[PATCH] kbuild: Allow a suffix with $(LLVM)

[PATCH] kbuild: Allow a suffix with $(LLVM)

[Nathan Chancellor]

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.
 
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 := $(LLVM)
+endif
+
+HOSTCC	= clang$(LLVM_SFX)
+HOSTCXX	= clang++$(LLVM_SFX)
 else
 HOSTCC	= gcc
 HOSTCXX	= g++
@@ -444,14 +448,14 @@ KBUILD_HOSTLDLIBS   := $(HOST_LFS_LIBS) $(HOSTLDLIBS)
 # Make variables (CC, etc...)
 CPP		= $(CC) -E
 ifneq ($(LLVM),)
-CC		= clang
-LD		= ld.lld
-AR		= llvm-ar
-NM		= llvm-nm
-OBJCOPY		= llvm-objcopy
-OBJDUMP		= llvm-objdump
-READELF		= llvm-readelf
-STRIP		= llvm-strip
+CC		= clang$(LLVM_SFX)
+LD		= ld.lld$(LLVM_SFX)
+AR		= llvm-ar$(LLVM_SFX)
+NM		= llvm-nm$(LLVM_SFX)
+OBJCOPY		= llvm-objcopy$(LLVM_SFX)
+OBJDUMP		= llvm-objdump$(LLVM_SFX)
+READELF		= llvm-readelf$(LLVM_SFX)
+STRIP		= llvm-strip$(LLVM_SFX)
 else
 CC		= $(CROSS_COMPILE)gcc
 LD		= $(CROSS_COMPILE)ld
diff --git a/tools/scripts/Makefile.include b/tools/scripts/Makefile.include
index 79d102304470..ab3b2a7dcc94 100644
--- a/tools/scripts/Makefile.include
+++ b/tools/scripts/Makefile.include
@@ -52,11 +52,15 @@ define allow-override
 endef
 
 ifneq ($(LLVM),)
-$(call allow-override,CC,clang)
-$(call allow-override,AR,llvm-ar)
-$(call allow-override,LD,ld.lld)
-$(call allow-override,CXX,clang++)
-$(call allow-override,STRIP,llvm-strip)
+ifneq ($(LLVM),1)
+LLVM_SFX := $(LLVM)
+endif
+
+$(call allow-override,CC,clang$(LLVM_SFX))
+$(call allow-override,AR,llvm-ar$(LLVM_SFX))
+$(call allow-override,LD,ld.lld$(LLVM_SFX))
+$(call allow-override,CXX,clang++$(LLVM_SFX))
+$(call allow-override,STRIP,llvm-strip$(LLVM_SFX))
 else
 # Allow setting various cross-compile vars or setting CROSS_COMPILE as a prefix.
 $(call allow-override,CC,$(CROSS_COMPILE)gcc)
@@ -69,9 +73,9 @@ endif
 CC_NO_CLANG := $(shell $(CC) -dM -E -x c /dev/null | grep -Fq "__clang__"; echo $$?)
 
 ifneq ($(LLVM),)
-HOSTAR  ?= llvm-ar
-HOSTCC  ?= clang
-HOSTLD  ?= ld.lld
+HOSTAR  ?= llvm-ar$(LLVM_SFX)
+HOSTCC  ?= clang$(LLVM_SFX)
+HOSTLD  ?= ld.lld$(LLVM_SFX)
 else
 HOSTAR  ?= ar
 HOSTCC  ?= gcc
diff --git a/tools/testing/selftests/lib.mk b/tools/testing/selftests/lib.mk
index a40add31a2e3..b3ab713537c6 100644
--- a/tools/testing/selftests/lib.mk
+++ b/tools/testing/selftests/lib.mk
@@ -1,7 +1,11 @@
 # This mimics the top-level Makefile. We do it explicitly here so that this
 # Makefile can operate with or without the kbuild infrastructure.
 ifneq ($(LLVM),)
-CC := clang
+ifneq ($(LLVM),1)
+LLVM_SFX := $(LLVM)
+endif
+
+CC := clang$(LLVM_SFX)
 else
 CC := $(CROSS_COMPILE)gcc
 endif

base-commit: 55de8686df7ed2b5237867b130e30c728bbd9db4
-- 
2.35.1

Re: [PATCH] kbuild: Allow a suffix with $(LLVM)

[Masahiro Yamada]

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






-- 
Best Regards
Masahiro Yamada

Re: [PATCH] kbuild: Allow a suffix with $(LLVM)

[Nathan Chancellor]

On Fri, Mar 04, 2022 at 08:16:00PM +0900, Masahiro Yamada wrote:
> 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.

Maybe just adding something like:

"... prefer to test an explicit version rather than the unsuffixed
executables like above, ..."

? I'll try to come up with a clearer way to word everything for v2.

> > 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.

Right, but we have that problem right now, as LLVM=0 is currently
treated like LLVM=1. I suppose I could add a line to the documentation
in a follow up change to clarify this.

> 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

I did think about this. I guess the only reason I did not do that in
this version is someone might have a different suffix scheme than
Debian's but it is probably better to be a little bit more precise based
on what we know in this moment. I will change it to that and update the
documentation.

> 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

I know I personally I would use the prefix form when testing with LLVM=1
so I think I will just go ahead and support that now, especially since
Peter had aimed to support a full path with his CC patch that we NAK'd.

> Lastly, I personally prefer to fully spell LLVM_SUFFIX
> as Nick originally suggested:
> https://lkml.org/lkml/2020/3/17/1477

Ack, I have changed this locally and I'll send a v2 along shortly once I
have written some documentation to codify these suggested changes.

Thank you for the comments and review, cheers!
Nathan