RE: how to creat watchpoint in kernel for data access debug

["Wang, Yalin" <Yalin.Wang@sonymobile.com>]

Hi  Will,

Thanks for your proposal,
The patch google made is just like
The one I tried before ,
Then the problems come :
After register the perf_event callback,
In the callback function ,
In google's patch , it is  function crbug_345917_handler( ),
It just call panic( ) ,
But My callback function will do some check ,
Sometimes, I want to bypass this time's breakpoint,
Problems is that I don't know how to bypass it,
If I return directly in the callback function ,
The breakpoint will trap again and again endless ..

Thank you very much .


-----Original Message-----
From: Will Deacon [mailto:will.deacon@arm.com] 
Sent: Wednesday, June 04, 2014 12:45 AM
To: Wang, Yalin
Cc: 'linux-mmc@vger.kernel.org'; 'linux-arch-owner@vger.kernel.org'
Subject: Re: how to creat watchpoint in kernel for data access debug

On Sat, May 24, 2014 at 04:48:20AM +0100, Wang, Yalin wrote:
> Hi  Will,

Hello,

Sorry for the delayed reply, it took me a while to work out what your issue is.

> Thanks for your suggestion,
> The scenario that I encounter is a little special :
> I found our kernel memory will be corrupt in stability test , Seems 
> that someone write a memory that doesn't belong to it .
> But I can't find who does it , the bug is hard to reproduce , So I 
> want make a debug SW in kernel , which can monitor some data access, 
> When someone access it , the callback function can check if it's right .
> If it's wrong, then crash the kernel do get a ram dump .
> 
> 
> So kgdb or perf seems not suitable in this condition , We need users 
> to use devices, not just test the device in Lab .

I think Google did something similar to this with ChromeOS on the Exynos5-based chromebooks:

  https://chromium-review.googlesource.com/#/c/188479/3/arch/arm/kernel/hw_breakpoint.c

I don't think that has a place in the mainline kernel, but you could certainly adapt it for your debugging purposes.

Will