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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
Date: Sun, 16 May 2021 06:56:47 +0900	[thread overview]
Message-ID: <20210515215647.GA61684@hyeyoo> (raw)
In-Reply-To: <41c65455-a35b-3ad3-54f9-49ca7105bfa9@suse.cz>

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


  reply	other threads:[~2021-05-15 21:57 UTC|newest]

Thread overview: 31+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-05-11 17:34 [PATCH v3] mm, slub: change run-time assertion in kmalloc_index() to compile-time Hyeonggon Yoo
2021-05-11 17:38 ` Hyeonggon Yoo
2021-05-11 18:08 ` Vlastimil Babka
2021-05-13  2:52 ` Andrew Morton
2021-05-13  3:12   ` Hyeonggon Yoo
2021-05-13  3:40     ` Andrew Morton
2021-05-13  6:28       ` Hyeonggon Yoo
2021-05-13  8:46         ` Marco Elver
2021-05-13  8:46           ` Marco Elver
2021-05-13  8:51         ` Vlastimil Babka
2021-05-13 10:31           ` Marco Elver
2021-05-13 11:37             ` Vlastimil Babka
2021-05-13 12:08               ` Hyeonggon Yoo
2021-05-13 12:10                 ` Hyeonggon Yoo
2021-05-13 12:03             ` Hyeonggon Yoo
2021-05-13 12:29               ` Marco Elver
2021-05-13 12:29                 ` Marco Elver
2021-05-13 12:38                 ` Hyeonggon Yoo
2021-05-13 13:08                 ` Hyeonggon Yoo
2021-05-13 12:44   ` [PATCH] kfence: test: fix for "mm, slub: change run-time assertion in kmalloc_index() to compile-time" Marco Elver
2021-05-15 21:09 ` [PATCH v3] mm, slub: change run-time assertion in kmalloc_index() to compile-time Hyeonggon Yoo
2021-05-15 21:24   ` Vlastimil Babka
2021-05-15 21:56     ` Hyeonggon Yoo [this message]
2021-05-16  6:34     ` Nathan Chancellor
2021-05-18  0:38       ` Hyeonggon Yoo
2021-05-18  0:43         ` Nathan Chancellor
2021-05-18  1:53           ` Hyeonggon Yoo
2021-05-18  9:28           ` Vlastimil Babka
2021-05-18 11:18             ` Hyeonggon Yoo
2021-05-18 11:34               ` Vlastimil Babka
2021-05-19  5:45                 ` Hyeonggon Yoo

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