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://github.com/llvm-mirror/clang/commit/c19a12dc3d441bec62eed55e312b76c12d6d9022
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.
Link: https://github.com/ClangBuiltLinux/linux/issues/213
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
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]>
On Tue, Oct 23, 2018 at 4:11 PM Nathan Chancellor
<[email protected]> wrote:
>
> 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://github.com/llvm-mirror/clang/commit/c19a12dc3d441bec62eed55e312b76c12d6d9022
>
> 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.
>
> Link: https://github.com/ClangBuiltLinux/linux/issues/213
> Suggested-by: H. Peter Anvin <[email protected]>
> Signed-off-by: Nathan Chancellor <[email protected]>
Thanks Nathan for this patch and the timings and HPA for the suggestions.
Tested-and-Reviewed-by: Nick Desaulniers <[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
>
--
Thanks,
~Nick Desaulniers
Commit-ID: f87419e1c9b5d38ea8a81b31e90aefa1be3fde5d
Gitweb: https://git.kernel.org/tip/f87419e1c9b5d38ea8a81b31e90aefa1be3fde5d
Author: Nathan Chancellor <[email protected]>
AuthorDate: Tue, 23 Oct 2018 16:11:25 -0700
Committer: Thomas Gleixner <[email protected]>
CommitDate: Mon, 5 Nov 2018 15:32:40 +0100
x86/build: 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://github.com/llvm-mirror/clang/commit/c19a12dc3d441bec62eed55e312b76c12d6d9022
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 <[email protected]>
Signed-off-by: Nathan Chancellor <[email protected]>
Signed-off-by: Thomas Gleixner <[email protected]>
Tested-by: Nick Desaulniers <[email protected]>
Reviewed-by: Nadav Amit <[email protected]>
Reviewed-by: Nick Desaulniers <[email protected]>
Cc: Borislav Petkov <[email protected]>
Cc: Kees Cook <[email protected]>
Cc: Masahiro Yamada <[email protected]>
Link: https://github.com/ClangBuiltLinux/linux/issues/213
Link: https://lkml.kernel.org/r/[email protected]
---
arch/x86/Makefile | 4 +---
1 file changed, 1 insertion(+), 3 deletions(-)
diff --git a/arch/x86/Makefile b/arch/x86/Makefile
index 5b562e464009..88398fdf8129 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)
Commit-ID: 437e88ab8f9e2ad90576ab74c4cf8f527bbf51cd
Gitweb: https://git.kernel.org/tip/437e88ab8f9e2ad90576ab74c4cf8f527bbf51cd
Author: Nathan Chancellor <[email protected]>
AuthorDate: Tue, 23 Oct 2018 16:11:25 -0700
Committer: Thomas Gleixner <[email protected]>
CommitDate: Mon, 5 Nov 2018 16:45:32 +0100
x86/build: 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://github.com/llvm-mirror/clang/commit/c19a12dc3d441bec62eed55e312b76c12d6d9022
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 <[email protected]>
Signed-off-by: Nathan Chancellor <[email protected]>
Signed-off-by: Thomas Gleixner <[email protected]>
Tested-by: Nick Desaulniers <[email protected]>
Reviewed-by: Nadav Amit <[email protected]>
Reviewed-by: Nick Desaulniers <[email protected]>
Cc: Borislav Petkov <[email protected]>
Cc: Kees Cook <[email protected]>
Cc: Masahiro Yamada <[email protected]>
Link: https://github.com/ClangBuiltLinux/linux/issues/213
Link: https://lkml.kernel.org/r/[email protected]
---
arch/x86/Makefile | 4 +---
1 file changed, 1 insertion(+), 3 deletions(-)
diff --git a/arch/x86/Makefile b/arch/x86/Makefile
index 5b562e464009..88398fdf8129 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)