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[35.247.111.240]) by smtp.gmail.com with ESMTPSA id c191sm2278922pfc.94.2021.05.20.08.47.49 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 20 May 2021 08:47:49 -0700 (PDT) Date: Thu, 20 May 2021 15:47:46 +0000 From: Sean Christopherson To: Joe Richey Cc: trivial@kernel.org, Joe Richey , Thomas Gleixner , Ingo Molnar , Borislav Petkov , x86@kernel.org, "H. Peter Anvin" , Paolo Bonzini , Mark Rutland , Lorenzo Pieralisi , Mauro Carvalho Chehab , Zhangfei Gao , Zhou Wang , linux-kernel@vger.kernel.org, kvm@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-media@vger.kernel.org, linux-accelerators@lists.ozlabs.org Subject: Re: [PATCH 0/6] Don't use BIT() macro in UAPI headers Message-ID: References: <20210520104343.317119-1-joerichey94@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210520104343.317119-1-joerichey94@gmail.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, May 20, 2021, Joe Richey wrote: > From: Joe Richey > > The BIT(n) macro is used in the kernel as an alias for (1 << n). > However, it is not defined in the UAPI headers, which means that any > UAPI header files must be careful not to use it, or else the user > will get a linker error. For example, compiling the following program: > > #include > #include > > // Detect if FSGSBASE instructions are enabled > int main() { > unsigned long val = getauxval(AT_HWCAP2); > return !(val & HWCAP2_FSGSBASE); > } > > Results in the following likner error: > > /usr/bin/ld: /tmp/cceFpAdR.o: in function `main': > gs.c:(.text+0x21): undefined reference to `BIT' > > This patch series changes all UAPI uses of BIT() to just be open-coded. > However, there really should be a check for this in checkpatch.pl Any reason not to provide such a patch in this series? :-) > Currently, the script actually _encourages_ users to use the BIT macro > even if adding things to UAPI. > > Running `rg "BIT\(" **/uapi/**` shows no more usage of BIT() in any > UAPI headers. Tested by building a basic kernel. Changes are trivial.