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#include <mach/machine/asm.h>
.text
.code16
/*
* Test the A20 address line; return true if it is enabled.
*/
ENTRY(i16_raw_test_a20)
xorw %ax,%ax
movw %ax,%fs
notw %ax
movw %ax,%gs
/* See if the values in already in the corresponding locations
are the same. */
movw %fs:0,%ax
cmpw %gs:16,%ax
jnz 1f
/* Yes; try changing one and see if they're still the same. */
movw %ax,%dx
notw %ax
movw %ax,%fs:0
cmpw %gs:16,%ax
movw %dx,%fs:0
jnz 1f
xorl %eax,%eax
ret
1:
movl $1,%eax
ret
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