vgabios: Work around lack of support for "calll" in x86emu emulation.

Replace 32 bit call instructions with 16 bit call instructions in the
vgabios to workaround problems in old versions of x86emu.  This change
allows fc13 and fc14 to boot.  (Other x86emu emulation bugs still
prevent fc11 and fc12 from booting.)

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>
diff --git a/scripts/vgafixup.py b/scripts/vgafixup.py
index 52fb934..2493f35 100644
--- a/scripts/vgafixup.py
+++ b/scripts/vgafixup.py
@@ -28,6 +28,8 @@
             out.append('retw $2\n')
         elif sline == 'leave':
             out.append('movl %ebp, %esp ; popl %ebp\n')
+        elif sline.startswith('call'):
+            out.append('pushw %ax ; callw' + sline[4:] + '\n')
         else:
             out.append(line)
     infile.close()
diff --git a/vgasrc/vgaentry.S b/vgasrc/vgaentry.S
index d9fe05b..a65136d 100644
--- a/vgasrc/vgaentry.S
+++ b/vgasrc/vgaentry.S
@@ -44,17 +44,34 @@
  * Entry points
  ****************************************************************/
 
+        // This macro is the same as ENTRY_ARG except the "calll"
+        // instruction is avoided to work around known issues in the
+        // emulation of some versions of x86emu.
+        .macro ENTRY_ARG_VGA cfunc
+        cli
+        cld
+        PUSHBREGS
+        movw %ss, %ax           // Move %ss to %ds
+        movw %ax, %ds
+        movl %esp, %ebx         // Backup %esp, then zero high bits
+        movzwl %sp, %esp
+        movl %esp, %eax         // First arg is pointer to struct bregs
+        pushw %ax ; callw \cfunc
+        movl %ebx, %esp         // Restore %esp (including high bits)
+        POPBREGS
+        .endm
+
         DECLFUNC entry_104f05
 entry_104f05:
-        ENTRY_ARG vbe_104f05
+        ENTRY_ARG_VGA vbe_104f05
         lretw
 
         DECLFUNC _optionrom_entry
 _optionrom_entry:
-        ENTRY_ARG vga_post
+        ENTRY_ARG_VGA vga_post
         lretw
 
         DECLFUNC entry_10
 entry_10:
-        ENTRY_ARG handle_10
+        ENTRY_ARG_VGA handle_10
         iretw