diff options
Diffstat (limited to 'arch/mips/include/asm/compiler.h')
| -rw-r--r-- | arch/mips/include/asm/compiler.h | 80 |
1 files changed, 80 insertions, 0 deletions
diff --git a/arch/mips/include/asm/compiler.h b/arch/mips/include/asm/compiler.h new file mode 100644 index 000000000..cc2eb1b06 --- /dev/null +++ b/arch/mips/include/asm/compiler.h @@ -0,0 +1,80 @@ +/* + * Copyright (C) 2004, 2007 Maciej W. Rozycki + * + * This file is subject to the terms and conditions of the GNU General Public + * License. See the file "COPYING" in the main directory of this archive + * for more details. + */ +#ifndef _ASM_COMPILER_H +#define _ASM_COMPILER_H + +/* + * With GCC 4.5 onwards we can use __builtin_unreachable to indicate to the + * compiler that a particular code path will never be hit. This allows it to be + * optimised out of the generated binary. + * + * Unfortunately at least GCC 4.6.3 through 7.3.0 inclusive suffer from a bug + * that can lead to instructions from beyond an unreachable statement being + * incorrectly reordered into earlier delay slots if the unreachable statement + * is the only content of a case in a switch statement. This can lead to + * seemingly random behaviour, such as invalid memory accesses from incorrectly + * reordered loads or stores. See this potential GCC fix for details: + * + * https://gcc.gnu.org/ml/gcc-patches/2015-09/msg00360.html + * + * It is unclear whether GCC 8 onwards suffer from the same issue - nothing + * relevant is mentioned in GCC 8 release notes and nothing obviously relevant + * stands out in GCC commit logs, but these newer GCC versions generate very + * different code for the testcase which doesn't exhibit the bug. + * + * GCC also handles stack allocation suboptimally when calling noreturn + * functions or calling __builtin_unreachable(): + * + * https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82365 + * + * We work around both of these issues by placing a volatile asm statement, + * which GCC is prevented from reordering past, prior to __builtin_unreachable + * calls. + * + * The .insn statement is required to ensure that any branches to the + * statement, which sadly must be kept due to the asm statement, are known to + * be branches to code and satisfy linker requirements for microMIPS kernels. + */ +#undef barrier_before_unreachable +#define barrier_before_unreachable() asm volatile(".insn") + +#if __GNUC__ > 3 || (__GNUC__ == 3 && __GNUC_MINOR__ >= 4) +#define GCC_IMM_ASM() "n" +#define GCC_REG_ACCUM "$0" +#else +#define GCC_IMM_ASM() "rn" +#define GCC_REG_ACCUM "accum" +#endif + +#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" +#else +#error "microMIPS compilation unsupported with GCC older than 4.9" +#endif /* CONFIG_CPU_MICROMIPS */ +#endif /* CONFIG_CPU_MIPSR6 */ + +#ifdef CONFIG_CPU_MIPSR6 +#define MIPS_ISA_LEVEL "mips64r6" +#define MIPS_ISA_ARCH_LEVEL MIPS_ISA_LEVEL +#define MIPS_ISA_LEVEL_RAW mips64r6 +#define MIPS_ISA_ARCH_LEVEL_RAW MIPS_ISA_LEVEL_RAW +#else +/* MIPS64 is a superset of MIPS32 */ +#define MIPS_ISA_LEVEL "mips64r2" +#define MIPS_ISA_ARCH_LEVEL "arch=r4000" +#define MIPS_ISA_LEVEL_RAW mips64r2 +#define MIPS_ISA_ARCH_LEVEL_RAW MIPS_ISA_LEVEL_RAW +#endif /* CONFIG_CPU_MIPSR6 */ + +#endif /* _ASM_COMPILER_H */ |