linux-kernel - Re: [RFC PATCH v2 2/4] uretprobes: trampoline implementation

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Date:	Wed, 9 Jan 2013 17:13:58 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Anton Arapov <anton@...hat.com>
Cc:	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Josh Stone <jistone@...hat.com>,
	Frank Eigler <fche@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...e.hu>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>
Subject: Re: [RFC PATCH v2 2/4] uretprobes: trampoline implementation

On 01/09, Anton Arapov wrote:
>
> The first time a uprobe with return consumer is hit for a process, a
> trampoline slot is obtained in the xol_area and initialized with a
> breakpoint instruction. This slot is subsequently used by all
> uretprobes.

See my reply to 0/4, I think we do not really need this.

> todo:
>   unify with xol_take_insn_slot()
> 
> Signed-off-by: Anton Arapov <anton@...hat.com>
> ---
>  include/linux/uprobes.h |  1 +
>  kernel/events/uprobes.c | 33 +++++++++++++++++++++++++++++++++
>  2 files changed, 34 insertions(+)
> 
> diff --git a/include/linux/uprobes.h b/include/linux/uprobes.h
> index 95d0002..bddfad6 100644
> --- a/include/linux/uprobes.h
> +++ b/include/linux/uprobes.h
> @@ -91,6 +91,7 @@ struct xol_area {
>  	 * the vma go away, and we must handle that reasonably gracefully.
>  	 */
>  	unsigned long 		vaddr;		/* Page(s) of instruction slots */
> +	unsigned long		rp_trampoline_vaddr; /* address of trampolines */
>  };
>  
>  struct uprobes_state {
> diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
> index 473db3f..0ad2ac3 100644
> --- a/kernel/events/uprobes.c
> +++ b/kernel/events/uprobes.c
> @@ -1208,6 +1208,39 @@ static unsigned long xol_get_insn_slot(struct uprobe *uprobe)
>  	return xol_vaddr;
>  }
>  
> +/*
> + * xol_get_trampoline_slot - A trampoline slot is obtained the first
> + * time a uprobe with return consumer is hit for a process. Use one
> + * trampoline slot for all probes pertaining to a process, i.e.
> + * one per xol_area.
> + */
> +static unsigned long xol_get_trampoline_slot(void)
> +{
> +	struct xol_area *area;
> +	unsigned long offset;
> +	uprobe_opcode_t bp_insn = UPROBE_SWBP_INSN;
> +	void *vaddr;
> +
> +	area = get_xol_area();
> +	if (!area)
> +		return 0;
> +
> +	if (!area->rp_trampoline_vaddr)
> +		area->rp_trampoline_vaddr = xol_take_insn_slot(area);
> +
> +	if (unlikely(!area->rp_trampoline_vaddr))
> +		return 0;
> +
> +	offset = area->rp_trampoline_vaddr & ~PAGE_MASK;
> +	vaddr = kmap_atomic(area->page);
> +	memcpy(vaddr + offset, &bp_insn, UPROBE_SWBP_INSN_SIZE);
> +	kunmap_atomic(vaddr);
> +
> +	flush_dcache_page(area->page);
> +
> +	return area->rp_trampoline_vaddr;
> +}
> +
>  /*
>   * xol_free_insn_slot - If slot was earlier allocated by
>   * @xol_get_insn_slot(), make the slot available for
> -- 
> 1.8.0.2
> 

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