Include instructions to extract Mac OS X SDK on Linux using 7zip and SleuthKit

contrib/macdeploy/extract-osx-sdk.sh

@@ -0,0 +1,29 @@
+#!/bin/bash
+set -e
+
+INPUTFILE="Xcode_7.3.1.dmg"
+HFSFILENAME="5.hfs"
+SDKDIR="Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.11.sdk"
+
+7z x "${INPUTFILE}" "${HFSFILENAME}"
+SDKNAME="$(basename "${SDKDIR}")"
+SDKDIRINODE=$(ifind -n "${SDKDIR}" "${HFSFILENAME}")
+fls "${HFSFILENAME}" -rpF ${SDKDIRINODE} |
+ while read type inode filename; do
+	inode="${inode::-1}"
+	if [ "${filename:0:14}" = "usr/share/man/" ]; then
+		continue
+	fi
+	filename="${SDKNAME}/$filename"
+	echo "Extracting $filename ..."
+	mkdir -p "$(dirname "$filename")"
+	if [ "$type" = "l/l" ]; then
+		ln -s "$(icat "${HFSFILENAME}" $inode)" "$filename"
+	else
+		icat "${HFSFILENAME}" $inode >"$filename"
+	fi
+done
+echo "Building ${SDKNAME}.tar.gz ..."
+MTIME="$(istat "${HFSFILENAME}" "${SDKDIRINODE}" | perl -nle 'm/Content Modified:\s+(.*?)\s\(/ && print $1')"
+find "${SDKNAME}" | sort | tar --no-recursion --mtime="${MTIME}" --mode='u+rw,go+r-w,a+X' --owner=0 --group=0 -c -T - | gzip -9n > "${SDKNAME}.tar.gz"
+echo 'All done!'

doc/README_osx.md

@@ -36,11 +36,26 @@ Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.1
 ```
 
 Unfortunately, the usual linux tools (7zip, hpmount, loopback mount) are incapable of opening this file.
-To create a tarball suitable for Gitian input, mount the dmg in OS X, then create it with:
+To create a tarball suitable for Gitian input, there are two options:
+
+Using Mac OS X, you can mount the dmg, and then create it with:
 ```
+  $ hdiutil attach Xcode_7.3.1.dmg
   $ tar -C /Volumes/Xcode/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/ -czf MacOSX10.11.sdk.tar.gz MacOSX10.11.sdk
 ```
 
+Alternatively, you can use 7zip and SleuthKit to extract the files one by one.
+The script contrib/macdeploy/extract-osx-sdk.sh automates this. First ensure
+the dmg file is in the current directory, and then run the script. You may wish
+to delete the intermediate 5.hfs file and MacOSX10.11.sdk (the directory) when
+you've confirmed the extraction succeeded.
+
+```bash
+apt-get install p7zip-full sleuthkit
+contrib/macdeploy/extract-osx-sdk.sh
+rm -rf 5.hfs MacOSX10.11.sdk
+```
+
 The Gitian descriptors build 2 sets of files: Linux tools, then Apple binaries
 which are created using these tools. The build process has been designed to
 avoid including the SDK's files in Gitian's outputs. All interim tarballs are