linux-kernel - Re: [PATCH v2 2.6.38-rc8-tip 6/20] 6: x86: analyze instruction and determine fixups.

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Message-ID: <20110318182457.GA24048@linux.vnet.ibm.com>
Date:	Fri, 18 Mar 2011 23:54:57 +0530
From:	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...e.hu>,
	Steven Rostedt <rostedt@...dmis.org>,
	Linux-mm <linux-mm@...ck.org>,
	Arnaldo Carvalho de Melo <acme@...radead.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andi Kleen <andi@...stfloor.org>,
	Christoph Hellwig <hch@...radead.org>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Oleg Nesterov <oleg@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	SystemTap <systemtap@...rces.redhat.com>,
	Jim Keniston <jkenisto@...ux.vnet.ibm.com>,
	Roland McGrath <roland@...k.frob.com>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	LKML <linux-kernel@...r.kernel.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: Re: [PATCH v2 2.6.38-rc8-tip 6/20] 6: x86: analyze instruction and
 determine fixups.

> 
> > +	ret = handle_riprel_insn(uprobe, &insn);
> > +	if (ret == -1)
> > +		/* rip-relative; can't XOL */
> > +		return 0;
> 
> So we return -1 from handle_riprel_insn() and return success?


handle_riprel_insn() returns 0 if the instruction is not rip-relative
returns 1 if its rip-relative but can use XOL slots.
returns -1 if its rip-relative but cannot use XOL.

We dont see any instructions that are rip-relative and cannot use XOL.
so the check and return are redundant and I will remove that in the next
patch.


Btw how
> deals handle_riprel_insn() with 32bit user space ?
> 

handle_riprel_insn() calls insn_rip_relative() which fails if
instruction isnot rip-relative and handle_riprel_insn returns
immediately.

The rest of your suggestions for this patch are taken.

> > +#endif
> > +	prepare_fixups(uprobe, &insn);
> > +	return 0;
> 

-- 
Thanks and Regards
Srikar
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