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From: Andrii Nakryiko <andrii.nakryiko@gmail.com>
To: "Toke Høiland-Jørgensen" <toke@redhat.com>
Cc: Alexei Starovoitov <ast@kernel.org>,
	Daniel Borkmann <daniel@iogearbox.net>,
	Martin KaFai Lau <kafai@fb.com>, Song Liu <songliubraving@fb.com>,
	Yonghong Song <yhs@fb.com>, Andrii Nakryiko <andriin@fb.com>,
	Doug Ledford <dledford@redhat.com>,
	Jason Gunthorpe <jgg@ziepe.ca>,
	"David S. Miller" <davem@davemloft.net>,
	Jakub Kicinski <jakub.kicinski@netronome.com>,
	Jesper Dangaard Brouer <brouer@redhat.com>,
	John Fastabend <john.fastabend@gmail.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Ingo Molnar <mingo@redhat.com>,
	Arnaldo Carvalho de Melo <acme@kernel.org>,
	Mark Rutland <mark.rutland@arm.com>,
	Alexander Shishkin <alexander.shishkin@linux.intel.com>,
	Jiri Olsa <jolsa@redhat.com>, Namhyung Kim <namhyung@kernel.org>,
	Shuah Khan <shuah@kernel.org>,
	Networking <netdev@vger.kernel.org>, bpf <bpf@vger.kernel.org>,
	open list <linux-kernel@vger.kernel.org>,
	linux-rdma@vger.kernel.org,
	"open list:KERNEL SELFTEST FRAMEWORK" 
	<linux-kselftest@vger.kernel.org>,
	clang-built-linux@googlegroups.com
Subject: Re: [PATCH bpf-next v2 02/10] tools/bpf/runqslower: Fix override option for VMLINUX_BTF
Date: Wed, 15 Jan 2020 14:31:37 -0800
Message-ID: <CAEf4BzZpGe-1S5_iwS8GBw9iiyFJmDUkOaO+2qaftRn_iy5cNA@mail.gmail.com> (raw)
In-Reply-To: <87v9pctlvn.fsf@toke.dk>

On Wed, Jan 15, 2020 at 2:06 PM Toke Høiland-Jørgensen <toke@redhat.com> wrote:
>
> Andrii Nakryiko <andrii.nakryiko@gmail.com> writes:
>
> > On Wed, Jan 15, 2020 at 6:13 AM Toke Høiland-Jørgensen <toke@redhat.com> wrote:
> >>
> >> From: Toke Høiland-Jørgensen <toke@redhat.com>
> >>
> >> The runqslower tool refuses to build without a file to read vmlinux BTF
> >> from. The build fails with an error message to override the location by
> >> setting the VMLINUX_BTF variable if autodetection fails. However, the
> >> Makefile doesn't actually work with that override - the error message is
> >> still emitted.
> >
> > Do you have example command with VMLINUX_BTF override that didn't work
> > (and what error message was emitted)?
>
> Before this patch:
>
> $ cd ~/build/linux/tools/bpf/runqslower
> $ make
> Makefile:18: *** "Can't detect kernel BTF, use VMLINUX_BTF to specify it explicitly".  Stop.
>
> $ make VMLINUX_BTF=~/build/linux/vmlinux
> Makefile:18: *** "Can't detect kernel BTF, use VMLINUX_BTF to specify it explicitly".  Stop.

Ok, so this is strange. Try make clean and run with V=1, it might help
to debug this. This could happen if ~/build/linux/vmlinux doesn't
exist, but I assume you double-checked that. It works for me just fine
(Makefile won't do VMLINUX_BTF := assignment, if it's defined through
make invocation, so your change should be a no-op in that regard):

$ make clean
$ make VMLINUX_BTF=~/linux-build/default/vmlinux V=1
...
.output/sbin/bpftool btf dump file ~/linux-build/default/vmlinux
format c > .output/vmlinux.h
...

Wonder what your output looks like?

>
> >> Fix this by only doing auto-detection if no override is set. And while
> >> we're at it, also look for a vmlinux file in the current kernel build dir
> >> if none if found on the running kernel.
> >>
> >> Fixes: 9c01546d26d2 ("tools/bpf: Add runqslower tool to tools/bpf")
> >> Signed-off-by: Toke Høiland-Jørgensen <toke@redhat.com>
> >> ---
> >>  tools/bpf/runqslower/Makefile |   16 ++++++++++------
> >>  1 file changed, 10 insertions(+), 6 deletions(-)
> >>
> >> diff --git a/tools/bpf/runqslower/Makefile b/tools/bpf/runqslower/Makefile
> >> index cff2fbcd29a8..fb93ce2bf2fe 100644
> >> --- a/tools/bpf/runqslower/Makefile
> >> +++ b/tools/bpf/runqslower/Makefile
> >> @@ -10,12 +10,16 @@ CFLAGS := -g -Wall
> >>
> >>  # Try to detect best kernel BTF source
> >>  KERNEL_REL := $(shell uname -r)
> >> -ifneq ("$(wildcard /sys/kernel/btf/vmlinux)","")
> >> -VMLINUX_BTF := /sys/kernel/btf/vmlinux
> >> -else ifneq ("$(wildcard /boot/vmlinux-$(KERNEL_REL))","")
> >> -VMLINUX_BTF := /boot/vmlinux-$(KERNEL_REL)
> >> -else
> >> -$(error "Can't detect kernel BTF, use VMLINUX_BTF to specify it explicitly")
> >> +ifeq ("$(VMLINUX_BTF)","")
> >> +  ifneq ("$(wildcard /sys/kernel/btf/vmlinux)","")
> >> +  VMLINUX_BTF := /sys/kernel/btf/vmlinux
> >> +  else ifneq ("$(wildcard /boot/vmlinux-$(KERNEL_REL))","")
> >> +  VMLINUX_BTF := /boot/vmlinux-$(KERNEL_REL)
> >> +  else ifneq ("$(wildcard $(abspath ../../../vmlinux))","")
> >> +  VMLINUX_BTF := $(abspath ../../../vmlinux)
> >
> > I'm planning to mirror runqslower into libbpf Github repo and this
> > ../../../vmlinux piece will be completely out of place in that
> > context. Also it only will help when building kernel in-tree. So I'd
> > rather not add this.
>
> Well building the kernel in-tree is something people sometimes want to do ;)
>
> Specifically, the selftests depend on this, so we should at least fix
> those; but I guess it could work to just pass in VMLINUX_BTF as part of
> the make -C from the selftests dir? I'll try that...

Yes, it can be handled through VMLINUX_BTF override for selftests. As
I said, this will be a self-contained example in libbpf's Github repo,
so this "in kernel tree" assumption doesn't stand there.


>
> -Toke
>

  reply index

Thread overview: 25+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-01-15 14:12 [PATCH bpf-next v2 00/10] tools: Use consistent libbpf include paths everywhere Toke Høiland-Jørgensen
2020-01-15 14:12 ` [PATCH bpf-next v2 01/10] samples/bpf: Don't try to remove user's homedir on clean Toke Høiland-Jørgensen
2020-01-15 15:21   ` Jesper Dangaard Brouer
2020-01-15 14:12 ` [PATCH bpf-next v2 02/10] tools/bpf/runqslower: Fix override option for VMLINUX_BTF Toke Høiland-Jørgensen
2020-01-15 16:59   ` Andrii Nakryiko
2020-01-15 22:06     ` Toke Høiland-Jørgensen
2020-01-15 22:31       ` Andrii Nakryiko [this message]
2020-01-16  9:05         ` Toke Høiland-Jørgensen
2020-01-16 17:14           ` Andrii Nakryiko
2020-01-15 14:12 ` [PATCH bpf-next v2 03/10] tools/runqslower: Use consistent include paths for libbpf Toke Høiland-Jørgensen
2020-01-15 14:12 ` [PATCH bpf-next v2 04/10] selftests: " Toke Høiland-Jørgensen
2020-01-15 14:12 ` [PATCH bpf-next v2 05/10] bpftool: " Toke Høiland-Jørgensen
2020-01-15 17:44   ` Andrii Nakryiko
2020-01-15 14:12 ` [PATCH bpf-next v2 06/10] perf: " Toke Høiland-Jørgensen
2020-01-15 14:12 ` [PATCH bpf-next v2 07/10] samples/bpf: " Toke Høiland-Jørgensen
2020-01-15 15:18   ` Jesper Dangaard Brouer
2020-01-15 15:41     ` Toke Høiland-Jørgensen
2020-01-15 14:12 ` [PATCH bpf-next v2 08/10] libbpf: Fix include of bpf_helpers.h when libbpf is installed on system Toke Høiland-Jørgensen
2020-01-15 14:12 ` [PATCH bpf-next v2 09/10] selftests: Remove tools/lib/bpf from include path Toke Høiland-Jørgensen
2020-01-15 17:22   ` Andrii Nakryiko
2020-01-15 14:12 ` [PATCH bpf-next v2 10/10] tools/runqslower: " Toke Høiland-Jørgensen
2020-01-15 18:06 ` [PATCH bpf-next v2 00/10] tools: Use consistent libbpf include paths everywhere Andrii Nakryiko
2020-01-15 22:10   ` Toke Høiland-Jørgensen
2020-01-15 21:19 ` Alexei Starovoitov
2020-01-15 22:09   ` Toke Høiland-Jørgensen

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