qemu: support alternate path of qemu binaries

Support using an alternate QEMU path for when we want to use a qemu
version not available in the SDK.

To use the alternate qemu version, export QEMU_BIN_PATH and point it
to the bin directory which contains the qemu executables.

For example:

export QEMU_BIN_PATH=/usr/local/bin

Signed-off-by: Anas Nashif <[email protected]>

Author: nashif

cmake/emu/qemu.cmake

@@ -3,10 +3,21 @@ if("${ARCH}" STREQUAL "x86")
 else()
   set_ifndef(QEMU_binary_suffix ${ARCH})
 endif()
+
+set(qemu_alternate_path $ENV{QEMU_BIN_PATH})
+if(qemu_alternate_path)
+find_program(
+  QEMU
+  PATHS ${qemu_alternate_path}
+  NO_DEFAULT_PATH
+  NAMES qemu-system-${QEMU_binary_suffix}
+  )
+else()
 find_program(
   QEMU
   qemu-system-${QEMU_binary_suffix}
   )
+endif()
 
 set(qemu_targets
   run

doc/application/application.rst

@@ -378,6 +378,12 @@ hardware. Follow these instructions to run an application via QEMU:
 Each time you execute the run command, your application is rebuilt and run
 again.
 
+
+.. note:: The ``run`` target will use the QEMU binary available from the Zephyr
+          SDK by default. To use an alternate version of QEMU, for example the
+          version installed on your host or a custom version, set the
+          environment variable ``QEMU_BIN_PATH`` to the alternate path.
+
 .. _application_debugging:
 .. _custom_board_definition: