linux-kernel - Re: [PATCH] lib/vdso: guard clockid before building u32 bitmask

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Message-ID: <CABFUUZHCEgr-SDuivnkRzjbYeuhE5XJaAkGbZYaL-A3vrZ7z7g@mail.gmail.com>
Date: Wed, 14 Jan 2026 17:31:48 +0800
From: sun jian <sun.jian.kdev@...il.com>
To: Thomas Weißschuh <thomas.weissschuh@...utronix.de>
Cc: Andy Lutomirski <luto@...nel.org>, Thomas Gleixner <tglx@...nel.org>, 
	Vincenzo Frascino <vincenzo.frascino@....com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] lib/vdso: guard clockid before building u32 bitmask

On Wed, Jan 14, 2026 at 4:56 PM Thomas Weißschuh
<thomas.weissschuh@...utronix.de> wrote:
> So this looks like a false-positive. Can you post the sparse warning?
Here is the sparse warning I saw:

  arch/x86/entry/vdso/vdso32/../../../../../lib/vdso/gettimeofday.c:454:26:
    warning: shift too big (40) for type unsigned long

It is emitted when checking the vdso32 include path via vclock_gettime.c.

Given that vdso_clockid_valid() bounds clock to <= CLOCK_AUX_LAST (23),
the shift cannot reach that value in practice. So I agree this is a sparse
false positive in this analysis context.

I'll drop this patch rather than adding a redundant runtime check.

Thanks,
Sun