Re: [PATCH bpf-next 2/4] bpf, x64: Fix tailcall hierarchy

[Leon Hwang <hffilwlqm@gmail.com>]

On 2024/2/14 19:25, Maciej Fijalkowski wrote:
> On Wed, Feb 14, 2024 at 01:47:45PM +0800, Leon Hwang wrote:
>>
>>
>> On 2024/1/5 12:15, Alexei Starovoitov wrote:
>>> On Thu, Jan 4, 2024 at 6:23 AM Leon Hwang <hffilwlqm@gmail.com> wrote:
>>>>
>>>>
>>>
>>> Other alternatives?
>>
>> I've finish the POC of an alternative, which passed all tailcall
>> selftests including these tailcall hierarchy ones.
>>
>> In this alternative, I use a new bpf_prog_run_ctx to wrap the original
>> ctx and the tcc_ptr, then get the tcc_ptr and recover the original ctx
>> in JIT.
>>
>> Then, to avoid breaking runtime with tailcall on other arch, I add an
>> arch-related check bpf_jit_supports_tail_call_cnt_ptr() to determin
>> whether to use bpf_prog_run_ctx.
>>
>> Here's the diff:
> 
> This is diff against your previous proposed solution, would be good to see

The previous proposed solution is buggy, when I have a deep analysis.

> how it currently looks being put together (this diff on top of your
> patch), would save us some effort to dig the patch up and include diff.
> 

But, we can not apply this patch with this diff. It's because it breaks
the runtime with tailcall of bpf progs, whose runtime entry is not
__bpf_prog_run(), e.g. trampoline-based fentry/fexit/fmod_ret.

So, is there any other bpf prog types whose runtime entry is not either
__bpf_prog_run() or trampoline?

I'd like to fix them in PATCH v2.

Thanks,
Leon