Re: [RFA] initialize err variable in load_section_callback()

["Theodore A. Roth" <troth at openavr dot org>]

On Wed, 20 Oct 2004, Andrew Cagney wrote:

> Theodore A. Roth wrote:
> > Hi,
> >
> > I just encountered a problem with using the "load" command with a remote
> > avr target. The first packet would be sent to the remote target and then
> > gdb would just give up with this error message:
> >
> >   (gdb) load
> >   Loading section .text, size 0x1f8 lma 0x0
> >   Sending packet: $M0,a:0c9446000c9463000c94#d7...Ack
> >   Packet received: OK
> >   Memory access error while loading section .text.
> >
> > It looks like load_section_callback() in symfile.c is assuming that a
> > call to target_write_memory_partial() will set the err variable.
> > Unfortunately, that is not a valid assumption.
> >
> > The attached patch got things working again, but this feels like a hack
> > to me since target_write_memory_partial() should really be setting err
> > to a sane value before returning.
> >
> > Patch is against today's cvs mainline.
>
> Here's the contract:
> /* Make a single attempt at transfering LEN bytes.  On a successful
>     transfer, the number of bytes actually transfered is returned and
>     ERR is set to 0.  When a transfer fails, -1 is returned (the number
>     of bytes actually transfered is not defined) and ERR is set to a
>     non-zero error indication.  */
> So the bug is further down the target stack.

Both target_write_memory_partial() and target_read_memory_partial()
break that contract then:

  int
  target_write_memory_partial (CORE_ADDR memaddr, char *buf, int len, int *err)
  {
    if (target_xfer_partial_p ())
      return target_xfer_partial (target_stack, TARGET_OBJECT_MEMORY, NULL,
                                  NULL, buf, memaddr, len);
    else
      return target_xfer_memory_partial (memaddr, buf, len, 1, err);
  }

If target_xfer_partial_p() returns true (which the avr port does), then
err is never set and the caller will see garbage if it didn't initialize
err.

Should the return value of the target_xfer_partial() call be checked, or
should err just be blindly see to zero?

---
Ted Roth
PGP Key ID: 0x18F846E9
Jabber ID: troth@jabber.org