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Sat, 15 May 2021 14:09:58 -0700 (PDT) Received: from hyeyoo ([121.135.181.35]) by smtp.gmail.com with ESMTPSA id f13sm6728644pfa.207.2021.05.15.14.09.53 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 15 May 2021 14:09:57 -0700 (PDT) Date: Sun, 16 May 2021 06:09:50 +0900 From: Hyeonggon Yoo <42.hyeyoo@gmail.com> To: vbabka@suse.cz, akpm@linux-foundation.org, iamjoonsoo.kim@lge.com, rientjes@google.com, penberg@kernel.org, cl@linux.com Cc: 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, akpm@linux-foundation.org Subject: Re: [PATCH v3] mm, slub: change run-time assertion in kmalloc_index() to compile-time Message-ID: <20210515210950.GA52841@hyeyoo> References: <20210511173448.GA54466@hyeyoo> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210511173448.GA54466@hyeyoo> X-Rspamd-Queue-Id: 29CF0A000384 Authentication-Results: imf23.hostedemail.com; dkim=pass header.d=gmail.com header.s=20161025 header.b=hLe8uQ8J; spf=pass (imf23.hostedemail.com: domain of 42hyeyoo@gmail.com designates 209.85.214.180 as permitted sender) smtp.mailfrom=42hyeyoo@gmail.com; dmarc=pass (policy=none) header.from=gmail.com X-Rspamd-Server: rspam04 X-Stat-Signature: umdckw3nujiitf95p4yte5uon6pjr5qn X-HE-Tag: 1621112998-368937 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: Hello Vlastimil, recently kbuild-all test bot reported compile error on clang 10.0.1, with defconfig. Nathan Chancellor wrote: > I think this happens because arch_prepare_optimized_kprobe() calls kzalloc() > with a size of MAX_OPTINSN_SIZE, which is > > #define MAX_OPTINSN_SIZE \ > (((unsigned long)optprobe_template_end - \ > (unsigned long)optprobe_template_entry) + \ > MAX_OPTIMIZED_LENGTH + JMP32_INSN_SIZE) > and the optprobe_template_{end,entry} are not evaluated as constants. > > I am not sure what the solution is. There seem to be a growing list of issues > with LLVM 10 that were fixed in LLVM 11, which might necessitate requiring > LLVM 11 and newer to build the kernel, given this affects a defconfig. > Cheers, > Nathan I think it's because kmalloc compiles successfully when size is constant, and kmalloc_index isn't. so I think compiler seems to be confused. currently if size is non-constant, kmalloc calls dummy function __kmalloc, which always returns NULL. so what about changing kmalloc to do compile-time assertion too, and track all callers that are calling kmalloc with non-constant argument. How do you think? If you think it is the solution, I'll do that work.