On Thu, Dec 10, 2020 at 5:59 PM Andrii Nakryiko <andrii@xxxxxxxxxx> wrote:
>
> bpf_testmod.ko build rule declared dependency on VMLINUX_BTF, but the variable
> itself was initialized after the rule was declared, which often caused
> bpf_testmod.ko to not be re-compiled. Fix by moving VMLINUX_BTF determination
> sooner.
>
> Also enforce bpf_testmod.ko recompilation when we detect that vmlinux image
> changed by removing bpf_testmod/bpf_testmod.ko. This is necessary to generate
> correct module's split BTF. Without it, Kbuild's module build logic might
> determine that nothing changed on the kernel side and thus bpf_testmod.ko
> shouldn't be rebuilt, so won't re-generate module BTF, which often leads to
> module's BTF with wrong string offsets against vmlinux BTF. Removing .ko file
> forces Kbuild to re-build the module.
>
> Reported-by: Alexei Starovoitov <ast@xxxxxxxxxx>
> Fixes: 9f7fa225894c ("selftests/bpf: Add bpf_testmod kernel module for testing")
> Signed-off-by: Andrii Nakryiko <andrii@xxxxxxxxxx>
Applied. Thanks
