prebuilt: failed extract-vmlinux attempt

README.adoc

@@ -582,12 +582,15 @@ but QEMU builds are pretty quick, and this further increases the probability of
 For gem5, do:
 
 ....
+git submodule update --init --depth 1 "$(./getvar linux_src_dir)"
 sudo apt-get install qemu-utils
 ./build-gem5
 ./run --gem5 --prebuilt
 ....
 
 `qemu-utils` is required because we currently distribute `.qcow2` files which <<gem5-qcow2,gem5 can't handle>>, so we need `qemu-img` to extract them first.
+
+The Linux kernel is required for `extract-vmlinux` to convert the compressed kernel image which QEMU understands into the raw vmlinux that gem5 understands: https://superuser.com/questions/298826/how-do-i-uncompress-vmlinuz-to-vmlinux
 ////
 
 [[host]]

common.py

@@ -30,6 +30,7 @@ submodules_dir = os.path.join(root_dir, 'submodules')
 buildroot_src_dir = os.path.join(submodules_dir, 'buildroot')
 gem5_default_src_dir = os.path.join(submodules_dir, 'gem5')
 linux_src_dir = os.path.join(submodules_dir, 'linux')
+extract_vmlinux = os.path.join(linux_src_dir, 'scripts', 'extract-vmlinux')
 qemu_src_dir = os.path.join(submodules_dir, 'qemu')
 parsec_benchmark_src_dir = os.path.join(submodules_dir, 'parsec-benchmark')
 ccache_dir = os.path.join('/usr', 'lib', 'ccache')

run

@@ -104,6 +104,14 @@ def main(args, extra_args=None):
             if not os.path.exists(common.qcow2_file):
                 raise_rootfs_not_found()
             common.raw_to_qcow2(prebuilt=args.prebuilt, reverse=True)
+        if not os.path.exists(common.vmlinux):
+            # This would allow us to run the prebuilt QEMU Linux image.
+            # but TODO cannot convert Image to vmlinux on aarch64:
+            # run-detectors: unable to find an interpreter for
+            if not os.path.exists(common.linux_image):
+                raise Exception('Linux kernel image not found. Did you compile it?\n' \
+                                'Tried: ' + common.vmlinux)
+            assert common.run_cmd([os.path.join(common.extract_vmlinux, common.linux_image)]) == 0
         os.makedirs(os.path.dirname(common.gem5_readfile), exist_ok=True)
         with open(common.gem5_readfile, 'w') as readfile:
             readfile.write(args.gem5_readfile)
@@ -175,7 +183,7 @@ def main(args, extra_args=None):
             qemu_executable = common.qemu_executable
             qemu_found = os.path.exists(qemu_executable)
         if not qemu_found:
-            raise Exception('Could not find the QEMU executable, did you forget to build or install it?\n' \
+            raise Exception('QEMU executable not found, did you forget to build or install it?\n' \
                             'Tried to use: ' + qemu_executable)
         if not os.path.exists(common.qcow2_file):
             if not os.path.exists(common.rootfs_raw_file):