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Don't automatically call gateA20_set() when returning from a real-mode

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call.
This commit is contained in:
Michael Brown 2007-01-04 04:32:18 +00:00
parent 0c03bb5a9a
commit 290c5ee779
1 changed files with 7 additions and 5 deletions
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12
src/arch/i386/transitions/librm.S
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@ -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