Re: [PATCH v2 bpf 3/5] bpf: enforce types for __arg_ctx-tagged arguments in global subprogs

[Eduard Zingerman <eddyz87@gmail.com>]

On Wed, 2024-01-17 at 14:33 -0800, Andrii Nakryiko wrote:
[...]

>   - for kprobes, we always accept `struct pt_regs *`, as that's what
>     actually is passed as a context to any kprobe program;
>   - for perf_event, we resolve typedefs down to actual struct type and
>     accept `struct {pt_regs,user_pt_regs,user_regs_struct} *` if kernel
>     architecture actually defines `bpf_user_pt_regs_t` as an alias for
>     the corresponding struct;
>     otherwise, canonical `struct bpf_perf_event_data *` is expected;
>   - for raw_tp/raw_tp.w programs, `u64/long *` are accepted, as that's
>     what's expected with BPF_PROG() usage; otherwise, canonical
>     `struct bpf_raw_tracepoint_args *` is expected;
>   - tp_btf supports both `struct bpf_raw_tracepoint_args *` and `u64 *`
>     formats, both are coded as expections as tp_btf is actually a TRACING
>     program type, which has no canonical context type;
>   - iterator programs accept `struct bpf_iter__xxx *` structs, currently
>     with no further iterator-type specific enforcement;
>   - fentry/fexit/fmod_ret/lsm/struct_ops all accept `u64 *`;
>   - classic tracepoint programs, as well as syscall and freplace
>     programs allow any user-provided type.

The "arg:..." rules become quite complex, do you plan to document
these either in kernel rst's or as doc-strings for relevant macros?

[...]