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Message-ID: <20190115154012.GG26443@infradead.org>
Date:   Tue, 15 Jan 2019 07:40:12 -0800
From:   Christoph Hellwig <hch@...radead.org>
To:     Björn Töpel <bjorn.topel@...il.com>
Cc:     linux-riscv@...ts.infradead.org, palmer@...ive.com,
        davidlee@...ive.com, daniel@...earbox.net, netdev@...r.kernel.org
Subject: Re: [RFC PATCH 0/3] RV64G eBPF JIT

Hi Björn,

at least for me patch 3 didn't make it to the list.

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@...ts.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-riscv
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