Re: [SCM] master: Switch to frysk.sys.ptrace.

[Mark Wielaard <mark@klomp.org>]

Hi Andrew,

On Wed, 2008-02-13 at 09:47 +0100, Mark Wielaard wrote:
> On Tue, 2008-02-12 at 18:50 +0000, cagney@sourceware.org wrote:
> > -        private int peek(long index, byte[] bytes, int offset, int length)
> > -	{
> > -	  if (mem != null)
> > -	    {
> > -	      try
> > -		{
> > -		  return mem.pread(index, bytes, offset, length);
> > -		}
> > -	      catch (Errno e)
> > -		{
> > -		  // try again through address space.
> > +        private void transfer(long index, byte[] bytes, int offset, int length,
> > +			      boolean write) {
> > +	    if (mem != null && !write) {
> > +		try {
> > +		    mem.pread(index, bytes, offset, length);
> > +		    return;
> > +		} catch (Errno e) {
> > +		    // Give up on mem; and fall back to ptrace.  This
> > +		    // can happen when /proc isn't mounted, or when a
> > +		    // process is terminating and the kernel scrubs
> > +		    // the /proc entry before its time.
> > +		    mem = null;
> >  		}
> >  	    }
> 
> Are you sure this change is right? The comment is right about those 2
> reasons for pread() possibly failing. But I don't believe that is the
> only case it can happen. Previously when a read occurred that failed,
> possibly because following a pointer in the inferior that was NULL or
> not yet initialized that would just cause a error reading from that
> particular (uninitialized) memory location. But now whenever that occurs
> once for an inferior you blow away mem so pread() can never be used
> anymore and we always fall back to having to do single peeks and pokes
> through the ptrace address space.

Did you have time to investigate this? If not, shall we revert it to the
original implementation till you do have time?

Thanks,

Mark