linux-kernel - Re: [RFC] [PATCH 1/7] User Space Breakpoint Assistance Layer (UBP)

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Date:	Mon, 18 Jan 2010 14:01:00 +0200
From:	Avi Kivity <avi@...hat.com>
To:	Peter Zijlstra <peterz@...radead.org>
CC:	ananth@...ibm.com, Jim Keniston <jkenisto@...ibm.com>,
	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	Ingo Molnar <mingo@...e.hu>,
	Arnaldo Carvalho de Melo <acme@...radead.org>,
	utrace-devel <utrace-devel@...hat.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Masami Hiramatsu <mhiramat@...hat.com>,
	Maneesh Soni <maneesh@...ibm.com>,
	Mark Wielaard <mjw@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFC] [PATCH 1/7] User Space Breakpoint Assistance Layer (UBP)

On 01/18/2010 01:44 PM, Peter Zijlstra wrote:
> On Mon, 2010-01-18 at 13:01 +0200, Avi Kivity wrote:
>    
>> You've made it clear that you don't like it, but not why.
>>
>> The kernel already manages the user's address space (except for
>> MAP_FIXED which is unreliable unless you've already reserved the address
>> space).  I don't see why adding a vma for debugging is so horrible.
>>      
> Well, the kernel only does what the user (and loader) tell it through
> mmap().

What I meant was that the kernel chooses the addresses (unless you go 
the MAP_FIXED way).  From the user's point of view, there is no change 
in behaviour: the kernel picks an address.  If the constraints have 
changed (because we reserve a range), that doesn't affect the user.

> Other than that we never (except this VDSO thing) inject vmas,
> and I see no reason to start doing that now.
>    

Maybe you place no value on uprobes.  But people who debug userspace 
likely will see a reason.

-- 
error compiling committee.c: too many arguments to function

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