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android: understand the disk images
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Ciro Santilli 六四事件 法轮功
184
README.adoc
184
README.adoc
@ -2627,7 +2627,7 @@ Instead, we used the QEMU `-initrd` option to point to the `.cpio` filesystem th
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Try removing that `-initrd` option to watch the kernel panic without rootfs at the end of boot.
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When using `.cpio`, there can be no filesystem persistency across boots, since all file operations happen in memory in a tmpfs:
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When using `.cpio`, there can be no <<disk-persistency,filesystem persistency>> across boots, since all file operations happen in memory in a tmpfs:
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....
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date >f
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@ -2727,6 +2727,23 @@ Setting up initramfs is very easy: our scripts just set `CONFIG_INITRAMFS_SOURCE
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http://nairobi-embedded.org/initramfs_tutorial.html shows a full manual setup.
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=== rootfs
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This is how `/proc/mounts` shows the root filesystem:
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* hard disk: `/dev/root on / type ext2 (rw,relatime,block_validity,barrier,user_xattr)`. That file does not exist however.
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* initrd: `rootfs on / type rootfs (rw)`
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* initramfs: `rootfs on / type rootfs (rw)`
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TODO: understand `/dev/root` better:
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* https://unix.stackexchange.com/questions/295060/why-on-some-linux-systems-does-the-root-filesystem-appear-as-dev-root-instead
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* https://superuser.com/questions/1213770/how-do-you-determine-the-root-device-if-dev-root-is-missing
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==== /dev/root
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See: <<rootfs>>
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=== gem5 initrd
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TODO we were not able to get it working yet: https://stackoverflow.com/questions/49261801/how-to-boot-the-linux-kernel-with-initrd-or-initramfs-with-gem5
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@ -11378,7 +11395,7 @@ then rebuild with:
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and then copy the link command to a separate Bash file. Then you can time and modify it easily.
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Some approximate refrence values on <<p51>>:
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Some approximate reference values on <<p51>>:
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* `opt`
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** unmodified: 10 seconds
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@ -11460,6 +11477,169 @@ TODO how to hack the AOSP kernel, userland and emulator?
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Other archs work as well as usual with `--arch` parameter. However, running in non-x86 is very slow due to the lack of KVM.
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Tested on: `8.1.0_r60`.
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==== Android image structure
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https://source.android.com/devices/bootloader/partitions-images
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The messy AOSP generates a ton of images instead of just one.
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When the emulator launches, we can see them through QEMU `-drive` arguments:
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....
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emulator: argv[23] = "-drive"
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emulator: argv[24] = "if=none,index=0,id=system,file=/path/to/aosp/8.1.0_r60/out/target/product/generic_x86_64/system-qemu.img,read-only"
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emulator: argv[25] = "-device"
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emulator: argv[26] = "virtio-blk-pci,drive=system,iothread=disk-iothread,modern-pio-notify"
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emulator: argv[27] = "-drive"
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emulator: argv[28] = "if=none,index=1,id=cache,file=/path/to/aosp/8.1.0_r60/out/target/product/generic_x86_64/cache.img.qcow2,overlap-check=none,cache=unsafe,l2-cache-size=1048576"
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emulator: argv[29] = "-device"
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emulator: argv[30] = "virtio-blk-pci,drive=cache,iothread=disk-iothread,modern-pio-notify"
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emulator: argv[31] = "-drive"
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emulator: argv[32] = "if=none,index=2,id=userdata,file=/path/to/aosp/8.1.0_r60/out/target/product/generic_x86_64/userdata-qemu.img.qcow2,overlap-check=none,cache=unsafe,l2-cache-size=1048576"
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emulator: argv[33] = "-device"
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emulator: argv[34] = "virtio-blk-pci,drive=userdata,iothread=disk-iothread,modern-pio-notify"
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emulator: argv[35] = "-drive"
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emulator: argv[36] = "if=none,index=3,id=encrypt,file=/path/to/aosp/8.1.0_r60/out/target/product/generic_x86_64/encryptionkey.img.qcow2,overlap-check=none,cache=unsafe,l2-cache-size=1048576"
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emulator: argv[37] = "-device"
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emulator: argv[38] = "virtio-blk-pci,drive=encrypt,iothread=disk-iothread,modern-pio-notify"
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emulator: argv[39] = "-drive"
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emulator: argv[40] = "if=none,index=4,id=vendor,file=/path/to/aosp/8.1.0_r60/out/target/product/generic_x86_64/vendor-qemu.img,read-only"
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emulator: argv[41] = "-device"
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emulator: argv[42] = "virtio-blk-pci,drive=vendor,iothread=disk-iothread,modern-pio-notify"
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....
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which tells us that the order is:
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....
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system
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cache
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userdata
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encryptionkey
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vendor-qemu
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....
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Then, on the terminal:
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....
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mount | grep vd
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....
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gives:
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....
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/dev/block/vda1 on /system type ext4 (ro,seclabel,relatime,data=ordered)
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/dev/block/vde1 on /vendor type ext4 (ro,seclabel,relatime,data=ordered)
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/dev/block/vdb on /cache type ext4 (rw,seclabel,nosuid,nodev,noatime,errors=panic,data=ordered)
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....
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and we see that the order of `vda`, `vdb`, etc. matches that in which `-drive` were given to QEMU.
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I think the root is the <<initrd>> given on the QEMU CLI:
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....
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rootfs on / type rootfs (ro,seclabel,size=886392k,nr_inodes=221598)
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....
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Tested on: `8.1.0_r60`.
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===== Android images read-only
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From `mount`, we can see that some of the mounted images are `ro`.
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In order to make `/system` and `/vendor` writable, we must use the `-writable-system` option:
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....
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./run-android -- -writable-system
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....
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* https://android.stackexchange.com/questions/110927/how-to-mount-system-rewritable-or-read-only-rw-ro/207200#207200
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* https://stackoverflow.com/questions/13089694/adb-remount-permission-denied-but-able-to-access-super-user-in-shell-android/43163693#43163693
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then:
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....
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su
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mount -o rw,remount /system
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date >/system/a
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....
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`/system` and vendor can be nuked quickly with:
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....
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./build-android --extra-args snod
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./build-android --extra-args vnod
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....
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as mentioned at: https://stackoverflow.com/questions/29023406/how-to-just-build-android-system-image and on:
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....
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./build-android --extra-args help
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....
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Tested on: `8.1.0_r60`.
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===== Android /data partition
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When I install an app like F-Droid, it goes under `/data` according to:
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....
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find / -iname '*fdroid*'
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....
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and it <<disk-persistency,persists across boots>>.
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`/data` is behind a RW LVM device:
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....
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/dev/block/dm-0 on /data type ext4 (rw,seclabel,nosuid,nodev,noatime,errors=panic,data=ordered)
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....
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but TODO I can't find where it comes from since I don't have the CLI tools mentioned at:
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* https://superuser.com/questions/131519/what-is-this-dm-0-device
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* https://unix.stackexchange.com/questions/185057/where-does-lvm-store-its-configuration
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However, by looking at:
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....
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./run-android -- -help
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....
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we see:
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....
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-data <file> data image (default <datadir>/userdata-qemu.img
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....
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which confirms the suspicion that this data goes in `userdata-qemu.img`.
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TODO: how to reset `userdata-qemu.img`? https://stackoverflow.com/questions/54446680/how-to-reset-the-userdata-image-when-building-android-aosp-and-running-it-on-the
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Tested on: `8.1.0_r60`.
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==== Install Android apps
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I don't know how to download files from the web on Vanilla android, the default browser does not download anything, and there is no `wget`:
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* https://android.stackexchange.com/questions/6984/how-to-download-files-from-the-web-in-the-android-browser
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* https://stackoverflow.com/questions/26775079/wget-in-android-terminal
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Installing with `adb install` does however work: https://stackoverflow.com/questions/7076240/install-an-apk-file-from-command-prompt
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link:https://f-droid.org[FDroid] installed fine like that, however it does not have permission to install apps: https://www.maketecheasier.com/install-apps-from-unknown-sources-android/
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And the `Settings` app crashes so I can't change it, logcat contains:
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....
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No service published for: wifip2p
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....
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which is mentioned at: https://stackoverflow.com/questions/47839955/android-8-settings-app-crashes-on-emulator-with-clean-aosp-build
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Tested on: `8.1.0_r60`.
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== About this repo
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=== Supported hosts
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@ -16,6 +16,10 @@ Download and build Android AOSP.
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https://github.com/cirosantilli/linux-kernel-module-cheat#android
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'''
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)
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self.add_argument(
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'--extra-args',
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default='',
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)
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self.add_argument(
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'targets',
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default=['build'],
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@ -59,12 +63,10 @@ https://github.com/cirosantilli/linux-kernel-module-cheat#android
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if 'build' in self.env['targets']:
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# The crappy android build system requires
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# https://stackoverflow.com/questions/7040592/calling-the-source-command-from-subprocess-popen
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self.sh.run_cmd('''\
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{}
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USE_CCACHE=1 make -j {}
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'''.format(
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self.sh.run_cmd('{}USE_CCACHE=1 make -j {} {}'.format(
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self.env['android_shell_setup'],
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self.env['nproc']
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self.env['nproc'],
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self.env['extra_args']
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),
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cwd=self.env['android_dir'],
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executable=shutil.which('bash'),
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17
common.py
17
common.py
@ -517,14 +517,6 @@ Valid emulators: {}
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common.extract_vmlinux = os.path.join(env['linux_source_dir'], 'scripts', 'extract-vmlinux')
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env['linux_buildroot_build_dir'] = join(env['buildroot_build_build_dir'], 'linux-custom')
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# Android
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if not env['_args_given']['android_base_dir']:
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env['android_base_dir'] = join(env['out_dir'], 'android')
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env['android_dir'] = join(env['android_base_dir'], env['android_version'])
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env['android_build_dir'] = join(env['android_dir'], 'out')
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env['repo_path'] = join(env['android_base_dir'], 'repo')
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env['repo_path_base64'] = env['repo_path'] + '.base64'
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# QEMU
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env['qemu_build_dir'] = join(env['out_dir'], 'qemu', env['qemu_build_id'])
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env['qemu_executable_basename'] = 'qemu-system-{}'.format(env['arch'])
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@ -721,7 +713,14 @@ Valid emulators: {}
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env['image'] = env['linux_image']
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env['disk_image'] = env['qcow2_file']
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# Android.
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# Android
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if not env['_args_given']['android_base_dir']:
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env['android_base_dir'] = join(env['out_dir'], 'android')
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env['android_dir'] = join(env['android_base_dir'], env['android_version'])
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env['android_build_dir'] = join(env['android_dir'], 'out')
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env['repo_path'] = join(env['android_base_dir'], 'repo')
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env['repo_path_base64'] = env['repo_path'] + '.base64'
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env['android_shell_setup'] = '''
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. build/envsetup.sh
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lunch aosp_{}-eng
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@ -16,10 +16,7 @@ https://github.com/cirosantilli/linux-kernel-module-cheat#android
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self.add_argument('extra-emulator-args', default='', nargs='?')
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def timed_main(self):
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self.sh.run_cmd('''\
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{}
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emulator -show-kernel -verbose {}
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'''.format(
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self.sh.run_cmd('{}emulator -show-kernel -verbose {}'.format(
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self.env['android_shell_setup'],
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self.env['extra_emulator_args']
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),
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