Re: [PATCH v3 3/3] overflow: Remove is_non_negative() and is_negative()

Vincent Mailhol
2026-01-01T15:10:44Z

On 20/12/2025 at 12:02, Vincent Mailhol wrote:
> The is_non_negative() and is_negative() function-like macros just
> exist as a workaround to silence the -Wtype-limits warning. Now that
> this warning is disabled, those two macros have lost their raison
> d'être. Remove them.
>
> This reverts commit dc7fe518b049 ("overflow: Fix -Wtype-limits
> compilation warnings").
>
> Suggested-by: Nicolas Schier <nsc@kernel.org>
> Link: https://lore.kernel.org/all/aUT_yWin_xslnOFh@derry.ads.avm.de
> Signed-off-by: Vincent Mailhol <mailhol@kernel.org>

So at the end, this patch got five kernel test robot reports:

https://lore.kernel.org/all/202512221735.mRV4BZqB-lkp@intel.com/
https://lore.kernel.org/all/202512230342.Lgha2HGH-lkp@intel.com/
https://lore.kernel.org/all/202512251340.UApIFw9R-lkp@intel.com/
https://lore.kernel.org/all/202512271618.33YepxDC-lkp@intel.com/
https://lore.kernel.org/all/202512280906.wt7UNpya-lkp@intel.com/

All these are the same smatch warning just triggered from a different
place. I think it is still too early to undo that workaround in
include/linux/overflow.h, otherwise developers would be getting that
smatch report too often.

I will send a v4 in which I will drop this patch. This basically means
that the v4 is a revert to v1...

> ---
> Changelog:
>
> v1 -> v2: new patch
> ---
> include/linux/overflow.h | 10 ++--------
> 1 file changed, 2 insertions(+), 8 deletions(-)
>
> diff --git a/include/linux/overflow.h b/include/linux/overflow.h
> index 736f633b2d5f..ab142d60c6b5 100644
> --- a/include/linux/overflow.h
> +++ b/include/linux/overflow.h
> @@ -36,12 +36,6 @@
> #define __type_min(T) ((T)((T)-type_max(T)-(T)1))
> #define type_min(t) __type_min(typeof(t))
>
> -/*
> - * Avoids triggering -Wtype-limits compilation warning,
> - * while using unsigned data types to check a < 0.
> - */
> -#define is_non_negative(a) ((a) > 0 || (a) == 0)
> -#define is_negative(a) (!(is_non_negative(a)))
>
> /*
> * Allows for effectively applying __must_check to a macro so we can have
> @@ -201,9 +195,9 @@ static inline bool __must_check __must_check_overflow(bool overflow)
> typeof(d) _d = d; \
> unsigned long long _a_full = _a; \
> unsigned int _to_shift = \
> - is_non_negative(_s) && _s < 8 * sizeof(*d) ? _s : 0; \
> + _s >= 0 && _s < 8 * sizeof(*d) ? _s : 0; \
> *_d = (_a_full << _to_shift); \
> - (_to_shift != _s || is_negative(*_d) || is_negative(_a) || \
> + (_to_shift != _s || *_d < 0 || _a < 0 || \
> (*_d >> _to_shift) != _a); \
> }))
>
>

Yours sincerely,
Vincent Mailhol