Re: [PATCH v2] selftests/bpf: clarify build error if no vmlinux

[Andrii Nakryiko]

On Tue, Dec 15, 2020 at 10:20 AM Kamal Mostafa <kamal@xxxxxxxxxxxxx> wrote:
>
> If Makefile cannot find any of the vmlinux's in its VMLINUX_BTF_PATHS list,
> it tries to run btftool incorrectly, with VMLINUX_BTF unset:
>
>     bpftool btf dump file $(VMLINUX_BTF) format c
>
> Such that the keyword 'format' is misinterpreted as the path to vmlinux.
> The resulting build error message is fairly cryptic:
>
>       GEN      vmlinux.h
>     Error: failed to load BTF from format: No such file or directory
>
> This patch makes the failure reason clearer by yielding this instead:
>
>     Makefile:...: *** cannot find a vmlinux for VMLINUX_BTF at any of
>     "{paths}".  Stop.
>
> Fixes: acbd06206bbb ("selftests/bpf: Add vmlinux.h selftest exercising tracing of syscalls")
> Cc: stable@xxxxxxxxxxxxxxx # 5.7+
> Signed-off-by: Kamal Mostafa <kamal@xxxxxxxxxxxxx>
> ---

Applied to bpf tree, thanks. This conflicted with a67079b03165
("selftests/bpf: fix bpf_testmod.ko recompilation logic"), I resolved
the conflict and capitalized "Cannot" in the error message.

>
> [v2] moves the check to right after the VMLINUX_BTF definition.
>
>  tools/testing/selftests/bpf/Makefile | 3 +++
>  1 file changed, 3 insertions(+)
>
> diff --git a/tools/testing/selftests/bpf/Makefile b/tools/testing/selftests/bpf/Makefile
> index 542768f5195b..7ba631f495f7 100644
> --- a/tools/testing/selftests/bpf/Makefile
> +++ b/tools/testing/selftests/bpf/Makefile
> @@ -146,6 +146,9 @@ VMLINUX_BTF_PATHS ?= $(if $(O),$(O)/vmlinux)                                \
>                      /sys/kernel/btf/vmlinux                            \
>                      /boot/vmlinux-$(shell uname -r)
>  VMLINUX_BTF ?= $(abspath $(firstword $(wildcard $(VMLINUX_BTF_PATHS))))
> +ifeq ($(VMLINUX_BTF),)
> +$(error cannot find a vmlinux for VMLINUX_BTF at any of "$(VMLINUX_BTF_PATHS)")
> +endif
>
>  DEFAULT_BPFTOOL := $(SCRATCH_DIR)/sbin/bpftool
>
> --
> 2.17.1
>