Make some clarifications in ToolchainExample.cmake

ToolchainExample.cmake

@@ -1,27 +1,37 @@
 # This is an example Toolchain file to cross-compile for ARM/MIPS/other
 # boards from x86_64. Copy & modify. Skip 4-8 if using LLVM less build
 #
+# x86_64 = "build"
+# ARM/MIPS/other board = "host" or "board"
+#
 # Steps:
-# 1) Install g++ and gcc cross-compilers
+# (note: hwloc is now optional)
+# 1) on build system, install g++ and gcc cross-compilers
 #    (apt install gcc-arm-linux-gnueabihf g++-arm-linux-gnueabihf)
-# 2) On your board, install libltdl, ocl-icd and libhwloc + their development headers
-# 3) copy the entire root filesystem of the board somewhere on your host,
+# 2) On the board, install ocl-icd and libhwloc (optional) + their development headers
+# 3) copy the entire root filesystem of the board somewhere to the build system,
 #    then set CMAKE_FIND_ROOT_PATH below to this path
-# 4) Build clang and llvm for the build machine and install them. ($BUILD_PREFIX)
-# 5) Build clang and llvm for the host machine and install them. ($HOST_PREFIX)
+# 4) Build clang and llvm for the build system and install them. ($BUILD_PREFIX)
+# 5) Build clang and llvm for the host and install them. ($HOST_PREFIX)
 # 6) copy llvm-config from build to host. (cp $BUILD_PREFIX/bin/llvm-config $HOST_PREFIX/bin/llvm-config)
 # 7) Install pkg-config for build
 # 8) Install hwloc, ocl-icd for host and set `PKG_CONFIG_PATH` env variable to the paths
 #    eg: export PKG_CONFIG_PATH=/path/to/hwloc/prefix/lib/pkgconfig:/path/to/opencl/prefix/lib/pkgconfig
 # 9) run cmake like this:
-#          cmake -DHOST_DEVICE_BUILD_HASH=<SOME_HASH> -DENABLE_LLVM=<0 if LLVM-less, 1 if with LLVM>
+#          cmake -DHOST_DEVICE_BUILD_HASH=<SOME_HASH> (see below)
+#           -DENABLE_LLVM=<0 if LLVM-less, 1 if with LLVM>
 #           -DCMAKE_TOOLCHAIN_FILE=<path-to-this-file>
 #           -DCMAKE_PREFIX_PATH=$HOST_PREFIX
 #           -DLLC_TRIPLE=<your-triple (e.g.arm-gnueabihf-linux-gnu)
 #           -DLLVM_HOST_TARGET=<your-triple (e.g.arm-gnueabihf-linux-gnu)
 #           -DLLC_HOST_CPU=<your-cpu (e.g. armv7a)>
 #           -DLLVM_BINDIR=$BUILD_PREFIX/bin
 #           <path-to-pocl-source>
+#
+# ... where SOME_HASH is a string that can be set to anything;
+# when loading OpenCL program binaries, PoCL uses it to check
+# that the PoCL which built the binary is compatible with the
+# PoCL that's loading the binary.
 
 SET(CMAKE_SYSTEM_NAME Linux)