linux-kernel - Re: [RFC PATCH v1 1/3] Revert "powerpc/bug: Provide better flexibility to WARN_ON/__WARN

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Date:   Tue, 20 Jun 2023 10:51:25 +0530
From:   Naveen N Rao <naveen@...nel.org>
To:     Christophe Leroy <christophe.leroy@...roup.eu>,
        Josh Poimboeuf <jpoimboe@...nel.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Nicholas Piggin <npiggin@...il.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Sathvika Vasireddy <sv@...ux.ibm.com>
Cc:     linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>
Subject: Re: [RFC PATCH v1 1/3] Revert "powerpc/bug: Provide better
 flexibility to WARN_ON/__WARN_FLAGS() with asm goto"

Christophe Leroy wrote:
> This reverts commit 1e688dd2a3d6759d416616ff07afc4bb836c4213.
> 
> That commit aimed at optimising the code around generation of
> WARN_ON/BUG_ON but this leads to a lot of dead code erroneously
> generated by GCC.
> 
>      text	   data	    bss	    dec	    hex	filename
>   9551585	3627834	 224376	13403795	 cc8693	vmlinux.before
>   9535281	3628358	 224376	13388015	 cc48ef	vmlinux.after
> 
> Once this change is reverted, in a standard configuration (pmac32 +
> function tracer) the text is reduced by 16k which is around 1.7%

Aneesh recently reported a build failure due to the use of 'asm goto' in  
WARN_ON(). We were able to root-cause it to the use of 'asm goto' with 
two config options: CONFIG_CC_OPTIMIZE_FOR_SIZE and 
CONFIG_DEBUG_SECTION_MISMATCH.

Along with the issues we found with 'asm goto' during objtool 
enablement, I think it might be better to disable it for now.
Acked-by: Naveen N Rao <naveen@...nel.org>


- Naveen