From: Josh Poimboeuf <jpoimboe@xxxxxxxxxx> Date: Fri, 6 May 2016 09:22:25 -0500 gcc support for __builtin_bswap16() was supposedly added for powerpc in gcc 4.6, and was then later added for other architectures in gcc 4.8. However, Stephen Rothwell reported that attempting to use it on powerpc in gcc 4.6 fails with: lib/vsprintf.c:160:2: error: initializer element is not constant lib/vsprintf.c:160:2: error: (near initialization for 'decpair[0]') lib/vsprintf.c:160:2: error: initializer element is not constant lib/vsprintf.c:160:2: error: (near initialization for 'decpair[1]') lib/vsprintf.c:160:2: error: initializer element is not constant lib/vsprintf.c:160:2: error: (near initialization for 'decpair[2]') lib/vsprintf.c:160:2: error: initializer element is not constant lib/vsprintf.c:160:2: error: (near initialization for 'decpair[3]') lib/vsprintf.c:160:2: error: initializer element is not constant I'm not entirely sure what those errors mean, but I don't see them on gcc 4.8. So let's consider gcc 4.8 to be the official starting point for __builtin_bswap16(). Arnd Bergmann adds: "I found the commit in gcc-4.8 that replaced the powerpc-specific implementation of __builtin_bswap16 with an architecture-independent one. Apparently the powerpc version (gcc-4.6 and 4.7) just mapped to the lhbrx/sthbrx instructions, so it ended up not being a constant, though the intent of the patch was mainly to add support for the builtin to x86. https://gcc.gnu.org/bugzilla/show_bug.cgi?id=52624 has the patch that went into gcc-4.8 and more information." Fixes: 7322dd755e7d ("byteswap: try to avoid __builtin_constant_p gcc bug") Reported-by: Stephen Rothwell <sfr@xxxxxxxxxxxxxxxx> Tested-by: Stephen Rothwell <sfr@xxxxxxxxxxxxxxxx> Acked-by: Arnd Bergmann <arnd@xxxxxxxx> Signed-off-by: Josh Poimboeuf <jpoimboe@xxxxxxxxxx> Signed-off-by: Stephen Rothwell <sfr@xxxxxxxxxxxxxxxx> --- include/linux/compiler-gcc.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/include/linux/compiler-gcc.h b/include/linux/compiler-gcc.h index eeae401..3d5202e 100644 --- a/include/linux/compiler-gcc.h +++ b/include/linux/compiler-gcc.h @@ -246,7 +246,7 @@ #define __HAVE_BUILTIN_BSWAP32__ #define __HAVE_BUILTIN_BSWAP64__ #endif -#if GCC_VERSION >= 40800 || (defined(__powerpc__) && GCC_VERSION >= 40600) +#if GCC_VERSION >= 40800 #define __HAVE_BUILTIN_BSWAP16__ #endif #endif /* CONFIG_ARCH_USE_BUILTIN_BSWAP */ -- 2.4.11 -- Cheers, Stephen Rothwell -- To unsubscribe from this list: send the line "unsubscribe linux-next" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
