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Message-ID: <CAJ+HfNi4Ht_+a7+-NWE0LLfGRXJDq1g0cpuyshHY=BJ-+UX4ig@mail.gmail.com> Date: Tue, 10 Dec 2019 06:32:45 +0100 From: Björn Töpel <bjorn.topel@...il.com> To: Luke Nelson <lukenels@...washington.edu> Cc: Daniel Borkmann <daniel@...earbox.net>, Alexei Starovoitov <ast@...nel.org>, Netdev <netdev@...r.kernel.org>, linux-riscv@...ts.infradead.org, bpf <bpf@...r.kernel.org>, Xi Wang <xi.wang@...il.com> Subject: Re: [PATCH bpf-next 2/8] riscv, bpf: add support for far branching On Mon, 9 Dec 2019 at 22:08, Luke Nelson <lukenels@...washington.edu> wrote: > > On Mon, Dec 9, 2019 at 9:32 AM Björn Töpel <bjorn.topel@...il.com> wrote: > > > > This commit adds branch relaxation to the BPF JIT, and with that > > support for far (offset greater than 12b) branching. > > > > The branch relaxation requires more than two passes to converge. For > > most programs it is three passes, but for larger programs it can be > > more. > > > > Signed-off-by: Björn Töpel <bjorn.topel@...il.com> > > We have been developing a formal verification tool for BPF JIT > compilers, which we have used in the past to find bugs in the RV64 > and x32 BPF JITs: > > https://unsat.cs.washington.edu/projects/serval/ > > Recently I added support for verifying the JIT for branch and jump > instructions, and thought it a good opportunity to verify these > patches that add support for far jumps and branching. > > I ported these patches to our tool and ran verification, which > didn't find any bugs according to our specification of BPF and > RISC-V. > > The tool and code are publicly available, and you can read a more > detailed writeup of the results here: > > https://github.com/uw-unsat/bpf-jit-verif/tree/far-jump-review > > Currently the tool works on a manually translated version of the > JIT from C to Rosette, but we are experimenting with ways of making > this process more automated. > > > Reviewed-by: Luke Nelson <lukenels@...washington.edu> > Cc: Xi Wang <xi.wang@...il.com> Wow! Very cool! Thanks a bunch for this!
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