linux-kernel - Re: [PATCH v1 0/5] Implement livepatch on PPC32

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Message-ID: <fd778195-8c5c-e6c3-c119-365730f6035a@csgroup.eu>
Date:   Tue, 14 Dec 2021 15:12:54 +0000
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     Heiko Carstens <hca@...ux.ibm.com>
CC:     Steven Rostedt <rostedt@...dmis.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Jiri Kosina <jikos@...nel.org>,
        Miroslav Benes <mbenes@...e.cz>,
        Petr Mladek <pmladek@...e.com>,
        Joe Lawrence <joe.lawrence@...hat.com>,
        Ingo Molnar <mingo@...hat.com>,
        "Naveen N . Rao" <naveen.n.rao@...ux.vnet.ibm.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
        "live-patching@...r.kernel.org" <live-patching@...r.kernel.org>,
        "linux-s390@...r.kernel.org" <linux-s390@...r.kernel.org>
Subject: Re: [PATCH v1 0/5] Implement livepatch on PPC32



Le 14/12/2021 à 15:25, Heiko Carstens a écrit :
> On Mon, Dec 13, 2021 at 05:50:52PM +0000, Christophe Leroy wrote:
>> Le 13/12/2021 à 18:33, Steven Rostedt a écrit :
>>> On Mon, 13 Dec 2021 17:30:48 +0000
>>> Christophe Leroy <christophe.leroy@...roup.eu> wrote:
>>>
>>>> Thanks, I will try that.
>>>>
>>>> I can't find ftrace_graph_func() in s390. Does it mean that s390 doesn't
>>>> have a working function tracer anymore ?
>>>>
>>>> I see your commit 0c0593b45c9b4 ("x86/ftrace: Make function graph use
>>>> ftrace directly") is dated 8 Oct 2021 while 5740a7c71ab6 ("s390/ftrace:
>>>> add HAVE_DYNAMIC_FTRACE_WITH_ARGS support") is 4 Oct 2021.
>>>
>>> Hmm, maybe not. I can't test it.
>>>
>>> This needs to be fixed if that's the case.
>>>
>>> Thanks for bringing it up!
> 
> It still works, we run the full ftrace/kprobes selftests from the
> kernel every day on multiple machines with several kernels (besides
> other Linus' tree, but also linux-next). That said, I wanted to change
> s390's code follow what x86 is currently doing anyway.
> 
> One thing to note: commit 5740a7c71ab6 ("s390/ftrace: add
> HAVE_DYNAMIC_FTRACE_WITH_ARGS support") looks only that simple because
> ftrace_caller _and_ ftrace_regs_caller used to save all register
> contents into the pt_regs structure, which never was a requirement,
> but implicitly fulfills the HAVE_DYNAMIC_FTRACE_WITH_ARGS
> requirements.
> Not sure if powerpc passes enough register contents via pt_regs for
> HAVE_DYNAMIC_FTRACE_WITH_ARGS though. Might be something to check?
> 

In fact there is no need to rework the function graph logic. It still 
works as is with HAVE_DYNAMIC_FTRACE_WITH_ARGS.

The problem was that the sefltests were failing with 
CONFIG_DYNAMIC_FTRACE_WITH_DIRECT_CALLS not being selected on powerpc.

As s390 selects CONFIG_DYNAMIC_FTRACE_WITH_DIRECT_CALLS, there is no 
problem.

Thanks
Christophe