From: Nathan Chancellor <[email protected]> Sent: October 23, 2018 at 11:11:25 PM GMT > To: Thomas Gleixner; Ingo Molnar; Borislav Petkov > Cc: H. Peter Anvin; [email protected], [email protected], Nadav > Amit; Kees Cook; Masahiro Yamada; Nick Desaulniers; Nathan Chancellor > Subject: [PATCH] x86: Remove -pipe from KBUILD_CFLAGS > > > Commit 77b0bf55bc67 ("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. > > https://na01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgithub.com%2Fllvm-mirror%2Fclang%2Fcommit%2Fc19a12dc3d441bec62eed55e312b76c12d6d9022&data=02%7C01%7Cnamit%40vmware.com%7C56678e0018894955601908d6393ce6d2%7Cb39138ca3cee4b4aa4d6cd83d9dd62f0%7C1%7C0%7C636759331072072215&sdata=AjoP%2BerS26K58QQINE0UDJ00ftyGMa5ovlaKvZViZ4w%3D&reserved=0 > > 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://na01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fbugs.llvm.org%2Fshow_bug.cgi%3Fid%3D39410&data=02%7C01%7Cnamit%40vmware.com%7C56678e0018894955601908d6393ce6d2%7Cb39138ca3cee4b4aa4d6cd83d9dd62f0%7C1%7C0%7C636759331072082215&sdata=MlOeR1p8%2BRROFxhjw3SQi0Uai9zuUeEesBxSMaM8wsg%3D&reserved=0) > but this is not as much of > a workaround anymore since it helps both GCC and Clang. > > Link: > https://na01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgithub.com%2FClangBuiltLinux%2Flinux%2Fissues%2F213&data=02%7C01%7Cnamit%40vmware.com%7C56678e0018894955601908d6393ce6d2%7Cb39138ca3cee4b4aa4d6cd83d9dd62f0%7C1%7C0%7C636759331072082215&sdata=q9iCdYa80V49o0BnZqFf3WYcMwRMl%2BtuS1MN8RZCPFI%3D&reserved=0 > Suggested-by: H. Peter Anvin <[email protected]> > Signed-off-by: Nathan Chancellor <[email protected]> > --- > arch/x86/Makefile | 4 +--- > 1 file changed, 1 insertion(+), 3 deletions(-) > > diff --git a/arch/x86/Makefile b/arch/x86/Makefile > index 73f4831283ac..672c689c1faa 100644 > --- a/arch/x86/Makefile > +++ b/arch/x86/Makefile > @@ -213,8 +213,6 @@ ifdef CONFIG_X86_64 > KBUILD_LDFLAGS += $(call ld-option, -z max-page-size=0x200000) > endif > > -# Speed up the build > -KBUILD_CFLAGS += -pipe > # Workaround for a gcc prelease that unfortunately was shipped in a suse > release > KBUILD_CFLAGS += -Wno-sign-compare > # > @@ -239,7 +237,7 @@ archheaders: > archmacros: > $(Q)$(MAKE) $(build)=arch/x86/kernel arch/x86/kernel/macros.s > > -ASM_MACRO_FLAGS = -Wa,arch/x86/kernel/macros.s -Wa,- > +ASM_MACRO_FLAGS = -Wa,arch/x86/kernel/macros.s > export ASM_MACRO_FLAGS > KBUILD_CFLAGS += $(ASM_MACRO_FLAGS) > > -- > 2.19.1
This pipe was a pain in the … I have actually already removed it in one version of the versions of my patch-set. Reviewed-by: Nadav Amit <[email protected]>
