Re: [RFC] [PATCH] powerpc: Add MSR_DE to MSR_KERNEL

On 06/25/2013 01:00:23 AM, Joakim Tjernlund wrote:

Scott Wood [off-list ref] wrote on 2013/06/25 02:51:00:

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On Fri, Jul 20, 2012 at 10:37:17AM +0200, Joakim Tjernlund wrote:

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Zang Roy-R61911 [off-list ref] wrote on 2012/07/20 =20

10:27:52:

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-----Original Message-----
From:

linuxppc-dev-bounces+tie-fei.zang=3Dfreescale.com@lists.ozlabs.org

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mailto:linuxppc-dev-bounces+tie-fei.zang=3Dfreescale.com@lists.ozlabs.org=

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On Behalf Of Joakim Tjernlund
Sent: Friday, June 01, 2012 6:36 AM
To: Wood Scott-B07421
Cc: linuxppc-dev@ozlabs.org; Dan Malek; Bob Cochran; Support
Subject: Re: [RFC] [PATCH] powerpc: Add MSR_DE to MSR_KERNEL

It just occurred to me that you guys have this already in your

Linux SDK so

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it can't be that bad.

No. MSR_DE is ONLY added when using CW debug in SDK.
Roy

Yes, and I later found that user space debugging is busted if you =20

turn
on MSR_DE in

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kernel.

So, how should we handle the CONFIG_BDI_SWITCH patch?  It seems =20

like it

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should at least have a warning in the kconfig help text that it =20

breaks

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userspace debugging (to the point of causing a kernel oops if it's
tried).  Or maybe it can deselect CONFIG_PPC_ADV_DEBUG_REGS?

It'd also be nice to keep things like this, that are a consequence =20

of
how

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external debug works on e500, separate from the Abatron-specific =20

stuff.

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=20
I was hoping the kernel would grow per context handling of MSR_DE. =20
Then
one could have
MSR_DE on in MSR_KERNEL but off in user space(unless gdb request it =20
on a
per process basis).

What if the external debugger wants debugging to work when in userspace =20
as well?  Plus, you wouldn't be able to debug from the very beginning =20
of an exception handler if the exception came from userspace.

-Scott=