mirror of
https://github.com/torvalds/linux.git
synced 2025-11-04 02:30:34 +02:00
4abaacc704
Remove a tautology; since
commit 0bddd227f3 ("Documentation: update for gcc 4.9 requirement")
which raised the minimally supported version of GCC to 4.9, this case is
always true.
Link: https://github.com/ClangBuiltLinux/linux/issues/427
Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
66 lines
2.6 KiB
C
66 lines
2.6 KiB
C
/*
|
|
* 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")
|
|
|
|
#define GCC_OFF_SMALL_ASM() "ZC"
|
|
|
|
#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
|
|
#elif defined(CONFIG_CPU_MIPSR5)
|
|
#define MIPS_ISA_LEVEL "mips64r5"
|
|
#define MIPS_ISA_ARCH_LEVEL MIPS_ISA_LEVEL
|
|
#define MIPS_ISA_LEVEL_RAW mips64r5
|
|
#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 */
|