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Sat, 15 May 2021 14:56:55 -0700 (PDT) Received: from hyeyoo ([121.135.181.35]) by smtp.gmail.com with ESMTPSA id l62sm6592567pfl.88.2021.05.15.14.56.50 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 15 May 2021 14:56:55 -0700 (PDT) Date: Sun, 16 May 2021 06:56:47 +0900 From: Hyeonggon Yoo <42.hyeyoo@gmail.com> To: Vlastimil Babka 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 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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <41c65455-a35b-3ad3-54f9-49ca7105bfa9@suse.cz> X-Rspamd-Queue-Id: BF225138 Authentication-Results: imf12.hostedemail.com; dkim=pass header.d=gmail.com header.s=20161025 header.b=Z9GvsUXC; spf=pass (imf12.hostedemail.com: domain of 42hyeyoo@gmail.com designates 209.85.216.50 as permitted sender) smtp.mailfrom=42hyeyoo@gmail.com; dmarc=pass (policy=none) header.from=gmail.com X-Rspamd-Server: rspam04 X-Stat-Signature: 4q9qe8osjjozskgkqg88nb4tw3bfe4c7 X-HE-Tag: 1621115814-531235 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: 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