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From: Nathan Chancellor <nathan@kernel.org>
To: Jean-Philippe Brucker <jean-philippe@linaro.org>
Cc: ast@kernel.org, daniel@iogearbox.net, andrii@kernel.org,
	shuah@kernel.org, ndesaulniers@google.com, kafai@fb.com,
	songliubraving@fb.com, yhs@fb.com, john.fastabend@gmail.com,
	kpsingh@kernel.org, quentin@isovalent.com, bpf@vger.kernel.org,
	linux-kselftest@vger.kernel.org, llvm@lists.linux.dev
Subject: Re: [PATCH bpf-next v2 1/6] tools: Help cross-building with clang
Date: Mon, 31 Jan 2022 10:04:53 -0700	[thread overview]
Message-ID: <YfgWtQkTj69zPZY/@dev-arch.archlinux-ax161> (raw)
In-Reply-To: <Yfft1sqfXGTAjwJ8@myrica>

On Mon, Jan 31, 2022 at 02:10:30PM +0000, Jean-Philippe Brucker wrote:
> Hi Nathan,
> 
> On Fri, Jan 28, 2022 at 06:10:24PM -0700, Nathan Chancellor wrote:
> > > diff --git a/tools/scripts/Makefile.include b/tools/scripts/Makefile.include
> > > index 071312f5eb92..b0be5f40a3f1 100644
> > > --- a/tools/scripts/Makefile.include
> > > +++ b/tools/scripts/Makefile.include
> > > @@ -87,7 +87,18 @@ LLVM_STRIP	?= llvm-strip
> > >  
> > >  ifeq ($(CC_NO_CLANG), 1)
> > >  EXTRA_WARNINGS += -Wstrict-aliasing=3
> > > -endif
> > > +
> > > +else ifneq ($(CROSS_COMPILE),)
> > > +CLANG_CROSS_FLAGS := --target=$(notdir $(CROSS_COMPILE:%-=%))
> > > +GCC_TOOLCHAIN_DIR := $(dir $(shell which $(CROSS_COMPILE)gcc))
> > 
> > Apologies for noticing this so late, I only ran into this recently.
> > 
> > This line causes a warning when running 'make clean' when
> > '$(CROSS_COMPILE)gcc' does not exist in PATH. For example:
> > 
> > $ make -skj"$(nproc)" ARCH=powerpc CROSS_COMPILE=powerpc-linux-gnu- LLVM=1 LLVM_IAS=0 clean
> > which: no powerpc-linux-gnu-gcc in ($PATH)
> > 
> > I only have powerpc-linux-gnu binutils in my PATH, not GCC, as I am only
> > working with clang.
> > 
> > This happens because of the 'resolve_btfids_clean target', which always
> > runs when running the 'clean' target on an in-tree build (since
> > $(objtree) = $(srctree)).
> > 
> > I tried looking into the best way to fix this but I am not at all
> > familiar with the tools/ build system; would you mind taking a look?
> > I see some machinery at the top of tools/bpf/Makefile for avoiding
> > running some commands under certain commands but I am unsure how to
> > shuffle that around to make everything work.
> 
> I think it's simpler than that, we should just suppress the errors from
> 'which'. It's fine that $(CROSS_COMPILE)gcc doesn't exist and
> $(GCC_TOOLCHAIN_DIR) is empty, but 'which' should keep quiet about it.

Ha, that's what I get for looking into something at the very end of a
long work week because that is a great and simple solution I probably
would not have seen :)

> I did test this patch with cross-build and no gcc, but Debian's 'which' is
> quiet by default so I missed the error. I'll send a fix shortly.

Ah, that is an interesting observation. TIL that Debian rolls their own
which [1], versus most other distros, which use GNU which [2].

I will keep an eye out for your patch so I can review it.

[1]: https://salsa.debian.org/debian/debianutils/-/blob/de14223e5bffe15e374a441302c528ffc1cbed57/which
[2]: https://savannah.gnu.org/projects/which/

Cheers,
Nathan

  reply	other threads:[~2022-01-31 17:05 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-12-16 16:38 [PATCH bpf-next v2 0/6] tools/bpf: Enable cross-building with clang Jean-Philippe Brucker
2021-12-16 16:38 ` [PATCH bpf-next v2 1/6] tools: Help " Jean-Philippe Brucker
2021-12-16 19:16   ` Nick Desaulniers
2022-01-29  1:10   ` Nathan Chancellor
2022-01-31 14:10     ` Jean-Philippe Brucker
2022-01-31 17:04       ` Nathan Chancellor [this message]
2021-12-16 16:38 ` [PATCH bpf-next v2 2/6] tools/resolve_btfids: Support cross-building the kernel " Jean-Philippe Brucker
2021-12-16 16:38 ` [PATCH bpf-next v2 3/6] tools/libbpf: Enable cross-building " Jean-Philippe Brucker
2021-12-16 16:38 ` [PATCH bpf-next v2 4/6] bpftool: " Jean-Philippe Brucker
2021-12-16 16:38 ` [PATCH bpf-next v2 5/6] tools/runqslower: " Jean-Philippe Brucker
2021-12-16 16:38 ` [PATCH bpf-next v2 6/6] selftests/bpf: " Jean-Philippe Brucker
2021-12-16 20:32 ` [PATCH bpf-next v2 0/6] tools/bpf: " patchwork-bot+netdevbpf

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