On Tue, Aug 18, 2020 at 6:37 PM Alexei Starovoitov <alexei.starovoitov@xxxxxxxxx> wrote: > > On Tue, Aug 18, 2020 at 06:31:51PM -0700, Andrii Nakryiko wrote: > > On Tue, Aug 18, 2020 at 6:21 PM Alexei Starovoitov > > <alexei.starovoitov@xxxxxxxxx> wrote: > > > > > > On Tue, Aug 18, 2020 at 03:39:12PM -0700, Andrii Nakryiko wrote: > > > > This patch set adds libbpf support to two new classes of CO-RE relocations: > > > > type-based (TYPE_EXISTS/TYPE_SIZE/TYPE_ID_LOCAL/TYPE_ID_TARGET) and enum > > > > value-vased (ENUMVAL_EXISTS/ENUMVAL_VALUE): > > > > > > > > LLVM patches adding these relocation in Clang: > > > > - __builtin_btf_type_id() ([0], [1], [2]); > > > > - __builtin_preserve_type_info(), __builtin_preserve_enum_value() ([3], [4]). > > > > > > I've applied patches 1-4, since they're somewhat indepedent of new features in 5+. > > > What should be the process to land the rest? > > > Land llvm first and add to bpf/README.rst that certain llvm commmits are necessary > > > to build the tests? > > > > Clang patches landed about two weeks ago, so they are already in Clang > > nightly builds. libbpf CI should work fine as it uses clang-12 nightly > > builds. > > > > > > > But CI will start failing. We can wait for that to be fixed, > > > but I wonder is there way to detect new clang __builtins automatically in > > > selftests and skip them if clang is too old? > > > > There is a way to detect built-ins availability (__has_builtin macro, > > [0]) from C code. If we want to do it from Makefile, though, we'd need > > to do feature detection similar to how we did reallocarray and > > libbpf-elf-mmap detection I just removed in the other patch set :). > > Then we'll also need to somehow blacklist tests. Maintaining that > > would be a pain, honestly. So far selftests/bpf assumed the latest > > Clang, though, so do you think we should change that, or you were > > worried that patches hadn't landed yet? > > I was hoping that libbpf.h can have builtins unconditionally, but selftests can > do feature detection automatically and mark them as 'skip'. > People have been forever complaining about constant need to upgrade clang. > In this case I think the feature is not fundamental enough (unlike the first > set of builtins) to force adoption of new clang. > If/when we start using these new builtins beyond selftests > that would be a different story. Ok, took some tinkering to do this for btf_type_id() tests, but everything works now as you described above. Posted v2.
