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From: Michael Ellerman <mpe@ellerman.id.au>
To: "Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com>
Cc: Ananth N Mavinakayanahalli <ananth@linux.vnet.ibm.com>,
	Masami Hiramatsu <mhiramat@kernel.org>,
	linuxppc-dev@lists.ozlabs.org
Subject: Re: [PATCH 1/2] powerpc/jprobes: Save and restore the parameter save area
Date: Thu, 18 May 2017 15:22:30 +1000	[thread overview]
Message-ID: <87d1b6lox5.fsf@concordia.ellerman.id.au> (raw)
In-Reply-To: <0572aa31dd57bef6f158ac97d0b666a0c545356a.1494871248.git.naveen.n.rao@linux.vnet.ibm.com>

"Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com> writes:

> As pointed out in x86 setjmp_pre_handler(), we need to save and restore
> the parameter save area since the jprobe hook might overwrite it. Since
> there is no easy way to identify the size of the parameter save area,
> we choose to save/restore a fixed 16 [double]word-sized area including
> the stack frame header.
>
> We introduce STACK_FRAME_PARM_SAVE to encode the offset of the parameter
> save area from the stack frame pointer. Remove the similarly named
> PARAMETER_SAVE_AREA_OFFSET in ptrace.c as those are currently not used
> anywhere.
>
> Signed-off-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
> ---
> Michael,
> I've set the limit to 16 parameters as being a "reasonable" number, but
> we could very well make this 24 or 32 if we want to be sure. Let me
> know what you prefer.

That sounds incredibly fragile. Are we really just guessing at the size
required? What happens if we under estimate, do we crash, silently
corrupt data .. ?

cheers

  parent reply	other threads:[~2017-05-18  5:22 UTC|newest]

Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-05-15 18:05 [PATCH 1/2] powerpc/jprobes: Save and restore the parameter save area Naveen N. Rao
2017-05-15 18:05 ` [PATCH 2/2] powerpc/jprobes: Validate break handler invocation as being due to a jprobe_return() Naveen N. Rao
2017-05-17  1:21   ` Masami Hiramatsu
2017-05-30 18:36     ` Naveen N. Rao
2017-05-17  1:12 ` [PATCH 1/2] powerpc/jprobes: Save and restore the parameter save area Masami Hiramatsu
2017-05-30 18:16   ` Naveen N. Rao
2017-05-18  5:22 ` Michael Ellerman [this message]
2017-05-30 18:14   ` Naveen N. Rao

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