program: relocation of program targeting a module fails if CONFIG_DEBUG_INFO_BTF_MODULES is disabled about ebpf

[lmb]

Thanks for the detailed report. @brycekahle maybe this is as easy as not generating an error if module BTF doesn't exist?

[brycekahle]

Yeah, that would probably work. If the program needs the module BTF then the CO-RE relocations will fail and poison the instructions. That error is a little harder to debug, but will still fail regardless.

[lmb]

The fix is going to be here somewhere:

ebpf/linker.go

Lines 149 to 155 in 7719d2f

	if kmodName != "" {
	kmodTarget, err := btf.LoadKernelModuleSpec(kmodName)
	if err != nil {
	return fmt.Errorf("load kernel module spec: %w", err)
	}
	targets = append(targets, kmodTarget)
	}

• LoadKernelModuleSpec should return a discernible error when the load fails due to the file not existing. Something like errors.Is(err, os.ErrNotFound).
• The code above should ignore the error if it is due to not being found.

@orishuss are you up for contributing a fix? We can probably test this by using a bogus kmodName and asserting that we don't get an error.