linux-kernel - Re: [PATCH 1/2] powerpc: ptrace CHECK_FULL

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Message-Id: <20070925005945.02E924D04B7@magilla.localdomain>
Date:	Mon, 24 Sep 2007 17:59:44 -0700 (PDT)
From:	Roland McGrath <roland@...hat.com>
To:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
Cc:	Paul Mackerras <paulus@...ba.org>, linuxppc-dev@...abs.org,
	David Woodhouse <dwmw2@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] powerpc: ptrace CHECK_FULL_REGS

> Yup, I think I ditched most of them.. for some reason I decided it
> couldn't happen, but maybe I'm wrong ?

Well, it's a BUG_ON.  It's supposed to be for something that "can't happen".
That's why it's a sanity check, not a wild assertion. ;-)

The 2/2 patch is an example of a bug that CHECK_FULL_REGS catches.
In the status quo, using PTRACE_PEEKUSR in a bug case crashes while using
PTRACE_GETREGS in the same place might get bogus data.  (In the actual bug
thus found, the data is not bogus and only the bit that FULL_REGS checks is.)

Thanks,
Roland
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