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Date:   Tue, 19 Jan 2021 11:31:43 -0300
From:   Arnaldo Carvalho de Melo <acme@kernel.org>
To:     Song Liu <songliubraving@fb.com>
Cc:     open list <linux-kernel@vger.kernel.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@redhat.com>,
        Alexander Shishkin <alexander.shishkin@linux.intel.com>,
        Namhyung Kim <namhyung@kernel.org>,
        Mark Rutland <mark.rutland@arm.com>,
        Jiri Olsa <jolsa@redhat.com>, Kernel Team <Kernel-team@fb.com>
Subject: Re: [PATCH v7 3/3] perf-stat: enable counting events for BPF programs
Message-ID: <20210119143143.GJ12699@kernel.org>
References: <20201229214214.3413833-1-songliubraving@fb.com>
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 <20210118193817.GG12699@kernel.org>
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Em Tue, Jan 19, 2021 at 12:48:19AM +0000, Song Liu escreveu:
> > On Jan 18, 2021, at 11:38 AM, Arnaldo Carvalho de Melo <acme@kernel.org> wrote:
> We are looking at two issues:
> 1. Cannot recursively attach;
> 2. prog FD 3 doesn't have valid btf. 
 
> #1 was caused by the verifier disallowing attaching fentry/fexit program 
> to program with type BPF_PROG_TYPE_TRACING (in bpf_check_attach_target). 
> This constraint was added when we only had fentry/fexit in the TRACING
> type. We have extended the TRACING type to many other use cases, like 
> "tp_btf/", "fmod_ret" and "iter/". Therefore, it is good time to revisit 
> this constraint. I will work on this. 
 
> For #2, we require the target program to have BTF. I guess we won't remove
> this requirement.
 
> While I work on improving #1, could you please test with some kprobe 
> programs? For example, we can use fileslower.py from bcc. 

Sure, and please consider improving the error messages to state what you
described above.

- Arnaldo