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objtool: Add a comment for the unreachable annotation macros 

Add a comment for the unreachable annotation macros to explain their
purpose and the '__COUNTER__' label hack.

Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1570e48d9f87e0fc6f0126c32e7e1de6e109cb67.1509974104.git.jpoimboe@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Josh Poimboeuf 2017-11-06 07:17:37 -06:00 committed by Ingo Molnar
parent 783711f0d2
commit d0c2e691d1
1 changed files with 5 additions and 0 deletions
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5
include/linux/compiler.h
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@ -187,6 +187,11 @@ void ftrace_likely_update(struct ftrace_likely_data *f, int val,
/* Unreachable code */
#ifdef CONFIG_STACK_VALIDATION
/*
* These macros help objtool understand GCC code flow for unreachable code.
* The __COUNTER__ based labels are a hack to make each instance of the macros
* unique, to convince GCC not to merge duplicate inline asm statements.
*/
#define annotate_reachable() ({ \
asm("%c0:\n\t" \
".pushsection .discard.reachable\n\t" \