linux-kernel - Re: [tip: objtool/urgent] compiler.h: Fix annotation macro misplacement with Clang

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Date:   Mon, 3 Jan 2022 18:58:02 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     llvm@...ts.linux.dev
Cc:     Josh Poimboeuf <jpoimboe@...hat.com>,
        linux-tip-commits@...r.kernel.org,
        kernel test robot <lkp@...el.com>,
        Peter Zijlstra <peterz@...radead.org>, x86@...nel.org,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Miroslav Benes <mbenes@...e.cz>, linux-kernel@...r.kernel.org
Subject: Re: [tip: objtool/urgent] compiler.h: Fix annotation macro
 misplacement with Clang

I wonder if clang folks have seen this and perhaps have a comment as to
why the volatile gets ingored... Added.

On Wed, Dec 22, 2021 at 09:10:30AM -0000, tip-bot2 for Josh Poimboeuf wrote:
> The following commit has been merged into the objtool/urgent branch of tip:
> 
> Commit-ID:     dcce50e6cc4d86a63dc0a9a6ee7d4f948ccd53a1
> Gitweb:        https://git.kernel.org/tip/dcce50e6cc4d86a63dc0a9a6ee7d4f948ccd53a1
> Author:        Josh Poimboeuf <jpoimboe@...hat.com>
> AuthorDate:    Mon, 08 Nov 2021 14:35:59 -08:00
> Committer:     Josh Poimboeuf <jpoimboe@...hat.com>
> CommitterDate: Tue, 21 Dec 2021 15:09:46 -08:00
> 
> compiler.h: Fix annotation macro misplacement with Clang
> 
> When building with Clang and CONFIG_TRACE_BRANCH_PROFILING, there are a
> lot of unreachable warnings, like:
> 
>   arch/x86/kernel/traps.o: warning: objtool: handle_xfd_event()+0x134: unreachable instruction
> 
> Without an input to the inline asm, 'volatile' is ignored for some
> reason and Clang feels free to move the reachable() annotation away from
> its intended location.
> 
> Fix that by re-adding the counter value to the inputs.
> 
> Fixes: f1069a8756b9 ("compiler.h: Avoid using inline asm operand modifiers")
> Fixes: c199f64ff93c ("instrumentation.h: Avoid using inline asm operand modifiers")
> Reported-by: kernel test robot <lkp@...el.com>
> Signed-off-by: Josh Poimboeuf <jpoimboe@...hat.com>
> Link: https://lore.kernel.org/r/0417e96909b97a406323409210de7bf13df0b170.1636410380.git.jpoimboe@redhat.com
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: x86@...nel.org
> Cc: Vasily Gorbik <gor@...ux.ibm.com>
> Cc: Miroslav Benes <mbenes@...e.cz>
> ---
>  include/linux/compiler.h        | 4 ++--
>  include/linux/instrumentation.h | 4 ++--
>  2 files changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/include/linux/compiler.h b/include/linux/compiler.h
> index 3d5af56..429dceb 100644
> --- a/include/linux/compiler.h
> +++ b/include/linux/compiler.h
> @@ -121,7 +121,7 @@ void ftrace_likely_update(struct ftrace_likely_data *f, int val,
>  	asm volatile(__stringify_label(c) ":\n\t"			\
>  		     ".pushsection .discard.reachable\n\t"		\
>  		     ".long " __stringify_label(c) "b - .\n\t"		\
> -		     ".popsection\n\t");				\
> +		     ".popsection\n\t" : : "i" (c));			\
>  })
>  #define annotate_reachable() __annotate_reachable(__COUNTER__)
>  
> @@ -129,7 +129,7 @@ void ftrace_likely_update(struct ftrace_likely_data *f, int val,
>  	asm volatile(__stringify_label(c) ":\n\t"			\
>  		     ".pushsection .discard.unreachable\n\t"		\
>  		     ".long " __stringify_label(c) "b - .\n\t"		\
> -		     ".popsection\n\t");				\
> +		     ".popsection\n\t" : : "i" (c));			\
>  })
>  #define annotate_unreachable() __annotate_unreachable(__COUNTER__)
>  
> diff --git a/include/linux/instrumentation.h b/include/linux/instrumentation.h
> index fa2cd8c..24359b4 100644
> --- a/include/linux/instrumentation.h
> +++ b/include/linux/instrumentation.h
> @@ -11,7 +11,7 @@
>  	asm volatile(__stringify(c) ": nop\n\t"				\
>  		     ".pushsection .discard.instr_begin\n\t"		\
>  		     ".long " __stringify(c) "b - .\n\t"		\
> -		     ".popsection\n\t");				\
> +		     ".popsection\n\t" : : "i" (c));			\
>  })
>  #define instrumentation_begin() __instrumentation_begin(__COUNTER__)
>  
> @@ -50,7 +50,7 @@
>  	asm volatile(__stringify(c) ": nop\n\t"				\
>  		     ".pushsection .discard.instr_end\n\t"		\
>  		     ".long " __stringify(c) "b - .\n\t"		\
> -		     ".popsection\n\t");				\
> +		     ".popsection\n\t" : : "i" (c));			\
>  })
>  #define instrumentation_end() __instrumentation_end(__COUNTER__)
>  #else

-- 
Regards/Gruss,
    Boris.

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