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[14.3.142.46]) by smtp.gmail.com with ESMTPSA id s1sm29753063pfb.103.2020.12.25.23.52.04 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 25 Dec 2020 23:52:06 -0800 (PST) Subject: Re: [PATCH] arch/x86: Propagate $(CLANG_FLAGS) to $(REALMODE_FLAGS) To: hpa@zytor.com, x86@kernel.org, linux-kernel@vger.kernel.org Cc: clang-built-linux@googlegroups.com, Thomas Gleixner , Ingo Molnar , Borislav Petkov , John Millikin References: <37DE7046-5096-4C0C-A96D-FD168A849DFD@zytor.com> From: John Millikin Message-ID: <6008226d-3655-df9c-6842-8161de365ff7@gmail.com> Date: Sat, 26 Dec 2020 16:52:03 +0900 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:78.0) Gecko/20100101 Thunderbird/78.6.0 MIME-Version: 1.0 In-Reply-To: <37DE7046-5096-4C0C-A96D-FD168A849DFD@zytor.com> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Content-Language: en-US Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 12/26/20 16:35, hpa@zytor.com wrote: > Why is CLANG_FLAGS non-null when unused? It would be better to centralize that. CLANG_FLAGS normally propagates through inclusion in the default KBUILD_CFLAGS and KBUILD_AFLAGS, set in `/Makefile':     # Makefile     KBUILD_CFLAGS += $(CLANG_FLAGS)     KBUILD_AFLAGS += $(CLANG_FLAGS)     export CLANG_FLAGS This default can be overridden by explicit assignment, as is done in some of the arch/x86 makefiles:     # arch/x86/realmode/rm/Makefile     KBUILD_CFLAGS    := $(REALMODE_CFLAGS) -D_SETUP -D_WAKEUP \                -I$(srctree)/arch/x86/boot     KBUILD_AFLAGS    := $(KBUILD_CFLAGS) -D__ASSEMBLY__     KBUILD_CFLAGS    += -fno-asynchronous-unwind-tables Since REALMODE_CFLAGS is being built up from a plain assignment, the Clang flags get lost. As a result Clang fails to compile the real-mode code when cross-compiling for an x86 target.     arch/x86/realmode/rm/header.S:36:1: error: unknown directive     .type real_mode_header STT_OBJECT ; .size real_mode_header, .-real_mode_header     ^     arch/x86/realmode/rm/header.S:36:37: error: unknown directive     .type real_mode_header STT_OBJECT ; .size real_mode_header, .-real_mode_header                                         ^     arch/x86/realmode/rm/header.S:41:62: error: unknown directive     .globl end_signature ; ; end_signature: ; .long 0x65a22c82 ; .type end_signature STT_OBJECT ; .size end_signature, .-end_signature                                                                  ^     arch/x86/realmode/rm/header.S:41:95: error: unknown directive     .globl end_signature ; ; end_signature: ; .long 0x65a22c82 ; .type end_signature STT_OBJECT ; .size end_signature, .-end_signature                                                                                                 ^ This patch allows the Clang-specific flags to propagate through the REALMODE_CFLAGS variable set in `arch/x86/Makefile' and consumed by certain arch/x86 targets, which fixes cross-compilation of x86 kernels.