On Wed, Dec 11, 2019 at 01:30:13PM +0100, Björn Töpel wrote:
> +
> +#define DEFINE_BPF_DISPATCHER(name) \
> + unsigned int name##func( \
> + const void *xdp_ctx, \
> + const struct bpf_insn *insnsi, \
> + unsigned int (*bpf_func)(const void *, \
> + const struct bpf_insn *)) \
> + { \
> + return bpf_func(xdp_ctx, insnsi); \
> + } \
> + EXPORT_SYMBOL(name##func); \
> + struct bpf_dispatcher name = BPF_DISPATCHER_INIT(name);
The dispatcher function is a normal function. EXPORT_SYMBOL doesn't make it
'noinline'. struct bpf_dispatcher takes a pointer to it and that address is
used for text_poke.
In patch 3 __BPF_PROG_RUN calls dfunc() from two places.
What stops compiler from inlining it? Or partially inlining it in one
or the other place?
I guess it works, because your compiler didn't inline it?
Could you share how asm looks for bpf_prog_run_xdp()
(where __BPF_PROG_RUN is called) and asm for name##func() ?
I hope my guess that compiler didn't inline it is correct. Then extra noinline
will not hurt and that's the only thing needed to avoid the issue.
