[syslinux] PXE looping on localboot

[H. Peter Anvin]

On 05/29/2012 10:11 AM, Vanush Misha Paturyan wrote:
> 
> Got this after doing "git bisect":
> 831f1a04fbbbb1f65d95858b1b435325f67981f2 is the first bad commit
> commit 831f1a04fbbbb1f65d95858b1b435325f67981f2
> Author: H. Peter Anvin <hpa at zytor.com>
> Date:   Fri Feb 12 13:37:20 2010 -0800
> 
>     pxelinux: move the stack to avoid AMI BIOS bug
>     
>     There is apparently some AMI BIOSes which leave a BEV stack just
>     below 7c00h, which means that they can't return from the PXE NBP.
>     Thus, for PXELINUX, move the stack down a few kilobytes.
>     
>     This particularly refers to the "rouilj/ops12" system my private
>     sysdump archive.
>     
>     Reported-and-tested-by: John Rouillard <rouilj at renesys.com>
>     Signed-off-by: H. Peter Anvin <hpa at zytor.com>
> 
> :040000 040000 a4eca2ce83128152f91d3d7faa7647f5ef6a67df
> c9e89c7e7e44b376c41648d7858fbd726d58b936 M	core
> 
> the first "bad" pxelinux reports itself as PXELINUX 3.85 pre9-4-g831f1a0
> 

OK, this is highly interesting, as this implies yet another BIOS which
squats on memory it has no right to mess with.

Could you try the attached patch and see if it works?

	-hpa
-------------- next part --------------
diff --git a/core/layout.inc b/core/layout.inc
index dab27dd..eeeffaa 100644
--- a/core/layout.inc
+++ b/core/layout.inc
@@ -38,7 +38,7 @@ TEXT_START	equ 7C00h
 		global STACK_LEN, STACK_TOP, STACK_BASE
 STACK_LEN	equ 4096
 %if IS_PXELINUX
-STACK_TOP	equ 7000h
+STACK_TOP	equ 6800h
 %else
 STACK_TOP	equ 7c00h
 %endif