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Date:   Fri, 17 Jan 2020 13:30:31 -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 <kuba@...nel.org>,
        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 v4 02/10] tools/bpf/runqslower: Fix override
 option for VMLINUX_BTF

On Fri, Jan 17, 2020 at 5:37 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.
>
> Fix this by including the value of VMLINUX_BTF in the expansion, and only
> emitting the error message if the *result* is empty. Also permit running
> 'make clean' even though no VMLINUX_BTF is set.
>
> Fixes: 9c01546d26d2 ("tools/bpf: Add runqslower tool to tools/bpf")
> Signed-off-by: Toke Høiland-Jørgensen <toke@...hat.com>
> ---

approach looks good, thanks, few nits below

>  tools/bpf/runqslower/Makefile |   18 +++++++++---------
>  1 file changed, 9 insertions(+), 9 deletions(-)
>
> diff --git a/tools/bpf/runqslower/Makefile b/tools/bpf/runqslower/Makefile
> index cff2fbcd29a8..b62fc9646c39 100644
> --- a/tools/bpf/runqslower/Makefile
> +++ b/tools/bpf/runqslower/Makefile
> @@ -10,13 +10,9 @@ 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")
> -endif
> +VMLINUX_BTF_PATHS := /sys/kernel/btf/vmlinux /boot/vmlinux-$(KERNEL_REL)
> +VMLINUX_BTF_PATH := $(abspath $(or $(VMLINUX_BTF),$(firstword \
> +       $(wildcard $(VMLINUX_BTF_PATHS)))))

you can drop abspath, relative path for VMLINUX_BTF would work just fine

>
>  abs_out := $(abspath $(OUTPUT))
>  ifeq ($(V),1)
> @@ -67,9 +63,13 @@ $(OUTPUT):
>         $(call msg,MKDIR,$@)
>         $(Q)mkdir -p $(OUTPUT)
>
> -$(OUTPUT)/vmlinux.h: $(VMLINUX_BTF) | $(OUTPUT) $(BPFTOOL)
> +$(OUTPUT)/vmlinux.h: $(VMLINUX_BTF_PATH) | $(OUTPUT) $(BPFTOOL)
>         $(call msg,GEN,$@)
> -       $(Q)$(BPFTOOL) btf dump file $(VMLINUX_BTF) format c > $@
> +       @if [ ! -e "$(VMLINUX_BTF_PATH)" ] ; then \

$(Q), not @

> +               echo "Couldn't find kernel BTF; set VMLINUX_BTF to specify its location."; \
> +               exit 1;\

nit: please align \'s (same above for VMLONUX_BTF_PATH) at the right
edge as it's done everywhere in this Makefile

> +       fi
> +       $(Q)$(BPFTOOL) btf dump file $(VMLINUX_BTF_PATH) format c > $@
>
>  $(OUTPUT)/libbpf.a: | $(OUTPUT)
>         $(Q)$(MAKE) $(submake_extras) -C $(LIBBPF_SRC)                         \
>

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