kunit: tool: stop using a shell to run kernel under QEMU

Note: this potentially breaks custom qemu_configs if people are using
them! But the fix for them is simple, don't specify multiple arguments
in one string and don't add on a redundant ''.

It feels a bit iffy to be using a shell in the first place.

There's the usual shenanigans where people could pass in arbitrary shell
commands via --kernel_arg (since we're just adding '' around the
kernel_cmdline) or via a custom qemu_config.
This isn't too much of a concern given the nature of this script (and
the qemu_config file is in python, you can do w/e you want already).

But it does have some other drawbacks.

One example of a kunit-specific pain point:
If the relevant qemu binary is missing, we get output like this:
> /bin/sh: line 1: qemu-system-aarch64: command not found
This in turn results in our KTAP parser complaining about
missing/invalid KTAP, but we don't directly show the error!
It's even more annoying to debug when you consider --raw_output only
shows KUnit output by default, i.e. you need --raw_output=all to see it.

Whereas directly invoking the binary, Python will raise a
FileNotFoundError for us, which is a noisier but more clear.

Making this change requires
* splitting parameters like ['-m 256'] into ['-m', '256'] in
kunit/qemu_configs/*.py
* change [''] to [] in kunit/qemu_configs/*.py since otherwise
QEMU fails w/ 'Device needs media, but drive is empty'
* dropping explicit quoting of the kernel cmdline
* using shlex.quote() when we print what command we're running
so the user can copy-paste and run it

Signed-off-by: Daniel Latypov <[e-mail]>
Reviewed-by: Brendan Higgins <[e-mail]>
Signed-off-by: Shuah Khan <[e-mail]>

tools/testing/kunit/kunit_kernel.py

···
 import logging
 import subprocess
 import os
+import shlex
 import shutil
 import signal
 import threading
···
 				'-nodefaults',
 				'-m', '1024',
 				'-kernel', kernel_path,
-				'-append', '\'' + ' '.join(params + [self._kernel_command_line]) + '\'',
+				'-append', ' '.join(params + [self._kernel_command_line]),
 				'-no-reboot',
 				'-nographic',
-				'-serial stdio'] + self._extra_qemu_params
-		print('Running tests with:\n$', ' '.join(qemu_command))
-		return subprocess.Popen(' '.join(qemu_command),
-					   stdin=subprocess.PIPE,
-					   stdout=subprocess.PIPE,
-					   stderr=subprocess.STDOUT,
-					   text=True, shell=True, errors='backslashreplace')
+				'-serial', 'stdio'] + self._extra_qemu_params
+		# Note: shlex.join() does what we want, but requires python 3.8+.
+		print('Running tests with:\n$', ' '.join(shlex.quote(arg) for arg in qemu_command))
+		return subprocess.Popen(qemu_command,
+					stdin=subprocess.PIPE,
+					stdout=subprocess.PIPE,
+					stderr=subprocess.STDOUT,
+					text=True, errors='backslashreplace')
 
 class LinuxSourceTreeOperationsUml(LinuxSourceTreeOperations):
 	"""An abstraction over command line operations performed on a source tree."""

tools/testing/kunit/qemu_configs/alpha.py

···
 			   qemu_arch='alpha',
 			   kernel_path='arch/alpha/boot/vmlinux',
 			   kernel_command_line='console=ttyS0',
-			   extra_qemu_params=[''])
+			   extra_qemu_params=[])

tools/testing/kunit/qemu_configs/arm.py

···
 			   qemu_arch='arm',
 			   kernel_path='arch/arm/boot/zImage',
 			   kernel_command_line='console=ttyAMA0',
-			   extra_qemu_params=['-machine virt'])
+			   extra_qemu_params=['-machine', 'virt'])

tools/testing/kunit/qemu_configs/arm64.py

···
 			   qemu_arch='aarch64',
 			   kernel_path='arch/arm64/boot/Image.gz',
 			   kernel_command_line='console=ttyAMA0',
-			   extra_qemu_params=['-machine virt', '-cpu cortex-a57'])
+			   extra_qemu_params=['-machine', 'virt', '-cpu', 'cortex-a57'])

tools/testing/kunit/qemu_configs/i386.py

···
 			   qemu_arch='x86_64',
 			   kernel_path='arch/x86/boot/bzImage',
 			   kernel_command_line='console=ttyS0',
-			   extra_qemu_params=[''])
+			   extra_qemu_params=[])

tools/testing/kunit/qemu_configs/powerpc.py

···
 			   qemu_arch='ppc64',
 			   kernel_path='vmlinux',
 			   kernel_command_line='console=ttyS0',
-			   extra_qemu_params=['-M pseries', '-cpu power8'])
+			   extra_qemu_params=['-M', 'pseries', '-cpu', 'power8'])

tools/testing/kunit/qemu_configs/riscv.py

···
 			   kernel_path='arch/riscv/boot/Image',
 			   kernel_command_line='console=ttyS0',
 			   extra_qemu_params=[
-					   '-machine virt',
-					   '-cpu rv64',
-					   '-bios opensbi-riscv64-generic-fw_dynamic.bin'])
+					   '-machine', 'virt',
+					   '-cpu', 'rv64',
+					   '-bios', 'opensbi-riscv64-generic-fw_dynamic.bin'])

tools/testing/kunit/qemu_configs/s390.py

···
 			   kernel_path='arch/s390/boot/bzImage',
 			   kernel_command_line='console=ttyS0',
 			   extra_qemu_params=[
-					   '-machine s390-ccw-virtio',
-					   '-cpu qemu',])
+					   '-machine', 's390-ccw-virtio',
+					   '-cpu', 'qemu',])

tools/testing/kunit/qemu_configs/sparc.py

···
 			   qemu_arch='sparc',
 			   kernel_path='arch/sparc/boot/zImage',
 			   kernel_command_line='console=ttyS0 mem=256M',
-			   extra_qemu_params=['-m 256'])
+			   extra_qemu_params=['-m', '256'])

tools/testing/kunit/qemu_configs/x86_64.py

···
 			   qemu_arch='x86_64',
 			   kernel_path='arch/x86/boot/bzImage',
 			   kernel_command_line='console=ttyS0',
-			   extra_qemu_params=[''])
+			   extra_qemu_params=[])