[bpf-next,v3,02/11] tools/bpf/runqslower: Fix override option for VMLINUX_BTF
diff mbox series

Message ID 157918093389.1357254.10041649215380772130.stgit@toke.dk
State New
Headers show
Series
  • tools: Use consistent libbpf include paths everywhere
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Commit Message

Toke Høiland-Jørgensen Jan. 16, 2020, 1:22 p.m. UTC
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, 10 insertions(+), 8 deletions(-)

Comments

Andrii Nakryiko Jan. 16, 2020, 6:54 p.m. UTC | #1
On Thu, Jan 16, 2020 at 5:23 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>
> ---
>  tools/bpf/runqslower/Makefile |   18 ++++++++++--------
>  1 file changed, 10 insertions(+), 8 deletions(-)
>
> diff --git a/tools/bpf/runqslower/Makefile b/tools/bpf/runqslower/Makefile
> index cff2fbcd29a8..89fb7cd30f1a 100644
> --- a/tools/bpf/runqslower/Makefile
> +++ b/tools/bpf/runqslower/Makefile
> @@ -10,12 +10,14 @@ 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")
> +VMLINUX_BTF_PATHS := $(VMLINUX_BTF) /sys/kernel/btf/vmlinux /boot/vmlinux-$(KERNEL_REL)
> +VMLINUX_BTF_PATH := $(firstword $(wildcard $(VMLINUX_BTF_PATHS)))

If user specifies VMLINUX_BTF pointing to non-existing file, but the
system has /sys/kernel/btf/vmlinux, the latter will still be used,
which is a very surprising behavior.

Also MAKECMDGOALS feels like a fragile hack to me. How about we move
this VMLINUX_BTF guessing (without $(error)) into vmlinux.h rule
itself and use shell if conditional after it to check for file
existance and print nice error. That way we'll be checking VMLINUX_BTF
only when it's really needed.

> +
> +ifeq ("$(VMLINUX_BTF_PATH)","")
> +ifneq ($(MAKECMDGOALS),clean)
> +$(error Could not find kernel BTF file (tried: $(VMLINUX_BTF_PATHS)). \
> +       Try setting $$VMLINUX_BTF)
> +endif
>  endif
>
>  abs_out := $(abspath $(OUTPUT))
> @@ -67,9 +69,9 @@ $(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 > $@
> +       $(Q)$(BPFTOOL) btf dump file $(VMLINUX_BTF_PATH) format c > $@
>
>  $(OUTPUT)/libbpf.a: | $(OUTPUT)
>         $(Q)$(MAKE) $(submake_extras) -C $(LIBBPF_SRC)                         \
>
Toke Høiland-Jørgensen Jan. 17, 2020, 9:44 a.m. UTC | #2
Andrii Nakryiko <andrii.nakryiko@gmail.com> writes:

> On Thu, Jan 16, 2020 at 5:23 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>
>> ---
>>  tools/bpf/runqslower/Makefile |   18 ++++++++++--------
>>  1 file changed, 10 insertions(+), 8 deletions(-)
>>
>> diff --git a/tools/bpf/runqslower/Makefile b/tools/bpf/runqslower/Makefile
>> index cff2fbcd29a8..89fb7cd30f1a 100644
>> --- a/tools/bpf/runqslower/Makefile
>> +++ b/tools/bpf/runqslower/Makefile
>> @@ -10,12 +10,14 @@ 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")
>> +VMLINUX_BTF_PATHS := $(VMLINUX_BTF) /sys/kernel/btf/vmlinux /boot/vmlinux-$(KERNEL_REL)
>> +VMLINUX_BTF_PATH := $(firstword $(wildcard $(VMLINUX_BTF_PATHS)))
>
> If user specifies VMLINUX_BTF pointing to non-existing file, but the
> system has /sys/kernel/btf/vmlinux, the latter will still be used,
> which is a very surprising behavior.

Hmm, yeah, good point.

> Also MAKECMDGOALS feels like a fragile hack to me. How about we move
> this VMLINUX_BTF guessing (without $(error)) into vmlinux.h rule
> itself and use shell if conditional after it to check for file
> existance and print nice error. That way we'll be checking VMLINUX_BTF
> only when it's really needed.

OK, sure, can do.

-Toke

Patch
diff mbox series

diff --git a/tools/bpf/runqslower/Makefile b/tools/bpf/runqslower/Makefile
index cff2fbcd29a8..89fb7cd30f1a 100644
--- a/tools/bpf/runqslower/Makefile
+++ b/tools/bpf/runqslower/Makefile
@@ -10,12 +10,14 @@  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")
+VMLINUX_BTF_PATHS := $(VMLINUX_BTF) /sys/kernel/btf/vmlinux /boot/vmlinux-$(KERNEL_REL)
+VMLINUX_BTF_PATH := $(firstword $(wildcard $(VMLINUX_BTF_PATHS)))
+
+ifeq ("$(VMLINUX_BTF_PATH)","")
+ifneq ($(MAKECMDGOALS),clean)
+$(error Could not find kernel BTF file (tried: $(VMLINUX_BTF_PATHS)). \
+	Try setting $$VMLINUX_BTF)
+endif
 endif
 
 abs_out := $(abspath $(OUTPUT))
@@ -67,9 +69,9 @@  $(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 > $@
+	$(Q)$(BPFTOOL) btf dump file $(VMLINUX_BTF_PATH) format c > $@
 
 $(OUTPUT)/libbpf.a: | $(OUTPUT)
 	$(Q)$(MAKE) $(submake_extras) -C $(LIBBPF_SRC)			       \