* Re: Usage of CXX in tools directory
2021-04-04 14:59 ` Usage of CXX in tools directory Sedat Dilek
@ 2021-04-04 15:19 ` Sedat Dilek
2021-04-06 18:39 ` Nick Desaulniers
1 sibling, 0 replies; 3+ messages in thread
From: Sedat Dilek @ 2021-04-04 15:19 UTC (permalink / raw)
To: Masahiro Yamada, Yonghong Song, Arnaldo Carvalho de Melo,
David Blaikie, Bill Wendling, Nick Desaulniers,
Nathan Chancellor, Alexei Starovoitov, Peter Zijlstra,
Mark Rutland, Alexander Shishkin, Ingo Molnar, Jiri Olsa,
Namhyung Kim
Cc: dwarves, bpf, kernel-team, linux-kbuild, linux-kernel, x86,
Clang-Built-Linux ML
> So you need to pass CXX=clang++ manually when playing in tools directory:
>
> MAKE="make V=1
> MAKE_OPTS="HOSTCC=clang HOSTCXX=clang++ HOSTLD=ld.lld CC=clang
> CXX=clang++ LD=ld.lld LLVM=1 LLVM_IAS=1"
> MAKE_OPTS="MAKE_OPTS $PAHOLE=/opt/pahole/bin/pahole"
>
> $ LC_ALL=C $MAKE $MAKE_OPTS -C tools/testing/selftests/bpf/ clean
> $ LC_ALL=C $MAKE $MAKE_OPTS -C tools/testing/selftests/bpf/
>
Correct:
MAKE="make V=1"
MAKE_OPTS="HOSTCC=clang HOSTCXX=clang++ HOSTLD=ld.lld CC=clang
CXX=clang++ LD=ld.lld LLVM=1 LLVM_IAS=1"
MAKE_OPTS="$MAKE_OPTS PAHOLE=/opt/pahole/bin/pahole"
- Sedat -
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: Usage of CXX in tools directory
2021-04-04 14:59 ` Usage of CXX in tools directory Sedat Dilek
2021-04-04 15:19 ` Sedat Dilek
@ 2021-04-06 18:39 ` Nick Desaulniers
1 sibling, 0 replies; 3+ messages in thread
From: Nick Desaulniers @ 2021-04-06 18:39 UTC (permalink / raw)
To: Sedat Dilek
Cc: Masahiro Yamada, Yonghong Song, Arnaldo Carvalho de Melo,
David Blaikie, Bill Wendling, Nathan Chancellor,
Alexei Starovoitov, Peter Zijlstra, Mark Rutland,
Alexander Shishkin, Ingo Molnar, Jiri Olsa, Namhyung Kim,
dwarves, bpf, kernel-team, Linux Kbuild mailing list, LKML,
maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT),
Clang-Built-Linux ML
On Sun, Apr 4, 2021 at 8:00 AM Sedat Dilek <sedat.dilek@gmail.com> wrote:
>
> [ Please CC me I am not subscribed to all mailing-lists ]
> [ Please CC some more folks if you like ]
>
> Hi,
>
> when dealing/experimenting with BPF together with pahole/dwarves and
> dwarf-v5 and clang-lto I fell over that there is usage of CXX in tools
> directory.
> Especially, I wanted to build and run test_progs from BPF selftests.
> One BPF selftest called "test_cpp" used GNU/g++ (and even /usr/bin/ld)
> and NOT LLVM/clang++.
>
> For details see the linux-bpf/dwarves thread "[PATCH dwarves]
> dwarf_loader: handle DWARF5 DW_OP_addrx properly" in [1].
>
> Lemme check:
>
> $ git grep CXX tools/
> tools/build/Build.include:cxx_flags = -Wp,-MD,$(depfile) -Wp,-MT,$@
> $(CXXFLAGS) -D"BUILD_STR(s)=\#s" $(CXXFLAGS_$(basetarget).o)
> $(CXXFLAGS_$(obj))
> tools/build/Makefile.build:quiet_cmd_cxx_o_c = CXX $@
> tools/build/Makefile.build: cmd_cxx_o_c = $(CXX) $(cxx_flags) -c -o $@ $<
> tools/build/Makefile.feature: feature-$(1) := $(shell $(MAKE)
> OUTPUT=$(OUTPUT_FEATURES) CC="$(CC)" CXX="$(CXX)"
> CFLAGS="$(EXTRA_CFLAGS) $(FEATURE_CHECK_CFLAGS-$(1))"
> CXXFLAGS="$(EXTRA_CXXFLAGS) $(FEATURE_CHECK_CXXFLAGS-$(1))"
> LDFLAGS="$(LDFLAGS) $(FEATURE_CHECK_LDFLAGS-$(1))" -C $(feature_dir)
> $(OUTPUT_FEATURES)test-$1.bin >/dev/nu
> ll 2>/dev/null && echo 1 || echo 0)
> tools/build/feature/Makefile:__BUILDXX = $(CXX) $(CXXFLAGS) -MD -Wall
> -Werror -o $@ $(patsubst %.bin,%.cpp,$(@F)) $(LDFLAGS)
> ...
> tools/perf/Makefile.config:USE_CXX = 0
> tools/perf/Makefile.config: CXXFLAGS +=
> -DHAVE_LIBCLANGLLVM_SUPPORT -I$(shell $(LLVM_CONFIG) --includedir)
> tools/perf/Makefile.config: $(call detected,CONFIG_CXX)
> tools/perf/Makefile.config: USE_CXX = 1
> tools/perf/Makefile.perf:export srctree OUTPUT RM CC CXX LD AR CFLAGS
> CXXFLAGS V BISON FLEX AWK
> tools/perf/Makefile.perf:ifeq ($(USE_CXX), 1)
> tools/perf/util/Build:perf-$(CONFIG_CXX) += c++/
> ...
> tools/scripts/Makefile.include:$(call allow-override,CXX,$(CROSS_COMPILE)g++)
> ...
> tools/testing/selftests/bpf/Makefile:CXX ?= $(CROSS_COMPILE)g++
> tools/testing/selftests/bpf/Makefile: $(call msg,CXX,,$@)
> tools/testing/selftests/bpf/Makefile: $(Q)$(CXX) $(CFLAGS) $^ $(LDLIBS) -o $@
>
> The problem is if you pass LLVM=1 there is no clang(++) assigned to
> CXX automagically.
>
> [2] says:
>
> LLVM has substitutes for GNU binutils utilities. Kbuild supports
> LLVM=1 to enable them.
>
> make LLVM=1
> They can be enabled individually. The full list of the parameters:
>
> make CC=clang LD=ld.lld AR=llvm-ar NM=llvm-nm STRIP=llvm-strip \
> OBJCOPY=llvm-objcopy OBJDUMP=llvm-objdump READELF=llvm-readelf \
> HOSTCC=clang HOSTCXX=clang++ HOSTAR=llvm-ar HOSTLD=ld.lld
>
> [ EndOfQuote ]
>
> So you need to pass CXX=clang++ manually when playing in tools directory:
Yes, CXX is not set by LLVM=1 in the top level Makefile. CXX is not
exported by the top level Makefile. I suspect that
tools/scripts/Mafefile.include (and possible
testing/selftests/bpf/Makefile) needs to check for LLVM=1 and set
CXX=clang++ explicitly.
>
> MAKE="make V=1
> MAKE_OPTS="HOSTCC=clang HOSTCXX=clang++ HOSTLD=ld.lld CC=clang
> CXX=clang++ LD=ld.lld LLVM=1 LLVM_IAS=1"
> MAKE_OPTS="MAKE_OPTS $PAHOLE=/opt/pahole/bin/pahole"
>
> $ LC_ALL=C $MAKE $MAKE_OPTS -C tools/testing/selftests/bpf/ clean
> $ LC_ALL=C $MAKE $MAKE_OPTS -C tools/testing/selftests/bpf/
>
> Unsure, if tools needs a special treatment in things of CXX or LLVM=1
> needs to be enhanced with CCX=clang++.
> If we have HOSTCXX why not have a CXX in toplevel Makefile?
>
> In "tools: Factor Clang, LLC and LLVM utils definitions" (see [3]) I
> did some factor-ing.
>
> For the records: Here Linus Git is my base.
>
> Ideas?
>
> Thanks.
>
> Regards,
> - Sedat -
>
> P.S.: Just a small note: I know there is less usage of CXX code in the
> linux-kernel.
>
> [1] https://lore.kernel.org/bpf/CA+icZUWh6YOkCKG72SndqUbQNwG+iottO4=cPyRRVjaHD2=0qw@mail.gmail.com/T/#m22907f838d2d27be24e8959a53473a62f21cecea
> [2] https://www.kernel.org/doc/html/latest/kbuild/llvm.html#llvm-utilities
> [3] https://git.kernel.org/linus/211a741cd3e124bffdc13ee82e7e65f204e53f60
--
Thanks,
~Nick Desaulniers
^ permalink raw reply [flat|nested] 3+ messages in thread