runtime/docs/infra/coredumps.md - sdk - Git at Google

 # Crash Dumps Archiving

 Testing framework and buildbot/LUCI infrastructure have support for archiving
 crash dumps and crashed binaries for unexpected crashes for postmortem
 debugging.

 This feature is enabled by passing `--copy-coredumps` to `tools/test.py` and
 is supported on all three major OSes we run our tests on.

 Currently crash dump archiving should be enabled on the majority of the VM
 bots, including those running in CQ.

 ### Known limitations

 * We don't archive crash dumps produced by subprocesses (e.g. service tests);
 * We don't produce and archive crash dumps for hanged processes.

 ### Maintainers

 For any questions about this infrastructure contact vegorov@, kustermann@ or
 athom@.

 ## Downloading dumps

 To find if a bot managed to upload any crashdumps open its log and search for
 `Archiving coredumps for crash`. Depending on the bot configuration you
 might need to look for uploaded artifacts in two different locations.

 ### Isolate Server

 Swarming bots upload dumps to the isolate server. In this case you will see
 something like this in the log:

 ```
 INFO: Core dump archiving is activated
 Archiving coredumps for crash (if possible):
 ----> Crash(language_2/call_method_implicit_tear_off_test/02: binary.release_x64_dart.exe 1556)
 +++ Copying 6e3e4b40-206e-4ae6-99e8-c2c94cc21a98.dmp.tar.gz to output_directory (C:\b\s\w\ioz_p_ei)
 +++ Copying release_x64_dart.exe.tar.gz to output_directory (C:\b\s\w\ioz_p_ei)
 ```

 If you see `+++ Copying ... to output_directory` this means that the bot
 is using isolate storage. In this case you need to look for
 `shard #... isolated out` link under the failed step.

 ![shard isolate out](images/isolated-out-link.png)

 This link would bring you to isolate server file browser where you will be
 able to download archived artifacts.

 ![Isolate Server Browser](images/isolated-out-browser.png)

 ### Cloud Storage

 Other bots upload collected artifacts into a `dart-temp-crash-archive` Cloud Storage bucket. In this case you will see
 `+++ Uploaded gs://dart-temp-crash-archive/...` in the output log. For example:

 ```
 Archiving coredumps for crash (if possible):
 ----> Crash(language_2/mixin_interface_check_test/mixin: binary.release_ia32_dart.exe 10620)

 --- Uploading into gs://dart-temp-crash-archive/0da77e10-d349-4c45-a146-0ce052972b03/ (https://storage.cloud.google.com/dart-temp-crash-archive/0da77e10-d349-4c45-a146-0ce052972b03/) ---
 Running command:  ['C:\\b\\s\\w\\ir\\cache\\vpython\\2d366b\\Scripts\\python.exe', 'C:\\b\\s\\w\\ir\\cache\\builder\\sdk\\third_party\\gsutil\\gsutil', 'cp', 'release_ia32_dart.exe.tar.gz', 'gs://dart-temp-crash-archive/0da77e10-d349-4c45-a146-0ce052972b03/release_ia32_dart.exe.tar.gz']
 +++ Uploaded gs://dart-temp-crash-archive/0da77e10-d349-4c45-a146-0ce052972b03/release_ia32_dart.exe.tar.gz (https://storage.cloud.google.com/dart-temp-crash-archive/0da77e10-d349-4c45-a146-0ce052972b03/release_ia32_dart.exe.tar.gz)
 Running command:  ['C:\\b\\s\\w\\ir\\cache\\vpython\\2d366b\\Scripts\\python.exe', 'C:\\b\\s\\w\\ir\\cache\\builder\\sdk\\third_party\\gsutil\\gsutil', 'cp', 'a92618b1-0f99-4c87-a9fb-adb3e44ad458.dmp.tar.gz', 'gs://dart-temp-crash-archive/0da77e10-d349-4c45-a146-0ce052972b03/a92618b1-0f99-4c87-a9fb-adb3e44ad458.dmp.tar.gz']
 +++ Uploaded gs://dart-temp-crash-archive/0da77e10-d349-4c45-a146-0ce052972b03/a92618b1-0f99-4c87-a9fb-adb3e44ad458.dmp.tar.gz (https://storage.cloud.google.com/dart-temp-crash-archive/0da77e10-d349-4c45-a146-0ce052972b03/a92618b1-0f99-4c87-a9fb-adb3e44ad458.dmp.tar.gz)
 --- Done ---
 ```

 In this case you can use `gsutil.py` from `depot_tools` (or `gsutil` from Cloud
 SDK) to download these artifacts:

 ```console
 $ gsutil.py cp gs://dart-temp-crash-archive/<src-path> <dst-path>
 ```

 ## Analyzing Dumps

 ### Linux

 ```console
 $ gdb <binary> <core>
 ```

 Because bots are running slightly different Linux versions that what is
 available on development machines `gdb` might not be able to properly
 resolve symbols and unwind the stack by itself.

 In this case you can:

 * spin up a Cloud Instance with a matching OS version and debug the dump
 on that instance;
 * create a sysroot that matches operating system on the bots and tell gdb to
 use that sysroot with `set sysroot` command.

 #### ARM/ARM64

 If you have a core produced on ARM or ARM64 bot and you would like to inspect
 it on a non-ARM development machine, then you will need `gdb-multiarch` and
 sysroot that matches OS version on the bot. Then you can use `set sysroot ...`
 and `set architecture ...` to configure `gdb-multiarch` before loading `core`.

 ### Mac

 ```console
 $ lldb <binary> -c <core>
 ```

 ### Windows

 Googlers can find WinDBG and CDB in `%depot_tools%\win_toolchain\vs_files\%toolchain_version%\win_sdk\Debuggers\x64\`.

 For quick investigation you can do

 ```console
 > cdb.exe -z <coredump.dmp>
 ...
 0:000> !uniqstack
 ...
 ```

 ## Implementation details

 Implementation of crash dump archiving consists of two parts:

 * Code in the testing framework (`UnexpectedCrashLogger` in
 `tools/testing/dart/test_progress.dart`) that detects unexpected crashes, that
 is situations when test _unexpectedly_ completes with a `Crash` status. In this
 case it logs a line about this crash into `unexpected-crashes` file in the
 root of the SDK checkout. This line has format `test,pid,binary` and identifies
 which test crashed, what was the process id and which binary crashed.
 * Code in the Python wrapper around testing framework (see `CoreDumpArchiver`
 in `tools/utils.py`) is responsible for
     * Before tests: configuring OS and/or environment to setup crashdump
       archiving in the OS specific way (see classes with names ending at
       `CoreDumpEnabler`);
     * After tests: trying to locate crashdumps written by OS or crash reporting
       library and match those to unexpected crashes reporting by testing
       framework (see classes with names ending at `CoreDumpArchiver`);
     * Selecting a subset of crashdumps and uploading those into a persistent
       storage (isolate server or Cloud Storage bucket).

 ### Linux

 We rely on builtin ability of the OS to generate core files (`man core`) when
 the program is terminated abnormally.

 We adjust core resource limits to `unlimited` before running tests. See `man setrlimit` for more information (search for `RLIMIT_CORE`).

 We verify that `/proc/sys/kernel/core_pattern` is set to `core.%p` which
 means that crash dumps would be produced in the current working directory (root of the SDK checkout for most tests) and mangled with the pid of the crashed
 process.

 Core dump archiving code then uses pids to match unexpected crashes with core
 dumps.

 See `LinuxCoreDumpArchiver` and `LinuxCoreDumpEnabler` in `tools/utils.py`.

 ### Mac

 Just like on Linux we rely on OS to produce core files (`man core`) and
 similarly set core resource limits to `unlimited`.

 Core files are also mangled with PID of the crashing process.

 The only difference from Linux is that on Mac core files are written into
 `/cores` directory instead of current working directory.

 See `MacOSCoreDumpArchiver` and `PosixCoreDumpEnabler` in `tools/utils.py`.

 ### Windows

 On Windows we rely on [Crashpad](https://chromium.googlesource.com/crashpad/crashpad/+/master/README.md)
 library to produce minidumps of the crashed process, because configuring
 builtin crash reporting functionality requires registry changes that are global,
 impossible without Administrator privileges and are overwritten by buildbot
 fleet management software running in background.

 Crashpad integration for `dart.exe` and `run_vm_tests.exe` binaries is
 controlled by `dart_use_crashpad` GN argument.

 This argument is set to `true` when `tools/gn.py` is run with `--use-crashpad`
 flag or with `DART_USE_CRASHPAD` environment variable set.

 If the binary is built with Crashpad integration it checks two environment
 variables on startup:

 * `DART_CRASHPAD_HANDLER` should contain path to `crashpad_handler.exe`
 Crashpad binary that implements out-of-process crash monitoring;
 * `DART_CRASHPAD_CRASHES_DIR` should contain path to a folder, which would be
 used as Crashpad crash database.

 If both variables are set then Crashpad handler will be started. If the handler
 catches main binary crashing it would write [minidump](https://docs.microsoft.com/en-us/windows/desktop/debug/minidump-files)
 into `%DART_CRASHPAD_CRASHES_DIR%\crashes` from where it would be picked up
 by crash archiving machinery.

 We match crash dumps to unexpected crashes by parsing them and extracting
 process id of the crashed process (see `utils/minidump.py` library).

 See `WindowsCoreDumpEnabler` and `WindowsCoreDumpArchiver` in `tools/utils.py`.

 **Note: `DART_CRASHPAD_CRASHES_DIR` is set by `WindowsCoreDumpEnabler` in
 `tools/utils.py`, while `DART_CRASHPAD_HANDLER` is set by `TestSuite` in
 `tools/testing/dart/test_suite.dart`.**

 **Note: Crashpad is optimized for end-user crash reporting use case and does not write full crash dumps.**
	# Crash Dumps Archiving

	Testing framework and buildbot/LUCI infrastructure have support for archiving
	crash dumps and crashed binaries for unexpected crashes for postmortem
	debugging.

	This feature is enabled by passing `--copy-coredumps` to `tools/test.py` and
	is supported on all three major OSes we run our tests on.

	Currently crash dump archiving should be enabled on the majority of the VM
	bots, including those running in CQ.

	### Known limitations

	* We don't archive crash dumps produced by subprocesses (e.g. service tests);
	* We don't produce and archive crash dumps for hanged processes.

	### Maintainers

	For any questions about this infrastructure contact vegorov@, kustermann@ or
	athom@.

	## Downloading dumps

	To find if a bot managed to upload any crashdumps open its log and search for
	`Archiving coredumps for crash`. Depending on the bot configuration you
	might need to look for uploaded artifacts in two different locations.

	### Isolate Server

	Swarming bots upload dumps to the isolate server. In this case you will see
	something like this in the log:

	```
	INFO: Core dump archiving is activated
	Archiving coredumps for crash (if possible):
	----> Crash(language_2/call_method_implicit_tear_off_test/02: binary.release_x64_dart.exe 1556)
	+++ Copying 6e3e4b40-206e-4ae6-99e8-c2c94cc21a98.dmp.tar.gz to output_directory (C:\b\s\w\ioz_p_ei)
	+++ Copying release_x64_dart.exe.tar.gz to output_directory (C:\b\s\w\ioz_p_ei)
	```

	If you see `+++ Copying ... to output_directory` this means that the bot
	is using isolate storage. In this case you need to look for
	`shard #... isolated out` link under the failed step.

	![shard isolate out](images/isolated-out-link.png)

	This link would bring you to isolate server file browser where you will be
	able to download archived artifacts.

	![Isolate Server Browser](images/isolated-out-browser.png)

	### Cloud Storage

	Other bots upload collected artifacts into a `dart-temp-crash-archive` Cloud Storage bucket. In this case you will see
	`+++ Uploaded gs://dart-temp-crash-archive/...` in the output log. For example:

	```
	Archiving coredumps for crash (if possible):
	----> Crash(language_2/mixin_interface_check_test/mixin: binary.release_ia32_dart.exe 10620)

	--- Uploading into gs://dart-temp-crash-archive/0da77e10-d349-4c45-a146-0ce052972b03/ (https://storage.cloud.google.com/dart-temp-crash-archive/0da77e10-d349-4c45-a146-0ce052972b03/) ---
	Running command: ['C:\\b\\s\\w\\ir\\cache\\vpython\\2d366b\\Scripts\\python.exe', 'C:\\b\\s\\w\\ir\\cache\\builder\\sdk\\third_party\\gsutil\\gsutil', 'cp', 'release_ia32_dart.exe.tar.gz', 'gs://dart-temp-crash-archive/0da77e10-d349-4c45-a146-0ce052972b03/release_ia32_dart.exe.tar.gz']
	+++ Uploaded gs://dart-temp-crash-archive/0da77e10-d349-4c45-a146-0ce052972b03/release_ia32_dart.exe.tar.gz (https://storage.cloud.google.com/dart-temp-crash-archive/0da77e10-d349-4c45-a146-0ce052972b03/release_ia32_dart.exe.tar.gz)
	Running command: ['C:\\b\\s\\w\\ir\\cache\\vpython\\2d366b\\Scripts\\python.exe', 'C:\\b\\s\\w\\ir\\cache\\builder\\sdk\\third_party\\gsutil\\gsutil', 'cp', 'a92618b1-0f99-4c87-a9fb-adb3e44ad458.dmp.tar.gz', 'gs://dart-temp-crash-archive/0da77e10-d349-4c45-a146-0ce052972b03/a92618b1-0f99-4c87-a9fb-adb3e44ad458.dmp.tar.gz']
	+++ Uploaded gs://dart-temp-crash-archive/0da77e10-d349-4c45-a146-0ce052972b03/a92618b1-0f99-4c87-a9fb-adb3e44ad458.dmp.tar.gz (https://storage.cloud.google.com/dart-temp-crash-archive/0da77e10-d349-4c45-a146-0ce052972b03/a92618b1-0f99-4c87-a9fb-adb3e44ad458.dmp.tar.gz)
	--- Done ---
	```

	In this case you can use `gsutil.py` from `depot_tools` (or `gsutil` from Cloud
	SDK) to download these artifacts:

	```console
	$ gsutil.py cp gs://dart-temp-crash-archive/<src-path> <dst-path>
	```

	## Analyzing Dumps

	### Linux

	```console
	$ gdb <binary> <core>
	```

	Because bots are running slightly different Linux versions that what is
	available on development machines `gdb` might not be able to properly
	resolve symbols and unwind the stack by itself.

	In this case you can:

	* spin up a Cloud Instance with a matching OS version and debug the dump
	on that instance;
	* create a sysroot that matches operating system on the bots and tell gdb to
	use that sysroot with `set sysroot` command.

	#### ARM/ARM64

	If you have a core produced on ARM or ARM64 bot and you would like to inspect
	it on a non-ARM development machine, then you will need `gdb-multiarch` and
	sysroot that matches OS version on the bot. Then you can use `set sysroot ...`
	and `set architecture ...` to configure `gdb-multiarch` before loading `core`.

	### Mac

	```console
	$ lldb <binary> -c <core>
	```

	### Windows

	Googlers can find WinDBG and CDB in `%depot_tools%\win_toolchain\vs_files\%toolchain_version%\win_sdk\Debuggers\x64\`.

	For quick investigation you can do

	```console
	> cdb.exe -z <coredump.dmp>
	...
	0:000> !uniqstack
	...
	```

	## Implementation details

	Implementation of crash dump archiving consists of two parts:

	* Code in the testing framework (`UnexpectedCrashLogger` in
	`tools/testing/dart/test_progress.dart`) that detects unexpected crashes, that
	is situations when test _unexpectedly_ completes with a `Crash` status. In this
	case it logs a line about this crash into `unexpected-crashes` file in the
	root of the SDK checkout. This line has format `test,pid,binary` and identifies
	which test crashed, what was the process id and which binary crashed.
	* Code in the Python wrapper around testing framework (see `CoreDumpArchiver`
	in `tools/utils.py`) is responsible for
	* Before tests: configuring OS and/or environment to setup crashdump
	archiving in the OS specific way (see classes with names ending at
	`CoreDumpEnabler`);
	* After tests: trying to locate crashdumps written by OS or crash reporting
	library and match those to unexpected crashes reporting by testing
	framework (see classes with names ending at `CoreDumpArchiver`);
	* Selecting a subset of crashdumps and uploading those into a persistent
	storage (isolate server or Cloud Storage bucket).

	### Linux

	We rely on builtin ability of the OS to generate core files (`man core`) when
	the program is terminated abnormally.

	We adjust core resource limits to `unlimited` before running tests. See `man setrlimit` for more information (search for `RLIMIT_CORE`).

	We verify that `/proc/sys/kernel/core_pattern` is set to `core.%p` which
	means that crash dumps would be produced in the current working directory (root of the SDK checkout for most tests) and mangled with the pid of the crashed
	process.

	Core dump archiving code then uses pids to match unexpected crashes with core
	dumps.

	See `LinuxCoreDumpArchiver` and `LinuxCoreDumpEnabler` in `tools/utils.py`.

	### Mac

	Just like on Linux we rely on OS to produce core files (`man core`) and
	similarly set core resource limits to `unlimited`.

	Core files are also mangled with PID of the crashing process.

	The only difference from Linux is that on Mac core files are written into
	`/cores` directory instead of current working directory.

	See `MacOSCoreDumpArchiver` and `PosixCoreDumpEnabler` in `tools/utils.py`.

	### Windows

	On Windows we rely on [Crashpad](https://chromium.googlesource.com/crashpad/crashpad/+/master/README.md)
	library to produce minidumps of the crashed process, because configuring
	builtin crash reporting functionality requires registry changes that are global,
	impossible without Administrator privileges and are overwritten by buildbot
	fleet management software running in background.

	Crashpad integration for `dart.exe` and `run_vm_tests.exe` binaries is
	controlled by `dart_use_crashpad` GN argument.

	This argument is set to `true` when `tools/gn.py` is run with `--use-crashpad`
	flag or with `DART_USE_CRASHPAD` environment variable set.

	If the binary is built with Crashpad integration it checks two environment
	variables on startup:

	* `DART_CRASHPAD_HANDLER` should contain path to `crashpad_handler.exe`
	Crashpad binary that implements out-of-process crash monitoring;
	* `DART_CRASHPAD_CRASHES_DIR` should contain path to a folder, which would be
	used as Crashpad crash database.

	If both variables are set then Crashpad handler will be started. If the handler
	catches main binary crashing it would write [minidump](https://docs.microsoft.com/en-us/windows/desktop/debug/minidump-files)
	into `%DART_CRASHPAD_CRASHES_DIR%\crashes` from where it would be picked up
	by crash archiving machinery.

	We match crash dumps to unexpected crashes by parsing them and extracting
	process id of the crashed process (see `utils/minidump.py` library).

	See `WindowsCoreDumpEnabler` and `WindowsCoreDumpArchiver` in `tools/utils.py`.

	**Note: `DART_CRASHPAD_CRASHES_DIR` is set by `WindowsCoreDumpEnabler` in
	`tools/utils.py`, while `DART_CRASHPAD_HANDLER` is set by `TestSuite` in
	`tools/testing/dart/test_suite.dart`.**

	Note: Crashpad is optimized for end-user crash reporting use case and does not write full crash dumps.