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DebuggingTips.md

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Debugging Tips

There are many ways to debug ANGLE using generic or platform-dependent tools. Here is a list of tips on how to use them.

Running ANGLE under apitrace on Linux

Apitrace captures traces of OpenGL commands for later analysis, allowing us to see how ANGLE translates OpenGL ES commands. In order to capture the trace, it inserts a driver shim using LD_PRELOAD that records the command and then forwards it to the OpenGL driver.

The problem with ANGLE is that it exposes the same symbols as the OpenGL driver so apitrace captures the entry point calls intended for ANGLE and reroutes them to the OpenGL driver. In order to avoid this problem, use the following:

  1. Link your application against the static ANGLE libraries (libGLESv2_static and libEGL_static) so they don't get shadowed by apitrace's shim.
  2. Ask apitrace to explicitly load the driver instead of using a dlsym on the current module. Otherwise apitrace will use ANGLE's symbols as the OpenGL driver entrypoint (causing infinite recursion). To do this you must point an environment variable to your GL driver. For example: export TRACE_LIBGL=/usr/lib/libGL.so.1. You can find your libGL with ldconfig -p | grep libGL.
  3. Link ANGLE against libGL instead of dlsyming the symbols at runtime; otherwise ANGLE won't use the replaced driver entry points. This is done with the gn arg angle_link_glx = true.

If you follow these steps, apitrace will work correctly aside from a few minor bugs like not being able to figure out what the default framebuffer size is if there is no glViewport command.

For example, to trace a run of hello_triangle, assuming the apitrace executables are in $PATH:

gn args out/Debug # add "angle_link_glx = true"
# edit samples/BUILD.gn and append "_static" to "angle_util", "libEGL", "libGLESv2"
ninja -C out/Debug
export TRACE_LIBGL="/usr/lib/libGL.so.1" # may require a different path
apitrace trace -o mytrace ./out/Debug/hello_triangle
qapitrace mytrace

Running ANGLE under GAPID on Linux

GAPID can be used to capture trace of Vulkan commands on Linux. For it to work, libvulkan has to be a shared library, instead of being statically linked into ANGLE, which is the default behavior. This is done with the gn arg:

angle_shared_libvulkan = true

When capturing traces of gtest based tests built inside Chromium checkout, make sure to run the tests with --single-process-tests argument.

Running ANGLE under GAPID on Android

GAPID can be used to capture a trace of the Vulkan or OpenGL ES command stream on Android. For it to work, ANGLE's libraries must have different names from the system OpenGL libraries. This is done with the gn arg:

angle_libs_suffix = "_ANGLE_DEV"

All NativeTest based tests share the same activity name, org.chromium.native_test.NativeUnitTestNativeActivity. Thus, prior to capturing your test trace, the specific test APK must be installed on the device. When you build the test, a test launcher is generated, for example, ./out/Release/bin/run_angle_end2end_tests. The best way to install the APK is to run this test launcher once.

In GAPID's "Capture Trace" dialog, "Package / Action:" should be:

android.intent.action.MAIN:org.chromium.native_test/org.chromium.native_test.NativeUnitTestNativeActivity

The mandatory extra intent argument for starting the activity is org.chromium.native_test.NativeTest.StdoutFile. Without it the test APK crashes. Test filters can be specified via either the org.chromium.native_test.NativeTest.CommandLineFlags or the org.chromium.native_test.NativeTest.Shard argument. Example "Intent Arguments:" values in GAPID's "Capture Trace" dialog:

-e org.chromium.native_test.NativeTest.StdoutFile /sdcard/chromium_tests_root/out.txt -e org.chromium.native_test.NativeTest.CommandLineFlags "--gtest_filter=*ES2_VULKAN"

or

-e org.chromium.native_test.NativeTest.StdoutFile /sdcard/chromium_tests_root/out.txt --esal org.chromium.native_test.NativeTest.Shard RendererTest.SimpleOperation/ES2_VULKAN,SimpleOperationTest.DrawWithTexture/ES2_VULKAN

Running ANGLE under RenderDoc

An application running through ANGLE can confuse RenderDoc, as RenderDoc hooks to EGL and ends up tracing the calls the application makes, instead of the calls ANGLE makes to its backend. As ANGLE is a special case, there's little support for it by RenderDoc, though there are workarounds.

Windows

On Windows, RenderDoc supports setting the environment variable RENDERDOC_HOOK_EGL to 0 to avoid this issue.

Linux

On Linux, there is no supported workaround by RenderDoc. See this issue. To capture Vulkan traces, the workaround is to build RenderDoc without GL(ES) support.

Building RenderDoc is straightforward. However, here are a few instructions to keep in mind.

# Install dependencies based on RenderDoc document.  Here are some packages that are unlikely to be already installed:
$ sudo apt install libxcb-keysyms1-dev python3-dev qt5-qmake libqt5svg5-dev libqt5x11extras5-dev

# Inside the RenderDoc directory:
$ cmake -DCMAKE_BUILD_TYPE=Release -Bbuild -H. -DENABLE_GLES=OFF -DENABLE_GL=OFF

# QT_SELECT=5 is necessary if your distribution doesn't default to Qt5
$ QT_SELECT=5 make -j -C build

# Run RenderDoc from the build directory:
$ ./build/bin/qrenderdoc

Additionally, libvulkan has to be a shared library, instead of being statically linked into ANGLE, which is the default behavior. This is done with the gn arg:

angle_shared_libvulkan = true

If your distribution does not provide a recent Vulkan SDK package, you would need to manually install that. This script tries to perform this installation as safely as possible. It would overwrite the system package's files, so follow at your own risk. Place this script just above the extracted SDK directory.

#! /bin/bash

if [ $# -lt 1 ]; then
  echo "Usage: $0 <version>"
  exit 1
fi

ver=$1

if [ ! -d "$ver" ]; then
  echo "$ver is not a directory"
fi

# Verify everything first
echo "Verifying files..."
echo "$ver"/x86_64/bin/vulkaninfo
test -f "$ver"/x86_64/bin/vulkaninfo || exit 1
echo "$ver"/x86_64/etc/explicit_layer.d/
test -d "$ver"/x86_64/etc/explicit_layer.d || exit 1
echo "$ver"/x86_64/lib/
test -d "$ver"/x86_64/lib || exit 1

echo "Verified. Performing copy..."

echo sudo cp "$ver"/x86_64/bin/vulkaninfo /usr/bin/vulkaninfo
sudo cp "$ver"/x86_64/bin/vulkaninfo /usr/bin/vulkaninfo
echo sudo cp "$ver"/x86_64/etc/explicit_layer.d/* /etc/explicit_layer.d/
sudo cp "$ver"/x86_64/etc/explicit_layer.d/* /etc/explicit_layer.d/
echo sudo rm /usr/lib/x86_64-linux-gnu/libvulkan.so*
sudo rm /usr/lib/x86_64-linux-gnu/libvulkan.so*
echo sudo cp -P "$ver"/x86_64/lib/lib* /usr/lib/x86_64-linux-gnu/
sudo cp -P "$ver"/x86_64/lib/lib* /usr/lib/x86_64-linux-gnu/

echo "Done."

Android

If you are on Linux, make sure not to use the build done in the previous section. The GL renderer disabled in the previous section is actually needed in this section.

Define the following environment variables, for example in .bashrc (values are examples):

export JAVA_HOME=/usr/local/buildtools/java/jdk
export ANDROID_SDK=$HOME/chromium/src/third_party/android_sdk/public
export ANDROID_NDK=$HOME/chromium/src/third_party/android_ndk
export ANDROID_NDK_HOME=$HOME/chromium/src/third_party/android_ndk

In the renderdoc directory, create Android builds of RenderDoc:

mkdir build-android-arm32
cd build-android-arm32/
cmake -DBUILD_ANDROID=On -DANDROID_ABI=armeabi-v7a ..
make -j
cd ../

mkdir build-android-arm64
cd build-android-arm64/
cmake -DBUILD_ANDROID=On -DANDROID_ABI=arm64-v8a ..
make -j
cd ../

Note that you need both arm32 and arm64 builds even if working with an arm64 device. See RenderDoc's documentation for more information.

When you run RenderDoc, choose the "Replay Context" from the bottom-left part of the UI (defaults to Local). When selecting the device, you should see the RenderDoc application running.

In ANGLE itself, make sure you add a suffix for its names to be different from the system's. Add this to gn args:

angle_libs_suffix = "_ANGLE_DEV"

Next, you need to install an ANGLE test apk. When you build the test, a test launcher is generated, for example, ./out/Release/bin/run_angle_end2end_tests. The best way to install the APK is to run this test launcher once.

In RenderDoc, use org.chromium.native_test as the Executable Path, and provide the following arguments:

-e org.chromium.native_test.NativeTest.StdoutFile /sdcard/chromium_tests_root/out.txt -e org.chromium.native_test.NativeTest.CommandLineFlags "--gtest_filter=*ES2_VULKAN"

Note that in the above, only a single command line argument is supported with RenderDoc. If testing dEQP on a non-default platform, the easiest way would be to modify GetDefaultAPIName() in src/tests/deqp_support/angle_deqp_gtest.cpp (and avoid --use-angle=X).