From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail6.bemta7.messagelabs.com (mail6.bemta7.messagelabs.com [216.82.255.55]) by kanga.kvack.org (Postfix) with ESMTP id 7620B6B004D for ; Tue, 29 Nov 2011 12:24:10 -0500 (EST) Date: Tue, 29 Nov 2011 18:18:22 +0100 From: Oleg Nesterov Subject: Re: [PATCH 2/5] uprobes: introduce uprobe_switch_to() Message-ID: <20111129171822.GA28234@redhat.com> References: <20111118110631.10512.73274.sendpatchset@srdronam.in.ibm.com> <20111128190614.GA4602@redhat.com> <20111128190655.GC4602@redhat.com> <1322510018.2921.161.camel@twins> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1322510018.2921.161.camel@twins> Sender: owner-linux-mm@kvack.org List-ID: To: Peter Zijlstra Cc: Srikar Dronamraju , Linus Torvalds , Andrew Morton , LKML , Linux-mm , Ingo Molnar , Andi Kleen , Christoph Hellwig , Steven Rostedt , Roland McGrath , Thomas Gleixner , Masami Hiramatsu , Arnaldo Carvalho de Melo , Anton Arapov , Ananth N Mavinakayanahalli , Jim Keniston , Stephen Wilson On 11/28, Peter Zijlstra wrote: > > On Mon, 2011-11-28 at 20:06 +0100, Oleg Nesterov wrote: > > +void uprobe_switch_to(struct task_struct *curr) > > +{ > > + struct uprobe_task *utask = curr->utask; > > + struct pt_regs *regs = task_pt_regs(curr); > > + > > + if (!utask || utask->state != UTASK_SSTEP) > > + return; > > + > > + if (!(regs->flags & X86_EFLAGS_TF)) > > + return; > > + > > + set_xol_ip(regs); > > +} > > > void __weak set_xol_ip(struct pt_regs *regs) > > { > > + int cpu = smp_processor_id(); > > + struct uprobe_task *utask = current->utask; > > + struct uprobe *uprobe = utask->active_uprobe; > > + > > + memcpy(uprobe_xol_slots[cpu], uprobe->insn, MAX_UINSN_BYTES); > > + > > + utask->xol_vaddr = fix_to_virt(UPROBE_XOL_FIRST_PAGE) > > + + UPROBES_XOL_SLOT_BYTES * cpu; > > + set_instruction_pointer(regs, utask->xol_vaddr); > > } > > So uprobe_switch_to() will always reset the IP to the start of the slot? > That sounds wrong, things like the RIP relative stuff needs multiple > instructions. Hmm. Could you explain? Especially the "multiple instructions" part. In any case we should reset the IP to the start of the slot. But yes, I'm afraid this is too simple. Before this patches pre_xol() is called when we already know ->xol_vaddr. But afaics x86 doesn't use this info (post_xol() does). So this looks equally correct or wrong. But perhaps we need another arch-dependent hook which takes ->xol_vaddr into account instead of simple memcpy(), to handle the RIP relative case. Or I misunderstood? Peter, all, I apologize in advance, I can't be responsive today. Oleg. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: email@kvack.org