On Wed, 20 May 2026 15:14:40 +0200 "Christophe Leroy (CS GROUP)" <[email protected]> wrote:
> Le 17/05/2026 à 15:54, David Laight a écrit : > > On Sun, 17 May 2026 12:14:21 +0800 > > Mingcong Bai <[email protected]> wrote: > > > >> Similar to commit b929926f01f2 ("sh: define __BIG_ENDIAN for math-emu"), > >> define __LITTLE_ENDIAN and __BIG_ENDIAN as 0 to mitigate build-time > >> warnings: > >> > >> ./include/math-emu/double.h:59:21: error: ‘__BIG_ENDIAN’ is not > >> defined, evaluates to ‘0’ [-Werror=undef] > >> 59 | #if __BYTE_ORDER == __BIG_ENDIAN > >> | > >> > >> Cc: [email protected] > >> Fixes: 13da9e200fe4 ("Revert "endian: #define __BYTE_ORDER"") > >> Reported-by: kernel test robot <[email protected]> > >> Closes: > >> https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Flore.kernel.org%2Foe-kbuild-all%2F202507301656.7FEX6J5W-lkp%40intel.com%2F&data=05%7C02%7Cchristophe.leroy%40csgroup.eu%7C08977974fb1c495e9bd508deb41bd275%7C8b87af7d86474dc78df45f69a2011bb5%7C0%7C0%7C639146228768693730%7CUnknown%7CTWFpbGZsb3d8eyJFbXB0eU1hcGkiOnRydWUsIlYiOiIwLjAuMDAwMCIsIlAiOiJXaW4zMiIsIkFOIjoiTWFpbCIsIldUIjoyfQ%3D%3D%7C0%7C%7C%7C&sdata=4qGulR%2BL7i7inksEbEH9jNGZS8HG80uvm3I9IyYzZww%3D&reserved=0 > >> Signed-off-by: Mingcong Bai <[email protected]> > >> --- > >> arch/powerpc/include/asm/sfp-machine.h | 4 +++- > >> 1 file changed, 3 insertions(+), 1 deletion(-) > >> > >> diff --git a/arch/powerpc/include/asm/sfp-machine.h > >> b/arch/powerpc/include/asm/sfp-machine.h > >> index 8b957aabb826d..db8525605c026 100644 > >> --- a/arch/powerpc/include/asm/sfp-machine.h > >> +++ b/arch/powerpc/include/asm/sfp-machine.h > >> @@ -319,10 +319,12 @@ > >> #define abort() > >> \ > >> return 0 > >> > >> -#ifdef __BIG_ENDIAN > >> +#ifdef __BIG_ENDIAN__ > >> #define __BYTE_ORDER __BIG_ENDIAN > >> +#define __LITTLE_ENDIAN 0 > >> #else > >> #define __BYTE_ORDER __LITTLE_ENDIAN > >> +#define __BIG_ENDIAN 0 > >> #endif > > > > I thought the expected/correct value for __BYTE_ORDER__ was either 1234 or > > 4321. > > (apart from pdp11's 2143). > > That's the case, in include/linux/kconfig.h we have: > > #ifdef CONFIG_CPU_BIG_ENDIAN > #define __BIG_ENDIAN 4321 > #else > #define __LITTLE_ENDIAN 1234 > #endif > > But as far as I understand the problem is that math-emu expects > __BIG_ENDIAN to be defined at all time as it has tests like: > > #if __BYTE_ORDER == __BIG_ENDIAN The gcc docs have (https://gcc.gnu.org/onlinedocs/cpp/Common-Predefined-Macros.html): __BYTE_ORDER__ __ORDER_LITTLE_ENDIAN__ __ORDER_BIG_ENDIAN__ __ORDER_PDP_ENDIAN__ __BYTE_ORDER__ is defined to one of the values __ORDER_LITTLE_ENDIAN__, __ORDER_BIG_ENDIAN__, or __ORDER_PDP_ENDIAN__ to reflect the layout of multi-byte and multi-word quantities in memory. If __BYTE_ORDER__ is equal to __ORDER_LITTLE_ENDIAN__ or __ORDER_BIG_ENDIAN__, then multi-byte and multi-word quantities are laid out identically: the byte (word) at the lowest address is the least significant or most significant byte (word) of the quantity, respectively. If __BYTE_ORDER__ is equal to __ORDER_PDP_ENDIAN__, then bytes in 16-bit words are laid out in a little-endian fashion, whereas the 16-bit subwords of a 32-bit quantity are laid out in big-endian fashion. You should use these macros for testing like this: /* Test for a little-endian machine */ #if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__ The doc doesn't mention the value, but __ORDER_BIG_ENDIAN__ is 4321 (decimal). So the math-emu code is neither following gcc's rules or the kernel ones. Your change will break anything that currently does: #ifdef __BIG_ENDIAN Any change would have to be limited to code that is implementing math-emu. -- David > > Christophe >
