From 117353815595c46a29a3aebec966ab94f6a4b3c8 Mon Sep 17 00:00:00 2001
From: Michael Brown <mcb30@ipxe.org>
Date: Tue, 19 Jan 2021 23:47:44 +0000
Subject: [PATCH] [build] Allow genfsimg to be used on third party UEFI
 binaries

Extract the PE header offset from the MZ header rather than assuming a
fixed offset as used in the binaries created by the iPXE build system.

This allows genfsimg to be used to create bootable filesystem images
from third party UEFI binaries such as the UEFI shell.

Signed-off-by: Michael Brown <mcb30@ipxe.org>
---
 src/util/genfsimg | 26 ++++++++++++++++++++++----
 1 file changed, 22 insertions(+), 4 deletions(-)

diff --git a/src/util/genfsimg b/src/util/genfsimg
index a1fad247e..5d0a2bdea 100755
--- a/src/util/genfsimg
+++ b/src/util/genfsimg
@@ -16,6 +16,18 @@ help() {
     echo " -p PAD   pad filesystem (in kB)"
 }
 
+# Get hex byte from binary file
+#
+get_byte() {
+    local FILENAME
+    local OFFSET
+
+    FILENAME="${1}"
+    OFFSET="${2}"
+
+    od -j "${OFFSET}" -N 1 -A n -t x1 -- "${FILENAME}" | tr -d " "
+}
+
 # Get hex word from binary file
 #
 get_word() {
@@ -37,12 +49,18 @@ efi_boot_name() {
 
     FILENAME="${1}"
 
-    PESIG=$(get_word "${FILENAME}" 192)
-    if [ "${PESIG}" != "5045" ] ; then
-	echo "${FILENAME}: not an EFI executable" >&2
+    MZSIG=$(get_word "${FILENAME}" 0)
+    if [ "${MZSIG}" != "4d5a" ] ; then
+	echo "${FILENAME}: invalid MZ header" >&2
 	exit 1
     fi
-    ARCH=$(get_word "${FILENAME}" 196)
+    PEOFF=$(get_byte "${FILENAME}" 0x3c)
+    PESIG=$(get_word "${FILENAME}" "0x${PEOFF}")
+    if [ "${PESIG}" != "5045" ] ; then
+	echo "${FILENAME}: invalid PE header" >&2
+	exit 1
+    fi
+    ARCH=$(get_word "${FILENAME}" $(( "0x${PEOFF}" + 4 )) )
     case "${ARCH}" in
 	"4c01" )
 	    echo "BOOTIA32.EFI"