* [PATCH RFC] x86: Don't include '-Wa,-' when building with Clang
@ 2018-10-23 0:37 Nathan Chancellor
[not found] ` <F3BBC06A-A9CB-4ABF-ADF4-6B0971FAE364@vmware.com>
0 siblings, 1 reply; 9+ messages in thread
From: Nathan Chancellor @ 2018-10-23 0:37 UTC (permalink / raw)
To: Thomas Gleixner, Ingo Molnar, Borislav Petkov
Cc: H. Peter Anvin, x86, linux-kernel, Nadav Amit, Kees Cook,
Masahiro Yamada, Nick Desaulniers, Nathan Chancellor
Commit 77b0bf55bc67 ("kbuild/Makefile: Prepare for using macros in
inline assembly code to work around asm() related GCC inlining bugs")
added this flag to KBUILD_CFLAGS, where it works perfectly fine with
GCC. However, when building with Clang, all of the object files compile
fine but the build hangs indefinitely at init/main.o, right before the
linking stage. Don't include this flag when building with Clang.
The kernel builds and boots to a shell in QEMU with both GCC and Clang
with this patch applied.
Link: https://github.com/ClangBuiltLinux/linux/issues/213
Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
---
The reason this patch is labeled RFC is while I can verify that this
fixes the issue, I'm not entirely sure why the '-Wa,-' works for GCC
and not Clang. I looked into what the flag means and I couldn't really
find anything so I just assume it's taking input from stdin? The issue
could stem from how GCC forks gas versus how Clang does it. If this
isn't of concern and the maintainers are happy with this patch as is,
feel free to take it.
arch/x86/Makefile | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)
diff --git a/arch/x86/Makefile b/arch/x86/Makefile
index 5b562e464009..4736dcc1caec 100644
--- a/arch/x86/Makefile
+++ b/arch/x86/Makefile
@@ -239,7 +239,10 @@ archheaders:
archmacros:
$(Q)$(MAKE) $(build)=arch/x86/kernel arch/x86/kernel/macros.s
-ASM_MACRO_FLAGS = -Wa,arch/x86/kernel/macros.s -Wa,-
+ASM_MACRO_FLAGS = -Wa,arch/x86/kernel/macros.s
+ifneq ($(cc-name),clang)
+ASM_MACRO_FLAGS += -Wa,-
+endif
export ASM_MACRO_FLAGS
KBUILD_CFLAGS += $(ASM_MACRO_FLAGS)
--
2.19.1
^ permalink raw reply related [flat|nested] 9+ messages in thread[parent not found: <F3BBC06A-A9CB-4ABF-ADF4-6B0971FAE364@vmware.com>]
* Re: [PATCH RFC] x86: Don't include '-Wa,-' when building with Clang [not found] ` <F3BBC06A-A9CB-4ABF-ADF4-6B0971FAE364@vmware.com> @ 2018-10-23 18:40 ` Nick Desaulniers 2018-10-23 20:01 ` H. Peter Anvin 0 siblings, 1 reply; 9+ messages in thread From: Nick Desaulniers @ 2018-10-23 18:40 UTC (permalink / raw) To: namit Cc: Nathan Chancellor, Thomas Gleixner, mingo, bp, hpa, x86, LKML, Kees Cook, Masahiro Yamada On Mon, Oct 22, 2018 at 10:11 PM Nadav Amit <namit@vmware.com> wrote: > > at 5:37 PM, Nathan Chancellor <natechancellor@gmail.com> wrote: > > Commit 77b0bf55bc67 ("kbuild/Makefile: Prepare for using macros in > inline assembly code to work around asm() related GCC inlining bugs") > added this flag to KBUILD_CFLAGS, where it works perfectly fine with > GCC. However, when building with Clang, all of the object files compile > fine but the build hangs indefinitely at init/main.o, right before the > linking stage. Don't include this flag when building with Clang. > > The kernel builds and boots to a shell in QEMU with both GCC and Clang > with this patch applied. > > Link: https://na01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgithub.com%2FClangBuiltLinux%2Flinux%2Fissues%2F213&data=02%7C01%7Cnamit%40vmware.com%7C871daebc2ca44947d28d08d638811fb5%7Cb39138ca3cee4b4aa4d6cd83d9dd62f0%7C1%7C0%7C636758524579997650&sdata=shuxW81QRrO3TSqbgf462wgZYdLeAKeQEdGRxmnUX30%3D&reserved=0 > Signed-off-by: Nathan Chancellor <natechancellor@gmail.com> > --- > > The reason this patch is labeled RFC is while I can verify that this > fixes the issue, I'm not entirely sure why the '-Wa,-' works for GCC > and not Clang. I looked into what the flag means and I couldn't really > find anything so I just assume it's taking input from stdin? The issue > could stem from how GCC forks gas versus how Clang does it. If this > isn't of concern and the maintainers are happy with this patch as is, > feel free to take it. > > arch/x86/Makefile | 5 ++++- > 1 file changed, 4 insertions(+), 1 deletion(-) > > diff --git a/arch/x86/Makefile b/arch/x86/Makefile > index 5b562e464009..4736dcc1caec 100644 > --- a/arch/x86/Makefile > +++ b/arch/x86/Makefile > @@ -239,7 +239,10 @@ archheaders: > archmacros: > $(Q)$(MAKE) $(build)=arch/x86/kernel arch/x86/kernel/macros.s > > -ASM_MACRO_FLAGS = -Wa,arch/x86/kernel/macros.s -Wa,- > +ASM_MACRO_FLAGS = -Wa,arch/x86/kernel/macros.s > +ifneq ($(cc-name),clang) > +ASM_MACRO_FLAGS += -Wa,- > +endif > export ASM_MACRO_FLAGS > KBUILD_CFLAGS += $(ASM_MACRO_FLAGS) > > > The '-Wa,-‘ was indeed used to take the input from stdin when the ‘-pipe’ > option is used in GCC. Perhaps clang ignores the ‘-pipe’ flag. > Clang documents support for `-pipe`. https://clang.llvm.org/docs/ClangCommandLineReference.html#cmdoption-clang-pipe $ clang hello_world.c -no-integrated-as -Wa,- is simple enough to reproduce the hang (notice no `-pipe`). `strace`'ing the above with and without `-Wa,-` shows clang hung in a `wait4` call after spawning as, while without `-Wa,-` shows it receiving a SIGCHLD. I've filed a bug against Clang to investigate: https://bugs.llvm.org/show_bug.cgi?id=39410 In the meantime, I think Nathan's patch is the correct way to work around this, if it is indeed a bug in Clang. Reviewed-and-Tested-by: Nick Desaulniers <ndesaulniers@google.com> https://stackoverflow.com/questions/1512933/when-should-i-use-gccs-pipe-option has some interesting perspectives on the use of `-pipe`. Thanks for the patch Nathan, and more info Nadav. -- Thanks, ~Nick Desaulniers ^ permalink raw reply [flat|nested] 9+ messages in thread
* Re: [PATCH RFC] x86: Don't include '-Wa,-' when building with Clang 2018-10-23 18:40 ` Nick Desaulniers @ 2018-10-23 20:01 ` H. Peter Anvin 2018-10-23 21:58 ` Nathan Chancellor 0 siblings, 1 reply; 9+ messages in thread From: H. Peter Anvin @ 2018-10-23 20:01 UTC (permalink / raw) To: Nick Desaulniers, namit Cc: Nathan Chancellor, Thomas Gleixner, mingo, bp, x86, LKML, Kees Cook, Masahiro Yamada On 10/23/18 11:40, Nick Desaulniers wrote: > On Mon, Oct 22, 2018 at 10:11 PM Nadav Amit <namit@vmware.com> wrote: >> >> at 5:37 PM, Nathan Chancellor <natechancellor@gmail.com> wrote: >> >> Commit 77b0bf55bc67 ("kbuild/Makefile: Prepare for using macros in >> inline assembly code to work around asm() related GCC inlining bugs") >> added this flag to KBUILD_CFLAGS, where it works perfectly fine with >> GCC. However, when building with Clang, all of the object files compile >> fine but the build hangs indefinitely at init/main.o, right before the >> linking stage. Don't include this flag when building with Clang. >> >> The kernel builds and boots to a shell in QEMU with both GCC and Clang >> with this patch applied. >> >> Link: https://na01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgithub.com%2FClangBuiltLinux%2Flinux%2Fissues%2F213&data=02%7C01%7Cnamit%40vmware.com%7C871daebc2ca44947d28d08d638811fb5%7Cb39138ca3cee4b4aa4d6cd83d9dd62f0%7C1%7C0%7C636758524579997650&sdata=shuxW81QRrO3TSqbgf462wgZYdLeAKeQEdGRxmnUX30%3D&reserved=0 >> Signed-off-by: Nathan Chancellor <natechancellor@gmail.com> >> --- >> >> The reason this patch is labeled RFC is while I can verify that this >> fixes the issue, I'm not entirely sure why the '-Wa,-' works for GCC >> and not Clang. I looked into what the flag means and I couldn't really >> find anything so I just assume it's taking input from stdin? The issue >> could stem from how GCC forks gas versus how Clang does it. If this >> isn't of concern and the maintainers are happy with this patch as is, >> feel free to take it. >> Perhaps someone could actually, you know, time the build and see how much -pipe actually matters, if at all? -hpa ^ permalink raw reply [flat|nested] 9+ messages in thread
* Re: [PATCH RFC] x86: Don't include '-Wa,-' when building with Clang 2018-10-23 20:01 ` H. Peter Anvin @ 2018-10-23 21:58 ` Nathan Chancellor 2018-10-23 22:04 ` hpa 2018-10-23 22:08 ` Nick Desaulniers 0 siblings, 2 replies; 9+ messages in thread From: Nathan Chancellor @ 2018-10-23 21:58 UTC (permalink / raw) To: H. Peter Anvin Cc: Nick Desaulniers, namit, Thomas Gleixner, mingo, bp, x86, LKML, Kees Cook, Masahiro Yamada On Tue, Oct 23, 2018 at 01:01:22PM -0700, H. Peter Anvin wrote: > On 10/23/18 11:40, Nick Desaulniers wrote: > > On Mon, Oct 22, 2018 at 10:11 PM Nadav Amit <namit@vmware.com> wrote: > >> > >> at 5:37 PM, Nathan Chancellor <natechancellor@gmail.com> wrote: > >> > >> Commit 77b0bf55bc67 ("kbuild/Makefile: Prepare for using macros in > >> inline assembly code to work around asm() related GCC inlining bugs") > >> added this flag to KBUILD_CFLAGS, where it works perfectly fine with > >> GCC. However, when building with Clang, all of the object files compile > >> fine but the build hangs indefinitely at init/main.o, right before the > >> linking stage. Don't include this flag when building with Clang. > >> > >> The kernel builds and boots to a shell in QEMU with both GCC and Clang > >> with this patch applied. > >> > >> Link: https://na01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgithub.com%2FClangBuiltLinux%2Flinux%2Fissues%2F213&data=02%7C01%7Cnamit%40vmware.com%7C871daebc2ca44947d28d08d638811fb5%7Cb39138ca3cee4b4aa4d6cd83d9dd62f0%7C1%7C0%7C636758524579997650&sdata=shuxW81QRrO3TSqbgf462wgZYdLeAKeQEdGRxmnUX30%3D&reserved=0 > >> Signed-off-by: Nathan Chancellor <natechancellor@gmail.com> > >> --- > >> > >> The reason this patch is labeled RFC is while I can verify that this > >> fixes the issue, I'm not entirely sure why the '-Wa,-' works for GCC > >> and not Clang. I looked into what the flag means and I couldn't really > >> find anything so I just assume it's taking input from stdin? The issue > >> could stem from how GCC forks gas versus how Clang does it. If this > >> isn't of concern and the maintainers are happy with this patch as is, > >> feel free to take it. > >> > > Perhaps someone could actually, you know, time the build and see how > much -pipe actually matters, if at all? > > -hpa > Thank you for the suggestion! With the attached diff for removing '-pipe' and 'make -j1' with defconfig (just to make sure any variance would stand out), here are my results: -pipe (GCC): real 15m55.202s user 14m17.748s sys 1m47.496s No -pipe (GCC): real 16m4.430s user 14m16.277s sys 1m46.604s -pipe (Clang): real 21m26.016s user 19m21.722s sys 2m2.606s No -pipe (Clang): real 21m27.822s user 19m22.092s sys 2m4.151s Certainly seems like -pipe doesn't make a ton of difference. If this is a better fix, I am happy to draft up a proper commit message and send it out for review. ================================================== 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) ^ permalink raw reply related [flat|nested] 9+ messages in thread
* Re: [PATCH RFC] x86: Don't include '-Wa,-' when building with Clang 2018-10-23 21:58 ` Nathan Chancellor @ 2018-10-23 22:04 ` hpa 2018-10-23 22:08 ` Nick Desaulniers 1 sibling, 0 replies; 9+ messages in thread From: hpa @ 2018-10-23 22:04 UTC (permalink / raw) To: Nathan Chancellor Cc: Nick Desaulniers, namit, Thomas Gleixner, mingo, bp, x86, LKML, Kees Cook, Masahiro Yamada On October 23, 2018 2:58:11 PM PDT, Nathan Chancellor <natechancellor@gmail.com> wrote: >On Tue, Oct 23, 2018 at 01:01:22PM -0700, H. Peter Anvin wrote: >> On 10/23/18 11:40, Nick Desaulniers wrote: >> > On Mon, Oct 22, 2018 at 10:11 PM Nadav Amit <namit@vmware.com> >wrote: >> >> >> >> at 5:37 PM, Nathan Chancellor <natechancellor@gmail.com> wrote: >> >> >> >> Commit 77b0bf55bc67 ("kbuild/Makefile: Prepare for using macros in >> >> inline assembly code to work around asm() related GCC inlining >bugs") >> >> added this flag to KBUILD_CFLAGS, where it works perfectly fine >with >> >> GCC. However, when building with Clang, all of the object files >compile >> >> fine but the build hangs indefinitely at init/main.o, right before >the >> >> linking stage. Don't include this flag when building with Clang. >> >> >> >> The kernel builds and boots to a shell in QEMU with both GCC and >Clang >> >> with this patch applied. >> >> >> >> Link: >https://na01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgithub.com%2FClangBuiltLinux%2Flinux%2Fissues%2F213&data=02%7C01%7Cnamit%40vmware.com%7C871daebc2ca44947d28d08d638811fb5%7Cb39138ca3cee4b4aa4d6cd83d9dd62f0%7C1%7C0%7C636758524579997650&sdata=shuxW81QRrO3TSqbgf462wgZYdLeAKeQEdGRxmnUX30%3D&reserved=0 >> >> Signed-off-by: Nathan Chancellor <natechancellor@gmail.com> >> >> --- >> >> >> >> The reason this patch is labeled RFC is while I can verify that >this >> >> fixes the issue, I'm not entirely sure why the '-Wa,-' works for >GCC >> >> and not Clang. I looked into what the flag means and I couldn't >really >> >> find anything so I just assume it's taking input from stdin? The >issue >> >> could stem from how GCC forks gas versus how Clang does it. If >this >> >> isn't of concern and the maintainers are happy with this patch as >is, >> >> feel free to take it. >> >> >> >> Perhaps someone could actually, you know, time the build and see how >> much -pipe actually matters, if at all? >> >> -hpa >> > >Thank you for the suggestion! With the attached diff for removing >'-pipe' and 'make -j1' with defconfig (just to make sure any variance >would stand out), here are my results: > >-pipe (GCC): > >real 15m55.202s >user 14m17.748s >sys 1m47.496s > >No -pipe (GCC): > >real 16m4.430s >user 14m16.277s >sys 1m46.604s > >-pipe (Clang): > >real 21m26.016s >user 19m21.722s >sys 2m2.606s > >No -pipe (Clang): > >real 21m27.822s >user 19m22.092s >sys 2m4.151s > >Certainly seems like -pipe doesn't make a ton of difference. If this is >a better fix, I am happy to draft up a proper commit message and send >it out for review. > >================================================== > >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) make -j1 makes the test useless. You should aim for optimal performance for your machine. -- Sent from my Android device with K-9 Mail. Please excuse my brevity. ^ permalink raw reply [flat|nested] 9+ messages in thread
* Re: [PATCH RFC] x86: Don't include '-Wa,-' when building with Clang 2018-10-23 21:58 ` Nathan Chancellor 2018-10-23 22:04 ` hpa @ 2018-10-23 22:08 ` Nick Desaulniers 2018-10-23 22:44 ` Nathan Chancellor 1 sibling, 1 reply; 9+ messages in thread From: Nick Desaulniers @ 2018-10-23 22:08 UTC (permalink / raw) To: Nathan Chancellor Cc: hpa, namit, Thomas Gleixner, mingo, bp, x86, LKML, Kees Cook, Masahiro Yamada On Tue, Oct 23, 2018 at 2:58 PM Nathan Chancellor <natechancellor@gmail.com> wrote: > > On Tue, Oct 23, 2018 at 01:01:22PM -0700, H. Peter Anvin wrote: > > On 10/23/18 11:40, Nick Desaulniers wrote: > > > On Mon, Oct 22, 2018 at 10:11 PM Nadav Amit <namit@vmware.com> wrote: > > >> > > >> at 5:37 PM, Nathan Chancellor <natechancellor@gmail.com> wrote: > > >> > > >> Commit 77b0bf55bc67 ("kbuild/Makefile: Prepare for using macros in > > >> inline assembly code to work around asm() related GCC inlining bugs") > > >> added this flag to KBUILD_CFLAGS, where it works perfectly fine with > > >> GCC. However, when building with Clang, all of the object files compile > > >> fine but the build hangs indefinitely at init/main.o, right before the > > >> linking stage. Don't include this flag when building with Clang. > > >> > > >> The kernel builds and boots to a shell in QEMU with both GCC and Clang > > >> with this patch applied. > > >> > > >> Link: https://na01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgithub.com%2FClangBuiltLinux%2Flinux%2Fissues%2F213&data=02%7C01%7Cnamit%40vmware.com%7C871daebc2ca44947d28d08d638811fb5%7Cb39138ca3cee4b4aa4d6cd83d9dd62f0%7C1%7C0%7C636758524579997650&sdata=shuxW81QRrO3TSqbgf462wgZYdLeAKeQEdGRxmnUX30%3D&reserved=0 > > >> Signed-off-by: Nathan Chancellor <natechancellor@gmail.com> > > >> --- > > >> > > >> The reason this patch is labeled RFC is while I can verify that this > > >> fixes the issue, I'm not entirely sure why the '-Wa,-' works for GCC > > >> and not Clang. I looked into what the flag means and I couldn't really > > >> find anything so I just assume it's taking input from stdin? The issue > > >> could stem from how GCC forks gas versus how Clang does it. If this > > >> isn't of concern and the maintainers are happy with this patch as is, > > >> feel free to take it. > > >> > > > > Perhaps someone could actually, you know, time the build and see how > > much -pipe actually matters, if at all? > > > > -hpa > > > > Thank you for the suggestion! With the attached diff for removing > '-pipe' and 'make -j1' with defconfig (just to make sure any variance > would stand out), here are my results: > > -pipe (GCC): > > real 15m55.202s > user 14m17.748s > sys 1m47.496s > > No -pipe (GCC): > > real 16m4.430s > user 14m16.277s > sys 1m46.604s > > -pipe (Clang): > > real 21m26.016s > user 19m21.722s > sys 2m2.606s > > No -pipe (Clang): > > real 21m27.822s > user 19m22.092s > sys 2m4.151s Looks like Clang eats `-pipe`: https://github.com/llvm-mirror/clang/blob/391667a023f79287f9c40868f34f08c161555556/lib/Driver/Driver.cpp#L962 commit r110007 has the log: Driver: Start ripping out support for -pipe, which is worthless and complicates too many other things. > > Certainly seems like -pipe doesn't make a ton of difference. If this is > a better fix, I am happy to draft up a proper commit message and send > it out for review. > > ================================================== > > 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) > -- Thanks, ~Nick Desaulniers ^ permalink raw reply [flat|nested] 9+ messages in thread
* Re: [PATCH RFC] x86: Don't include '-Wa,-' when building with Clang 2018-10-23 22:08 ` Nick Desaulniers @ 2018-10-23 22:44 ` Nathan Chancellor 2018-10-23 22:53 ` Nick Desaulniers 0 siblings, 1 reply; 9+ messages in thread From: Nathan Chancellor @ 2018-10-23 22:44 UTC (permalink / raw) To: Nick Desaulniers Cc: hpa, namit, Thomas Gleixner, mingo, bp, x86, LKML, Kees Cook, Masahiro Yamada On Tue, Oct 23, 2018 at 03:08:53PM -0700, Nick Desaulniers wrote: > On Tue, Oct 23, 2018 at 2:58 PM Nathan Chancellor > <natechancellor@gmail.com> wrote: > > > > On Tue, Oct 23, 2018 at 01:01:22PM -0700, H. Peter Anvin wrote: > > > On 10/23/18 11:40, Nick Desaulniers wrote: > > > > On Mon, Oct 22, 2018 at 10:11 PM Nadav Amit <namit@vmware.com> wrote: > > > >> > > > >> at 5:37 PM, Nathan Chancellor <natechancellor@gmail.com> wrote: > > > >> > > > >> Commit 77b0bf55bc67 ("kbuild/Makefile: Prepare for using macros in > > > >> inline assembly code to work around asm() related GCC inlining bugs") > > > >> added this flag to KBUILD_CFLAGS, where it works perfectly fine with > > > >> GCC. However, when building with Clang, all of the object files compile > > > >> fine but the build hangs indefinitely at init/main.o, right before the > > > >> linking stage. Don't include this flag when building with Clang. > > > >> > > > >> The kernel builds and boots to a shell in QEMU with both GCC and Clang > > > >> with this patch applied. > > > >> > > > >> Link: https://na01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgithub.com%2FClangBuiltLinux%2Flinux%2Fissues%2F213&data=02%7C01%7Cnamit%40vmware.com%7C871daebc2ca44947d28d08d638811fb5%7Cb39138ca3cee4b4aa4d6cd83d9dd62f0%7C1%7C0%7C636758524579997650&sdata=shuxW81QRrO3TSqbgf462wgZYdLeAKeQEdGRxmnUX30%3D&reserved=0 > > > >> Signed-off-by: Nathan Chancellor <natechancellor@gmail.com> > > > >> --- > > > >> > > > >> The reason this patch is labeled RFC is while I can verify that this > > > >> fixes the issue, I'm not entirely sure why the '-Wa,-' works for GCC > > > >> and not Clang. I looked into what the flag means and I couldn't really > > > >> find anything so I just assume it's taking input from stdin? The issue > > > >> could stem from how GCC forks gas versus how Clang does it. If this > > > >> isn't of concern and the maintainers are happy with this patch as is, > > > >> feel free to take it. > > > >> > > > > > > Perhaps someone could actually, you know, time the build and see how > > > much -pipe actually matters, if at all? > > > > > > -hpa > > > > > > > Thank you for the suggestion! With the attached diff for removing > > '-pipe' and 'make -j1' with defconfig (just to make sure any variance > > would stand out), here are my results: > > > > -pipe (GCC): > > > > real 15m55.202s > > user 14m17.748s > > sys 1m47.496s > > > > No -pipe (GCC): > > > > real 16m4.430s > > user 14m16.277s > > sys 1m46.604s > > > > -pipe (Clang): > > > > real 21m26.016s > > user 19m21.722s > > sys 2m2.606s > > > > No -pipe (Clang): > > > > real 21m27.822s > > user 19m22.092s > > sys 2m4.151s > > Looks like Clang eats `-pipe`: > https://github.com/llvm-mirror/clang/blob/391667a023f79287f9c40868f34f08c161555556/lib/Driver/Driver.cpp#L962 > commit r110007 has the log: > Driver: Start ripping out support for -pipe, which is worthless > and complicates > too many other things. > In that case, we can either keep this change (I'll resend with the explanation that Clang doesn't respect -pipe) or we can just rip out -pipe for GCC too. Here are three separate results for GCC with my normal jobs flag: -pipe (GCC): real 3m40.813s real 3m44.449s real 3m39.648s No -pipe (GCC): real 3m38.492s real 3m38.335s real 3m38.975s Practically no variance. Thanks, Nathan > > > > Certainly seems like -pipe doesn't make a ton of difference. If this is > > a better fix, I am happy to draft up a proper commit message and send > > it out for review. > > > > ================================================== > > > > 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) > > > > > -- > Thanks, > ~Nick Desaulniers ^ permalink raw reply [flat|nested] 9+ messages in thread
* Re: [PATCH RFC] x86: Don't include '-Wa,-' when building with Clang 2018-10-23 22:44 ` Nathan Chancellor @ 2018-10-23 22:53 ` Nick Desaulniers 2018-10-23 23:01 ` hpa 0 siblings, 1 reply; 9+ messages in thread From: Nick Desaulniers @ 2018-10-23 22:53 UTC (permalink / raw) To: Nathan Chancellor Cc: hpa, namit, Thomas Gleixner, mingo, bp, x86, LKML, Kees Cook, Masahiro Yamada On Tue, Oct 23, 2018 at 3:44 PM Nathan Chancellor <natechancellor@gmail.com> wrote: > > On Tue, Oct 23, 2018 at 03:08:53PM -0700, Nick Desaulniers wrote: > > On Tue, Oct 23, 2018 at 2:58 PM Nathan Chancellor > > <natechancellor@gmail.com> wrote: > > > > > > On Tue, Oct 23, 2018 at 01:01:22PM -0700, H. Peter Anvin wrote: > > > > On 10/23/18 11:40, Nick Desaulniers wrote: > > > > > On Mon, Oct 22, 2018 at 10:11 PM Nadav Amit <namit@vmware.com> wrote: > > > > >> > > > > >> at 5:37 PM, Nathan Chancellor <natechancellor@gmail.com> wrote: > > > > >> > > > > >> Commit 77b0bf55bc67 ("kbuild/Makefile: Prepare for using macros in > > > > >> inline assembly code to work around asm() related GCC inlining bugs") > > > > >> added this flag to KBUILD_CFLAGS, where it works perfectly fine with > > > > >> GCC. However, when building with Clang, all of the object files compile > > > > >> fine but the build hangs indefinitely at init/main.o, right before the > > > > >> linking stage. Don't include this flag when building with Clang. > > > > >> > > > > >> The kernel builds and boots to a shell in QEMU with both GCC and Clang > > > > >> with this patch applied. > > > > >> > > > > >> Link: https://na01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgithub.com%2FClangBuiltLinux%2Flinux%2Fissues%2F213&data=02%7C01%7Cnamit%40vmware.com%7C871daebc2ca44947d28d08d638811fb5%7Cb39138ca3cee4b4aa4d6cd83d9dd62f0%7C1%7C0%7C636758524579997650&sdata=shuxW81QRrO3TSqbgf462wgZYdLeAKeQEdGRxmnUX30%3D&reserved=0 > > > > >> Signed-off-by: Nathan Chancellor <natechancellor@gmail.com> > > > > >> --- > > > > >> > > > > >> The reason this patch is labeled RFC is while I can verify that this > > > > >> fixes the issue, I'm not entirely sure why the '-Wa,-' works for GCC > > > > >> and not Clang. I looked into what the flag means and I couldn't really > > > > >> find anything so I just assume it's taking input from stdin? The issue > > > > >> could stem from how GCC forks gas versus how Clang does it. If this > > > > >> isn't of concern and the maintainers are happy with this patch as is, > > > > >> feel free to take it. > > > > >> > > > > > > > > Perhaps someone could actually, you know, time the build and see how > > > > much -pipe actually matters, if at all? > > > > > > > > -hpa > > > > > > > > > > Thank you for the suggestion! With the attached diff for removing > > > '-pipe' and 'make -j1' with defconfig (just to make sure any variance > > > would stand out), here are my results: > > > > > > -pipe (GCC): > > > > > > real 15m55.202s > > > user 14m17.748s > > > sys 1m47.496s > > > > > > No -pipe (GCC): > > > > > > real 16m4.430s > > > user 14m16.277s > > > sys 1m46.604s > > > > > > -pipe (Clang): > > > > > > real 21m26.016s > > > user 19m21.722s > > > sys 2m2.606s > > > > > > No -pipe (Clang): > > > > > > real 21m27.822s > > > user 19m22.092s > > > sys 2m4.151s > > > > Looks like Clang eats `-pipe`: > > https://github.com/llvm-mirror/clang/blob/391667a023f79287f9c40868f34f08c161555556/lib/Driver/Driver.cpp#L962 > > commit r110007 has the log: > > Driver: Start ripping out support for -pipe, which is worthless > > and complicates > > too many other things. > > > > In that case, we can either keep this change (I'll resend with the > explanation that Clang doesn't respect -pipe) or we can just rip out > -pipe for GCC too. Here are three separate results for GCC with my > normal jobs flag: > > -pipe (GCC): > > real 3m40.813s > real 3m44.449s > real 3m39.648s > > No -pipe (GCC): > > real 3m38.492s > real 3m38.335s > real 3m38.975s > > Practically no variance. Thanks for these measurements. With these in mind I agree with HPA that `-pipe -Wa,-` doesn't buy us anything, and would be simpler to remove it for compatibility with Clang. > > Thanks, > Nathan > > > > > > > Certainly seems like -pipe doesn't make a ton of difference. If this is > > > a better fix, I am happy to draft up a proper commit message and send > > > it out for review. > > > > > > ================================================== > > > > > > 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) > > > > > > > > > -- > > Thanks, > > ~Nick Desaulniers -- Thanks, ~Nick Desaulniers ^ permalink raw reply [flat|nested] 9+ messages in thread
* Re: [PATCH RFC] x86: Don't include '-Wa,-' when building with Clang 2018-10-23 22:53 ` Nick Desaulniers @ 2018-10-23 23:01 ` hpa 0 siblings, 0 replies; 9+ messages in thread From: hpa @ 2018-10-23 23:01 UTC (permalink / raw) To: Nick Desaulniers, Nathan Chancellor Cc: namit, Thomas Gleixner, mingo, bp, x86, LKML, Kees Cook, Masahiro Yamada On October 23, 2018 3:53:10 PM PDT, Nick Desaulniers <ndesaulniers@google.com> wrote: >On Tue, Oct 23, 2018 at 3:44 PM Nathan Chancellor ><natechancellor@gmail.com> wrote: >> >> On Tue, Oct 23, 2018 at 03:08:53PM -0700, Nick Desaulniers wrote: >> > On Tue, Oct 23, 2018 at 2:58 PM Nathan Chancellor >> > <natechancellor@gmail.com> wrote: >> > > >> > > On Tue, Oct 23, 2018 at 01:01:22PM -0700, H. Peter Anvin wrote: >> > > > On 10/23/18 11:40, Nick Desaulniers wrote: >> > > > > On Mon, Oct 22, 2018 at 10:11 PM Nadav Amit ><namit@vmware.com> wrote: >> > > > >> >> > > > >> at 5:37 PM, Nathan Chancellor <natechancellor@gmail.com> >wrote: >> > > > >> >> > > > >> Commit 77b0bf55bc67 ("kbuild/Makefile: Prepare for using >macros in >> > > > >> inline assembly code to work around asm() related GCC >inlining bugs") >> > > > >> added this flag to KBUILD_CFLAGS, where it works perfectly >fine with >> > > > >> GCC. However, when building with Clang, all of the object >files compile >> > > > >> fine but the build hangs indefinitely at init/main.o, right >before the >> > > > >> linking stage. Don't include this flag when building with >Clang. >> > > > >> >> > > > >> The kernel builds and boots to a shell in QEMU with both GCC >and Clang >> > > > >> with this patch applied. >> > > > >> >> > > > >> Link: >https://na01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgithub.com%2FClangBuiltLinux%2Flinux%2Fissues%2F213&data=02%7C01%7Cnamit%40vmware.com%7C871daebc2ca44947d28d08d638811fb5%7Cb39138ca3cee4b4aa4d6cd83d9dd62f0%7C1%7C0%7C636758524579997650&sdata=shuxW81QRrO3TSqbgf462wgZYdLeAKeQEdGRxmnUX30%3D&reserved=0 >> > > > >> Signed-off-by: Nathan Chancellor <natechancellor@gmail.com> >> > > > >> --- >> > > > >> >> > > > >> The reason this patch is labeled RFC is while I can verify >that this >> > > > >> fixes the issue, I'm not entirely sure why the '-Wa,-' works >for GCC >> > > > >> and not Clang. I looked into what the flag means and I >couldn't really >> > > > >> find anything so I just assume it's taking input from stdin? >The issue >> > > > >> could stem from how GCC forks gas versus how Clang does it. >If this >> > > > >> isn't of concern and the maintainers are happy with this >patch as is, >> > > > >> feel free to take it. >> > > > >> >> > > > >> > > > Perhaps someone could actually, you know, time the build and >see how >> > > > much -pipe actually matters, if at all? >> > > > >> > > > -hpa >> > > > >> > > >> > > Thank you for the suggestion! With the attached diff for removing >> > > '-pipe' and 'make -j1' with defconfig (just to make sure any >variance >> > > would stand out), here are my results: >> > > >> > > -pipe (GCC): >> > > >> > > real 15m55.202s >> > > user 14m17.748s >> > > sys 1m47.496s >> > > >> > > No -pipe (GCC): >> > > >> > > real 16m4.430s >> > > user 14m16.277s >> > > sys 1m46.604s >> > > >> > > -pipe (Clang): >> > > >> > > real 21m26.016s >> > > user 19m21.722s >> > > sys 2m2.606s >> > > >> > > No -pipe (Clang): >> > > >> > > real 21m27.822s >> > > user 19m22.092s >> > > sys 2m4.151s >> > >> > Looks like Clang eats `-pipe`: >> > >https://github.com/llvm-mirror/clang/blob/391667a023f79287f9c40868f34f08c161555556/lib/Driver/Driver.cpp#L962 >> > commit r110007 has the log: >> > Driver: Start ripping out support for -pipe, which is worthless >> > and complicates >> > too many other things. >> > >> >> In that case, we can either keep this change (I'll resend with the >> explanation that Clang doesn't respect -pipe) or we can just rip out >> -pipe for GCC too. Here are three separate results for GCC with my >> normal jobs flag: >> >> -pipe (GCC): >> >> real 3m40.813s >> real 3m44.449s >> real 3m39.648s >> >> No -pipe (GCC): >> >> real 3m38.492s >> real 3m38.335s >> real 3m38.975s >> >> Practically no variance. > >Thanks for these measurements. With these in mind I agree with HPA >that `-pipe -Wa,-` doesn't buy us anything, and would be simpler to >remove it for compatibility with Clang. > >> >> Thanks, >> Nathan >> >> > > >> > > Certainly seems like -pipe doesn't make a ton of difference. If >this is >> > > a better fix, I am happy to draft up a proper commit message and >send >> > > it out for review. >> > > >> > > ================================================== >> > > >> > > 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) >> > > >> > >> > >> > -- >> > Thanks, >> > ~Nick Desaulniers So -pipe actually hurts sightly. Let's kill it. -- Sent from my Android device with K-9 Mail. Please excuse my brevity. ^ permalink raw reply [flat|nested] 9+ messages in thread
end of thread, other threads:[~2018-10-23 23:02 UTC | newest]
Thread overview: 9+ messages (download: mbox.gz follow: Atom feed
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2018-10-23 0:37 [PATCH RFC] x86: Don't include '-Wa,-' when building with Clang Nathan Chancellor
[not found] ` <F3BBC06A-A9CB-4ABF-ADF4-6B0971FAE364@vmware.com>
2018-10-23 18:40 ` Nick Desaulniers
2018-10-23 20:01 ` H. Peter Anvin
2018-10-23 21:58 ` Nathan Chancellor
2018-10-23 22:04 ` hpa
2018-10-23 22:08 ` Nick Desaulniers
2018-10-23 22:44 ` Nathan Chancellor
2018-10-23 22:53 ` Nick Desaulniers
2018-10-23 23:01 ` hpa
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