: Mark Brown <broonie@...nel.org>
To: Yeoreum Yun <yeoreum.yun@....com>
Cc: catalin.marinas@....com, pcc@...gle.com, will@...nel.org,
	anshuman.khandual@....com, joey.gouly@....com,
	yury.khrustalev@....com, maz@...nel.org, oliver.upton@...ux.dev,
	frederic@...nel.org, akpm@...ux-foundation.org, surenb@...gle.com,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	linux-doc@...r.kernel.org
Subject: Re: [PATCH v6 6/9] kselftest/arm64/mte: add address tag related
 macro and function

On Wed, Jun 11, 2025 at 10:41:04AM +0100, Yeoreum Yun wrote:
> Add address tag related macro and function to test MTE_FAR feature.

> +void *mte_insert_atag(void *ptr)
> +{
> +	unsigned char atag;
> +
> +	srandom(time(NULL));
> +	atag =  mtefar_support ? (random() % MT_ATAG_MASK) + 1 : 0;
> +	return (void *)MT_SET_ATAG((unsigned long)ptr, atag);
> +}

Ah, this is where the time.h inclusion came from - it just got split
into the wrong patch.  I would move that srandom() into the main()
function, we don't need to reset the RNG every time we generate a tag
and since time() has a resolution of a second depending on how fast the
machine is we might manage to end up setting exactly the same value for
every tag insertion the program does which would seem to defeat the
point of using a RNG here.

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