On 04/23/2019 06:06 AM, Andrii Nakryiko wrote:
> On Mon, Apr 22, 2019 at 5:58 PM Daniel Borkmann <daniel@xxxxxxxxxxxxx> wrote:
>> On 04/19/2019 03:18 AM, Andrii Nakryiko wrote:
>>> On Tue, Apr 9, 2019 at 2:20 PM Daniel Borkmann <daniel@xxxxxxxxxxxxx> wrote:
>>>>
>> [...]
>>>> + def->type = BPF_MAP_TYPE_ARRAY;
>>>> + def->key_size = sizeof(int);
>>>> + def->value_size = data->d_size;
>>>> + def->max_entries = 1;
>>>> + def->map_flags = type == LIBBPF_MAP_RODATA ?
>>>> + BPF_F_RDONLY_PROG : 0;
>>>
>>> This is breaking BPF programs (even those that don't use global data,
>>> as they still have .rodata section, though I haven't investigated its
>>> contents) on kernels that don't yet support BPF_F_RDONLY_PROG flag
>>> yet. We probably need to probe support for that flag first, before
>>> using it. Just giving heads up, as I just discovered it trying to sync
>>> libbpf on github.
>>
>> Thanks for reporting! On a quick look test_progs (modulo global data test)
>> seems to pass with an slightly older kernel. I'll retry with a latest LLVM git
>> tree tomorrow with our test suite. Did you see a specific one failing or do you
>> have a reproducer in case it's something not covered where I could look into?
>
> You need to add something like this to trigger .rodata section
> generation (BPF code doesn't have to use that struct, it just needs to
> be present):
>
> const struct { int x, y; } bla = {};
>
> This will cause libbpf to create a map for .rodata and specify
> BPF_F_RDONLY_PROG flag, which on older kernels will be rejected.
Fair enough, working on a fix in that case. Thanks!
