linux-kernel - Re: [PATCH] tracing/function-branch-tracer: support for x86-64

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Date:	Thu, 4 Dec 2008 00:33:00 +0100
From:	"Frédéric Weisbecker" <fweisbec@...il.com>
To:	"Alexander van Heukelum" <heukelum@...tmail.fm>
Cc:	"Ingo Molnar" <mingo@...e.hu>,
	"Steven Rostedt" <rostedt@...dmis.org>,
	"Tim Bird" <tim.bird@...sony.com>,
	"Linux Kernel" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] tracing/function-branch-tracer: support for x86-64

2008/12/3 Alexander van Heukelum <heukelum@...tmail.fm>:
> Hi Frederic,
>
> The changes to entry_64.S look simple enough. The order of
> saving the registers on the stack is not important in any
> way, right?
>[...]

No they don't matter.
All arguments should be saved on ftrace_graph_caller to not loose them
on call entry hooking.

On return (return_to_handler), I thought that I only needed to save
%rax (return value), the other scratch registers shouldn't matter at
the return state and the others will be saved by the return hooker.

But when I only save %rax, my system crashes. I don't know why so I
kept saving all scratch registers.

> I think this can be done with:
>
> _ASM_EXTABLE(1b,3b)
> _ASM_EXTABLE(2b,3b)
>
> (from: arch/x86/include/asm/asm.h)

Thanks. That and the generic move have actually been implemented by
Steven very recently:
http://lkml.org/lkml/2008/12/2/280
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