Someone at Dell must have a full-time job designing ways to screw up
implementations of INT 15,e820. This latest gem is courtesy of a Dell
Xanadu system, which arbitrarily decides to obliterate the contents of
%esi.
Preserve %esi, %edi and %ebp across calls to INT 15,e820, in case
someone tries a variation on this trick in future.
pushl %ebx
pushl %ecx
pushl %edx
+ pushl %esi /* Some implementations corrupt %esi, so we */
+ pushl %edi /* preserve %esi, %edi and %ebp to be paranoid */
+ pushl %ebp
pushw %es
- pushw %di
pushw %ds
popw %es
movw $underlying_e820_cache, %di
stc
pushfw
lcall *%cs:int15_vector
- popw %di
popw %es
+ popl %ebp
+ popl %edi
+ popl %esi
/* Check for error return from underlying e820 call */
jc 2f /* CF set: error */
cmpl $SMAP, %eax
memset ( &e820buf, 0, sizeof ( e820buf ) );
do {
+ /* Some BIOSes corrupt %esi for fun. Guard against
+ * this by telling gcc that all non-output registers
+ * may be corrupted.
+ */
__asm__ __volatile__ ( REAL_CODE ( "stc\n\t"
"int $0x15\n\t"
"pushfw\n\t"
"D" ( __from_data16 ( &e820buf ) ),
"c" ( sizeof ( e820buf ) ),
"d" ( SMAP )
- : "memory" );
+ : "esi", "memory" );
if ( smap != SMAP ) {
DBG ( "INT 15,e820 failed SMAP signature check\n" );