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From e1db3e675ae4ccbeea5de9f4b74a618e42eac1a3 Mon Sep 17 00:00:00 2001
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From: Nick Bertrand <nick@physics.umn.edu>
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Date: Tue, 31 Jul 2012 19:00:05 -0700
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Subject: [PATCH] Save Dell BIOS chunk in PXELINUX
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Our site has many Dell OptiPlex 790s, all of which are unable to use the
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'localboot' PXELINUX option as they either hang at 'Booting from local disk...'
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or immediately reboot depending on which SYSLINUX version is used. Many people
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have suggested using chain.c32 to chain load the local disk as a workaround,
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but this causes problems with Windows 7 BitLocker as it detects the chain load
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and forces the user to enter the recovery key. While searching for another
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option I determined that the problem seems to stem from the BIOS storing some
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information in the memory range 0x47CC-0x47FF, which is overwritten when
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PXELINUX loads. I couldn't figure out a clean way to avoid that memory region
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as it falls in the middle of the 4.x bss16 region, so I decided to create a
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copy of it instead. By copying that information out of the way during PXELINUX
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initialization and copying it back before returning control via 'localboot 0',
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the computer successfully boots to the local disk.
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Some additional info:
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BIOS revision: A13
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PXE versions: Intel Boot Agent GE v1.3.81, Intel Boot Agent PXE Base Code (PXE-2.1 build 089)
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Versions of SYSLINUX affected: 3.83, 4.03, 4.04, 4.05, possibly others
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Resulting symptom for localboot option vs SYSLINUX version:
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localboot 0 localboot -1
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3.83 Reboot Reboot
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4.03 Reboot Reboot
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4.04 Hang Reboot
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4.05 Hang Reboot
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This patch does not fix the reboot issue when using 'localboot -1'. I believe
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this patch should also help those with OptiPlex 990s, but I don't have one to
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test with to confirm.
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Below is a patch against commit 0a0e0e41cad93cd16c323cf16f40264a21eedd6c of
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the git.kernel.org/pub/scm/boot/syslinux/syslinux.git repository.
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--
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---
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core/pxelinux.asm | 18 ++++++++++++++++++
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1 file changed, 18 insertions(+)
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diff --git a/core/pxelinux.asm b/core/pxelinux.asm
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index e8818a6..b58ed2a 100644
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--- a/core/pxelinux.asm
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+++ b/core/pxelinux.asm
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@@ -132,6 +132,13 @@ _start1:
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mov ds,ax
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mov es,ax
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+ ; Copy chunk of memory used by Dell BIOS on OptiPlex 790s
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+ ; Allows control to return to PXE Boot Agent for localboot
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+ mov esi,47cch
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+ mov edi,DellBIOSChunk
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+ mov ecx,13
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+ rep movsd
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+
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%if 0 ; debugging code only... not intended for production use
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; Clobber the stack segment, to test for specific pathologies
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mov di,STACK_BASE
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@@ -289,6 +296,14 @@ local_boot:
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; Restore the environment we were called with
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pm_call reset_pxe
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call cleanup_hardware
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+
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+ ; Copy Dell BIOS chunk back into place
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+ cld
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+ mov esi,DellBIOSChunk
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+ mov edi,47cch
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+ mov ecx,13
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+ rep movsd
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+
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lss sp,[InitStack]
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pop gs
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pop fs
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@@ -564,3 +579,6 @@ IPInfo:
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.ServerIP resd 1
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.GatewayIP resd 1
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.Netmask resd 1
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+
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+ section .earlybss
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+DellBIOSChunk resd 13 ; 52 bytes to store Dell BIOS chunk
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--
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2.5.0
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