From: Steven Rostedt <rostedt@goodmis.org>
To: linux-kernel@vger.kernel.org
Cc: Ingo Molnar <mingo@elte.hu>,
Andrew Morton <akpm@linux-foundation.org>,
Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>,
Frederic Weisbecker <fweisbec@gmail.com>
Subject: Re: [RFC][PATCH 06/12] ftrace/x86: Add save_regs for i386 function calls
Date: Wed, 06 Jun 2012 10:37:37 -0400 [thread overview]
Message-ID: <1338993457.13348.547.camel@gandalf.stny.rr.com> (raw)
In-Reply-To: <20120606040014.660425497@goodmis.org>
On Tue, 2012-06-05 at 23:51 -0400, Steven Rostedt wrote:
> +ENTRY(ftrace_regs_caller)
> + pushf /* push flags before compare */
> + cmpl $0, function_trace_stop
> + jne ftrace_exit
> +
> +
Masami,
Do we really need to push before the compare? As the compare flags are
really meaningless with calling functions, and here we are only trying
to hide what the cmpl did. If something else was tracing without regs,
and we put a probe just after the nop, then it would include the cmpl
changes. My version of the patch doesn't restore the flags, so two
probes would have different values. But again, do we care? What would
need to know the value of cmp flags when calling into a function when
they are not going to be restored anyway.
-- Steve
next prev parent reply other threads:[~2012-06-06 14:37 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-06-06 3:50 [RFC][PATCH 00/12] kprobes/ftrace: Making ftrace usable for kprobes Steven Rostedt
2012-06-06 3:50 ` [RFC][PATCH 01/12] ftrace: Pass ftrace_ops as third parameter to function trace callback Steven Rostedt
2012-06-06 3:51 ` [RFC][PATCH 02/12] ftrace: Consolidate arch dependent functions with list function Steven Rostedt
2012-06-06 3:51 ` [RFC][PATCH 03/12] ftrace: Return pt_regs to function trace callback (x86_64 only so far) Steven Rostedt
2012-06-06 3:51 ` [RFC][PATCH 04/12] ftrace/x86_32: Push ftrace_ops in as 3rd parameter to function tracer Steven Rostedt
2012-06-06 3:51 ` [RFC][PATCH 05/12] ftrace/x86: Add separate function to save regs Steven Rostedt
2012-06-06 3:51 ` [RFC][PATCH 06/12] ftrace/x86: Add save_regs for i386 function calls Steven Rostedt
2012-06-06 14:37 ` Steven Rostedt [this message]
2012-06-06 15:18 ` Masami Hiramatsu
2012-06-06 3:51 ` [RFC][PATCH 07/12] ftrace: add ftrace_set_filter_ip() for address based filter Steven Rostedt
2012-06-06 3:51 ` [RFC][PATCH 08/12] kprobes: Inverse taking of module_mutex with kprobe_mutex Steven Rostedt
2012-06-06 3:51 ` [RFC][PATCH 09/12] kprobes: cleanup to separate probe-able check Steven Rostedt
2012-06-06 3:51 ` [RFC][PATCH 10/12] kprobes: Move locks into appropriate functions Steven Rostedt
2012-06-06 3:51 ` [RFC][PATCH 11/12] kprobes: introduce ftrace based optimization Steven Rostedt
2012-06-06 3:51 ` [RFC][PATCH 12/12] kprobes/x86: ftrace based optimization for x86 Steven Rostedt
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