[bpf-next,v4,02/10] tools/bpf/runqslower: Fix override option for VMLINUX_BTF

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.

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@redhat.com>
---
 tools/bpf/runqslower/Makefile |   18 +++++++++---------
 1 file changed, 9 insertions(+), 9 deletions(-)

On Fri, Jan 17, 2020 at 5:37 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.
>
> 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@redhat.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)                         \
>

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

> On Fri, Jan 17, 2020 at 5:37 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.
>>
>> 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@redhat.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