linux-kernel - RE: [PATCH] workqueue: fix enum type for gcc-13

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Message-ID: <99ea6e86d2594b40a6de96cc821c447b@AcuMS.aculab.com>
Date:   Wed, 18 Jan 2023 09:31:18 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Arnd Bergmann' <arnd@...nel.org>, Tejun Heo <tj@...nel.org>
CC:     Arnd Bergmann <arnd@...db.de>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        Richard Clark <richard.xnu.clark@...il.com>,
        Jonathan Neuschäfer <j.neuschaefer@....net>,
        "Andrey Grodzovsky" <andrey.grodzovsky@....com>,
        Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH] workqueue: fix enum type for gcc-13

From: Arnd Bergmann
> Sent: 17 January 2023 16:41
> 
> In gcc-13, the WORK_STRUCT_WQ_DATA_MASK constant is a signed 64-bit
> type on 32-bit architectures because the enum definition has both
> negative numbers and numbers above LONG_MAX in it:
> 
...
>  	/* convenience constants */
>  	WORK_STRUCT_FLAG_MASK	= (1UL << WORK_STRUCT_FLAG_BITS) - 1,
> -	WORK_STRUCT_WQ_DATA_MASK = ~WORK_STRUCT_FLAG_MASK,
> +	WORK_STRUCT_WQ_DATA_MASK = (unsigned long)~WORK_STRUCT_FLAG_MASK,
>  	WORK_STRUCT_NO_POOL	= (unsigned long)WORK_OFFQ_POOL_NONE << WORK_OFFQ_POOL_SHIFT,

How can that make any difference?
You aren't changing the value or type (which makes no difference)
of WORK_STRUCT_WQ_DATA_MASK.
Indeed you require it to have the high bit set.

So if the enum contains a -1 somewhere gcc-13 will promote
everything to s64.

Either declare gcc-13 as 'BROKEN' or change the:
	return (void *)(data & WORK_STRUCT_WQ_DATA_MASK);
to
	return (void *)(data & ~WORK_STRUCT_FLAG_MASK);

or use #defines.

	David

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