From: Rikard Falkeborn <rikard.falkeborn@xxxxxxxxx> Subject: linux/bits.h: fix compilation error with GENMASK GENMASK() has an input check which uses __builtin_choose_expr() to enable a compile time sanity check of its inputs if they are known at compile time. However, it turns out that __builtin_constant_p() does not always return a compile time constant [0]. It was thought this problem was fixed with gcc 4.9 [1], but apparently this is not the case [2]. Switch to use __is_constexpr() instead which always returns a compile time constant, regardless of its inputs. [0]: https://lore.kernel.org/lkml/42b4342b-aefc-a16a-0d43-9f9c0d63ba7a@xxxxxxxxxxxxxxxxxx [1]: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=19449 [2]: https://lore.kernel.org/lkml/1ac7bbc2-45d9-26ed-0b33-bf382b8d858b@xxxxxxxxxxxxxxxxxxx Link: https://lkml.kernel.org/r/20210511203716.117010-1-rikard.falkeborn@xxxxxxxxx Signed-off-by: Rikard Falkeborn <rikard.falkeborn@xxxxxxxxx> Reported-by: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx> Acked-by: Arnd Bergmann <arnd@xxxxxxxx> Reviewed-by: Andy Shevchenko <andy.shevchenko@xxxxxxxxx> Cc: Ard Biesheuvel <ardb@xxxxxxxxxx> Cc: Yury Norov <yury.norov@xxxxxxxxx> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- include/linux/bits.h | 2 +- include/linux/const.h | 8 ++++++++ include/linux/minmax.h | 10 ++-------- tools/include/linux/bits.h | 2 +- tools/include/linux/const.h | 8 ++++++++ 5 files changed, 20 insertions(+), 10 deletions(-) --- a/include/linux/bits.h~linux-bitsh-fix-compilation-error-with-genmask +++ a/include/linux/bits.h @@ -22,7 +22,7 @@ #include <linux/build_bug.h> #define GENMASK_INPUT_CHECK(h, l) \ (BUILD_BUG_ON_ZERO(__builtin_choose_expr( \ - __builtin_constant_p((l) > (h)), (l) > (h), 0))) + __is_constexpr((l) > (h)), (l) > (h), 0))) #else /* * BUILD_BUG_ON_ZERO is not available in h files included from asm files, --- a/include/linux/const.h~linux-bitsh-fix-compilation-error-with-genmask +++ a/include/linux/const.h @@ -3,4 +3,12 @@ #include <vdso/const.h> +/* + * This returns a constant expression while determining if an argument is + * a constant expression, most importantly without evaluating the argument. + * Glory to Martin Uecker <Martin.Uecker@xxxxxxxxxxxxxxxxxxxxx> + */ +#define __is_constexpr(x) \ + (sizeof(int) == sizeof(*(8 ? ((void *)((long)(x) * 0l)) : (int *)8))) + #endif /* _LINUX_CONST_H */ --- a/include/linux/minmax.h~linux-bitsh-fix-compilation-error-with-genmask +++ a/include/linux/minmax.h @@ -2,6 +2,8 @@ #ifndef _LINUX_MINMAX_H #define _LINUX_MINMAX_H +#include <linux/const.h> + /* * min()/max()/clamp() macros must accomplish three things: * @@ -17,14 +19,6 @@ #define __typecheck(x, y) \ (!!(sizeof((typeof(x) *)1 == (typeof(y) *)1))) -/* - * This returns a constant expression while determining if an argument is - * a constant expression, most importantly without evaluating the argument. - * Glory to Martin Uecker <Martin.Uecker@xxxxxxxxxxxxxxxxxxxxx> - */ -#define __is_constexpr(x) \ - (sizeof(int) == sizeof(*(8 ? ((void *)((long)(x) * 0l)) : (int *)8))) - #define __no_side_effects(x, y) \ (__is_constexpr(x) && __is_constexpr(y)) --- a/tools/include/linux/bits.h~linux-bitsh-fix-compilation-error-with-genmask +++ a/tools/include/linux/bits.h @@ -22,7 +22,7 @@ #include <linux/build_bug.h> #define GENMASK_INPUT_CHECK(h, l) \ (BUILD_BUG_ON_ZERO(__builtin_choose_expr( \ - __builtin_constant_p((l) > (h)), (l) > (h), 0))) + __is_constexpr((l) > (h)), (l) > (h), 0))) #else /* * BUILD_BUG_ON_ZERO is not available in h files included from asm files, --- a/tools/include/linux/const.h~linux-bitsh-fix-compilation-error-with-genmask +++ a/tools/include/linux/const.h @@ -3,4 +3,12 @@ #include <vdso/const.h> +/* + * This returns a constant expression while determining if an argument is + * a constant expression, most importantly without evaluating the argument. + * Glory to Martin Uecker <Martin.Uecker@xxxxxxxxxxxxxxxxxxxxx> + */ +#define __is_constexpr(x) \ + (sizeof(int) == sizeof(*(8 ? ((void *)((long)(x) * 0l)) : (int *)8))) + #endif /* _LINUX_CONST_H */ _
