linux-kernel - Re: [PATCH] powerpc/ftrace: fix syscall tracing on PPC64_ELF_ABI

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Date:   Tue, 06 Dec 2022 09:50:08 +1100
From:   Michael Ellerman <mpe@...erman.id.au>
To:     Michael Jeanson <mjeanson@...icios.com>,
        Christophe Leroy <christophe.leroy@...roup.eu>,
        Steven Rostedt <rostedt@...dmis.org>
Cc:     "stable@...r.kernel.org" <stable@...r.kernel.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Nicholas Piggin <npiggin@...il.com>,
        Michal Suchanek <msuchanek@...e.de>,
        "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Subject: Re: [PATCH] powerpc/ftrace: fix syscall tracing on PPC64_ELF_ABI_V1

Michael Jeanson <mjeanson@...icios.com> writes:
> On 2022-12-05 15:11, Michael Jeanson wrote:
>>>>> Michael Jeanson <mjeanson@...icios.com> writes:
>>>>>> In v5.7 the powerpc syscall entry/exit logic was rewritten in C, on
>>>>>> PPC64_ELF_ABI_V1 this resulted in the symbols in the syscall table
>>>>>> changing from their dot prefixed variant to the non-prefixed ones.
>>>>>>
>>>>>> Since ftrace prefixes a dot to the syscall names when matching them to
>>>>>> build its syscall event list, this resulted in no syscall events being
>>>>>> available.
>>>>>>
>>>>>> Remove the PPC64_ELF_ABI_V1 specific version of
>>>>>> arch_syscall_match_sym_name to have the same behavior across all powerpc
>>>>>> variants.
>>>>>
>>>>> This doesn't seem to work for me.
>>>>>
>>>>> Event with it applied I still don't see anything in
>>>>> /sys/kernel/debug/tracing/events/syscalls
>>>>>
>>>>> Did we break it in some other way recently?
>>>>>
>>>>> cheers
>
> I did some further testing, my config also enabled KALLSYMS_ALL, when I remove 
> it there is indeed no syscall events.

Aha, OK that explains it I guess.

I was using ppc64_guest_defconfig which has ABI_V1 and FTRACE_SYSCALLS,
but does not have KALLSYMS_ALL. So I guess there's some other bug
lurking in there.

cheers