On Thu, Mar 3, 2022 at 8:47 AM Nathan Chancellor <nathan@xxxxxxxxxx> wrote: > > The LLVM make variable allows a developer to quickly switch between the > GNU and LLVM tools. However, it does not handle versioned binaries, such > as the ones shipped by Debian, as LLVM=1 just defines the tool variables > with the unversioned binaries. > > There was some discussion during the review of the patch that introduces > LLVM=1 around versioned binaries, ultimately coming to the conclusion > that developers can just add the folder that contains the unversioned > binaries to their PATH, as Debian's versioned suffixed binaries are > really just symlinks to the unversioned binaries in /usr/lib/llvm-#/bin: > > $ realpath /usr/bin/clang-14 > /usr/lib/llvm-14/bin/clang > > $ PATH=/usr/lib/llvm-14/bin:$PATH make ... LLVM=1 > > However, that can be cumbersome to developers who are constantly testing > series with different toolchains and versions. It is simple enough to > support these versioned binaries directly in the Kbuild system by > allowing the developer to specify the version suffix with LLVM=, which > is shorter than the above suggestion: > > $ make ... LLVM=-14 > > It does not change the meaning of LLVM=1 (which will continue to use > unversioned binaries) and it does not add too much additional complexity > to the existing $(LLVM) code, while allowing developers to quickly test > their series with different versions of the whole LLVM suite of tools. > > Link: https://lore.kernel.org/r/20200317215515.226917-1-ndesaulniers@xxxxxxxxxx/ > Link: https://lore.kernel.org/r/20220224151322.072632223@xxxxxxxxxxxxx/ > Suggested-by: Peter Zijlstra <peterz@xxxxxxxxxxxxx> > Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx> > Reviewed-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx> > Signed-off-by: Nathan Chancellor <nathan@xxxxxxxxxx> > --- > > RFC -> v1: https://lore.kernel.org/r/Yh%2FegU1LZudfrgVy@dev-arch.thelio-3990X/ > > * Tidy up commit message slightly. > > * Add tags. > > * Add links to prior discussions for context. > > * Add change to tools/testing/selftests/lib.mk. > > I would like for this to go through the Kbuild tree, please ack as > necessary. > > Documentation/kbuild/llvm.rst | 7 +++++++ > Makefile | 24 ++++++++++++++---------- > tools/scripts/Makefile.include | 20 ++++++++++++-------- > tools/testing/selftests/lib.mk | 6 +++++- > 4 files changed, 38 insertions(+), 19 deletions(-) > > diff --git a/Documentation/kbuild/llvm.rst b/Documentation/kbuild/llvm.rst > index d32616891dcf..5805a8473a36 100644 > --- a/Documentation/kbuild/llvm.rst > +++ b/Documentation/kbuild/llvm.rst > @@ -60,6 +60,13 @@ They can be enabled individually. The full list of the parameters: :: > OBJCOPY=llvm-objcopy OBJDUMP=llvm-objdump READELF=llvm-readelf \ > HOSTCC=clang HOSTCXX=clang++ HOSTAR=llvm-ar HOSTLD=ld.lld > > +If your LLVM tools have a suffix and you prefer to test an explicit version rather > +than the unsuffixed executables, use ``LLVM=<suffix>``. For example: :: > + > + make LLVM=-14 > + > +will use ``clang-14``, ``ld.lld-14``, etc. > + > The integrated assembler is enabled by default. You can pass ``LLVM_IAS=0`` to > disable it. Perhaps, it might be worth mentioning the difference between LLVM=1 and LLVM=<suffix> The current behavior is, any value other than '1' is regarded as a suffix. > diff --git a/Makefile b/Makefile > index a82095c69fdd..963840c00eae 100644 > --- a/Makefile > +++ b/Makefile > @@ -424,8 +424,12 @@ HOST_LFS_LDFLAGS := $(shell getconf LFS_LDFLAGS 2>/dev/null) > HOST_LFS_LIBS := $(shell getconf LFS_LIBS 2>/dev/null) > > ifneq ($(LLVM),) > -HOSTCC = clang > -HOSTCXX = clang++ > +ifneq ($(LLVM),1) > +LLVM_SFX := $(LLVM) > +endif I am OK with this, but please note LLVM=0 uses 'clang0', 'ld.lld0' instead of disabling LLVM explicitly. This might be a small surprise because LLVM_IAS=0 is used to disable the integrated assembler. If you want handle LLVM=<suffix> only when <suffix> start with a hyphen, you can do like this: ifneq ($(filter -%, $(LLVM)),) LLVM_SFX := $(LLVM) endif In the future, If somebody requests to support make LLVM=/path/to/my/own/llvm/dir/ to use llvm tools in that path, we can expand the code like this: # "LLVM=foo/bar/" is a syntax sugar of "LLVM=1 LLVM_PFX=foo/bar" # "LLVM=-foo" is a syntax sugar of "LLVM=1 LLVM_SFX=-foo" ifneq ($(filter %/, $(LLVM)),) LLVM_PFX := $(LLVM) else ifneq ($(filter -%, $(LLVM)),) LLVM_SFX := $(LLVM) endif Lastly, I personally prefer to fully spell LLVM_SUFFIX as Nick originally suggested: https://lkml.org/lkml/2020/3/17/1477 -- Best Regards Masahiro Yamada
