x86/build: Remove -pipe from KBUILD_CFLAGS
Commit77b0bf55bc
("kbuild/Makefile: Prepare for using macros in inline assembly code to work around asm() related GCC inlining bugs") added -Wa,- to KBUILD_CFLAGS, which breaks compiling with Clang (hangs indefinitely at compiling init/main.o). This happens because while Clang accepts -pipe (and has it documented in its list of supported flags), it silently ignores it after this 2010 commit (thanks to Nick Desaulniers for tracking this down), meaning that gas just infinitely waits for stdin and never receives it.c19a12dc3d
Initially, I had suggested just add -Wa,- to KBUILD_CFLAGS when GCC was being used but that was before realizing it is because Clang doesn't do anything with -pipe. H. Peter Anvin suggested checking to see if -pipe gives us any gains out of GCC. Turns out it might actually be hurting: With -pipe: real 3m40.813s real 3m44.449s real 3m39.648s Without -pipe: real 3m38.492s real 3m38.335s real 3m38.975s The issue of -Wa,- being passed along to gas without -pipe being supported should still probably be fixed on the LLVM side (open issue: https://bugs.llvm.org/show_bug.cgi?id=39410) but this is not as much of a workaround anymore since it helps both GCC and Clang. Suggested-by: H. Peter Anvin <hpa@zytor.com> Signed-off-by: Nathan Chancellor <natechancellor@gmail.com> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Tested-by: Nick Desaulniers <ndesaulniers@google.com> Reviewed-by: Nadav Amit <namit@vmware.com> Reviewed-by: Nick Desaulniers <ndesaulniers@google.com> Cc: Borislav Petkov <bp@alien8.de> Cc: Kees Cook <keescook@chromium.org> Cc: Masahiro Yamada <yamada.masahiro@socionext.com> Link: https://github.com/ClangBuiltLinux/linux/issues/213 Link: https://lkml.kernel.org/r/20181023231125.27976-1-natechancellor@gmail.com
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@ -213,8 +213,6 @@ ifdef CONFIG_X86_64
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KBUILD_LDFLAGS += $(call ld-option, -z max-page-size=0x200000)
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endif
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# Speed up the build
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KBUILD_CFLAGS += -pipe
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# Workaround for a gcc prelease that unfortunately was shipped in a suse release
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KBUILD_CFLAGS += -Wno-sign-compare
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#
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@ -239,7 +237,7 @@ archheaders:
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archmacros:
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$(Q)$(MAKE) $(build)=arch/x86/kernel arch/x86/kernel/macros.s
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ASM_MACRO_FLAGS = -Wa,arch/x86/kernel/macros.s -Wa,-
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ASM_MACRO_FLAGS = -Wa,arch/x86/kernel/macros.s
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export ASM_MACRO_FLAGS
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KBUILD_CFLAGS += $(ASM_MACRO_FLAGS)
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