From d08b8ccc476215ceee6e3370f0c1732d5f83f5ef Mon Sep 17 00:00:00 2001 From: Paul Burton Date: Wed, 7 Nov 2018 23:05:46 +0000 Subject: [PATCH] MIPS: Simplify GCC_OFF_SMALL_ASM definition The GCC_OFF_SMALL_ASM macro defines the constraint to use for instructions needing "small offsets", typically the LL or SC instructions. Historically these had 16 bit offsets, but microMIPS & MIPS32/MIPS64r6 onwards reduced the width of the offset field. GCC 4.9 & higher supports a ZC constraint which matches the offset requirements of the LL & SC instructions. Where supported we can use the ZC constraint regardless of ISA, and it will handle the requirements of the ISA correctly. As such we require 3 cases: - GCC 4.9 & higher can use ZC. - GCC older than 4.9 must use the older R constraint, which does not take into account microMIPS or MIPSr6. - microMIPS builds therefore require GCC 4.9 or higher. MIPSr6 support was only introduced in newer compilers anyway so it can be ignored here. The current code complicates this a little by specifically having MIPSr6 bypass the GCC version check, and using the R constraint for pre-MIPSr6 builds even if the compiler supports ZC which would be equivalent. Simplify this such that the code straightforwardly implements the 3 cases outlined above. For non-GCC compilers we presume that ZC is safe to use. In practice the only non-GCC compiler of interest is clang and it has supported the ZC constraint since version 3.7.0. It seems safe enough to presume that nobody will expect to built a working kernel using a clang version older than that, and if they do then they'll have bigger problems. As such we don't check the clang version number & just presume ZC is usable when the compiler is not GCC. Signed-off-by: Paul Burton Patchwork: https://patchwork.linux-mips.org/patch/20999/ Cc: linux-mips@linux-mips.org --- arch/mips/include/asm/compiler.h | 18 +++++++----------- 1 file changed, 7 insertions(+), 11 deletions(-) diff --git a/arch/mips/include/asm/compiler.h b/arch/mips/include/asm/compiler.h index 9196fca4335d..f77e99f1722e 100644 --- a/arch/mips/include/asm/compiler.h +++ b/arch/mips/include/asm/compiler.h @@ -43,18 +43,14 @@ #undef barrier_before_unreachable #define barrier_before_unreachable() asm volatile(".insn") -#ifdef CONFIG_CPU_MIPSR6 -/* All MIPS R6 toolchains support the ZC constrain */ -#define GCC_OFF_SMALL_ASM() "ZC" -#else -#ifndef CONFIG_CPU_MICROMIPS -#define GCC_OFF_SMALL_ASM() "R" -#elif __GNUC__ > 4 || (__GNUC__ == 4 && __GNUC_MINOR__ >= 9) -#define GCC_OFF_SMALL_ASM() "ZC" +#if !defined(CONFIG_CC_IS_GCC) || \ + (__GNUC__ > 4) || (__GNUC__ == 4 && __GNUC_MINOR__ >= 9) +# define GCC_OFF_SMALL_ASM() "ZC" +#elif defined(CONFIG_CPU_MICROMIPS) +# error "microMIPS compilation unsupported with GCC older than 4.9" #else -#error "microMIPS compilation unsupported with GCC older than 4.9" -#endif /* CONFIG_CPU_MICROMIPS */ -#endif /* CONFIG_CPU_MIPSR6 */ +# define GCC_OFF_SMALL_ASM() "R" +#endif #ifdef CONFIG_CPU_MIPSR6 #define MIPS_ISA_LEVEL "mips64r6" -- 2.20.1