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= Building WebKit with Clang Address Sanitizer (ASan) =

This page describes how to build WebKit with the clang Address Sanitizer (ASan) for various ports.

== Building the Apple Mac OS X port with ASan ==

Building the Apple Mac OS X port with the clang Address Sanitizer currently requires a custom build of trunk clang, plus an Xcode toolchain derived from OSX10.9.xctoolchain.

NOTE:  These instructions are currently an '''untested''' work-in-progress, but we hope to automate it with tools soon.

 1. Install Mac OS X 10.9.1 (Mavericks) on a Mac.  Don't use 10.9 as it contains a bug that causes a crash on every HTTP redirect.
 2. Install Xcode developer tools, including the Mac OS X 10.9 SDK.  These instructions assume the 10.9 SDK is located here:
{{{
/Applications/Xcode.app/Contents/Developer/Toolchains/OSX10.9.xctoolchain/
}}}
 3. Make a copy of the `OSX10.9.xctoolchain` and call it `ASAN.xctoolchain`:
{{{
sudo ditto /Applications/Xcode.app/Contents/Developer/Toolchains/OSX10.9.xctoolchain /Applications/Xcode.app/Contents/Developer/Toolchains/ASAN.xctoolchain
}}}
 4. Edit `ASAN.xctoolchain/ToolchainInfo.plist` to change the `Identifier` string from `com.apple.dt.toolchain.OSX10_9` to `com.apple.dt.toolchain.ASAN`.
{{{
sudo vi /Applications/Xcode.app/Contents/Developer/Toolchains/ASAN.xctoolchain/ToolchainInfo.plist
}}}
 5. Build trunk clang/llvm.  The address sanitizer should be built by default for Mac OS X.  See http://www.llvm.org/docs/ for details.  Subversion revision r204316 of clang/llvm is known to build WebKit for Mac OS X.  Newer versions may introduce new warnings or compiler bugs that must be fixed before proceeding.
 6. Ditto the clang/llvm build output into `/Applications/Xcode.app/Contents/Developer/Toolchains/ASAN.xctoolchain` to replace the version of clang/llvm in the original toolchain.
{{{
TBD
}}}
 7. Fix the ID of `libclang_rt.asan_osx_dynamic.dylib` to its installation path using the `install_name_tool`:
{{{
sudo xcrun install_name_tool -id /Applications/Xcode.app/Contents/Developer/Toolchains/ASAN.xctoolchain/usr/lib/clang/3.5.0/lib/darwin/libclang_rt.asan_osx_dynamic.dylib /Applications/Xcode.app/Contents/Developer/Toolchains/ASAN.xctoolchain/usr/lib/clang/3.5.0/lib/darwin/libclang_rt.asan_osx_dynamic.dylib
}}}
 8. Copy `libclang_rt.asan_osx_dynamic.dylib` into your `WebKitBuild/Release` directory:
{{{
ditto /Applications/Xcode.app/Contents/Developer/Toolchains/ASAN.xctoolchain/usr/lib/clang/3.5.0/lib/darwin/libclang_rt.asan_osx_dynamic.dylib WebKitBuild/Release/
}}}
 9. Build WebKit with additional xcodebuild arguments to load `asan.xcconfig`, find the ASan ignore list, and build with the new compiler:
{{{
make release ARGS="-xcconfig $PWD/Tools/asan/asan.xcconfig ASAN_IGNORE=$PWD/Tools/asan/webkit-asan-ignore.txt TOOLCHAINS=com.apple.dt.toolchain.ASAN"
}}}
 10. When running apps that load WebKit built with ASan, the `ASAN_OPTIONS` environment variable needs to be set to make sure the app crashes when you hit an issue, and to prevent false-positives for some intrinsics Mac OS X (e.g., memcpy and memmove are the same function).  For example, to launch Safari:
{{{
ASAN_OPTIONS="replace_intrin=0:abort_on_error=1:handle_segv=0" ./Tools/Scripts/run-safari --release --no-saved-state
}}}
 You should also be able to run DumpRenderTree and WebKitTestRunner in a similar fashion:
{{{
ASAN_OPTIONS="replace_intrin=0:abort_on_error=1:handle_segv=0" ./Tools/Scripts/run-webkit-tests --release --no-build
}}}