ukify: pack FWHEADERMAGIC directly instead of using bytes.fromhex

The current implementation

    FWHEADERMAGIC = 'feeddead'
    magic = bytes.fromhex(FWHEADERMAGIC)
    struct.pack('<p', magic)

returns a single null byte b'\x00', which is not equal to 0xfeeddead in any
endianness.

(cherry picked from commit fe689d2d7946593001bb3d0e32d51d694af5d50d)

src/ukify/test/test_ukify.py

@@ -21,6 +21,7 @@ import os
 import pathlib
 import re
 import shutil
+import struct
 import subprocess
 import sys
 import tempfile
@@ -875,6 +876,20 @@ def test_inspect_json_profiles(tmp_path, capsys):
     shutil.rmtree(tmp_path)
 
 
+def test_parse_efifw_dir(tmp_path):
+    fwdir = tmp_path / 'fw0'
+    fwdir.mkdir()
+    payload = b'EFIFW0'
+    (fwdir / 'firmware.bin').write_bytes(payload)
+
+    fwname = fwdir.name.encode() + b'\0'
+
+    comp = (ukify.FWHEADERMAGIC, ukify.EFIFW_HEADER_SIZE, len(fwname), len(payload))
+    blob = ukify.parse_efifw_dir(fwdir)
+    assert comp == struct.unpack_from('<IIII', blob[: ukify.EFIFW_HEADER_SIZE])
+    assert (fwname + payload) == blob[ukify.EFIFW_HEADER_SIZE :]
+
+
 def test_inspect_json_alternative_set_sections(tmp_path, capsys):
     # '.dtbauto' and '.efifw' are alternative-sets (one entry per hardware variant): every occurrence
     # must be preserved, and they are always reported as a list, even for a single entry. The two are

src/ukify/ukify.py

@@ -1242,8 +1242,8 @@ NULL_DEVICE = b'\0' * DEVICE_STRUCT_SIZE
 DEVICE_TYPE_DEVICETREE = 1
 DEVICE_TYPE_UEFI_FW = 2
 
-# Keep in sync with efifirmware.h
-FWHEADERMAGIC = 'feeddead'
+# Keep in sync with src/boot/efi-firmware.h
+FWHEADERMAGIC = 0xFEEDDEAD
 EFIFW_HEADER_SIZE = 4 + 4 + 4 + 4
 
 
@@ -1358,10 +1358,9 @@ def parse_efifw_dir(path: Path) -> bytes:
     # terminated by NULL.
     fwid = b'' + dirname.encode() + b'\0'
     fwid_len = len(fwid)
-    magic = bytes.fromhex(FWHEADERMAGIC)
 
     efifw_header_blob = b''
-    efifw_header_blob += struct.pack('<p', magic)
+    efifw_header_blob += struct.pack('<I', FWHEADERMAGIC)
     efifw_header_blob += struct.pack('<I', EFIFW_HEADER_SIZE)
     efifw_header_blob += struct.pack('<I', fwid_len)
     efifw_header_blob += struct.pack('<I', payload_len)