[PATCH] ARM: ptrace: fix ptrace_read_user for !CONFIG_MMU platforms - Russell King

From: linux@arm.linux.org.uk (Russell King - ARM Linux)
To: linux-arm-kernel@lists.infradead.org
Subject: [PATCH] ARM: ptrace: fix ptrace_read_user for !CONFIG_MMU platforms
Date: Tue, 21 Feb 2012 11:35:48 +0000	[thread overview]
Message-ID: <20120221113548.GK22562@n2100.arm.linux.org.uk> (raw)
In-Reply-To: <20120221105250.GC19696@mudshark.cambridge.arm.com>

On Tue, Feb 21, 2012 at 10:52:50AM +0000, Will Deacon wrote:
> On Tue, Feb 21, 2012 at 10:10:52AM +0000, Russell King - ARM Linux wrote:
> > On Tue, Feb 21, 2012 at 10:00:41AM +0000, Will Deacon wrote:
> > > On Tue, Feb 21, 2012 at 08:36:12AM +0000, Russell King - ARM Linux wrote:
> > > > Maybe no one uses a debugger for uclinux programs?
> > > 
> > > I confess to finding this by inspection rather than a debugging failure.
> > 
> > There is another explanation - that is no one in the uclinux world uses
> > mainline kernels, and this bug has been fixed ages ago in some uclinux
> > kernel tree.
> > 
> > That directly raises the question of the value of having the uclinux
> > baggage in the mainline kernel if no one is using mainline kernels for
> > uclinux work.  If the uclinux folk aren't willing to pass up bug fixes,
> > then having it in mainline is, frankly, a waste of space.
> 
> I know the validation guys in ARM use mainline kernels for bringup on
> MMU-less CPUs (ok, they have extra patches on top but these tend to be
> platform-specific hacks since they're running on an RTL emulator. Plus they do
> periodically rebase onto new release kernels.). Debugging tends to be at a
> much lower level than GDB can provide though (i.e. waveforms), so this would
> have gone un-noticed.
> 
> I think it's worth keeping the support, particularly in light of the recent
> interest in M-class CPUs on the list.

In any case, I think we need to know whether this really is a problem or
not.  If no one has noticed that this is broken in the last 2.5 years,
that implies that no one is using this, and so there's no point either
the kernel or gdb carrying support which no one is using.

The other thing is, as this has been broken right from the start, has
gdb under uclinux even been tested?

I don't think fixing this in mainline until we know the full story behind
this is the right thing to be doing.  There's no point fixing a feature
which no one's using.