Add support for GCC-4.5's __builtin_unreachable() to compiler.h (v2) (38938c87) · Commits · 戴 / test

Starting with version 4.5, GCC has a new built-in function __builtin_unreachable() that can be used in places like the kernel's BUG() where inline assembly is used to transfer control flow. This eliminated the need for an endless loop in these places. The patch adds a new macro 'unreachable()' that will expand to either __builtin_unreachable() or an endless loop depending on the compiler version. Change from v1: Simplify unreachable() for non-GCC 4.5 case. Signed-off-by:

David Daney <ddaney@caviumnetworks.com> Acked-by:

Ralf Baechle <ralf@linux-mips.org> Signed-off-by:

Linus Torvalds <torvalds@linux-foundation.org>

include/linux/compiler-gcc4.h

+14 −0

Original line number	Diff line number	Diff line
		@@ -36,4 +36,18 @@
		the kernel context */
		#define __cold __attribute__((__cold__))


		#if __GNUC_MINOR__ >= 5
		/*
		* Mark a position in code as unreachable. This can be used to
		* suppress control flow warnings after asm blocks that transfer
		* control elsewhere.
		*
		* Early snapshots of gcc 4.5 don't support this and we can't detect
		* this in the preprocessor, but we can live with this because they're
		* unreleased. Really, we need to have autoconf for the kernel.
		*/
		#define unreachable() __builtin_unreachable()
		#endif

		#endif

include/linux/compiler.h

+5 −0

Original line number	Diff line number	Diff line
		@@ -144,6 +144,11 @@ void ftrace_likely_update(struct ftrace_branch_data *f, int val, int expect);
		# define barrier() __memory_barrier()
		#endif

		/* Unreachable code */
		#ifndef unreachable
		# define unreachable() do { } while (1)
		#endif

		#ifndef RELOC_HIDE
		# define RELOC_HIDE(ptr, off) \
		({ unsigned long __ptr; \

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