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Date:   Mon, 14 Feb 2022 22:54:23 +0530
From:   "Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com>
Subject: Re: [PATCH v2 11/13] powerpc/ftrace: directly call of function graph
 tracer by ftrace caller
To:     Christophe Leroy <christophe.leroy@csgroup.eu>,
        Jiri Kosina <jikos@kernel.org>,
        Joe Lawrence <joe.lawrence@redhat.com>,
        Josh Poimboeuf <jpoimboe@redhat.com>,
        Miroslav Benes <mbenes@suse.cz>,
        Ingo Molnar <mingo@redhat.com>, Petr Mladek <pmladek@suse.com>,
        Steven Rostedt <rostedt@goodmis.org>
Cc:     "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>
References: <cover.1640017960.git.christophe.leroy@csgroup.eu>
        <04d196585ff81bde06a000bd9c633a33a5b21130.1640017960.git.christophe.leroy@csgroup.eu>
In-Reply-To: <04d196585ff81bde06a000bd9c633a33a5b21130.1640017960.git.christophe.leroy@csgroup.eu>
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Christophe Leroy wrote:
> Modify function graph tracer to be handled directly by the standard
> ftrace caller.
>=20
> This is made possible as powerpc now supports
> CONFIG_DYNAMIC_FTRACE_WITH_ARGS.
>=20
> This change simplifies the call of function graph ftrace.
>=20
> Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
> ---
>  arch/powerpc/include/asm/ftrace.h             |  6 ++
>  arch/powerpc/kernel/trace/ftrace.c            | 11 ++++
>  arch/powerpc/kernel/trace/ftrace_32.S         | 53 +--------------
>  .../powerpc/kernel/trace/ftrace_64_mprofile.S | 64 +------------------
>  4 files changed, 20 insertions(+), 114 deletions(-)
>=20
> diff --git a/arch/powerpc/include/asm/ftrace.h b/arch/powerpc/include/asm=
/ftrace.h
> index 45c3d6f11daa..70b457097098 100644
> --- a/arch/powerpc/include/asm/ftrace.h
> +++ b/arch/powerpc/include/asm/ftrace.h
> @@ -38,6 +38,12 @@ static __always_inline void ftrace_instruction_pointer=
_set(struct ftrace_regs *f
>  {
>  	regs_set_return_ip(&fregs->regs, ip);
>  }
> +
> +struct ftrace_ops;
> +
> +#define ftrace_graph_func ftrace_graph_func
> +void ftrace_graph_func(unsigned long ip, unsigned long parent_ip,
> +		       struct ftrace_ops *op, struct ftrace_regs *fregs);
>  #endif
>  #endif /* __ASSEMBLY__ */
> =20
> diff --git a/arch/powerpc/kernel/trace/ftrace.c b/arch/powerpc/kernel/tra=
ce/ftrace.c
> index ce673764cb69..74a176e394ef 100644
> --- a/arch/powerpc/kernel/trace/ftrace.c
> +++ b/arch/powerpc/kernel/trace/ftrace.c
> @@ -917,6 +917,9 @@ static int ftrace_modify_ftrace_graph_caller(bool ena=
ble)
>  	unsigned long stub =3D (unsigned long)(&ftrace_graph_stub);
>  	ppc_inst_t old, new;
> =20
> +	if (IS_ENABLED(CONFIG_DYNAMIC_FTRACE_WITH_ARGS))
> +		return 0;
> +
>  	old =3D ftrace_call_replace(ip, enable ? stub : addr, 0);
>  	new =3D ftrace_call_replace(ip, enable ? addr : stub, 0);
> =20
> @@ -955,6 +958,14 @@ unsigned long prepare_ftrace_return(unsigned long pa=
rent, unsigned long ip,
>  out:
>  	return parent;
>  }

For x86, commit 0c0593b45c9b4e ("x86/ftrace: Make function graph use=20
ftrace directly") also adds recursion check before the call to=20
function_graph_enter() in prepare_ftrace_return(). Do we need that on
powerpc as well?


- Naveen