linux-kernel - [PATCH 4.19 073/110] compiler.h: update definition of unreachable()

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Message-Id: <20190418160445.180360887@linuxfoundation.org>
Date:   Thu, 18 Apr 2019 19:57:02 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Andy Lutomirski <luto@...capital.net>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Nathan Chancellor <natechancellor@...il.com>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Miguel Ojeda <miguel.ojeda.sandonis@...il.com>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 4.19 073/110] compiler.h: update definition of unreachable()

[ Upstream commit fe0640eb30b7da261ae84d252ed9ed3c7e68dfd8 ]

Fixes the objtool warning seen with Clang:
arch/x86/mm/fault.o: warning: objtool: no_context()+0x220: unreachable
instruction

Fixes commit 815f0ddb346c ("include/linux/compiler*.h: make compiler-*.h
mutually exclusive")

Josh noted that the fallback definition was meant to work around a
pre-gcc-4.6 bug. GCC still needs to work around
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82365, so compiler-gcc.h
defines its own version of unreachable().  Clang and ICC can use this
shared definition.

Link: https://github.com/ClangBuiltLinux/linux/issues/204
Suggested-by: Andy Lutomirski <luto@...capital.net>
Suggested-by: Josh Poimboeuf <jpoimboe@...hat.com>
Tested-by: Nathan Chancellor <natechancellor@...il.com>
Signed-off-by: Nick Desaulniers <ndesaulniers@...gle.com>
Signed-off-by: Miguel Ojeda <miguel.ojeda.sandonis@...il.com>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 include/linux/compiler.h | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/include/linux/compiler.h b/include/linux/compiler.h
index 269d376f5a11..81c2238b884c 100644
--- a/include/linux/compiler.h
+++ b/include/linux/compiler.h
@@ -124,7 +124,10 @@ void ftrace_likely_update(struct ftrace_likely_data *f, int val,
 # define ASM_UNREACHABLE
 #endif
 #ifndef unreachable
-# define unreachable() do { annotate_reachable(); do { } while (1); } while (0)
+# define unreachable() do {		\
+	annotate_unreachable();		\
+	__builtin_unreachable();	\
+} while (0)
 #endif
 
 /*
-- 
2.19.1