| Message ID | 20180918023157.23951-1-stefan@agner.ch (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | kbuild: allow to use GCC toolchain not in Clang search path | expand |
Hi Stefan, 2018-09-18 11:31 GMT+09:00 Stefan Agner <stefan@agner.ch>: > When using a GCC cross toolchain which is not in a compiled in > Clang search path, Clang reverts to the system assembler and > linker. This leads to assembler or linker errors, depending on > which tool is first used for a given architecture. > > It seems that Clang is not searching $PATH for a matching > assembler or linker. The current code passes the absolute path of toolchains to --gcc-toolchain option. In my understanding, this is enough for Clang to find the proper linker and the assembler. Why is the --prefix option also needed ? Am I missing something? > Make sure that Clang picks up the correct assembler or linker by > passing the cross compilers bin directory as search path. > > This allows to use Clang provided by distributions with GCC > toolchains not in /usr/bin. > > Link: https://github.com/ClangBuiltLinux/linux/issues/78 > Signed-off-by: Stefan Agner <stefan@agner.ch> > --- > Nick, I removed your Reviewed-by since I had to change variable > assignment slightly... > > Makefile | 8 +++++--- > 1 file changed, 5 insertions(+), 3 deletions(-) > > diff --git a/Makefile b/Makefile > index 4d5c883a98e5..d5de2db4b549 100644 > --- a/Makefile > +++ b/Makefile > @@ -495,13 +495,15 @@ endif > ifeq ($(cc-name),clang) > ifneq ($(CROSS_COMPILE),) > CLANG_TARGET := --target=$(notdir $(CROSS_COMPILE:%-=%)) > -GCC_TOOLCHAIN := $(realpath $(dir $(shell which $(LD)))/..) > +GCC_TOOLCHAIN_DIR := $(dir $(shell which $(LD))) > +CLANG_PREFIX := --prefix=$(GCC_TOOLCHAIN_DIR) > +GCC_TOOLCHAIN := $(realpath $(GCC_TOOLCHAIN_DIR)/..) > endif > ifneq ($(GCC_TOOLCHAIN),) > CLANG_GCC_TC := --gcc-toolchain=$(GCC_TOOLCHAIN) > endif > -KBUILD_CFLAGS += $(CLANG_TARGET) $(CLANG_GCC_TC) > -KBUILD_AFLAGS += $(CLANG_TARGET) $(CLANG_GCC_TC) > +KBUILD_CFLAGS += $(CLANG_TARGET) $(CLANG_GCC_TC) $(CLANG_PREFIX) > +KBUILD_AFLAGS += $(CLANG_TARGET) $(CLANG_GCC_TC) $(CLANG_PREFIX) > KBUILD_CFLAGS += $(call cc-option, -no-integrated-as) > KBUILD_AFLAGS += $(call cc-option, -no-integrated-as) > endif > -- > 2.19.0 >
On 17.09.2018 20:06, Masahiro Yamada wrote: > Hi Stefan, > > 2018-09-18 11:31 GMT+09:00 Stefan Agner <stefan@agner.ch>: >> When using a GCC cross toolchain which is not in a compiled in >> Clang search path, Clang reverts to the system assembler and >> linker. This leads to assembler or linker errors, depending on >> which tool is first used for a given architecture. >> >> It seems that Clang is not searching $PATH for a matching >> assembler or linker. > > > The current code passes the absolute path of toolchains > to --gcc-toolchain option. > In my understanding, this is enough for Clang > to find the proper linker and the assembler. > > > Why is the --prefix option also needed ? > It seems that Clang makes a difference between "toolchain" and search path for toolchain binaries. Without this patch building fails for the described use case, see the github link for more context. -- Stefan > > Am I missing something? > > > >> Make sure that Clang picks up the correct assembler or linker by >> passing the cross compilers bin directory as search path. >> >> This allows to use Clang provided by distributions with GCC >> toolchains not in /usr/bin. >> >> Link: https://github.com/ClangBuiltLinux/linux/issues/78 >> Signed-off-by: Stefan Agner <stefan@agner.ch> >> --- >> Nick, I removed your Reviewed-by since I had to change variable >> assignment slightly... >> >> Makefile | 8 +++++--- >> 1 file changed, 5 insertions(+), 3 deletions(-) >> >> diff --git a/Makefile b/Makefile >> index 4d5c883a98e5..d5de2db4b549 100644 >> --- a/Makefile >> +++ b/Makefile >> @@ -495,13 +495,15 @@ endif >> ifeq ($(cc-name),clang) >> ifneq ($(CROSS_COMPILE),) >> CLANG_TARGET := --target=$(notdir $(CROSS_COMPILE:%-=%)) >> -GCC_TOOLCHAIN := $(realpath $(dir $(shell which $(LD)))/..) >> +GCC_TOOLCHAIN_DIR := $(dir $(shell which $(LD))) >> +CLANG_PREFIX := --prefix=$(GCC_TOOLCHAIN_DIR) >> +GCC_TOOLCHAIN := $(realpath $(GCC_TOOLCHAIN_DIR)/..) >> endif >> ifneq ($(GCC_TOOLCHAIN),) >> CLANG_GCC_TC := --gcc-toolchain=$(GCC_TOOLCHAIN) >> endif >> -KBUILD_CFLAGS += $(CLANG_TARGET) $(CLANG_GCC_TC) >> -KBUILD_AFLAGS += $(CLANG_TARGET) $(CLANG_GCC_TC) >> +KBUILD_CFLAGS += $(CLANG_TARGET) $(CLANG_GCC_TC) $(CLANG_PREFIX) >> +KBUILD_AFLAGS += $(CLANG_TARGET) $(CLANG_GCC_TC) $(CLANG_PREFIX) >> KBUILD_CFLAGS += $(call cc-option, -no-integrated-as) >> KBUILD_AFLAGS += $(call cc-option, -no-integrated-as) >> endif >> -- >> 2.19.0 >>
Hi Stefan, 2018-09-18 12:11 GMT+09:00 Stefan Agner <stefan@agner.ch>: > On 17.09.2018 20:06, Masahiro Yamada wrote: >> Hi Stefan, >> >> 2018-09-18 11:31 GMT+09:00 Stefan Agner <stefan@agner.ch>: >>> When using a GCC cross toolchain which is not in a compiled in >>> Clang search path, Clang reverts to the system assembler and >>> linker. This leads to assembler or linker errors, depending on >>> which tool is first used for a given architecture. >>> >>> It seems that Clang is not searching $PATH for a matching >>> assembler or linker. >> >> >> The current code passes the absolute path of toolchains >> to --gcc-toolchain option. >> In my understanding, this is enough for Clang >> to find the proper linker and the assembler. >> >> >> Why is the --prefix option also needed ? >> > > It seems that Clang makes a difference between "toolchain" and search path for toolchain binaries. > > Without this patch building fails for the described use case, see the github link for more context. OK, I confirmed this patch fixed the problem. I will wait a little more just in case Nick has comments about this. Thanks.
On Mon, Sep 17, 2018 at 7:32 PM Stefan Agner <stefan@agner.ch> wrote: > > When using a GCC cross toolchain which is not in a compiled in > Clang search path, Clang reverts to the system assembler and > linker. This leads to assembler or linker errors, depending on > which tool is first used for a given architecture. > > It seems that Clang is not searching $PATH for a matching > assembler or linker. Yes, Clang uses what's called a sysroot, which is meant to be more hygenic than $PATH, IIUC. This is surprising to folks familiar with $PATH, but really helps include the correct headers and use the correct toolchain when cross compiling, at the cost of freedom to put the cross toolchain wherever in the filesystem. (this is my understanding of sysroot, I just learned about it yesterday, so take this with a grain of salt). > > Make sure that Clang picks up the correct assembler or linker by > passing the cross compilers bin directory as search path. > > This allows to use Clang provided by distributions with GCC > toolchains not in /usr/bin. IIUC, its just utilities in binutils we're using (as, bfd.ld, objcopy), not GCC, but maybe that's just being pedantic. > > Link: https://github.com/ClangBuiltLinux/linux/issues/78 > Signed-off-by: Stefan Agner <stefan@agner.ch> > --- > Nick, I removed your Reviewed-by since I had to change variable > assignment slightly... Yes, thank you, that's the right thing to do. > > Makefile | 8 +++++--- > 1 file changed, 5 insertions(+), 3 deletions(-) > > diff --git a/Makefile b/Makefile > index 4d5c883a98e5..d5de2db4b549 100644 > --- a/Makefile > +++ b/Makefile > @@ -495,13 +495,15 @@ endif > ifeq ($(cc-name),clang) > ifneq ($(CROSS_COMPILE),) > CLANG_TARGET := --target=$(notdir $(CROSS_COMPILE:%-=%)) > -GCC_TOOLCHAIN := $(realpath $(dir $(shell which $(LD)))/..) > +GCC_TOOLCHAIN_DIR := $(dir $(shell which $(LD))) > +CLANG_PREFIX := --prefix=$(GCC_TOOLCHAIN_DIR) Yep: https://clang.llvm.org/docs/ClangCommandLineReference.html#cmdoption-clang-b-dir > +GCC_TOOLCHAIN := $(realpath $(GCC_TOOLCHAIN_DIR)/..) > endif > ifneq ($(GCC_TOOLCHAIN),) > CLANG_GCC_TC := --gcc-toolchain=$(GCC_TOOLCHAIN) > endif > -KBUILD_CFLAGS += $(CLANG_TARGET) $(CLANG_GCC_TC) > -KBUILD_AFLAGS += $(CLANG_TARGET) $(CLANG_GCC_TC) > +KBUILD_CFLAGS += $(CLANG_TARGET) $(CLANG_GCC_TC) $(CLANG_PREFIX) > +KBUILD_AFLAGS += $(CLANG_TARGET) $(CLANG_GCC_TC) $(CLANG_PREFIX) > KBUILD_CFLAGS += $(call cc-option, -no-integrated-as) > KBUILD_AFLAGS += $(call cc-option, -no-integrated-as) > endif > -- > 2.19.0 > Thanks for this patch Stefan. Reviewed-and-tested-by: Nick Desaulniers <ndesaulniers@google.com>
2018-09-19 2:16 GMT+09:00 Nick Desaulniers <ndesaulniers@google.com>: > On Mon, Sep 17, 2018 at 7:32 PM Stefan Agner <stefan@agner.ch> wrote: >> >> When using a GCC cross toolchain which is not in a compiled in >> Clang search path, Clang reverts to the system assembler and >> linker. This leads to assembler or linker errors, depending on >> which tool is first used for a given architecture. >> >> It seems that Clang is not searching $PATH for a matching >> assembler or linker. > > Yes, Clang uses what's called a sysroot, which is meant to be more > hygenic than $PATH, IIUC. This is surprising to folks familiar with > $PATH, but really helps include the correct headers and use the > correct toolchain when cross compiling, at the cost of freedom to put > the cross toolchain wherever in the filesystem. (this is my > understanding of sysroot, I just learned about it yesterday, so take > this with a grain of salt). > >> >> Make sure that Clang picks up the correct assembler or linker by >> passing the cross compilers bin directory as search path. >> >> This allows to use Clang provided by distributions with GCC >> toolchains not in /usr/bin. > > IIUC, its just utilities in binutils we're using (as, bfd.ld, > objcopy), not GCC, but maybe that's just being pedantic. > >> >> Link: https://github.com/ClangBuiltLinux/linux/issues/78 >> Signed-off-by: Stefan Agner <stefan@agner.ch> >> --- >> Nick, I removed your Reviewed-by since I had to change variable >> assignment slightly... > > Yes, thank you, that's the right thing to do. > >> >> Makefile | 8 +++++--- >> 1 file changed, 5 insertions(+), 3 deletions(-) >> >> diff --git a/Makefile b/Makefile >> index 4d5c883a98e5..d5de2db4b549 100644 >> --- a/Makefile >> +++ b/Makefile >> @@ -495,13 +495,15 @@ endif >> ifeq ($(cc-name),clang) >> ifneq ($(CROSS_COMPILE),) >> CLANG_TARGET := --target=$(notdir $(CROSS_COMPILE:%-=%)) >> -GCC_TOOLCHAIN := $(realpath $(dir $(shell which $(LD)))/..) >> +GCC_TOOLCHAIN_DIR := $(dir $(shell which $(LD))) >> +CLANG_PREFIX := --prefix=$(GCC_TOOLCHAIN_DIR) > > Yep: https://clang.llvm.org/docs/ClangCommandLineReference.html#cmdoption-clang-b-dir > >> +GCC_TOOLCHAIN := $(realpath $(GCC_TOOLCHAIN_DIR)/..) >> endif >> ifneq ($(GCC_TOOLCHAIN),) >> CLANG_GCC_TC := --gcc-toolchain=$(GCC_TOOLCHAIN) >> endif >> -KBUILD_CFLAGS += $(CLANG_TARGET) $(CLANG_GCC_TC) >> -KBUILD_AFLAGS += $(CLANG_TARGET) $(CLANG_GCC_TC) >> +KBUILD_CFLAGS += $(CLANG_TARGET) $(CLANG_GCC_TC) $(CLANG_PREFIX) >> +KBUILD_AFLAGS += $(CLANG_TARGET) $(CLANG_GCC_TC) $(CLANG_PREFIX) >> KBUILD_CFLAGS += $(call cc-option, -no-integrated-as) >> KBUILD_AFLAGS += $(call cc-option, -no-integrated-as) >> endif >> -- >> 2.19.0 >> > > Thanks for this patch Stefan. > Reviewed-and-tested-by: Nick Desaulniers <ndesaulniers@google.com> > -- > Thanks, > ~Nick Desaulniers Applied to linux-kbuild/fixes. Thanks!
diff --git a/Makefile b/Makefile index 4d5c883a98e5..d5de2db4b549 100644 --- a/Makefile +++ b/Makefile @@ -495,13 +495,15 @@ endif ifeq ($(cc-name),clang) ifneq ($(CROSS_COMPILE),) CLANG_TARGET := --target=$(notdir $(CROSS_COMPILE:%-=%)) -GCC_TOOLCHAIN := $(realpath $(dir $(shell which $(LD)))/..) +GCC_TOOLCHAIN_DIR := $(dir $(shell which $(LD))) +CLANG_PREFIX := --prefix=$(GCC_TOOLCHAIN_DIR) +GCC_TOOLCHAIN := $(realpath $(GCC_TOOLCHAIN_DIR)/..) endif ifneq ($(GCC_TOOLCHAIN),) CLANG_GCC_TC := --gcc-toolchain=$(GCC_TOOLCHAIN) endif -KBUILD_CFLAGS += $(CLANG_TARGET) $(CLANG_GCC_TC) -KBUILD_AFLAGS += $(CLANG_TARGET) $(CLANG_GCC_TC) +KBUILD_CFLAGS += $(CLANG_TARGET) $(CLANG_GCC_TC) $(CLANG_PREFIX) +KBUILD_AFLAGS += $(CLANG_TARGET) $(CLANG_GCC_TC) $(CLANG_PREFIX) KBUILD_CFLAGS += $(call cc-option, -no-integrated-as) KBUILD_AFLAGS += $(call cc-option, -no-integrated-as) endif
When using a GCC cross toolchain which is not in a compiled in Clang search path, Clang reverts to the system assembler and linker. This leads to assembler or linker errors, depending on which tool is first used for a given architecture. It seems that Clang is not searching $PATH for a matching assembler or linker. Make sure that Clang picks up the correct assembler or linker by passing the cross compilers bin directory as search path. This allows to use Clang provided by distributions with GCC toolchains not in /usr/bin. Link: https://github.com/ClangBuiltLinux/linux/issues/78 Signed-off-by: Stefan Agner <stefan@agner.ch> --- Nick, I removed your Reviewed-by since I had to change variable assignment slightly... Makefile | 8 +++++--- 1 file changed, 5 insertions(+), 3 deletions(-)