On Thu, Mar 3, 2022 at 8:47 AM Nathan Chancellor nathan@kernel.org 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@google.com/ Link: https://lore.kernel.org/r/20220224151322.072632223@infradead.org/ Suggested-by: Peter Zijlstra peterz@infradead.org Reviewed-by: Kees Cook keescook@chromium.org Reviewed-by: Nick Desaulniers ndesaulniers@google.com Signed-off-by: Nathan Chancellor nathan@kernel.org
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