linux-kernel - Re: utrace comments

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Message-ID: <20070430093331.GB11345@flint.arm.linux.org.uk>
Date:	Mon, 30 Apr 2007 10:33:31 +0100
From:	Russell King <rmk+lkml@....linux.org.uk>
To:	Christoph Hellwig <hch@....de>
Cc:	Christoph Hellwig <hch@...radead.org>,
	Roland McGrath <roland@...hat.com>,
	linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org
Subject: Re: utrace comments

On Mon, Apr 30, 2007 at 11:22:00AM +0200, Christoph Hellwig wrote:
> On Mon, Apr 30, 2007 at 10:18:09AM +0100, Russell King wrote:
> > Roland's idea of single-stepping is that it *must* be supported by
> > hardware for utrace to use it.  There are a number of architectures
> > which can only do single-stepping by modifying the text of the
> > program being single stepped.  ARM is one such example.
> > 
> > As such, even when utrace is complete, some architectures will never
> > support in-kernel single step with utrace.  I believe Roland's idea
> > is to have single step supported on these via some vapourware userspace
> > library.
> 
> Does the current arm ptrace code support single stepping in kernelspace?
> If yes we absolutely need to continue to support it.

single stepping of user space code via standard ptrace calls, yes.

> > I'd also like to see utrace become *optional*
> > for architectures to support, rather than as it currently stands as
> > a *mandatory* requirement when merged.
> 
> No way we'd keep both the old ptrace mess and utrace in the same tree.

Given the stated arguments from yourself and Roland, that only leaves
one solution to that.

I have no real problem with a decision being made to drop kernel-based
single stepping _provided_ we have some replacement strategy in place
and readily available.  At the moment I've not seen such a strategy.

I'm not sure if Roland's expecting architecture maintainers to
create such a strategy themselves - which would probably turn out to
being far worse since you could end up with different implementations
for each architecture.

-- 
Russell King
 Linux kernel    2.6 ARM Linux   - http://www.arm.linux.org.uk/
 maintainer of:
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