linux-kernel - Re: [PATCHv9 2.6.35-rc4-tip 2/13] uprobes: Breakpoint insertion/removal in user space applications.

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Message-ID: <20100720042814.GA13624@infradead.org>
Date:	Tue, 20 Jul 2010 00:28:14 -0400
From:	Christoph Hellwig <hch@...radead.org>
To:	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
Cc:	Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...e.hu>,
	Steven Rostedt <rostedt@...dmis.org>,
	Randy Dunlap <rdunlap@...otime.net>,
	Arnaldo Carvalho de Melo <acme@...radead.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Christoph Hellwig <hch@...radead.org>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	Oleg Nesterov <oleg@...hat.com>,
	Mark Wielaard <mjw@...hat.com>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Naren A Devaiah <naren.devaiah@...ibm.com>,
	Jim Keniston <jkenisto@...ux.vnet.ibm.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	"Frank Ch. Eigler" <fche@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: Re: [PATCHv9 2.6.35-rc4-tip 2/13]  uprobes: Breakpoint
 insertion/removal in user space applications.

> +struct user_bkpt_arch_info {
> +	void (*set_ip)(struct pt_regs *regs, unsigned long vaddr);
> +	int (*validate_address)(struct task_struct *tsk, unsigned long vaddr);
> +	int (*read_opcode)(struct task_struct *tsk, unsigned long vaddr,
> +						user_bkpt_opcode_t *opcode);
> +	int (*set_bkpt)(struct task_struct *tsk,
> +				struct user_bkpt *user_bkpt);
> +	int (*set_orig_insn)(struct task_struct *tsk,
> +				struct user_bkpt *user_bkpt, bool check);
> +	bool (*is_bkpt_insn)(struct user_bkpt *user_bkpt);
> +	int (*analyze_insn)(struct task_struct *tsk,
> +					struct user_bkpt *user_bkpt);
> +	int (*pre_xol)(struct task_struct *tsk,
> +				struct user_bkpt *user_bkpt,
> +				struct user_bkpt_task_arch_info *tskinfo,
> +				struct pt_regs *regs);
> +	int (*post_xol)(struct task_struct *tsk,
> +				struct user_bkpt *user_bkpt,
> +				struct user_bkpt_task_arch_info *tskinfo,
> +				struct pt_regs *regs);
> +};

Just wondering why these are function pointers.  Do we exepect an
architecture to provide different versions of these for say 32 vs 64-bit
binaries?  If not just making these arch provided helpers might be a lot
simpler.  Especially in the current version where only very few of these
are overriden by the architecture at all.

> +unsigned long uprobes_read_vm(struct task_struct *tsk, void __user *vaddr,
> +					void *kbuf, unsigned long nbytes)
> +{
> +	if (tsk == current) {
> +		unsigned long nleft = copy_from_user(kbuf, vaddr, nbytes);
> +		return nbytes - nleft;
> +	} else
> +		return access_process_vm(tsk, (unsigned long) vaddr, kbuf,
> +							nbytes, 0);
> +}
> +
> +unsigned long uprobes_write_data(struct task_struct *tsk,
> +				void __user *vaddr, const void *kbuf,
> +				unsigned long nbytes)
> +{
> +	unsigned long nleft;
> +
> +	if (tsk == current) {
> +		nleft = copy_to_user(vaddr, kbuf, nbytes);
> +		return nbytes - nleft;
> +	} else
> +		return access_process_vm(tsk, (unsigned long) vaddr,
> +						(void *) kbuf, nbytes, 1);
> +}

Any reason for the naming mismatch between _read_vm and _write_data?

Also I wonder if the optimization for tsk == current should be folded
directly into access_process_vm instead of adding these wrappers.

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