Proof of concept; works, but has several hard-coded hacks.

diff --git a/src/arch/i386/interface/pcbios/int13.c b/src/arch/i386/interface/pcbios/int13.c
index aeb66adeb31263ff3ae95e80b31d46d7bcae9eb9..a4563a05132afe0d52865c71a9d9ca06b992f4fa 100644 (file)
--- a/src/arch/i386/interface/pcbios/int13.c
+++ b/src/arch/i386/interface/pcbios/int13.c
@@ -355,12 +355,18 @@ static int int13_cdrom_status_terminate ( struct int13_drive *drive,
  */
 static void int13 ( struct i386_all_regs *ix86 ) {
        int command = ix86->regs.ah;
+       unsigned int bios_drive = ix86->regs.dl;
+       unsigned int original_bios_drive = bios_drive;
        struct int13_drive *drive;
        int status;
 
        list_for_each_entry ( drive, &drives, list ) {
-               if ( drive->drive != ix86->regs.dl )
+               if ( drive->drive > bios_drive )
                        continue;
+               if ( drive->drive < bios_drive ) {
+                       original_bios_drive--;
+                       continue;
+               }
                
                DBG ( "INT 13,%04x (%02x): ", ix86->regs.ax, drive->drive );
 
@@ -421,6 +427,13 @@ static void int13 ( struct i386_all_regs *ix86 ) {
 
                break;
        }
+
+       /* Remap BIOS drive */
+       if ( bios_drive != original_bios_drive ) {
+               DBG ( "INT 13,%04x (%02x) remapped to (%02x)\n",
+                     ix86->regs.ax, bios_drive, original_bios_drive );
+       }
+       ix86->regs.dl = original_bios_drive;
 }
 
 /**
@@ -434,19 +447,42 @@ static void hook_int13 ( void ) {
         */
        __asm__  __volatile__ (
               TEXT16_CODE ( "\nint13_wrapper:\n\t"
-                            "orb $0, %%al\n\t" /* clear OF */
+                            /* Preserve %ax and %dx for future reference */
+                            "pushw %%bp\n\t"
+                            "movw %%sp, %%bp\n\t"                           
+                            "pushw %%ax\n\t"
+                            "pushw %%dx\n\t"
+                            /* Clear OF, set CF, call int13() */
+                            "orb $0, %%al\n\t" 
                             "stc\n\t"
-                            "pushl %0\n\t" /* call int13() */
+                            "pushl %0\n\t"
                             "pushw %%cs\n\t"
                             "call prot_call\n\t"
-                            "jo 1f\n\t" /* chain if OF not set */
+                            /* Chain if OF not set */
+                            "jo 1f\n\t"
                             "pushfw\n\t"
                             "lcall *%%cs:int13_vector\n\t"
                             "\n1:\n\t"
-                            "call 2f\n\t" /* return with flags intact */
-                            "lret $2\n\t"
+                            /* Overwrite flags for iret */
+                            "pushfw\n\t"
+                            "popw 6(%%bp)\n\t"
+                            /* Restore %dl (except for %ah=0x08 or 0x15) */
+                            "cmpb $0x08, -1(%%bp)\n\t"
+
+                            "jne 7f\n\t"
+                            "movb $2, %%dl\n\t"
+                            "jmp 2f\n\t"
+                            "\n7:\n\t"
+
+                            "je 2f\n\t"
+                            "cmpb $0x15, -1(%%bp)\n\t"
+                            "je 2f\n\t"
+                            "movb -4(%%bp), %%dl\n\t"
                             "\n2:\n\t"
-                            "ret $4\n\t" ) : : "i" ( int13 ) );
+                            /* Return */
+                            "movw %%bp, %%sp\n\t"
+                            "popw %%bp\n\t"
+                            "iret\n\t" ) : : "i" ( int13 ) );
 
        hook_bios_interrupt ( 0x13, ( unsigned int ) int13_wrapper,
                              &int13_vector );
@@ -541,6 +577,9 @@ void register_int13_drive ( struct int13_drive *drive ) {
                drive->drive = ( num_drives | 0x80 );
        if ( num_drives <= ( drive->drive & 0x7f ) )
                num_drives = ( ( drive->drive & 0x7f ) + 1 );
+
+       num_drives = 2;
+
        put_real ( num_drives, BDA_SEG, BDA_NUM_DRIVES );
 
        DBG ( "Registered INT13 drive %02x with C/H/S geometry %d/%d/%d\n",