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Date:   Sun, 16 May 2021 06:56:47 +0900
From:   Hyeonggon Yoo <42.hyeyoo@gmail.com>
To:     Vlastimil Babka <vbabka@suse.cz>
Cc:     akpm@linux-foundation.org, iamjoonsoo.kim@lge.com,
        rientjes@google.com, penberg@kernel.org, cl@linux.com,
        linux-mm@kvack.org, linux-kernel@vger.kernel.org,
        nathan@kernel.org, naresh.kamboju@linaro.org,
        clang-built-linux@googlegroups.com, linux-next@vger.kernel.org,
        ndesaulniers@google.com, lkft-triage@lists.linaro.org,
        sfr@canb.auug.org.au, arnd@arndb.de, Marco Elver <elver@google.com>
Subject: Re: [PATCH v3] mm, slub: change run-time assertion in
 kmalloc_index() to compile-time
Message-ID: <20210515215647.GA61684@hyeyoo>
References: <20210511173448.GA54466@hyeyoo>
 <20210515210950.GA52841@hyeyoo>
 <41c65455-a35b-3ad3-54f9-49ca7105bfa9@suse.cz>
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On Sat, May 15, 2021 at 11:24:25PM +0200, Vlastimil Babka wrote:
>
> That's a misunderstanding. __kmalloc() is not a dummy function, you
> probably found only the header declaration.
>

Sorry, that was totally my misunderstanding.
I was reading dummy function in arch/alpha/boot/bootpz.c:415.
I wrongly configured the tool.

> It appears clang 10.0.1 is mistakenly evaluating __builtin_constant_p()
> as true. Probably something to do with LTO, because MAX_OPTINSN_SIZE
> seems it could be a "link-time constant".

That is what I was missing. Thank you for kindly explaining it.

> Maybe we could extend Marco Elver's followup patch that uses
> BUILD_BUG_ON vs BUG() depending on size_is_constant parameter. It could
> use BUG() also if the compiler is LLVM < 11 or something. What would be
> the proper code for this condition?

Fixing clang's bug in linux kernel doesn't seem to be a solution.
So now I understand why Nathan said we might require LLVM > 11.

I thought I should do something to fix it because I sent the patch.
but I was misunderstanding a lot. Thank you sincerely for letting me know.

Thanks,

Hyeonggon