linux-kernel - Re: [PATCH 09/10] arm64: select DYNAMIC_DEBUG_RELATIVE

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Message-ID: <94b816aa-ad36-75e6-8782-d141dec2e803@rasmusvillemoes.dk>
Date:   Fri, 26 Apr 2019 12:05:57 +0200
From:   Rasmus Villemoes <linux@...musvillemoes.dk>
To:     Arnd Bergmann <arnd@...db.de>,
        Rasmus Villemoes <linux@...musvillemoes.dk>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Will Deacon <will.deacon@....com>,
        Jason Baron <jbaron@...mai.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        clang-built-linux@...glegroups.com,
        Nathan Chancellor <natechancellor@...il.com>,
        Nick Desaulniers <ndesaulniers@...gle.com>
Subject: Re: [PATCH 09/10] arm64: select DYNAMIC_DEBUG_RELATIVE_POINTERS

On 26/04/2019 11.39, Arnd Bergmann wrote:
> On Tue, Apr 9, 2019 at 11:26 PM Rasmus Villemoes
> <linux@...musvillemoes.dk> wrote:
>>
>> Similar to GENERIC_BUG_RELATIVE_POINTERS, one can now relativize the
>> four const char* members of struct _ddebug, thus saving 16 bytes per
>> instance (one for each pr_debug(), dev_debug() etc. in a
>> CONFIG_DYNAMIC_DEBUG kernel). The asm-generic implementation seems to
>> work out-of-the-box, though this is only compile-tested.
>>
>> Signed-off-by: Rasmus Villemoes <linux@...musvillemoes.dk>
> 
> This causes a build regression when compiling with clang,
> see http://staging-storage.kernelci.org/next-clang/master/next-20190424/arm64/allmodconfig/clang-8/build.log

Yes, see also https://github.com/ClangBuiltLinux/linux/issues/456 .

The quickest short-term fix is to append "if CC_IS_GCC" to the select
statements. Then when a fix lands in clang one can change that to "if
CC_IS_GCC || CLANG_VERSION >= something". It's probably best if we fix
-next builds ASAP instead of waiting for knowing the proper value of
"something". Nathan, Nick, WDYT?

I had 0day verify my patches before sending them out officially, and
thought it also did clang builds. But apparently not, or not with enough
arch/.config combinations?

Rasmus