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From: Andrew Morton <akpm@linux-foundation.org>
To: Yankai Xu <815559068@qq.com>
Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org
Subject: Re: [PATCH] mm/gfp: cast GFP_ZONE_TABLE entries to long to avoid shift overflow
Date: Thu, 11 Dec 2025 12:04:48 -0800	[thread overview]
Message-ID: <20251211120448.817a352350813ae84cb600b3@linux-foundation.org> (raw)
In-Reply-To: <tencent_917BFA629ACDD8A2E6A32C53CEA147C66409@qq.com>

On Thu, 11 Dec 2025 18:24:05 +0800 Yankai Xu <815559068@qq.com> wrote:

> 
> When a new zone is added to enum zone_type in mmzone.h, the existing
> GFP_ZONE_TABLE macro causes a compile-time shift overflow.

Thanks.

Please quote the compiler warning messages and describe how to
reproduce this.  Please include this info in the patch changelog and
maintain it.

> This happens
> because enum zone_type is of type int. The shift is logically
> valid because it has been checked by 16 * GFP_ZONES_SHIFT > BITS_PER_LONG previously.
> 
> Fixed this by casting each value in GFP_ZONE_TABLE to type long.
> 
> ...
>
>  #define GFP_ZONE_TABLE ( \
> -	(ZONE_NORMAL << 0 * GFP_ZONES_SHIFT)				\
> +	((long)ZONE_NORMAL << 0 * GFP_ZONES_SHIFT)			\

It would be nice to find something nicer than this.  Perhaps a type of
something was poorly chosen.


  reply	other threads:[~2025-12-11 20:04 UTC|newest]

Thread overview: 3+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2025-12-11 10:24 Yankai Xu
2025-12-11 20:04 ` Andrew Morton [this message]
2025-12-12  7:19   ` Yankai Xu

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