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Allow boot sector to completely destroy real-mode stack, but still

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manage to return control.
This commit is contained in:
Michael Brown 2007-01-09 14:13:59 +00:00
parent a9369bb503
commit a2ffe8c123
1 changed files with 15 additions and 10 deletions
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25
src/arch/i386/interface/pcbios/int13.c
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@ -599,27 +599,32 @@ int int13_boot ( unsigned int drive ) {
hook_bios_interrupt ( 0x19, ( unsigned int ) int13_exec_fail,
&int19_vector );
/* Boot the loaded sector */
__asm__ __volatile__ ( REAL_CODE ( /* Save segment registers */
"pushw %%ds\n\t"
"pushw %%es\n\t"
"pushw %%fs\n\t"
"pushw %%gs\n\t"
/* Boot the loaded sector
*
* We assume that the boot sector may completely destroy our
* real-mode stack, so we preserve everything we need in
* static storage.
*/
__asm__ __volatile__ ( REAL_CODE ( /* Save return address off-stack */
"popw %%cs:int13_saved_retaddr\n\t"
/* Save stack pointer */
"movw %%ss, %%ax\n\t"
"movw %%ax, %%cs:int13_saved_ss\n\t"
"movw %%sp, %%cs:int13_saved_sp\n\t"
/* Jump to boot sector */
"ljmp $0, $0x7c00\n\t"
/* Preserved variables */
"\nint13_saved_ss: .word 0\n\t"
"\nint13_saved_sp: .word 0\n\t"
"\nint13_saved_retaddr: .word 0\n\t"
/* Boot failure return point */
"\nint13_exec_fail:\n\t"
/* Restore stack pointer */
"movw %%cs:int13_saved_ss, %%ax\n\t"
"movw %%ax, %%ss\n\t"
"movw %%cs:int13_saved_sp, %%sp\n\t"
"popw %%gs\n\t"
"popw %%fs\n\t"
"popw %%es\n\t"
"popw %%ds\n\t" )
/* Return via saved address */
"jmp *%%cs:int13_saved_retaddr\n\t")
: "=d" ( discard_d ) : "d" ( drive )
: "eax", "ebx", "ecx", "esi", "edi", "ebp" );