On Wed, Oct 20, 2021 at 05:05:02PM -0700, Alexei Starovoitov wrote:
> On Wed, Oct 20, 2021 at 01:09:51PM +0200, Peter Zijlstra wrote:
> > @@ -446,25 +440,8 @@ static void emit_bpf_tail_call_indirect(
> > {
> > int tcc_off = -4 - round_up(stack_depth, 8);
> > u8 *prog = *pprog, *start = *pprog;
> > - int pop_bytes = 0;
> > - int off1 = 42;
> > - int off2 = 31;
> > - int off3 = 9;
> > -
> > - /* count the additional bytes used for popping callee regs from stack
> > - * that need to be taken into account for each of the offsets that
> > - * are used for bailing out of the tail call
> > - */
> > - pop_bytes = get_pop_bytes(callee_regs_used);
> > - off1 += pop_bytes;
> > - off2 += pop_bytes;
> > - off3 += pop_bytes;
> > -
> > - if (stack_depth) {
> > - off1 += 7;
> > - off2 += 7;
> > - off3 += 7;
> > - }
> > + static int out_label = -1;
>
> Interesting idea!
I nicked it from emit_bpf_tail_call() in the 32bit jit :-) It seemed a
lot more robust than the 64bit one and I couldn't figure out why the
difference.
> All insn emits trying to do the right thing from the start.
> Here the logic assumes that there will be at least two passes over image.
> I think that is correct, but we never had such assumption.
That's not exactly true; I think image is NULL on every first run, so
all insn that depend on it will be wrong to start with. Equally there's
a number of insn that seem to depend on addrs[i], that also requires at
least two passes.
> A comment is certainly must have.
I can certainly add one, although I think we'll disagree on the comment
style :-)
> The race is possible too. Not sure whether READ_ONCE/WRITE_ONCE
> are really warranted though. Might be overkill.
Is there concurrency on the jit?
> Once you have a git branch with all the changes I can give it a go.
Ok, I'll go polish this thing and stick it in the tree mentioned in the
cover letter.
> Also you can rely on our BPF CI.
> Just cc your patchset to bpf@vger and add [PATCH bpf-next] to a subject.
> In patchwork there will be "bpf/vmtest-bpf-next" link that
> builds kernel, selftests and runs everything.
What's a patchwork and where do I find it?
> It's pretty much the same as selftests/bpf/vmtest.sh, but with the latest
> clang nightly and other deps like pahole.
nice.
