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| author | Michael Brown | 2007-01-04 05:32:18 +0100 |
|---|---|---|
| committer | Michael Brown | 2007-01-04 05:32:18 +0100 |
| commit | 290c5ee779764d76ddded979b390008daa71aec9 (patch) | |
| tree | eb6349a6f409d9a58104c01a864c4f208ab2d613 /src/arch/i386/transitions/librm.S | |
| parent | Make open() and close() an official part of the netdevice API. (diff) | |
| download | ipxe-290c5ee779764d76ddded979b390008daa71aec9.tar.gz ipxe-290c5ee779764d76ddded979b390008daa71aec9.tar.xz ipxe-290c5ee779764d76ddded979b390008daa71aec9.zip | |
Don't automatically call gateA20_set() when returning from a real-mode
call.
Diffstat (limited to 'src/arch/i386/transitions/librm.S')
| -rw-r--r-- | src/arch/i386/transitions/librm.S | 12 |
1 files changed, 7 insertions, 5 deletions
diff --git a/src/arch/i386/transitions/librm.S b/src/arch/i386/transitions/librm.S index 32faad4a..9edbd473 100644 --- a/src/arch/i386/transitions/librm.S +++ b/src/arch/i386/transitions/librm.S @@ -428,8 +428,13 @@ prot_call: * function will be passed back to the protected-mode caller. A * result of this is that this routine cannot be called directly from * C code, since it clobbers registers that the C ABI expects the - * callee to preserve. Gate A20 will be re-enabled in case the - * real-mode routine disabled it. + * callee to preserve. Gate A20 will *not* be automatically + * re-enabled. Since we always run from an even megabyte of memory, + * we are guaranteed to return successfully to the protected-mode + * code, which should then call gateA20_set() if it suspects that gate + * A20 may have been disabled. Note that enabling gate A20 is a + * potentially slow operation that may also cause keyboard input to be + * lost; this is why it is not done automatically. * * librm.h defines a convenient macro REAL_CODE() for using real_call. * See librm.h and realmode.h for details and examples. @@ -477,9 +482,6 @@ real_call: .section ".text" .code32 1: - /* Set up environment expected by C code */ - call gateA20_set - /* Restore registers and return */ popal ret |