linux-kernel - Re: bpf_errno. Was: [PATCH RFC bpf-next 1/3] bpf: report probe fault to BPF stderr

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Message-ID: <09bc63a92ba1c9042d57bf19258e28e3cd00be57.camel@gmail.com>
Date: Wed, 08 Oct 2025 13:30:19 -0700
From: Eduard Zingerman <eddyz87@...il.com>
To: Kumar Kartikeya Dwivedi <memxor@...il.com>
Cc: Alexei Starovoitov <alexei.starovoitov@...il.com>, Leon Hwang	
 <hffilwlqm@...il.com>, Andrii Nakryiko <andrii@...nel.org>, Menglong Dong	
 <menglong.dong@...ux.dev>, Menglong Dong <menglong8.dong@...il.com>, Alexei
 Starovoitov <ast@...nel.org>, bpf <bpf@...r.kernel.org>, LKML
 <linux-kernel@...r.kernel.org>,  linux-trace-kernel
 <linux-trace-kernel@...r.kernel.org>, jiang.biao@...ux.dev
Subject: Re: bpf_errno. Was: [PATCH RFC bpf-next 1/3] bpf: report probe
 fault to BPF stderr

On Wed, 2025-10-08 at 22:08 +0200, Kumar Kartikeya Dwivedi wrote:

[...]

> Since we're piling on ideas, one of the other things that I think
> could be useful in general (and maybe should be done orthogonally to
> bpf_errno)
> is making some empty nop function and making it not traceable reliably
                                                  ^^^^^^^^^^^^^
                                   You mean traceable, right?
		   So that user attaches a bpf program to it,
		  and debugs bpf programs using bpf programs?

> across arches and invoke it in the bpf exception handler.
> Then if we expose prog_stream_dump_stack() as a kfunc (should be
> trivial), the user can write anything to stderr that is relevant to
> get more information on the fault.
> 
> It is then up to the user to decide the rate of messages for such
> faults etc. and get more information if needed.