On Fri, Oct 28, 2022 at 11:57 AM Yonghong Song <yhs@xxxxxxxx> wrote:
>
>
>
> On 10/28/22 10:13 AM, Andrii Nakryiko wrote:
> > On Thu, Oct 27, 2022 at 6:33 PM Yonghong Song <yhs@xxxxxxxx> wrote:
> >>
> >>
> >>
> >> On 10/27/22 4:14 PM, Andrii Nakryiko wrote:
> >>> On Tue, Oct 25, 2022 at 3:28 PM Eduard Zingerman <eddyz87@xxxxxxxxx> wrote:
> >>>>
> >>>> Hi BPF community,
> >>>>
> >>>> AFAIK there is a long standing feature request to use kernel headers
> >>>> alongside `vmlinux.h` generated by `bpftool`. For example significant
> >>>> effort was put to add an attribute `bpf_dominating_decl` (see [1]) to
> >>>> clang, unfortunately this effort was stuck due to concerns regarding C
> >>>> language semantics.
> >>>>
> >>>
> >>> Maybe we should make another attempt to implement bpf_dominating_decl?
> >>> That seems like a more elegant solution than any other implemented or
> >>> discussed alternative. Yonghong, WDYT?
> >>
> >> I would say it would be very difficult for upstream to agree with
> >> bpf_dominating_decl. We already have lots of discussions and we
> >> likely won't be able to satisfy Aaron who wants us to emit
> >> adequate diagnostics which will involve lots of other work
> >> and he also thinks this is too far away from C standard and he
> >> wants us to implement in a llvm/clang tool which is not what
> >> we want.
> >
> > Ok, could we change the problem to detecting if some type is defined.
> > Would it be possible to have something like
> >
> > #if !__is_type_defined(struct abc)
> > struct abc {
> > };
> > #endif
> >
> > I think we talked about this and there were problems with this
> > approach, but I don't remember details and how insurmountable the
> > problem is. Having a way to check whether some type is defined would
> > be very useful even outside of -target bpf parlance, though, so maybe
> > it's the problem worth attacking?
>
> Yes, we discussed this before. This will need to add additional work
> in preprocessor. I just made a discussion topic in llvm discourse
>
> https://discourse.llvm.org/t/add-a-type-checking-macro-is-type-defined-type/66268
>
> Let us see whether we can get some upstream agreement or not.
>
Thanks for starting the conversation! I'll be following along.
> >
> >>
> >>>
> >>> BTW, I suggest splitting libbpf btf_dedup and btf_dump changes into a
> >>> separate series and sending them as non-RFC sooner. Those improvements
> >>> are independent of all the header guards stuff, let's get them landed
> >>> sooner.
> >>>
> >>>> After some discussion with Alexei and Yonghong I'd like to request
> >>>> your comments regarding a somewhat brittle and partial solution to
> >>>> this issue that relies on adding `#ifndef FOO_H ... #endif` guards in
> >>>> the generated `vmlinux.h`.
> >>>>
> >>>
> >>> [...]
> >>>
> >>>> Eduard Zingerman (12):
> >>>> libbpf: Deduplicate unambigous standalone forward declarations
> >>>> selftests/bpf: Tests for standalone forward BTF declarations
> >>>> deduplication
> >>>> libbpf: Support for BTF_DECL_TAG dump in C format
> >>>> selftests/bpf: Tests for BTF_DECL_TAG dump in C format
> >>>> libbpf: Header guards for selected data structures in vmlinux.h
> >>>> selftests/bpf: Tests for header guards printing in BTF dump
> >>>> bpftool: Enable header guards generation
> >>>> kbuild: Script to infer header guard values for uapi headers
> >>>> kbuild: Header guards for types from include/uapi/*.h in kernel BTF
> >>>> selftests/bpf: Script to verify uapi headers usage with vmlinux.h
> >>>> selftests/bpf: Known good uapi headers for test_uapi_headers.py
> >>>> selftests/bpf: script for infer_header_guards.pl testing
> >>>>
> >>>> scripts/infer_header_guards.pl | 191 +++++
> >>>> scripts/link-vmlinux.sh | 13 +-
> >>>> tools/bpf/bpftool/btf.c | 4 +-
> >>>> tools/lib/bpf/btf.c | 178 ++++-
> >>>> tools/lib/bpf/btf.h | 7 +-
> >>>> tools/lib/bpf/btf_dump.c | 232 +++++-
> >>>> .../selftests/bpf/good_uapi_headers.txt | 677 ++++++++++++++++++
> >>>> tools/testing/selftests/bpf/prog_tests/btf.c | 152 ++++
> >>>> .../selftests/bpf/prog_tests/btf_dump.c | 11 +-
> >>>> .../bpf/progs/btf_dump_test_case_decl_tag.c | 39 +
> >>>> .../progs/btf_dump_test_case_header_guards.c | 94 +++
> >>>> .../bpf/test_uapi_header_guards_infer.sh | 33 +
> >>>> .../selftests/bpf/test_uapi_headers.py | 197 +++++
> >>>> 13 files changed, 1816 insertions(+), 12 deletions(-)
> >>>> create mode 100755 scripts/infer_header_guards.pl
> >>>> create mode 100644 tools/testing/selftests/bpf/good_uapi_headers.txt
> >>>> create mode 100644 tools/testing/selftests/bpf/progs/btf_dump_test_case_decl_tag.c
> >>>> create mode 100644 tools/testing/selftests/bpf/progs/btf_dump_test_case_header_guards.c
> >>>> create mode 100755 tools/testing/selftests/bpf/test_uapi_header_guards_infer.sh
> >>>> create mode 100755 tools/testing/selftests/bpf/test_uapi_headers.py
> >>>>
> >>>> --
> >>>> 2.34.1
> >>>>
