Re: [PATCH bpf-next v2 02/10] tools/bpf/runqslower: Fix override option for VMLINUX_BTF

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 08:59:15 -0800
Message-ID: <CAEf4BzbqY8zivZy637Xy=iTECzBAYQ7vo=M7TvsLM2Yp12bJpg@mail.gmail.com> (raw)
In-Reply-To: <157909757089.1192265.9038866294345740126.stgit@toke.dk>

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)?

>
> 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.

> +  else
> +  $(error "Can't detect kernel BTF, use VMLINUX_BTF to specify it explicitly")
> +  endif
>  endif
>
>  abs_out := $(abspath $(OUTPUT))
>