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

[Mark Wielaard <mark@klomp.org>]

Hi Andrew,

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.

Cheers,

Mark