On Tue, 10 Sep 2024 11:23:29 -0700 Andrii Nakryiko <andrii.nakryiko@xxxxxxxxx> wrote: > + arm ML and maintainers > > On Wed, Sep 4, 2024 at 6:02 PM Andrii Nakryiko > <andrii.nakryiko@xxxxxxxxx> wrote: > > > > Hey, > > > > I just recently realized that we are still missing multi-kprobe > > support for ARM64, which depends on CONFIG_FPROBE. And CONFIG_FPROBE > > seems to require CONFIG_HAVE_RETHOOK, which, it turns out, is not > > implemented for ARM64. > > > > It took me a while to realize what's going on, as I roughly remembered > > (and confirmed through lore search) that Masami's original rethook > > patches had arm64-specific bits. Long story short: > > > > 0f8f8030038a Revert "arm64: rethook: Add arm64 rethook implementation" > > 83acdce68949 arm64: rethook: Add arm64 rethook implementation > > > > The patch was landed and then reverted. I found some discussion online > > and it seems like the plan was to land arch-specific bits shortly > > after bpf-next PR. > > > > But it seems like that never happened. Why? > > > > I see s390x, RISC-V, loongarch (I'm not even mentioning x86-64) all > > have CONFIG_HAVE_RETHOOK, even powerpc is getting one (see [0]), it > > seems. How come ARM64 is the one left out? > > > > Can anyone please provide some context? And if that's just an > > oversight, can we prioritize landing this for ARM64 ASAP? > > > > [0] https://lore.kernel.org/bpf/20240830113131.7597-1-adubey@xxxxxxxxxxxxx/ > > > > Masami, Steven, > > Does Linus have to be in CC to get any reply here? Come on, it's been > almost a full week. Sorry about bothering you, let me check that. But I think we eventually need my fprobe-on-fgraph patch which allows all architecture uses ftrace_regs instead of pt_regs for ftrace/fgraph users. That allows arm64 to implement fprobe. > > Maybe ARM64 folks have some context?... And hopefully desire to see > this through so that ARM64 doesn't stick out as a lesser-supported > platform as far as tracing goes compared to loongarch, s390x, and > powerpc (which just landed rethook support, see [2]). I think lesser-supported or not is not a matter, but they need to keep their architecutre healthy. Mark said that the current rethook implementation is not acceptable because arm64 can not manually generate pt_regs. So we need to use ftrace_regs for that. So eventually, we need my fprobe series. https://lore.kernel.org/bpf/164338038439.2429999.17564843625400931820.stgit@devnote2/ Thank you, > > Note that there was already an implementation (see [1]), but for some > reason it never made it. > > [1] https://lore.kernel.org/bpf/164338038439.2429999.17564843625400931820.stgit@devnote2/ > [2] https://lore.kernel.org/bpf/172562357215.467568.2172858907419105155.b4-ty@xxxxxxxxxxxxxx/ > > > > > -- Andrii -- Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>
