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| author | H. Peter Anvin <hpa@zytor.com> | 2008-02-15 22:35:18 -0800 |
|---|---|---|
| committer | H. Peter Anvin <hpa@zytor.com> | 2008-02-15 22:54:15 -0800 |
| commit | defcbbc6527cd20bd45e42fab53d7e185156df48 (patch) | |
| tree | 7cdba63b1d0b72d001b2f0cfb4b2162a48fef151 | |
| parent | 7234f292a43f971899b4a10fc5130c400c4aa3b2 (diff) | |
| download | syslinux.git-defcbbc6527cd20bd45e42fab53d7e185156df48.tar.gz syslinux.git-defcbbc6527cd20bd45e42fab53d7e185156df48.tar.xz syslinux.git-defcbbc6527cd20bd45e42fab53d7e185156df48.zip | |
Don't close the A20 gate; leave it open
Don't close the A20 gate (restore to previous state); leave it open.
This is good for performance, but also avoids a nasty race condition
when leaving protected mode to then quickly re-enter protected mode.
| -rw-r--r-- | bcopy32.inc | 9 | ||||
| -rw-r--r-- | com32.inc | 2 | ||||
| -rw-r--r-- | config.inc | 11 |
3 files changed, 21 insertions, 1 deletions
diff --git a/bcopy32.inc b/bcopy32.inc index b62d3ac4..99a16d88 100644 --- a/bcopy32.inc +++ b/bcopy32.inc @@ -190,7 +190,9 @@ simple_pm_call: pop fs pop es pop ds +%if DISABLE_A20 call disable_a20 +%endif popfd ; Re-enables interrupts pop ebp @@ -412,6 +414,8 @@ a20_test: pop es ret +%if DISABLE_A20 + disable_a20: pushad ; @@ -464,6 +468,8 @@ a20d_none: popad ret +%endif + ; ; Routine to empty the 8042 KBC controller. If dl != 0 ; then we will test A20 in the loop and exit if A20 is @@ -594,8 +600,9 @@ trampoline_to_pm: align 2 A20List dw a20_dunno, a20_none, a20_bios, a20_kbc, a20_fast +%if DISABLE_A20 A20DList dw a20d_dunno, a20d_none, a20d_bios, a20d_kbc, a20d_fast -a20_adjust_cnt equ ($-A20List)/2 +%endif A20Type dw A20_NONE ; A20 type @@ -210,7 +210,9 @@ com32_enter_rm: jmp bx ; Go to whereever we need to go... com32_done: +%if DISABLE_A20 call disable_a20 +%endif sti jmp enter_command @@ -28,6 +28,17 @@ MAX_FKEYS equ 12 ; Number of F-key help files %assign DO_WBINVD 0 ; Should we use WBINVD or not? ; +; Set this to return the A20 gate to its previous state, instead of +; leaving it open. This has caused problems, because there appear +; to be a race condition between disabling the A20 gate and trying to +; re-enter protected mode, causing the A20 gate disable to take effect +; after we have already done the A20 enabled check, with disastrous +; consequences. Plus, there seems to be little or no demand for it. +; +%assign DISABLE_A20 0 + + +; ; Version number definitinons ; %ifndef DEPEND ; Generated file |