Re: [PATCH v4 3/9] bpf/btf: Add a function to search a member of a struct/union

[Alexei Starovoitov]

On Wed, Aug 2, 2023 at 11:38 AM Steven Rostedt <rostedt@xxxxxxxxxxx> wrote:
>
> On Wed, 2 Aug 2023 11:24:12 -0700
> Alexei Starovoitov <alexei.starovoitov@xxxxxxxxx> wrote:
>
> > This is a non starter.
> > bpf progs expect arch dependent 'struct pt_regs *' and we cannot change that.
>
> If the progs are compiled into native code, isn't there optimizations that
> could be done? That is, if ftrace_regs is available, and the bpf program is
> just using the subset of pt_regs, is it possible that it could be compiled
> to use ftrace_regs?
>
> Forgive my ignorance on how BPF programs turn into executables when running
> in the kernel.

Right. It's possible for the verifier to do an offset rewrite,
forbid certain access, always return 0 on load from certain offset,
and so on.
It's all non trivial amount of work.
ftrace_partial_regs() from ftrace_regs into pt_regs is so much simpler.