Re: [RFC][PATCH 1/4 v4] ftrace/x86: Add separate function to save regs

From: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: linux-kernel@vger.kernel.org, Ingo Molnar <mingo@elte.hu>,
	Andrew Morton <akpm@linux-foundation.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Frederic Weisbecker <fweisbec@gmail.com>,
	"H. Peter Anvin" <hpa@zytor.com>,
	Alexander van Heukelum <heukelum@fastmail.fm>,
	yrl.pp-manager.tt@hitachi.com
Subject: Re: [RFC][PATCH 1/4 v4] ftrace/x86: Add separate function to save regs
Date: Thu, 12 Jul 2012 21:12:40 +0900	[thread overview]
Message-ID: <4FFEBF38.7080406@hitachi.com> (raw)
In-Reply-To: <20120711195745.107705970@goodmis.org>

(2012/07/12 4:50), Steven Rostedt wrote:
> From: Steven Rostedt <srostedt@redhat.com>
> 
> Add a way to have different functions calling different trampolines.
> If a ftrace_ops wants regs saved on the return, then have only the
> functions with ops registered to save regs. Functions registered by
> other ops would not be affected, unless the functions overlap.
> 
> If one ftrace_ops registered functions A, B and C and another ops
> registered fucntions to save regs on A, and D, then only functions
> A and D would be saving regs. Function B and C would work as normal.
> Although A is registered by both ops: normal and saves regs; this is fine
> as saving the regs is needed to satisfy one of the ops that calls it
> but the regs are ignored by the other ops function.
> 
> x86_64 implements the full regs saving, and i386 just passes a NULL
> for regs to satisfy the ftrace_ops passing. Where an arch must supply
> both regs and ftrace_ops parameters, even if regs is just NULL.
> 
> It is OK for an arch to pass NULL regs. All function trace users that
> require regs passing must add the flag FTRACE_OPS_FL_SAVE_REGS when
> registering the ftrace_ops. If the arch does not support saving regs
> then the ftrace_ops will fail to register. The flag
> FTRACE_OPS_FL_SAVE_REGS_IF_SUPPORTED may be set that will prevent the
> ftrace_ops from failing to register. In this case, the handler may
> either check if regs is not NULL or check if ARCH_SUPPORTS_FTRACE_SAVE_REGS.
> If the arch supports passing regs it will set this macro and pass regs
> for ops that request them. All other archs will just pass NULL.

OK, this is good for me:)

Reviewed-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>

Thank you!

> 
> Cc: Alexander van Heukelum <heukelum@fastmail.fm>
> Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
> ---

-- 
Masami HIRAMATSU
Software Platform Research Dept. Linux Technology Center
Hitachi, Ltd., Yokohama Research Laboratory
E-mail: masami.hiramatsu.pt@hitachi.com