From: Andrii Nakryiko <andrii.nakryiko@gmail.com>
To: Yonghong Song <yhs@fb.com>
Cc: Nick Desaulniers <ndesaulniers@google.com>,
bpf <bpf@vger.kernel.org>, Andrii Nakryiko <andrii@kernel.org>,
Arnaldo Carvalho de Melo <arnaldo.melo@gmail.com>,
Kernel Team <kernel-team@fb.com>,
Sedat Dilek <sedat.dilek@gmail.com>
Subject: Re: [PATCH bpf-next v3 1/5] selftests: set CC to clang in lib.mk if LLVM is set
Date: Tue, 13 Apr 2021 16:22:55 -0700 [thread overview]
Message-ID: <CAEf4Bzb46saNHyYbmyu8zgnx3SBHq_n5q-rQVviY5DsDnJPL8Q@mail.gmail.com> (raw)
In-Reply-To: <e07d9794-75c1-f554-d827-26a02a6b09f1@fb.com>
On Tue, Apr 13, 2021 at 3:27 PM Yonghong Song <yhs@fb.com> wrote:
>
>
>
> On 4/13/21 3:13 PM, Nick Desaulniers wrote:
> > On Tue, Apr 13, 2021 at 3:05 PM Andrii Nakryiko
> > <andrii.nakryiko@gmail.com> wrote:
> >>
> >> On Tue, Apr 13, 2021 at 8:34 AM Yonghong Song <yhs@fb.com> wrote:
> >>>
> >>> selftests/bpf/Makefile includes lib.mk. With the following command
> >>> make -j60 LLVM=1 LLVM_IAS=1 <=== compile kernel
> >>> make -j60 -C tools/testing/selftests/bpf LLVM=1 LLVM_IAS=1 V=1
> >>> some files are still compiled with gcc. This patch
> >>> fixed lib.mk issue which sets CC to gcc in all cases.
> >>>
> >>> Cc: Sedat Dilek <sedat.dilek@gmail.com>
> >>> Signed-off-by: Yonghong Song <yhs@fb.com>
> >>> ---
> >>> tools/testing/selftests/lib.mk | 4 ++++
> >>> 1 file changed, 4 insertions(+)
> >>>
> >>> diff --git a/tools/testing/selftests/lib.mk b/tools/testing/selftests/lib.mk
> >>> index a5ce26d548e4..9a41d8bb9ff1 100644
> >>> --- a/tools/testing/selftests/lib.mk
> >>> +++ b/tools/testing/selftests/lib.mk
> >>> @@ -1,6 +1,10 @@
> >>> # This mimics the top-level Makefile. We do it explicitly here so that this
> >>> # Makefile can operate with or without the kbuild infrastructure.
> >>> +ifneq ($(LLVM),)
> >>> +CC := clang
> >>
> >> Does this mean that cross-compilation with Clang doesn't work at all
> >> or is achieved in some other way?
> >
> > Right, this probably doesn't support cross compilation w/ Clang.
> > Rather than invoke `$(CROSS_COMPILE) clang`, you'd do `clang
> > --target=$(CROSS_COMPILE)`. Even then, cross linking executables is
> > hairy. But at least this should enable native compilation, which is a
> > start.
>
> See https://clang.llvm.org/docs/CrossCompilation.html.
> As Nick said, clang prefers --target=$(CROSS_COMPILE) to
> indicate cross compilation. User can pass additional
> flags (CFLAGS) for cross compilation for the time being.
> This is the same as main kernel Makefile.
>
> 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
> else
> CC = $(CROSS_COMPILE)gcc
> LD = $(CROSS_COMPILE)ld
> AR = $(CROSS_COMPILE)ar
> NM = $(CROSS_COMPILE)nm
> OBJCOPY = $(CROSS_COMPILE)objcopy
> OBJDUMP = $(CROSS_COMPILE)objdump
> READELF = $(CROSS_COMPILE)readelf
> STRIP = $(CROSS_COMPILE)strip
> endif
>
Ok, sounds good. We can improve cross-compilation separately.
Acked-by: Andrii Nakryiko <andrii@kernel.org>
> >>
> >>
> >>> +else
> >>> CC := $(CROSS_COMPILE)gcc
> >>> +endif
> >>>
> >>> ifeq (0,$(MAKELEVEL))
> >>> ifeq ($(OUTPUT),)
> >>> --
> >>> 2.30.2
> >>>
> >
> >
> >
next prev parent reply other threads:[~2021-04-13 23:23 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-13 15:34 [PATCH bpf-next v3 0/5] bpf: tools: support build selftests/bpf with clang Yonghong Song
2021-04-13 15:34 ` [PATCH bpf-next v3 1/5] selftests: set CC to clang in lib.mk if LLVM is set Yonghong Song
2021-04-13 22:04 ` Andrii Nakryiko
2021-04-13 22:13 ` Nick Desaulniers
2021-04-13 22:27 ` Yonghong Song
2021-04-13 22:34 ` Nick Desaulniers
2021-04-13 23:22 ` Andrii Nakryiko [this message]
2021-04-13 15:34 ` [PATCH bpf-next v3 2/5] tools: allow proper CC/CXX/... override with LLVM=1 in Makefile.include Yonghong Song
2021-04-13 15:34 ` [PATCH bpf-next v3 3/5] selftests/bpf: fix test_cpp compilation failure with clang Yonghong Song
2021-04-13 22:05 ` Andrii Nakryiko
2021-04-13 15:34 ` [PATCH bpf-next v3 4/5] selftests/bpf: silence clang compilation warnings Yonghong Song
2021-04-13 22:07 ` Andrii Nakryiko
2021-04-13 22:17 ` Nick Desaulniers
2021-04-13 22:37 ` Yonghong Song
2021-04-13 15:34 ` [PATCH bpf-next v3 5/5] bpftool: fix a clang compilation warning Yonghong Song
2021-04-13 19:36 ` [PATCH bpf-next v3 0/5] bpf: tools: support build selftests/bpf with clang Martin KaFai Lau
2021-04-16 0:21 ` Alexei Starovoitov
2021-04-16 3:59 ` Yonghong Song
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