Commit 6c4e0cb3 authored by Heiko Carstens's avatar Heiko Carstens Committed by Alexander Gordeev
Browse files

s390/bitops: Switch to generic ffs() if supported by compiler 



Use generic ffs() / __builtin_ffs() if supported by the compiler. GCC 16
will have support for __builtin_ffs().
See gcc commit f50cff9766c5 ("s390: Implement clz and ctz for SI mode").

In the distant future when GCC 16 becomes the minimum supported version,
this allows to get rid of the flogr inline assembly.

Kernel image size is reduced by ~500 bytes (gcc 16 beta + defconfig).

Acked-by: default avatarAlexander Gordeev <agordeev@linux.ibm.com>
Signed-off-by: default avatarHeiko Carstens <hca@linux.ibm.com>
Signed-off-by: default avatarAlexander Gordeev <agordeev@linux.ibm.com>
parent 7b80a23c

arch/s390/Kconfig

+7 −0
Original line number Diff line number Diff line
@@ -49,6 +49,13 @@ config KASAN_SHADOW_OFFSET 
	depends on KASAN

	default 0x1C000000000000



config CC_HAS_BUILTIN_FFS

	def_bool !(CC_IS_GCC && GCC_VERSION < 160000)

	help

	  GCC versions before 16.0.0 generate library calls to ffs()

	  for __builtin_ffs() even when __has_builtin(__builtin_ffs)

	  is true.



config CC_ASM_FLAG_OUTPUT_BROKEN

	def_bool CC_IS_GCC && GCC_VERSION < 140200

	help

arch/s390/include/asm/bitops.h

+8 −0
Original line number Diff line number Diff line
@@ -122,6 +122,8 @@ static inline bool test_bit_inv(unsigned long nr, 
	return test_bit(nr ^ (BITS_PER_LONG - 1), ptr);

}



#ifndef CONFIG_CC_HAS_BUILTIN_FFS



/**

 * __flogr - find leftmost one

 * @word - The word to search
@@ -194,6 +196,12 @@ static __always_inline __flatten int ffs(int word) 
	return BITS_PER_LONG - __flogr(-val & val);

}



#else /* CONFIG_CC_HAS_BUILTIN_FFS */



#include <asm-generic/bitops/builtin-ffs.h>



#endif /* CONFIG_CC_HAS_BUILTIN_FFS */



#include <asm-generic/bitops/builtin-__ffs.h>

#include <asm-generic/bitops/ffz.h>

#include <asm-generic/bitops/builtin-__fls.h>