On Tue, Jan 2, 2024 at 11:01 AM Andrii Nakryiko <andrii@xxxxxxxxxx> wrote:
>
> Support __arg_ctx global function argument tag semantics even on older kernels
> that don't natively support it through btf_decl_tag("arg:ctx").
>
> Patch #1 does a bunch of internal renaming to make internal function naming
> consistent. We were doing it lazily up until now, but mixing single and double
> underscored names are confusing, so let's bite a bullet and get it over the
> finish line in one go.
>
> Patches #3-#7 are preparatory work to allow to postpone BTF loading into the
> kernel until after all the BPF program relocations (including global func
> appending to main programs) are done. Patch #5 is perhaps the most important
> and establishes pre-created stable placeholder FDs, so that relocations can
> embed valid map FDs into ldimm64 instructions.
>
> Once BTF is done after relocation, what's left is to adjust BTF information to
> have each main program's copy of each used global subprog to point to its own
> adjusted FUNC -> FUNC_PROTO type chain (if they use __arg_ctx) in such a way
> as to satisfy type expectations of BPF verifier regarding the PTR_TO_CTX
> argument definition. See patch #8 for details.
>
> Patch #9 adds few more __arg_ctx use cases (edge cases like multiple arguments
> having __arg_ctx, etc) to test_global_func_ctx_args.c, to make it simple to
> validate that this logic indeed works on old kernels. It does.
>
Oops, I forgot to add version history. It's basically:
v1->v2:
- do internal functions renaming in patch #1 (Alexei);
- extract cloning of FUNC -> FUNC_PROTO information into separate
function (Alexei);
> Andrii Nakryiko (9):
> libbpf: name internal functions consistently
> libbpf: make uniform use of btf__fd() accessor inside libbpf
> libbpf: use explicit map reuse flag to skip map creation steps
> libbpf: don't rely on map->fd as an indicator of map being created
> libbpf: use stable map placeholder FDs
> libbpf: move exception callbacks assignment logic into relocation step
> libbpf: move BTF loading step after relocation step
> libbpf: implement __arg_ctx fallback logic
> selftests/bpf: add arg:ctx cases to test_global_funcs tests
>
> tools/lib/bpf/libbpf.c | 1055 ++++++++++-------
> tools/lib/bpf/libbpf_internal.h | 24 +
> .../bpf/progs/test_global_func_ctx_args.c | 49 +
> 3 files changed, 725 insertions(+), 403 deletions(-)
>
> --
> 2.34.1
>
