From: Frederic Weisbecker <fweisbec@gmail.com>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: linux-kernel@vger.kernel.org, Ingo Molnar <mingo@elte.hu>,
Andrew Morton <akpm@linux-foundation.org>,
Peter Zijlstra <peterz@infradead.org>,
Li Zefan <lizf@cn.fujitsu.com>, Jiri Olsa <jolsa@redhat.com>
Subject: Re: [PATCH 2/4] tracing/function-graph: x86_64 stack allocation cleanup
Date: Sun, 13 Sep 2009 19:05:21 +0200 [thread overview]
Message-ID: <20090913170517.GB4859@nowhere> (raw)
In-Reply-To: <20090913030616.992539807@goodmis.org>
On Sat, Sep 12, 2009 at 11:05:45PM -0400, Steven Rostedt wrote:
> From: Jiri Olsa <jolsa@redhat.com>
>
> Only 24 bytes needs to be reserved on the stack for the function graph
> tracer on x86_64.
>
> Signed-off-by: Jiri Olsa <jolsa@redhat.com>
> LKML-Reference: <20090729085837.GB4998@jolsa.lab.eng.brq.redhat.com>
> Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
> ---
> arch/x86/kernel/entry_64.S | 6 +++---
> 1 files changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S
> index c251be7..d59fe32 100644
> --- a/arch/x86/kernel/entry_64.S
> +++ b/arch/x86/kernel/entry_64.S
> @@ -146,7 +146,7 @@ ENTRY(ftrace_graph_caller)
> END(ftrace_graph_caller)
>
> GLOBAL(return_to_handler)
> - subq $80, %rsp
> + subq $24, %rsp
That's theoretically a good fix.
But Steve, do you remember the weird issues we had while only
saving the theoretically strict needed stack space here?
It made the function graph tracer crashing in x86-64, and we
never found out why we needed to save more stack than needed.
Sorry that may sound like a FUD message but I can't explain
the reason of this, and I fear we may met it again.
Well, at least that may help us finding out the real resons of
such crashes, but...
next prev parent reply other threads:[~2009-09-13 17:05 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-09-13 3:05 [PATCH 0/4] [GIT PULL] tracing: more fixes for v2.6.32 Steven Rostedt
2009-09-13 3:05 ` [PATCH 1/4] ftrace: __start_mcount_loc should be .init.rodata Steven Rostedt
2009-09-13 3:05 ` [PATCH 2/4] tracing/function-graph: x86_64 stack allocation cleanup Steven Rostedt
2009-09-13 17:05 ` Frederic Weisbecker [this message]
2009-09-13 17:47 ` Steven Rostedt
2009-09-13 17:55 ` Frederic Weisbecker
2009-09-13 3:05 ` [PATCH 3/4] tracing/profile: fix profile_disable vs module_unload Steven Rostedt
2009-09-13 3:05 ` [PATCH 4/4] tracing/filters: add filter Documentation Steven Rostedt
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