Re: [PATCH 4/8] x86: Add support for rd/wr fs/gs base

From: Andy Lutomirski
Date: Fri Apr 10 2015 - 19:16:09 EST

On Fri, Apr 10, 2015 at 4:05 PM, Andi Kleen <andi@xxxxxxxxxxxxxx> wrote:
>> One might argue that this code serves no purpose, but it's there, so
>> we had better keep our per-invocation usage of DEBUG_STACK within 4k.
> Only if you run NKLD. I doubt KDB or GDB support nesting.
> We can ask Jan if he still uses it.

You can trigger these things in various ways with kprobes,
single-stepping, and user-space watchpoints. These things can
definitely nest in interesting ways. Whether or not the IST shift
mechanism is involved if they nest is a complicated question, because
there's also the "debug" IDT in play.

OMG this code is overcomplicated.

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