On Fri, 19 Dec 2025 23:39:48 +0100
Vincent Mailhol <[email protected]> wrote:
> The function like macro __is_nonneg() casts its argument to (long long)
> in an attempt to silence -Wtype-limits warnings on unsigned values.
nak.
The cast is needed for pointer types, not for -Wtype-limits.
which is why the '#if __SIZEOF_POINTER__ == __SIZEOF_LONG_LONG__'
test is there.
David
>
> But this workaround is incomplete as proven here:
>
> $ cat foo.c
> #include <linux/minmax.h>
>
> int foo(unsigned int a)
> {
> return __is_nonneg(a);
> }
> $ make CFLAGS_KERNEL="-Wtype-limits" foo.o
> CALL scripts/checksyscalls.sh
> DESCEND objtool
> INSTALL libsubcmd_headers
> CC foo.o
> foo.c: In function 'foo':
> ./include/linux/minmax.h:68:57: warning: comparison is always true due to
> limited range of data type [-Wtype-limits]
> 68 | #define __is_nonneg(ux) statically_true((long long)(ux) >= 0)
> | ^~
> ./include/linux/compiler.h:350:50: note: in definition of macro
> 'statically_true'
> 350 | #define statically_true(x) (__builtin_constant_p(x) && (x))
> | ^
> foo.c:5:16: note: in expansion of macro '__is_nonneg'
> 5 | return __is_nonneg(a);
> | ^~~~~~~~~~~
> ./include/linux/minmax.h:68:57: warning: comparison is always true due to
> limited range of data type [-Wtype-limits]
> 68 | #define __is_nonneg(ux) statically_true((long long)(ux) >= 0)
> | ^~
> ./include/linux/compiler.h:350:57: note: in definition of macro
> 'statically_true'
> 350 | #define statically_true(x) (__builtin_constant_p(x) && (x))
> | ^
> foo.c:5:16: note: in expansion of macro '__is_nonneg'
> 5 | return __is_nonneg(a);
> | ^~~~~~~~~~~
>
> And because -Wtype-limits is now globally disabled, such a workaround
> now becomes useless. Remove the __is_nonneg()'s cast and its related
> comment.
>
> Signed-off-by: Vincent Mailhol <[email protected]>
> ---
> Changelog:
>
> v1 -> v2: new patch
> ---
> include/linux/minmax.h | 5 +----
> 1 file changed, 1 insertion(+), 4 deletions(-)
>
> diff --git a/include/linux/minmax.h b/include/linux/minmax.h
> index a0158db54a04..3e2e3e539ba1 100644
> --- a/include/linux/minmax.h
> +++ b/include/linux/minmax.h
> @@ -52,9 +52,6 @@
> /*
> * Check whether a signed value is always non-negative.
> *
> - * A cast is needed to avoid any warnings from values that aren't signed
> - * integer types (in which case the result doesn't matter).
> - *
> * On 64-bit any integer or pointer type can safely be cast to 'long long'.
> * But on 32-bit we need to avoid warnings about casting pointers to integers
> * of different sizes without truncating 64-bit values so 'long' or 'long
> long'
> @@ -65,7 +62,7 @@
> * but they are handled by the !is_signed_type() case).
> */
> #if __SIZEOF_POINTER__ == __SIZEOF_LONG_LONG__
> -#define __is_nonneg(ux) statically_true((long long)(ux) >= 0)
> +#define __is_nonneg(ux) statically_true((ux) >= 0)
> #else
> #define __is_nonneg(ux) statically_true( \
> (typeof(__builtin_choose_expr(sizeof(ux) > 4, 1LL, 1L)))(ux) >= 0)
>
