[syslinux] isolinux problem since 3.74

[Stillwell, Bryan]

On Wed, 2009-10-14 at 23:50 +0000, H. Peter Anvin wrote:
> On 10/14/2009 01:26 PM, Stillwell, Bryan wrote:
> > BTW, I tried booting with pxelinux 3.75 and the same config files the CD
> > uses, and it works fine.  Maybe all those zero entries which are seen
> > when booting off the CD are causing the problem?  I've been told the
> > Linux kernel ignores them.
> 
> The Linux kernel should ignore them, as should Syslinux, but there is of
> course always the possibility there is a bug.

There does seem to be a bug in syslinux.  If the extended attributes are
set to 0 (which is out of spec and I'm working on getting fixed), it
causes a hang at this piece of code in memscan.c:

    if (!(e820buf->extattr & 1))
      continue;

This causes an infinite loop since we never move on to the next entry in
the memory map.  Changing it to this code appears to do what is expected
for me:

    if (!(e820buf->extattr & 1)) {
      ireg.ebx.l = oreg.ebx.l;
      continue;
    }


Bryan