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[209.85.208.176]) by smtp.gmail.com with ESMTPSA id z84sm2160327lfa.54.2020.07.09.17.53.41 for (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 09 Jul 2020 17:53:41 -0700 (PDT) Received: by mail-lj1-f176.google.com with SMTP id j11so4463673ljo.7 for ; Thu, 09 Jul 2020 17:53:41 -0700 (PDT) X-Received: by 2002:a2e:9b42:: with SMTP id o2mr37491111ljj.102.1594342420759; Thu, 09 Jul 2020 17:53:40 -0700 (PDT) MIME-Version: 1.0 References: <20200709221102.323356-1-cesarb@cesarb.eti.br> In-Reply-To: <20200709221102.323356-1-cesarb@cesarb.eti.br> From: Linus Torvalds Date: Thu, 9 Jul 2020 17:53:24 -0700 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH] Restore gcc check in mips asm/unroll.h To: Cesar Eduardo Barros , Nick Desaulniers Cc: Linux Kernel Mailing List Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Jul 9, 2020 at 3:11 PM Cesar Eduardo Barros wrote: > > While raising the gcc version requirement to 4.9, the compile-time check > in the unroll macro was accidentally changed from being used on gcc and > clang to being used on clang only. > > Restore the gcc check, changing it from "gcc >= 4.7" to "all gcc". This is clearly a thinko on my side: the old CONFIG_GCC_VERSION >= 40700 became pointless, so I removed, it, but it was mixed with an "||" so we actually wanted to make it unconditional on gcc, and instead now it checks for CLANG version even when it shouldn't. My bad, and your patch is obviously correct. At the same time, I do wonder if we could just remove the check for CLANG_VERSION >= 80000 too, and just remove all the compiler check hackery entirely? Older versions of clang weren't very good at compiling the Linux kernel in the first place. Do people actually use old clang versions? That sounds like a really bad idea. People who used to build the kernel with clang tended to actually get their clang version from the clang git sources afaik (I still do, but that's because I test experimental new features that aren't released yet), exactly because back in the bad old days there were so many problems. These days you can use release versions, but they'd presumably not be older than clang-8. Adding Nick - is it really reasonable to build any kernel with any clang version before 8.0.0? It turns out that the arm side also has a check for clang < 8 because of -mcmodel=tiny, so raising the minimum required clang version to that would solve that issue too. Right now we don't mention minimum clang/llvm versions in our docs at all, because we only mention gcc. Mayeb this would be good to clarify. Linus