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

[Will Deacon]

Hi Russell,

On Fri, Feb 24, 2012 at 06:16:21PM +0000, Russell King - ARM Linux wrote:
> On Fri, Feb 24, 2012 at 02:36:55PM +0000, Will Deacon wrote:
> > It seems as though my ptrace patch makes *no difference* because these
> > tools don't even use the PT_ADDR_TEXT etc magic offsets! As a result,
> > trying to set a breakpoint by symbol fails miserably because it tries to
> > poke the symbol offset directly, without adding on the base address of the
> > text.
> > 
> > Are there any tools available that use these magic numbers or are mine just
> > too old? Given that the whole thing dies after a while with:
> > 
> > [  909.062821] [430] gdbserver: obsolete system call 02b37558.
> > 
> > I'm not entirely convinced by the stability of what I'm using (that syscall
> > number looks like an address to me).
> 
> That suggests that this stuff definitely hasn't been tested, and there's
> no users of it (if there were I'm sure someone - either gdb folk or
> some kernel people) would've seen a bug report.

My glancing at the latest GDB sources does suggest that this stuff ought to
be getting used, so I should probably try building a nommu configuration
from a more recent codebase. It seems that you're right that nobody is using
this stuff though.

> Therefore, I propose that we remove this code from the kernel unless
> there's someone out there who can positively test this stuff as definitely
> working.

I started looking at nommu recently and I've got a few fixes for the kernel
(I'll post them once it's all tidied up). Let's leave this in until I've
either (a) validated that recent GDB builds work or (b) lost the will to
live and come crawling back to my beloved MMU.

Will