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[prefix] When we have to hook INT 19, chain to original handler if possible

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When the BIOS doesn't support BBS, hooking INT 19 is the only way to add
ourselves as a boot device.  If we have to do this, we should at least
try to chain to the original INT 19 vector if our boot fails.

Idea suggested by Andrew Schran <aschran@google.com>
This commit is contained in:
Michael Brown
2008-06-14 13:49:26 +01:00
parent a71b4df1c9
commit cd0e9bcd22
1 changed files with 14 additions and 2 deletions
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16
src/arch/i386/prefix/romprefix.S
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@@ -173,6 +173,8 @@ hook_int19:
call print_message call print_message
xorw %ax, %ax xorw %ax, %ax
movw %ax, %es movw %ax, %es
pushl %es:( 0x19 * 4 )
popl orig_int19
pushw %cs pushw %cs
pushw $int19_entry pushw $int19_entry
popl %es:( 0x19 * 4 ) popl %es:( 0x19 * 4 )
@@ -345,14 +347,24 @@ bev_entry:
/* INT19 entry point /* INT19 entry point
* *
* Called via the hooked INT 19 if we detected a non-PnP BIOS. * Called via the hooked INT 19 if we detected a non-PnP BIOS. We
* attempt to return via the original INT 19 vector (if we were able to
* store it).
*/ */
int19_entry: int19_entry:
pushw %cs pushw %cs
call exec call exec
/* No real way to return from INT19 */ movl %cs:orig_int19, %eax
testl %eax, %eax
je 1f
/* Chain to original INT 19 vector */
ljmp *%cs:orig_int19
1: /* No chained vector: issue INT 18 as a last resort */
int $0x18 int $0x18
.size int19_entry, . - int19_entry .size int19_entry, . - int19_entry
orig_int19:
.long 0
.size orig_int19, . - orig_int19
/* Execute as a boot device /* Execute as a boot device
* *