From: Arnd Bergmann arnd@arndb.de Subject: linux/compiler-clang.h: define HAVE_BUILTIN_BSWAP*

Separating compiler-clang.h from compiler-gcc.h inadventently dropped the definitions of the three HAVE_BUILTIN_BSWAP macros, which requires falling back to the open-coded version and hoping that the compiler detects it.

Since all versions of clang support the __builtin_bswap interfaces, add back the flags and have the headers pick these up automatically.

This results in a 4% improvement of compilation speed for arm defconfig.

Note: it might also be worth revisiting which architectures set CONFIG_ARCH_USE_BUILTIN_BSWAP for one compiler or the other, today this is set on six architectures (arm32, csky, mips, powerpc, s390, x86), while another ten architectures define custom helpers (alpha, arc, ia64, m68k, mips, nios2, parisc, sh, sparc, xtensa), and the rest (arm64, h8300, hexagon, microblaze, nds32, openrisc, riscv) just get the unoptimized version and rely on the compiler to detect it.

A long time ago, the compiler builtins were architecture specific, but nowadays, all compilers that are able to build the kernel have correct implementations of them, though some may not be as optimized as the inline asm versions.

The patch that dropped the optimization landed in v4.19, so as discussed it would be fairly safe to backport this revert to stable kernels to the 4.19/5.4/5.10 stable kernels, but there is a remaining risk for regressions, and it has no known side-effects besides compile speed.

Link: https://lkml.kernel.org/r/20210226161151.2629097-1-arnd@kernel.org Link: https://lore.kernel.org/lkml/20210225164513.3667778-1-arnd@kernel.org/ Fixes: 815f0ddb346c ("include/linux/compiler*.h: make compiler-*.h mutually exclusive") Signed-off-by: Arnd Bergmann arnd@arndb.de Reviewed-by: Nathan Chancellor nathan@kernel.org Reviewed-by: Kees Cook keescook@chromium.org Acked-by: Miguel Ojeda ojeda@kernel.org Acked-by: Nick Desaulniers ndesaulniers@google.com Acked-by: Luc Van Oostenryck luc.vanoostenryck@gmail.com Cc: Masahiro Yamada masahiroy@kernel.org Cc: Nick Hu nickhu@andestech.com Cc: Greentime Hu green.hu@gmail.com Cc: Vincent Chen deanbo422@gmail.com Cc: Paul Walmsley paul.walmsley@sifive.com Cc: Palmer Dabbelt palmer@dabbelt.com Cc: Albert Ou aou@eecs.berkeley.edu Cc: Guo Ren guoren@kernel.org Cc: Randy Dunlap rdunlap@infradead.org Cc: Sami Tolvanen samitolvanen@google.com Cc: Marco Elver elver@google.com Cc: Arvind Sankar nivedita@alum.mit.edu Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

include/linux/compiler-clang.h | 6 ++++++ 1 file changed, 6 insertions(+)

--- a/include/linux/compiler-clang.h~linux-compiler-clangh-define-have_builtin_bswap +++ a/include/linux/compiler-clang.h @@ -31,6 +31,12 @@ #define __no_sanitize_thread #endif

+#if defined(CONFIG_ARCH_USE_BUILTIN_BSWAP) +#define __HAVE_BUILTIN_BSWAP32__ +#define __HAVE_BUILTIN_BSWAP64__ +#define __HAVE_BUILTIN_BSWAP16__ +#endif /* CONFIG_ARCH_USE_BUILTIN_BSWAP */ + #if __has_feature(undefined_behavior_sanitizer) /* GCC does not have __SANITIZE_UNDEFINED__ */ #define __no_sanitize_undefined \ _