1 files changed, 36 insertions, 0 deletions
diff --git a/x86-bare-metal/multiboot/scripts/check_mbhdr.awk b/x86-bare-metal/multiboot/scripts/check_mbhdr.awk
new file mode 100644
index 0000000..1471d69
--- /dev/null
+++ b/x86-bare-metal/multiboot/scripts/check_mbhdr.awk
@@ -0,0 +1,36 @@
+BEGIN {
+    # > xxd -d -e -c 4 IMG
+    #   00004096: 1badb002  ....
+    #
+    # Split at colon to easily extract file offset.
+    FS = ":"
+
+    # An OS image must contain an additional header called Multiboot header,
+    # besides the headers of the format used by the OS image. The Multiboot
+    # header must be contained completely within the first 8192 bytes of the OS
+    # image, and must be longword (32-bit) aligned. In general, it should come
+    # as early as possible, and may be embedded in the beginning of the text
+    # segment after the real executable header.
+    #
+    # https://www.gnu.org/software/grub/manual/multiboot/multiboot.html
+    MBHDR_LIMIT = 8192;
+    MBHDR_ALIGN = 4;
+
+    MBHDR_SIZE  = 3 * 4;
+}
+
+/1badb002/ {
+    print $0" off="$1
+
+    if ($1 > MBHDR_LIMIT - MBHDR_SIZE) {
+        print "FAIL: multiboot header must be in the first "$MBHDR_SIZE" bytes of the image!"
+        exit 1
+    }
+
+    if ($1 % MBHDR_ALIGN != 0) {
+        print "FAIL: multiboot header must be 32bit aligned!"
+        exit 1
+    }
+
+    exit 0
+}