Re: [PATCH v4 net-next] arm: eBPF JIT compiler

[Daniel Borkmann]

On 08/22/2017 05:08 PM, Daniel Borkmann wrote:
> On 08/22/2017 08:36 AM, Shubham Bansal wrote:
> [...]
> > +
> > +static int out_offset = -1; /* initialized on the first pass of build_body() */
>
> Hm, why is this a global var actually? There can be
> multiple parallel calls to bpf_int_jit_compile(), we
> don't take a global lock on this. Unless I'm missing
> something this should really reside in jit_ctx, no?

Hm, okay, it's for generating the out jmp offsets in
tail call emission which are supposed to always be the
same relative offsets; should be fine then.

> Given this is on emit_bpf_tail_call(), did you get
> tail calls working the way I suggested to test?
>
> > +static int emit_bpf_tail_call(struct jit_ctx *ctx)
> >   {
> [...]
> > +    const int idx0 = ctx->idx;
> > +#define cur_offset (ctx->idx - idx0)
> > +#define jmp_offset (out_offset - (cur_offset))
> [...]
> > +
> > +    /* out: */
> > +    if (out_offset == -1)
> > +        out_offset = cur_offset;
> > +    if (cur_offset != out_offset) {
> > +        pr_err_once("tail_call out_offset = %d, expected %d!\n",
> > +                cur_offset, out_offset);
> > +        return -1;
> > +    }
> > +    return 0;
> > +#undef cur_offset
> > +#undef jmp_offset
> >   }