linux-kernel - Re: [PATCH -tip v5 06/10] kprobes/x86: Cleanup save/restore registers

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Message-ID: <20091124201919.GC5071@nowhere>
Date:	Tue, 24 Nov 2009 21:19:22 +0100
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Masami Hiramatsu <mhiramat@...hat.com>
Cc:	Ingo Molnar <mingo@...e.hu>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	lkml <linux-kernel@...r.kernel.org>,
	systemtap <systemtap@...rces.redhat.com>,
	DLE <dle-develop@...ts.sourceforge.net>,
	Jim Keniston <jkenisto@...ibm.com>,
	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	Christoph Hellwig <hch@...radead.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	"H. Peter Anvin" <hpa@...or.com>,
	Anders Kaseorg <andersk@...lice.com>,
	Tim Abbott <tabbott@...lice.com>,
	Andi Kleen <andi@...stfloor.org>,
	Jason Baron <jbaron@...hat.com>,
	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
Subject: Re: [PATCH -tip v5 06/10] kprobes/x86: Cleanup save/restore
	registers

On Tue, Nov 24, 2009 at 10:39:13AM -0500, Masami Hiramatsu wrote:
> Frederic Weisbecker wrote:
> > On Mon, Nov 23, 2009 at 06:22:04PM -0500, Masami Hiramatsu wrote:
> >> +#ifdef CONFIG_X86_64
> >> +#define SAVE_REGS_STRING		\
> >> +	/* Skip cs, ip, orig_ax. */	\
> >> +	"	subq $24, %rsp\n"	\
> >> +	"	pushq %rdi\n"		\
> >> +	"	pushq %rsi\n"		\
> >> +	"	pushq %rdx\n"		\
> >> +	"	pushq %rcx\n"		\
> >> +	"	pushq %rax\n"		\
> >> +	"	pushq %r8\n"		\
> >> +	"	pushq %r9\n"		\
> >> +	"	pushq %r10\n"		\
> >> +	"	pushq %r11\n"		\
> >> +	"	pushq %rbx\n"		\
> >> +	"	pushq %rbp\n"		\
> >> +	"	pushq %r12\n"		\
> >> +	"	pushq %r13\n"		\
> >> +	"	pushq %r14\n"		\
> >> +	"	pushq %r15\n"
> >> +#define RESTORE_REGS_STRING		\
> >> +	"	popq %r15\n"		\
> >> +	"	popq %r14\n"		\
> >> +	"	popq %r13\n"		\
> >> +	"	popq %r12\n"		\
> >> +	"	popq %rbp\n"		\
> >> +	"	popq %rbx\n"		\
> >> +	"	popq %r11\n"		\
> >> +	"	popq %r10\n"		\
> >> +	"	popq %r9\n"		\
> >> +	"	popq %r8\n"		\
> >> +	"	popq %rax\n"		\
> >> +	"	popq %rcx\n"		\
> >> +	"	popq %rdx\n"		\
> >> +	"	popq %rsi\n"		\
> >> +	"	popq %rdi\n"		\
> > 
> > 
> > BTW, do you really need to push/pop every registers
> > before/after calling a probe handler?
> 
> Yes, in both cases (kretprobe/optprpbe) it needs to
> emulate kprobes behavior. kprobes can be used as
> fault injection, it should pop pt_regs.
> 
> > Is it possible to only save/restore the scratch ones?
> 
> Hmm, what code did you mean?



Ah this chain of push/pop is there to dump a struct pt_regs for
the handler?
Sorry, I just thought it was to save the registers from the probed
function.

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