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

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Date:   Wed, 15 Jan 2020 08:59:15 -0800
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Toke Høiland-Jørgensen <toke@...hat.com>
Cc:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        Andrii Nakryiko <andriin@...com>,
        Doug Ledford <dledford@...hat.com>,
        Jason Gunthorpe <jgg@...pe.ca>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <jakub.kicinski@...ronome.com>,
        Jesper Dangaard Brouer <brouer@...hat.com>,
        John Fastabend <john.fastabend@...il.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Shuah Khan <shuah@...nel.org>,
        Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>,
        linux-rdma@...r.kernel.org,
        "open list:KERNEL SELFTEST FRAMEWORK" 
        <linux-kselftest@...r.kernel.org>,
        clang-built-linux@...glegroups.com
Subject: Re: [PATCH bpf-next v2 02/10] tools/bpf/runqslower: Fix override
 option for VMLINUX_BTF

On Wed, Jan 15, 2020 at 6:13 AM Toke Høiland-Jørgensen <toke@...hat.com> wrote:
>
> From: Toke Høiland-Jørgensen <toke@...hat.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@...hat.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))
>