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90 lines
3.7 KiB
90 lines
3.7 KiB
7 months ago
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# NDK Bisection tool
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This is an example bisection for an NDK build system. This example specifically
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bisects the sample NDK Teapot app. All steps (setup and otherwise) for bisection
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can be found in `DO_BISECTION.sh`. This shell script is meant to show the
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process required to bisect a compiler problem in an arbitrary NDK app build
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system.
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There are three necessary setup steps to run this example:
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1. Install the NDK (known to work with r12b)
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1. See here for NDK: https://developer.android.com/ndk/index.html
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2. Go here for older NDK downloads: https://github.com/android-ndk/ndk/wiki
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1. Install the compiler wrapper provided with this repo. See
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compiler_wrapper.py for more details.
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1. Essentially you must go into the NDK source (or where you build system
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stores its toolchain), rename your compilers to <compiler>.real, and
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create a symlink pointing to compiler_wrapper.py named <compiler>
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(where your compiler used to be).
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2. If you're using the toolchains that come with the NDK they live at:
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`<ndk_path>/toolchains/<arch>/prebuilt/<host>/bin`
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example:
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`<ndk_path>/toolchains/llvm/prebuilt/linux-x86_64/bin/clang`
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1. Plug in an Arm7 compatible Android device with usb debugging enabled.
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1. This bisection example was tested with a Nexus 5X
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2. It should be relatively simple to change the example to work with other
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types of devices. Just change the scripts, and change PATCH1 to use a
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different build flavor (like x86). See below for more details.
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This example contains two patches:
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`PATCH1` - This is the necessary changes to the build system to make the
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bisection easier. More specifically, it adds an arm7 build flavor to gradle.
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By default, this project will build objects for all possible architectures and
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package them into one big apk. These object files meant for another
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architecture just sit there and don't actually execute. By adding a build
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flavor for arm7, our compiler wrapper won't try to bisect object files meant
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for another device.
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`PATCH2` - This patch is what inserts the "compiler error". This is a simple
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nullptr error in one of the source files, but it is meant to mimic bad code
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generation. The result of the error is the app simply crashes immediately
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after starting.
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## Using another device architecture
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If we want to bisect for an x86-64 device we first need to provide a arch
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specific build flavor in our app/build.gradle file:
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```
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create("x86-64") {
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ndk.abiFilters.add("x86_64")
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}
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```
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We want to add this under the same "productFlavors" section that our arm7
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build flavor is in (see PATCH1). Now we should have the "installx86-64Debug"
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task in our build system. We can use this to build and install an x86-64
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version of our app.
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Now we want to change our `test_setup.sh` script to run our new gradle task:
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```
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./gradlew installx86-64Debug
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```
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Keep in mind, these specific build flavors are not required. If your build
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system makes these device specific builds difficult to implement, the
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bisection tool will function perfectly fine without them. However, the
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downside of not having targetting a single architecture is the bisection will
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take longer (as it will need to search across more object files).
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## Additional Documentation
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These are internal Google documents, if you are a developer external to
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Google please ask whoever gave you this sample for access or copies to the
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documentation. If you cannot gain access, the various READMEs paired with the
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bisector should help you.
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* Ahmad's original presentation: https://goto.google.com/zxdfyi
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* Bisection tool update design doc: https://goto.google.com/zcwei
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* Bisection tool webpage: https://goto.google.com/ruwpyi
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* Compiler wrapper webpage: https://goto.google.com/xossn
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