Re: [RFC PATCH 0/3] RV64G eBPF JIT

["Björn Töpel" <bjorn.topel@gmail.com>]

Den tis 15 jan. 2019 kl 16:40 skrev Christoph Hellwig <hch@infradead.org>:
>
> Hi Björn,
>
> at least for me patch 3 didn't make it to the list.
>

Hmm, held back: "Your message to linux-riscv awaits moderator
approval". Exceeded the 40k limit.

I'll wait until the moderator wakes up (Palmer?).


Björn

> On Tue, Jan 15, 2019 at 09:35:15AM +0100, Björn Töpel wrote:
> > Hi!
> >
> > I've been hacking on a RV64G eBPF JIT compiler, and would like some
> > feedback.
> >
> > Codewise, it needs some refactoring. Currently there's a bit too much
> > copy-and-paste going on, and I know some places where I could optimize
> > the code generation a bit (mostly BPF_K type of instructions, dealing
> > with immediates).
> >
> > From a features perspective, two things are missing:
> >
> > * tail calls
> > * "far-branches", i.e. conditional branches that reach beyond 13b.
> >
> > The test_bpf.ko (only tested on 4.20!) passes all tests.
> >
> > I've done all the tests on QEMU (version 3.1.50), so no real hardware.
> >
> > Some questions/observations:
> >
> > * I've added "HAVE_EFFICIENT_UNALIGNED_ACCESS" to
> >   arch/riscv/Kconfig. Is this assumption correct?
> >
> > * emit_imm() just relies on lui, adds and shifts. No fancy xori cost
> >   optimizations like GCC does.
> >
> > * Suggestions on how to implement the tail call, given that the
> >   prologue/epilogue has variable size. I will dig into the details of
> >   mips/arm64/x86. :-)
> >
> > Next steps (prior patch proper) is cleaning up the code, add tail
> > calls, and making sure that bpftool disassembly works correctly.
> >
> > All input are welcome. This is my first RISC-V hack, so I sure there
> > are a lot things to improve!
> >
> >
> > Thanks,
> > Björn
> >
> >
> > Björn Töpel (3):
> >   riscv: set HAVE_EFFICIENT_UNALIGNED_ACCESS
> >   riscv: add build infra for JIT compiler
> >   bpf, riscv: added eBPF JIT for RV64G
> >
> >  arch/riscv/Kconfig            |    2 +
> >  arch/riscv/Makefile           |    4 +
> >  arch/riscv/net/Makefile       |    5 +
> >  arch/riscv/net/bpf_jit_comp.c | 1612 +++++++++++++++++++++++++++++++++
> >  4 files changed, 1623 insertions(+)
> >  create mode 100644 arch/riscv/net/Makefile
> >  create mode 100644 arch/riscv/net/bpf_jit_comp.c
> >
> > --
> > 2.19.1
> >
> >
> > _______________________________________________
> > linux-riscv mailing list
> > linux-riscv@lists.infradead.org
> > http://lists.infradead.org/mailman/listinfo/linux-riscv
> ---end quoted text---

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