1 files changed, 40 insertions, 0 deletions
diff --git a/boot/segdesc.inc b/boot/segdesc.inc
new file mode 100644
index 0000000..b4d14dc
--- /dev/null
+++ b/boot/segdesc.inc
@@ -0,0 +1,40 @@
+; segment type
+SEG_ACCESSED     = 0001b
+SEG_CODE_READ    = 0010b
+SEG_DATA_WRITE   = 0010b
+SEG_CODE_CONFORM = 0100b
+SEG_DATA_EXPDOWN = 0100b
+SEG_EXECUTE      = 1000b
+
+; privilege level
+SEG_PRIV0 = (00b shl 0x05)
+SEG_PRIV1 = (01b shl 0x05)
+SEG_PRIV2 = (10b shl 0x05)
+SEG_PRIV3 = (11b shl 0x05)
+
+; other flags
+SEG_DESCTYPE = (1b shl 0x04) ; descriptor type
+SEG_PRES     = (1b shl 0x07) ; present
+SEG_SAVL     = (1b shl 0x0C) ; available for system use
+SEG_LONG     = (1b shl 0x0D) ; long mode
+SEG_SIZE     = (1b shl 0x0E) ; size
+SEG_GRAN     = (1b shl 0x0F) ; granularity
+
+; segment descriptor flag sets for convenience
+GDT_CODE_32 = SEG_DESCTYPE or SEG_PRES or SEG_SIZE or SEG_GRAN or SEG_EXECUTE or SEG_CODE_READ
+GDT_DATA_32 = SEG_DESCTYPE or SEG_PRES or SEG_SIZE or SEG_GRAN or SEG_DATA_WRITE
+GDT_CODE_64 = SEG_DESCTYPE or SEG_PRES or SEG_LONG or SEG_EXECUTE or SEG_CODE_READ
+GDT_DATA_64 = SEG_DESCTYPE or SEG_PRES or SEG_LONG or SEG_DATA_WRITE
+
+struc seg_desc base*, limit*, flag* {
+	assert 0x0 <= limit & limit <= 0x000fffff
+	assert 0x0 <= base  & base  <= 0xffffffff
+	assert (flag or 0xf0ff) = 0xf0ff
+
+	. dq ((limit shl 0x20) and 0x000f000000000000) or \
+	     ((flag  shl 0x28) and 0x00f0ff0000000000) or \
+	     ((base  shl 0x10) and 0x000000ff00000000) or \
+	     ((base  shl 0x20) and 0xff00000000000000) or \
+	     ((base  shl 0x10) and 0x00000000ffff0000) or \
+	     ((limit shl 0x00) and 0x000000000000ffff)
+}