Date:   Tue, 14 Dec 2021 15:25:57 +0100
From:   Heiko Carstens <hca@linux.ibm.com>
To:     Christophe Leroy <christophe.leroy@csgroup.eu>
Cc:     Steven Rostedt <rostedt@goodmis.org>,
        Josh Poimboeuf <jpoimboe@redhat.com>,
        Jiri Kosina <jikos@kernel.org>,
        Miroslav Benes <mbenes@suse.cz>,
        Petr Mladek <pmladek@suse.com>,
        Joe Lawrence <joe.lawrence@redhat.com>,
        Ingo Molnar <mingo@redhat.com>,
        "Naveen N . Rao" <naveen.n.rao@linux.vnet.ibm.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "linuxppc-dev@lists.ozlabs.org" <linuxppc-dev@lists.ozlabs.org>,
        "live-patching@vger.kernel.org" <live-patching@vger.kernel.org>,
        "linux-s390@vger.kernel.org" <linux-s390@vger.kernel.org>
Subject: Re: [PATCH v1 0/5] Implement livepatch on PPC32
Message-ID: <YbipdU5X4HNDWIni@osiris>
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On Mon, Dec 13, 2021 at 05:50:52PM +0000, Christophe Leroy wrote:
> Le 13/12/2021 ? 18:33, Steven Rostedt a ?crit?:
> > On Mon, 13 Dec 2021 17:30:48 +0000
> > Christophe Leroy <christophe.leroy@csgroup.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?