Subject: Re: [PATCH v11 net-next 12/12] bpf: mini eBPF library, test stubs and verifier testsuite

From: Daniel Borkmann <[email-masked]>
Date: Wed, 17 Sep 2014 09:16:18 +0200

On 09/10/2014 08:08 PM, Alexei Starovoitov wrote:
> On Wed, Sep 10, 2014 at 4:35 AM, Daniel Borkmann <[email-masked]> wrote:
>>
>> Since we already have an extensive BPF test suite, that is, lib/test_bpf.c,
>> which currently also does sanity checks for the classic BPF verifier, is
>> there a reason these verifier test cases cannot be extended/integrated there
>> as well but have to go to kernel/bpf/test_stub.c resp.
>> samples/bpf/test_verifier.c ?
>> I don't like that we put testing code into kernel/bpf/ whereas we already
>> have a BPF test infrastructure in the kernel elsewhere.
>
> yes. there is a reason. Verifier needs to be tested from user space,
> since it works on fds. Process local map_fd are part of the eBPF
> programs. Therefore one is testing things from kernel and
> another from userspace. We definitely need both.
> Currently there is no use case to call verifier from inside
> the kernel. I'm not sure there will be one. Verifier's main
> purpose is to check user supplied programs and provide
> humans an understandable error messages of what
> is 'unsafe' in particular program.
> Eventually we will integrate this verifier messages with
> program compilation. Like, the user would write a program
> in C then invoke a wrapper of compiler and verifier, which
> will point to lines in C code which are doing something
> wrong like loops or out of bounds access. Currently verifier
> complains about particular 'unsafe' instruction, but
> humans have hard time correlating asm to C.

That actually still doesn't answer my question why the test stub
cannot live in lib/test_bpf where we have our actual testing
framework for eBPF/BPF, also since you exactly only build test_stub.c
when TEST_BPF is enabled which is the Kconfig for lib/test_bpf.