fixed int86 to return correctly from BIOS calls that internally change

to protected mode and back to real mode, undoing our unreal mode hack in
the process.

diff --git a/src/boot/boot2.s b/src/boot/boot2.s
index f2aab01..7067a8f 100644 (file)
--- a/src/boot/boot2.s
+++ b/src/boot/boot2.s
@@ -763,6 +763,9 @@ rmidt:      .short 0x3ff
 
 saved_esp: .long 0
 saved_ebp: .long 0
+saved_eax: .long 0
+saved_es: .word 0
+saved_ds: .word 0
 
        # drop back to unreal mode to call 16bit interrupt
        .global int86
@@ -809,17 +812,18 @@ int86:
        # ignore fs and gs for now, don't think I'm going to need them
        mov saved_esp, %esp
 
+       # move to the real-mode stack, accessible from ss=0
+       # just in case the BIOS call screws up our unreal mode
+       mov $0x7be0, %esp
+
        # call 16bit interrupt
 int_op:        int $0
 
-       mov saved_ebp, %ebp
-       mov 12(%ebp), %esp
-       add $38, %esp
-       push %ds
-       push %es
-       pushfw
-       pushal
-       mov saved_esp, %esp
+       # save all registers that we'll clobber before having the
+       # chance to populate the int86regs structure
+       mov %eax, saved_eax
+       mov %ds, saved_ds
+       mov %es, saved_es
 
        # re-enable protection
        mov %cr0, %eax
@@ -836,6 +840,18 @@ int_op:    int $0
        mov %ax, %ss
        nop
 
+       mov saved_ebp, %ebp
+       mov 12(%ebp), %esp
+       add $38, %esp
+       mov saved_ds, %ax
+       pushw %ax
+       mov saved_es, %ax
+       pushw %ax
+       pushfw
+       mov saved_eax, %eax
+       pushal
+       mov saved_esp, %esp
+
        # restore 32bit interrupt descriptor table
        lidt (saved_idtr)
        sti