From d0c2e691d1cbe43662df3a08a4933f13acc352c3 Mon Sep 17 00:00:00 2001 From: Josh Poimboeuf Date: Mon, 6 Nov 2017 07:17:37 -0600 Subject: 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 Signed-off-by: Josh Poimboeuf Cc: Peter Zijlstra Cc: Thomas Gleixner Link: http://lkml.kernel.org/r/1570e48d9f87e0fc6f0126c32e7e1de6e109cb67.1509974104.git.jpoimboe@redhat.com Signed-off-by: Ingo Molnar --- include/linux/compiler.h | 5 +++++ 1 file changed, 5 insertions(+) (limited to 'include') diff --git a/include/linux/compiler.h b/include/linux/compiler.h index 202710420d6d..f8734fca54ce 100644 --- a/include/linux/compiler.h +++ b/include/linux/compiler.h @@ -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" \ -- cgit From 10259821ac47dbefa6f83ae57f1fa9f1f2c54b3d Mon Sep 17 00:00:00 2001 From: Josh Poimboeuf Date: Mon, 6 Nov 2017 07:17:38 -0600 Subject: objtool: Make unreachable annotation inline asms explicitly volatile Add 'volatile' to the unreachable annotation macro inline asm statements. They're already implicitly volatile because they don't have output constraints, but it's clearer and more robust to make them explicitly volatile. Suggested-by: Linus Torvalds Signed-off-by: Josh Poimboeuf Cc: Peter Zijlstra Cc: Thomas Gleixner Link: http://lkml.kernel.org/r/28659257b7a6adf4a7f65920dad70b2b0226e996.1509974104.git.jpoimboe@redhat.com Signed-off-by: Ingo Molnar --- include/linux/compiler.h | 16 ++++++++-------- 1 file changed, 8 insertions(+), 8 deletions(-) (limited to 'include') diff --git a/include/linux/compiler.h b/include/linux/compiler.h index f8734fca54ce..4fac29cdffd1 100644 --- a/include/linux/compiler.h +++ b/include/linux/compiler.h @@ -193,16 +193,16 @@ void ftrace_likely_update(struct ftrace_likely_data *f, int val, * unique, to convince GCC not to merge duplicate inline asm statements. */ #define annotate_reachable() ({ \ - asm("%c0:\n\t" \ - ".pushsection .discard.reachable\n\t" \ - ".long %c0b - .\n\t" \ - ".popsection\n\t" : : "i" (__COUNTER__)); \ + asm volatile("%c0:\n\t" \ + ".pushsection .discard.reachable\n\t" \ + ".long %c0b - .\n\t" \ + ".popsection\n\t" : : "i" (__COUNTER__)); \ }) #define annotate_unreachable() ({ \ - asm("%c0:\n\t" \ - ".pushsection .discard.unreachable\n\t" \ - ".long %c0b - .\n\t" \ - ".popsection\n\t" : : "i" (__COUNTER__)); \ + asm volatile("%c0:\n\t" \ + ".pushsection .discard.unreachable\n\t" \ + ".long %c0b - .\n\t" \ + ".popsection\n\t" : : "i" (__COUNTER__)); \ }) #define ASM_UNREACHABLE \ "999:\n\t" \ -- cgit