Don't pass dummy disk images to gem5

After https://gem5.atlassian.net/browse/GEM5-337:

- gem5 baremetal can run without any disk images, just like QEMU
- gem5 X86 can run with a single disk image and no horrendous dummy vmlinux
  and second disk image

build-gem5

@@ -61,18 +61,7 @@ https://github.com/cirosantilli/linux-kernel-module-cheat-regression#gem5-unit-t
             verbose = ['--verbose', LF]
         else:
             verbose = []
-        if self.env['arch'] == 'x86_64':
+        if self.env['is_arm']:
-            dummy_img_path = os.path.join(disks_dir, 'linux-bigswap2.img')
-            with open(dummy_img_path, 'wb') as dummy_img_file:
-                zeroes = b'\x00' * (2 ** 16)
-                for i in range(2 ** 10):
-                    dummy_img_file.write(zeroes)
-            self.sh.run_cmd(['mkswap', dummy_img_path, LF])
-            with open(os.path.join(binaries_dir, 'x86_64-vmlinux-2.6.22.9'), 'w'):
-                # This file must always be present, despite --kernel overriding that default and selecting the kernel.
-                # I'm not even joking. No one has ever built x86 gem5 without the magic dist dir present.
-                pass
-        elif self.env['arch'] == 'arm' or self.env['arch'] == 'aarch64':
             gem5_system_source_dir = os.path.join(self.env['gem5_source_dir'], 'system')
 
             # dtb

common.py

@@ -844,7 +844,6 @@ Incompatible archs are skipped.
         # gem5
         if not env['_args_given']['gem5_build_dir']:
             env['gem5_build_dir'] = join(env['gem5_out_dir'], env['gem5_build_id'])
-        env['gem5_fake_iso'] = join(env['gem5_out_dir'], 'fake.iso')
         env['gem5_m5term'] = join(env['gem5_build_dir'], 'm5term')
         env['gem5_build_build_dir'] = join(env['gem5_build_dir'], 'build')
         env['gem5_executable_dir'] = join(env['gem5_build_build_dir'], env['gem5_arch'])
@@ -1065,7 +1064,7 @@ Incompatible archs are skipped.
 
         # Image
         if env['baremetal'] is not None:
-            env['disk_image'] = env['gem5_fake_iso']
+            env['disk_image'] = None
             env['image'] = self.resolve_baremetal_executable(env['baremetal'])
             source_path_noext = os.path.splitext(join(
                 env['root_dir'],
@@ -1094,7 +1093,7 @@ Incompatible archs are skipped.
                 if not env['_args_given']['linux_exec']:
                     env['image'] = env['vmlinux']
                 if env['ramfs']:
-                    env['disk_image'] = env['gem5_fake_iso']
+                    env['disk_image'] = None
                 else:
                     env['disk_image'] = env['rootfs_raw_file']
             else:

run

@@ -471,11 +471,7 @@ Extra options to append at the end of the emulator command line.
         if self.env['emulator'] == 'gem5':
             if self.env['quiet']:
                 show_stdout = False
-            if not self.env['baremetal'] is None:
+            if self.env['baremetal'] is None and self.env['userland'] is None:
-                if not os.path.exists(self.env['gem5_fake_iso']):
-                    os.makedirs(os.path.dirname(self.env['gem5_fake_iso']), exist_ok=True)
-                    self.sh.write_string_to_file(self.env['gem5_fake_iso'], 'a' * 512)
-            elif self.env['userland'] is None:
                 if not os.path.exists(self.env['rootfs_raw_file']):
                     if not os.path.exists(self.env['qcow2_file']):
                         raise_rootfs_not_found()
@@ -536,11 +532,12 @@ Extra options to append at the end of the emulator command line.
                         extra_emulator_args.extend(['-r', str(cpt_dirs_sorted_by_tick.index(cpt_dir) + 1)])
                     cmd.extend([
                         self.env['gem5_fs_file'], LF,
-                        '--disk-image', self.env['disk_image'], LF,
                         '--kernel', self.env['image'], LF,
                         '--num-cpus', str(self.env['cpus']), LF,
                         '--script', self.env['gem5_readfile_file'], LF,
                     ])
+                    if self.env['disk_image'] is not None:
+                        cmd.extend(['--disk-image', self.env['disk_image'], LF])
                     if self.env['arch'] == 'x86_64':
                         if self.env['kvm']:
                             cmd.extend(['--cpu-type', 'X86KvmCPU', LF])
@@ -608,11 +605,12 @@ Extra options to append at the end of the emulator command line.
                         '--bootscript', self.env['gem5_readfile_file'], LF,
                         '--big-cpus', str((self.env['cpus'] + 1) // 2), LF,
                         '--cpu-type', cpu_type, LF,
-                        '--disk', self.env['disk_image'], LF,
                         '--kernel', self.env['image'], LF,
                         '--little-cpus', str(self.env['cpus'] // 2), LF,
                         '--root', '/dev/vda', LF,
                     ])
+                    if self.env['disk_image'] is not None:
+                        cmd.extend(['--disk', self.env['disk_image'], LF])
                     if self.env['dtb']:
                         cmd.extend([
                             '--dtb',
@@ -749,6 +747,12 @@ Extra options to append at the end of the emulator command line.
                             if not os.path.exists(self.env['rootfs_raw_file']):
                                 raise_rootfs_not_found()
                             self.raw_to_qcow2(qemu_which=self.env['qemu_which'])
+                        if rr:
+                            extra_emulator_args.extend([
+                            '-drive', 'driver=blkreplay,if=none,image=img-direct,id=img-blkreplay', LF,
+                            '-device', 'ide-hd,drive=img-blkreplay', LF,
+                        ])
+                    if self.env['disk_image'] is not None:
                         extra_emulator_args.extend([
                             '-drive',
                             'file={},format=qcow2,if={}{}{}'.format(
@@ -759,11 +763,6 @@ Extra options to append at the end of the emulator command line.
                             ),
                             LF,
                         ])
-                        if rr:
-                            extra_emulator_args.extend([
-                            '-drive', 'driver=blkreplay,if=none,image=img-direct,id=img-blkreplay', LF,
-                            '-device', 'ide-hd,drive=img-blkreplay', LF,
-                        ])
                 if rr:
                     extra_emulator_args.extend([
                         '-object', 'filter-replay,id=replay,netdev=net0', LF,