linux-kernel - Re: [PATCH] uprobes: Document xol_area and arch

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Date:	Tue, 19 Nov 2013 20:24:19 +0100
From:	Ingo Molnar <mingo@...nel.org>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Ingo Molnar <mingo@...e.hu>,
	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] uprobes: Document xol_area and arch_uprobe->insn/ixol


* Oleg Nesterov <oleg@...hat.com> wrote:

> On 11/11, Ingo Molnar wrote:
> >
> > * Oleg Nesterov <oleg@...hat.com> wrote:
> >
> > > On 11/11, Ingo Molnar wrote:
> > > >
> > > > You guys are changing code that reads like gobbledygook to people
> > > > reading it for the first time.
> > >
> > > Not that I am trying to defense uprobes, but this is equally true for
> > > any piece of kernel code, at least to me ;)
> >
> > I'm really not suggesting to do overly much - only for some minimal blurb
> > like the scheduler has in most places:
> 
> OK. Let me try to make a first step to improve this a little bit...
> 
> How about the patch below? Srikar?
> 
> 
> Subject: [PATCH] uprobes: Document xol_area and arch_uprobe->insn/ixol
> 
> Document xol_area and arch_uprobe.
> 
> Signed-off-by: Oleg Nesterov <oleg@...hat.com>
> ---
>  kernel/events/uprobes.c |   15 +++++++++++++++
>  1 files changed, 15 insertions(+), 0 deletions(-)
> 
> diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
> index 51a7f53..b886a5e 100644
> --- a/kernel/events/uprobes.c
> +++ b/kernel/events/uprobes.c
> @@ -73,6 +73,17 @@ struct uprobe {
>  	struct inode		*inode;		/* Also hold a ref to inode */
>  	loff_t			offset;
>  	unsigned long		flags;
> +
> +	/*
> +	 * The generic code assumes that it has two members of unknown type
> +	 * owned by the arch-specific code:
> +	 *
> +	 * 	insn -	copy_insn() saves the original instruction here for
> +	 *		arch_uprobe_analyze_insn().
> +	 *
> +	 *	ixol -	potentially modified instruction to execute out of
> +	 *		line, copied to xol_area by xol_get_insn_slot().
> +	 */
>  	struct arch_uprobe	arch;
>  };
>  
> @@ -86,6 +97,10 @@ struct return_instance {
>  };
>  
>  /*
> + * Execute out of line area: anonymous executable mapping installed
> + * by the probed task to execute the copy of the original instruction
> + * mangled by set_swbp().
> + *
>   * On a breakpoint hit, thread contests for a slot.  It frees the
>   * slot after singlestep. Currently a fixed number of slots are
>   * allocated.

Looks perfect to me!

Thanks,

	Ingo
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