| Message ID | 20190207220155.81351-3-ndesaulniers@google.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | None | expand |
On Thu, Feb 07, 2019 at 02:01:51PM -0800, ndesaulniers@google.com wrote: > This is needed because clang doesn't select which linker to use based on > $LD but rather -fuse-ld=$(LD). This is problematic especially for > cc-ldoption, which checks for linker flag support via invoking the > compiler, rather than the linker. > > Link: https://github.com/ClangBuiltLinux/linux/issues/342 > Suggested-by: Nathan Chancellor <natechancellor@gmail.com> > Signed-off-by: Nick Desaulniers <ndesaulniers@google.com> > --- > Makefile | 3 +++ > 1 file changed, 3 insertions(+) > > diff --git a/Makefile b/Makefile > index 0eae4277206e..6307c17259ea 100644 > --- a/Makefile > +++ b/Makefile > @@ -502,6 +502,9 @@ endif > CLANG_FLAGS += -no-integrated-as > KBUILD_CFLAGS += $(CLANG_FLAGS) > KBUILD_AFLAGS += $(CLANG_FLAGS) > +ifneq ($(shell $(LD) --version 2>&1 | head -n 1 | grep LLD),) > +CLANG_FLAGS += -fuse-ld=lld > +endif This section needs to be moved up above KBUILD_CFLAGS otherwise it never actually gets passed along. With that change, please add: Reviewed-by: Nathan Chancellor <natechancellor@gmail.com> Tested-by: Nathan Chancellor <natechancellor@gmail.com> > export CLANG_FLAGS > endif > > -- > 2.20.1.791.gb4d0f1c61a-goog >
On Thu, Feb 7, 2019 at 9:51 PM Nathan Chancellor <natechancellor@gmail.com> wrote: > > On Thu, Feb 07, 2019 at 02:01:51PM -0800, ndesaulniers@google.com wrote: > > This is needed because clang doesn't select which linker to use based on > > $LD but rather -fuse-ld=$(LD). This is problematic especially for > > cc-ldoption, which checks for linker flag support via invoking the > > compiler, rather than the linker. > > > > Link: https://github.com/ClangBuiltLinux/linux/issues/342 > > Suggested-by: Nathan Chancellor <natechancellor@gmail.com> > > Signed-off-by: Nick Desaulniers <ndesaulniers@google.com> > > --- > > Makefile | 3 +++ > > 1 file changed, 3 insertions(+) > > > > diff --git a/Makefile b/Makefile > > index 0eae4277206e..6307c17259ea 100644 > > --- a/Makefile > > +++ b/Makefile > > @@ -502,6 +502,9 @@ endif > > CLANG_FLAGS += -no-integrated-as > > KBUILD_CFLAGS += $(CLANG_FLAGS) > > KBUILD_AFLAGS += $(CLANG_FLAGS) > > +ifneq ($(shell $(LD) --version 2>&1 | head -n 1 | grep LLD),) > > +CLANG_FLAGS += -fuse-ld=lld Sorry, Sedat reports [0] that this is not quite correct; if $(LD) matches LLD, then we need to set -fuse-ld=$(LD), not -fuse-ld=lld, since you may have lld installed as lld-7 or lld-8, for example: https://github.com/ClangBuiltLinux/linux/issues/358 > > +endif > > This section needs to be moved up above KBUILD_CFLAGS otherwise it never > actually gets passed along. > > With that change, please add: > > Reviewed-by: Nathan Chancellor <natechancellor@gmail.com> > Tested-by: Nathan Chancellor <natechancellor@gmail.com> > > > export CLANG_FLAGS > > endif > > > > -- > > 2.20.1.791.gb4d0f1c61a-goog > >
On Fri, Feb 08, 2019 at 09:27:19AM -0800, Nick Desaulniers wrote: > On Thu, Feb 7, 2019 at 9:51 PM Nathan Chancellor > <natechancellor@gmail.com> wrote: > > > > On Thu, Feb 07, 2019 at 02:01:51PM -0800, ndesaulniers@google.com wrote: > > > This is needed because clang doesn't select which linker to use based on > > > $LD but rather -fuse-ld=$(LD). This is problematic especially for > > > cc-ldoption, which checks for linker flag support via invoking the > > > compiler, rather than the linker. > > > > > > Link: https://github.com/ClangBuiltLinux/linux/issues/342 > > > Suggested-by: Nathan Chancellor <natechancellor@gmail.com> > > > Signed-off-by: Nick Desaulniers <ndesaulniers@google.com> > > > --- > > > Makefile | 3 +++ > > > 1 file changed, 3 insertions(+) > > > > > > diff --git a/Makefile b/Makefile > > > index 0eae4277206e..6307c17259ea 100644 > > > --- a/Makefile > > > +++ b/Makefile > > > @@ -502,6 +502,9 @@ endif > > > CLANG_FLAGS += -no-integrated-as > > > KBUILD_CFLAGS += $(CLANG_FLAGS) > > > KBUILD_AFLAGS += $(CLANG_FLAGS) > > > +ifneq ($(shell $(LD) --version 2>&1 | head -n 1 | grep LLD),) > > > +CLANG_FLAGS += -fuse-ld=lld > > Sorry, Sedat reports [0] that this is not quite correct; if $(LD) > matches LLD, then we need to set -fuse-ld=$(LD), not -fuse-ld=lld, > since you may have lld installed as lld-7 or lld-8, for example: > https://github.com/ClangBuiltLinux/linux/issues/358 > We'll need to make sure that it is compatible with the way that Clang expects arguments to '-fuse-ld=' because it looks like 'ld.' is automatically appended. https://github.com/llvm/llvm-project/blob/5be3dbdb082ffba4f846e3572ea802d156dd8d34/clang/lib/Driver/ToolChain.cpp#L438-L468 > > > +endif > > > > This section needs to be moved up above KBUILD_CFLAGS otherwise it never > > actually gets passed along. > > > > With that change, please add: > > > > Reviewed-by: Nathan Chancellor <natechancellor@gmail.com> > > Tested-by: Nathan Chancellor <natechancellor@gmail.com> > > > > > export CLANG_FLAGS > > > endif > > > > > > -- > > > 2.20.1.791.gb4d0f1c61a-goog > > > > > > > -- > Thanks, > ~Nick Desaulniers
On Sat, Feb 9, 2019 at 2:27 AM Nick Desaulniers <ndesaulniers@google.com> wrote: > > On Thu, Feb 7, 2019 at 9:51 PM Nathan Chancellor > <natechancellor@gmail.com> wrote: > > > > On Thu, Feb 07, 2019 at 02:01:51PM -0800, ndesaulniers@google.com wrote: > > > This is needed because clang doesn't select which linker to use based on > > > $LD but rather -fuse-ld=$(LD). This is problematic especially for > > > cc-ldoption, which checks for linker flag support via invoking the > > > compiler, rather than the linker. What do you mean by 'problematic' ? I see no build error in arch/arm64/kernel/vdso/Makefile, at least. Clang uses BFD linker by default, which may not match to the $(LD) passed in. Is this what you mean? > > > Link: https://github.com/ClangBuiltLinux/linux/issues/342 > > > Suggested-by: Nathan Chancellor <natechancellor@gmail.com> > > > Signed-off-by: Nick Desaulniers <ndesaulniers@google.com> > > > --- > > > Makefile | 3 +++ > > > 1 file changed, 3 insertions(+) > > > > > > diff --git a/Makefile b/Makefile > > > index 0eae4277206e..6307c17259ea 100644 > > > --- a/Makefile > > > +++ b/Makefile > > > @@ -502,6 +502,9 @@ endif > > > CLANG_FLAGS += -no-integrated-as > > > KBUILD_CFLAGS += $(CLANG_FLAGS) > > > KBUILD_AFLAGS += $(CLANG_FLAGS) > > > +ifneq ($(shell $(LD) --version 2>&1 | head -n 1 | grep LLD),) > > > +CLANG_FLAGS += -fuse-ld=lld > > Sorry, Sedat reports [0] that this is not quite correct; if $(LD) > matches LLD, then we need to set -fuse-ld=$(LD), not -fuse-ld=lld, > since you may have lld installed as lld-7 or lld-8, for example: > https://github.com/ClangBuiltLinux/linux/issues/358 Hmm, $(LD) might be a full path. Looks like Clang can take a full-path for -fuse-ld=, but does it work for GCC? > > > +endif > > > > This section needs to be moved up above KBUILD_CFLAGS otherwise it never > > actually gets passed along. > > > > With that change, please add: > > > > Reviewed-by: Nathan Chancellor <natechancellor@gmail.com> > > Tested-by: Nathan Chancellor <natechancellor@gmail.com> > > > > > export CLANG_FLAGS > > > endif > > > > > > -- > > > 2.20.1.791.gb4d0f1c61a-goog > > > > > > > -- > Thanks, > ~Nick Desaulniers
On Mon, Feb 11, 2019 at 4:33 PM Masahiro Yamada <yamada.masahiro@socionext.com> wrote: [ ... ] > > > > Link: https://github.com/ClangBuiltLinux/linux/issues/342 > > > > Suggested-by: Nathan Chancellor <natechancellor@gmail.com> > > > > Signed-off-by: Nick Desaulniers <ndesaulniers@google.com> > > > > --- > > > > Makefile | 3 +++ > > > > 1 file changed, 3 insertions(+) > > > > > > > > diff --git a/Makefile b/Makefile > > > > index 0eae4277206e..6307c17259ea 100644 > > > > --- a/Makefile > > > > +++ b/Makefile > > > > @@ -502,6 +502,9 @@ endif > > > > CLANG_FLAGS += -no-integrated-as > > > > KBUILD_CFLAGS += $(CLANG_FLAGS) > > > > KBUILD_AFLAGS += $(CLANG_FLAGS) > > > > +ifneq ($(shell $(LD) --version 2>&1 | head -n 1 | grep LLD),) > > > > +CLANG_FLAGS += -fuse-ld=lld > > > > Sorry, Sedat reports [0] that this is not quite correct; if $(LD) > > matches LLD, then we need to set -fuse-ld=$(LD), not -fuse-ld=lld, > > since you may have lld installed as lld-7 or lld-8, for example: > > https://github.com/ClangBuiltLinux/linux/issues/358 > > > Hmm, $(LD) might be a full path. > > Looks like Clang can take a full-path for -fuse-ld=, > but does it work for GCC? > Nope. GCC expects "-fuse-ld={bfd,gold,lld} ". Adding suffix "$-VER" was not recognized while building a llvm-toolchain, so I guess this will be the same for the Linux kernel side. - Sedat - [1] https://gcc.gnu.org/onlinedocs/gcc/Link-Options.html [2] https://github.com/ClangBuiltLinux/linux/issues/358
On Thu, Feb 7, 2019 at 9:51 PM Nathan Chancellor <natechancellor@gmail.com> wrote: > > On Thu, Feb 07, 2019 at 02:01:51PM -0800, ndesaulniers@google.com wrote: > > This is needed because clang doesn't select which linker to use based on > > $LD but rather -fuse-ld=$(LD). This is problematic especially for > > cc-ldoption, which checks for linker flag support via invoking the > > compiler, rather than the linker. > > > > Link: https://github.com/ClangBuiltLinux/linux/issues/342 > > Suggested-by: Nathan Chancellor <natechancellor@gmail.com> > > Signed-off-by: Nick Desaulniers <ndesaulniers@google.com> > > --- > > Makefile | 3 +++ > > 1 file changed, 3 insertions(+) > > > > diff --git a/Makefile b/Makefile > > index 0eae4277206e..6307c17259ea 100644 > > --- a/Makefile > > +++ b/Makefile > > @@ -502,6 +502,9 @@ endif > > CLANG_FLAGS += -no-integrated-as > > KBUILD_CFLAGS += $(CLANG_FLAGS) > > KBUILD_AFLAGS += $(CLANG_FLAGS) > > +ifneq ($(shell $(LD) --version 2>&1 | head -n 1 | grep LLD),) > > +CLANG_FLAGS += -fuse-ld=lld > > +endif > > This section needs to be moved up above KBUILD_CFLAGS otherwise it never > actually gets passed along. Great catch! I had that correct in my Pixel kernel patches; messed that up forward porting them. Included in v2 (sending imminently).
On Mon, Feb 11, 2019 at 7:33 AM Masahiro Yamada <yamada.masahiro@socionext.com> wrote: > > On Sat, Feb 9, 2019 at 2:27 AM Nick Desaulniers <ndesaulniers@google.com> wrote: > > > > On Thu, Feb 7, 2019 at 9:51 PM Nathan Chancellor > > <natechancellor@gmail.com> wrote: > > > > > > On Thu, Feb 07, 2019 at 02:01:51PM -0800, ndesaulniers@google.com wrote: > > > > This is needed because clang doesn't select which linker to use based on > > > > $LD but rather -fuse-ld=$(LD). This is problematic especially for > > > > cc-ldoption, which checks for linker flag support via invoking the > > > > compiler, rather than the linker. > > What do you mean by 'problematic' ? > > I see no build error in > arch/arm64/kernel/vdso/Makefile, at least. > > Clang uses BFD linker by default, > which may not match to the $(LD) passed in. > > Is this what you mean? Right, when using a linker other than BFD, we want cc-ldoption to tell us whether that linker supports a linker flag or not.
On Mon, Feb 11, 2019 at 8:05 AM Sedat Dilek <sedat.dilek@gmail.com> wrote: > > On Mon, Feb 11, 2019 at 4:33 PM Masahiro Yamada > <yamada.masahiro@socionext.com> wrote: > [ ... ] > > > > > Link: https://github.com/ClangBuiltLinux/linux/issues/342 > > > > > Suggested-by: Nathan Chancellor <natechancellor@gmail.com> > > > > > Signed-off-by: Nick Desaulniers <ndesaulniers@google.com> > > > > > --- > > > > > Makefile | 3 +++ > > > > > 1 file changed, 3 insertions(+) > > > > > > > > > > diff --git a/Makefile b/Makefile > > > > > index 0eae4277206e..6307c17259ea 100644 > > > > > --- a/Makefile > > > > > +++ b/Makefile > > > > > @@ -502,6 +502,9 @@ endif > > > > > CLANG_FLAGS += -no-integrated-as > > > > > KBUILD_CFLAGS += $(CLANG_FLAGS) > > > > > KBUILD_AFLAGS += $(CLANG_FLAGS) > > > > > +ifneq ($(shell $(LD) --version 2>&1 | head -n 1 | grep LLD),) > > > > > +CLANG_FLAGS += -fuse-ld=lld > > > > > > Sorry, Sedat reports [0] that this is not quite correct; if $(LD) > > > matches LLD, then we need to set -fuse-ld=$(LD), not -fuse-ld=lld, > > > since you may have lld installed as lld-7 or lld-8, for example: > > > https://github.com/ClangBuiltLinux/linux/issues/358 > > > > > > Hmm, $(LD) might be a full path. > > > > Looks like Clang can take a full-path for -fuse-ld=, > > but does it work for GCC? > > > > Nope. GCC expects "-fuse-ld={bfd,gold,lld} ". > Adding suffix "$-VER" was not recognized while building a > llvm-toolchain, so I guess this will be the same for the Linux kernel > side. Well for now, let's add support for just `ld.lld` since a build of llvm will create such a symlink. If folks really need to differentiate between different versions of lld, let's cross that bridge when we get there.
diff --git a/Makefile b/Makefile index 0eae4277206e..6307c17259ea 100644 --- a/Makefile +++ b/Makefile @@ -502,6 +502,9 @@ endif CLANG_FLAGS += -no-integrated-as KBUILD_CFLAGS += $(CLANG_FLAGS) KBUILD_AFLAGS += $(CLANG_FLAGS) +ifneq ($(shell $(LD) --version 2>&1 | head -n 1 | grep LLD),) +CLANG_FLAGS += -fuse-ld=lld +endif export CLANG_FLAGS endif
This is needed because clang doesn't select which linker to use based on $LD but rather -fuse-ld=$(LD). This is problematic especially for cc-ldoption, which checks for linker flag support via invoking the compiler, rather than the linker. Link: https://github.com/ClangBuiltLinux/linux/issues/342 Suggested-by: Nathan Chancellor <natechancellor@gmail.com> Signed-off-by: Nick Desaulniers <ndesaulniers@google.com> --- Makefile | 3 +++ 1 file changed, 3 insertions(+)