X-Git-Url: https://git.saurik.com/apple/boot.git/blobdiff_plain/14c7c974991c850bfa0348affbd4bee3223205ee..57c72a9a9f2a263d364c2df1178760bd057c390f:/i386/boot2/boot2.s

diff --git a/i386/boot2/boot2.s b/i386/boot2/boot2.s
index ec16572..f8b70b4 100644
--- a/i386/boot2/boot2.s
+++ b/i386/boot2/boot2.s
@@ -42,9 +42,13 @@
 #define data32  .byte 0x66
 #define retf    .byte 0xcb
 
-
     .file "boot2.s"
 
+    .data
+
+EXPORT(_chainbootdev)  .byte 0x80
+EXPORT(_chainbootflag) .byte 0x00
+
 .text
 
 # - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
@@ -75,12 +79,17 @@ LABEL(boot2)
     data32
     call    __real_to_prot      # Enter protected mode.
 
+    fninit                      # FPU init
+
     # We are now in 32-bit protected mode.
     # Transfer execution to C by calling boot().
 
     pushl   %edx                # bootdev
     call    _boot
 
+    testb   $0xff, _chainbootflag
+    jnz     start_chain_boot    # Jump to a foreign booter
+
     call    __prot_to_real      # Back to real mode.
 
     data32
@@ -96,3 +105,22 @@ LABEL(boot2)
 
     retf                        # Hardcode a far return
 
+start_chain_boot:
+    xorl    %edx, %edx
+    movb    _chainbootdev, %dl  # Setup DL with the BIOS device number
+
+    call    __prot_to_real      # Back to real mode.
+
+    data32
+    call    __switch_stack      # Restore original stack
+    
+    pop     %es                 # Restore original ES and DS
+    pop     %ds
+    popl    %edi                # Restore all general purpose registers
+    popl    %esi                # except EAX.
+    popl    %ebp
+    popl    %ebx
+    popl    %ecx
+
+    data32
+    ljmp    $0, $0x7c00         # Jump to boot code already in memory