generalizing the 16bit interrupt hack to an arbitray int86() call

[bootcensus] / src / boot / boot2.s

diff --git a/src/boot/boot2.s b/src/boot/boot2.s
index 37f1026..e4088f4 100644 (file)
--- a/src/boot/boot2.s
+++ b/src/boot/boot2.s
@@ -554,10 +554,9 @@ kbc_wait_write:
 numbuf: .space 16
 
 
-# this is not boot loader code. It's called later on by the main
-# kernel code in 32bit protected mode. It's placed here because
-# it needs to be in base memory as it returns and runs in real mode.
-
+# this is not boot loader code. It's called later on by the main kernel
+# code in 32bit protected mode. It's placed here because it needs to be
+# located in base memory as it returns and runs in real mode.
        .code32
        .align 4
        # place to save the protected mode IDTR pseudo-descriptor
@@ -571,9 +570,14 @@ idtaddr:.long 0
 rmidt: .short 0x3ff
        .long 0
 
-       # drop back to unreal mode to set video mode
-       .global set_mode13h
-set_mode13h:
+saved_esp: .long 0
+saved_ebp: .long 0
+
+       # drop back to unreal mode to call 16bit interrupt
+       .global int86
+int86:
+       push %ebp
+       mov %esp, %ebp
        pushal
        cli
        # save protected mode IDTR and replace it with the real mode vectors
@@ -597,9 +601,26 @@ set_mode13h:
        mov %ax, %ss
        nop
 
-       # switch video mode by calling the video bios
-       mov $0x13, %ax
-       int $0x10
+       # modify the int instruction
+       mov $int_op, %ebx
+       movb 4(%ebp), %al
+       movb %al, 1(%ebx)
+
+       # load registers from the int86regs struct
+       mov %esp, saved_esp
+       mov %ebp, saved_ebp
+       mov 8(%ebp), %esp
+       popal
+       mov saved_esp, %esp
+
+       # call 16bit interrupt
+int_op:        int $0
+
+       mov saved_ebp, %ebp
+       mov 8(%ebp), %esp
+       add $32, %esp
+       pushal
+       mov saved_esp, %esp
 
        # re-enable protection
        mov %cr0, %eax
@@ -620,6 +641,7 @@ set_mode13h:
        lidt (saved_idtr)
        sti
        popal
+       pop %ebp
        ret