linux-kernel - Re: [PATCH bpf-next v4 02/10] tools/bpf/runqslower: Fix override option for VMLINUX

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Date:   Mon, 20 Jan 2020 12:04:09 +0100
From:   Toke Høiland-Jørgensen <toke@...hat.com>
To:     Andrii Nakryiko <andrii.nakryiko@...il.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

Andrii Nakryiko <andrii.nakryiko@...il.com> writes:

> 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

OK.

>>
>>  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 @

This was actually deliberate, since I was replacing an $(error) (which
doesn't show up in V=1 output). But OK, I guess we can output the whole
if statement as well on verbose builds...

>> +               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

Right, I'll try to fix those up (for the whole series). My emacs is
being a bit weird with displaying tabstops, so some of these look
aligned when I'm editing. I'll see if I can figure out how to fix this
so it becomes obvious while I'm making changes...

-Toke