linux-kernel - Re: [PATCH] scripts/Makefile.clang: set --target for host based on make -v

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Message-ID: <CAKwvOdmUMhEe=nqyF-L08c7FL-NWus63JEe=G1MkboB47xjfsA@mail.gmail.com>
Date:   Fri, 17 Jun 2022 16:26:02 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Nathan Chancellor <nathan@...nel.org>
Cc:     Masahiro Yamada <masahiroy@...nel.org>,
        Michal Marek <michal.lkml@...kovi.net>,
        Tom Rix <trix@...hat.com>,
        Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        clang-built-linux <llvm@...ts.linux.dev>
Subject: Re: [PATCH] scripts/Makefile.clang: set --target for host based on
 make -v

On Fri, Jun 17, 2022 at 4:21 PM Nathan Chancellor <nathan@...nel.org> wrote:
>
> On Fri, Jun 17, 2022 at 01:39:48PM -0700, Nick Desaulniers wrote:
> > We're working on providing statically linked images of clang to host on
> > kernel.org. We're building them in Alpine Linux based Docker containers,
> > which are MUSL based systems.
> >
> > In order to keep bootstrapping simpler, I'd like for them to have an
> > implicit default --target of x86_64-alpine-linux-musl (set via LLVM's
> > cmake variable LLVM_DEFAULT_TARGET_TRIPLE).
> >
> > Similarly, if one were to use a different build of clang meant for a
> > glibc or bionic based system on a MUSL based host, we'd prefer to use
> > the correct MUSL based triple for target hosts.
> >
> > Borrowed from the Zen of Python: Explicit is better than implicit. Let's
> > be explicit about the target triple for HOSTCC when building with
> > HOSTCC=clang or LLVM=1.
> >
> > Signed-off-by: Nick Desaulniers <ndesaulniers@...gle.com>
>
> I have tested this with a few different distributions on both aarch64
> and x86_64:
>
> Reviewed-by: Nathan Chancellor <nathan@...nel.org>
> Tested-by: Nathan Chancellor <nathan@...nel.org>
>
> One small comment below.
>
> > ---
> >  Makefile               |  3 +--
> >  scripts/Makefile.clang | 10 ++++++++++
> >  2 files changed, 11 insertions(+), 2 deletions(-)
> >
> > diff --git a/Makefile b/Makefile
> > index 1a6678d817bd..87712d9b043c 100644
> > --- a/Makefile
> > +++ b/Makefile
> > @@ -600,10 +600,9 @@ endif
> >  # CC_VERSION_TEXT is referenced from Kconfig (so it needs export),
> >  # and from include/config/auto.conf.cmd to detect the compiler upgrade.
> >  CC_VERSION_TEXT = $(subst $(pound),,$(shell LC_ALL=C $(CC) --version 2>/dev/null | head -n 1))
> > +HOSTCC_VERSION_TEXT = $(subst $(pound),,$(shell LC_ALL=C $(HOSTCC) --version 2>/dev/null | head -n 1))
> >
> > -ifneq ($(findstring clang,$(CC_VERSION_TEXT)),)
> >  include $(srctree)/scripts/Makefile.clang
> > -endif
> >
> >  # Include this also for config targets because some architectures need
> >  # cc-cross-prefix to determine CROSS_COMPILE.
> > diff --git a/scripts/Makefile.clang b/scripts/Makefile.clang
> > index 87285b76adb2..a4505cd62d7b 100644
> > --- a/scripts/Makefile.clang
> > +++ b/scripts/Makefile.clang
> > @@ -1,3 +1,4 @@
> > +ifneq ($(findstring clang,$(CC_VERSION_TEXT)),)
> >  # Individual arch/{arch}/Makefiles should use -EL/-EB to set intended
> >  # endianness and -m32/-m64 to set word size based on Kconfigs instead of
> >  # relying on the target triple.
> > @@ -39,3 +40,12 @@ CLANG_FLAGS        += -Werror=ignored-optimization-argument
> >  KBUILD_CFLAGS        += $(CLANG_FLAGS)
> >  KBUILD_AFLAGS        += $(CLANG_FLAGS)
> >  export CLANG_FLAGS
> > +endif
> > +
> > +# If HOSTCC is clang, set the host target triple explicitly; do not rely on
> > +# implicit defaults.
> > +ifneq ($(findstring clang,$(HOSTCC_VERSION_TEXT)),)
> > +HOST_TRIPLE          := --target=$(shell make --version | head -n2 | tail -n1 | cut -d ' ' -f 3)
>
> Should we use $(MAKE) instead of make here? I guess the only case where

oh! yeah, good call. I think so.  Will wait until next Tuesday
(Juneteenth holiday in the US on Monday) to send a v2. Thanks for
taking a look!

> it would matter is if someone was calling make via an explicit path and
> did not have it available in their PATH so maybe it is not worth
> worrying about.
>
> > +KBUILD_HOSTCFLAGS    += $(HOST_TRIPLE)
> > +KBUILD_HOSTLDFLAGS   += $(HOST_TRIPLE)
> > +endif
> >
> > base-commit: 79fe0f863f920c5fcf9dea61676742f813f0b7a6
> > --
> > 2.36.1.476.g0c4daa206d-goog
> >
> >



-- 
Thanks,
~Nick Desaulniers