[syslinux] iPXE chain to lpxelinux.0 6.03-pre17 inconsistencies and failures

[Alexander Perlis]

I believe I'm seeing a bug in lpxelinux.0 6.03-pre17 but I need some 
advice on how to isolate and troubleshoot this. (I can't try pre18 at 
the moment, but did try 4.07 and 5.10 and saw similar behavior, also 
with pxelinux.0, so although I'll give pre18 a try soon, some 
isolation/troubleshooting advice will be a good education no matter what.)

To get to our PXE-launched tools from hosts on a subnet without proper 
DHCP support (e.g., on a NAT or in a different building), we're trying 
to use small iPXE USB thumb drives and/or iPXE CD-ROMs, obtained from 
rom-o-matic.eu, which then chainload to lpxelinux.0 off our actual PXE 
server. (We used pxelinux-options to put a "-b pxe.ip.address" into 
lpxelinux.0, so that it would know the server IP for grabbing the 
subsequent libxxx and config files.)

On some hosts we successfully get all the way to the graphical 
vesamenu.c32 under lpxelinux.0, while on other hosts we reach the 
initial lpxelinux.0 banner line but then the host hangs (and server 
shows no attempt to grab libxxx or config files), while on other hosts 
there is a reboot as soon as control is handed to lpxelinux.0 (and 
unclear whether the banner line is printed, as the reboot blanks the 
screen too quickly).

  Intel Macs: local-ipxe->lpxelinux.0->banner->vesamenu.c32->success
  Dell GX620: local-ipxe->lpxelinux.0->banner->hang
  Dell 780:   local-ipxe->lpxelinux.0->instant-reboot

I'm not sure how to dig deeper. I'm using the precompiled binaries. Is 
it easy to compile a debug version that spits out verbose progress prior 
and after the banner and perhaps pauses for user input?

I'm guessing ipxe is somehow setting the stage in a way that is caught 
by something finicky in lpxelinux.0 on certain hardware, or perhaps 
there's a bug in how ipxe sets the stage. Just to eliminate that latter 
variable, any recommendations for a non-ipxe-way to boot off a CD or USB 
to then PXE-boot to a specific server (not via DHCP)?

Alex