AddressSanitizer (ASan) is a fast compiler-based tool for detecting memory bugs in native code. It is comparable to Valgrind (Memcheck tool), but, unlike it, ASan:
- + detects overflows on stack and global objects
- - does not detect uninitialized reads and memory leaks
- + is much faster (two-three times slowdown compared to Valgrind’s 20-100x)
- + has less memory overhead
This document describes how to build and run parts of the Android platform with AddressSanitizer. If you are looking to build a standalone (i.e. SDK/NDK) application with AddressSanitizer, see the AddressSanitizerOnAndroid public project site instead.
AddressSanitizer consists of a compiler (
external/clang) and a runtime library
Note: Use the current master
branch to gain access to the SANITIZE_TARGET
feature and the ability to build the entire Android platform with
AddressSanitizer at once. Otherwise, you are limited to using
Building with Clang
As a first step to building an ASan-instrumented binary, make sure that your
code builds with Clang. This is done by default on the master branch, so there should be nothing
you need to do. If you believe that the module you'd like to test is being built with GCC,
you can switch to Clang by adding
to the build rules. Clang may find bugs in your code that GCC missed.
Building executables with AddressSanitizer
LOCAL_SANITIZE:=address to the build rule of the
When a bug is detected, ASan prints a verbose report both to the standard
output and to
logcat and then crashes the process.
Building shared libraries with AddressSanitizer
Due to the way ASan works, a library built with ASan cannot be used by an executable that's built without ASan.
Note: In runtime situations where an ASan library is
loaded into an incorrect process, you will see unresolved symbol messages
To sanitize a shared library that is used in multiple executables, not all of
which are built with ASan, you'll need two copies of the library. The
recommended way to do this is to add the following to
for the module in question:
LOCAL_SANITIZE:=address LOCAL_MODULE_RELATIVE_PATH := asan
This puts the library in
/system/lib/asan instead of
/system/lib. Then, run your executable with:
For system daemons, add the following to the appropriate section of
setenv LD_LIBRARY_PATH /system/lib/asan
setting moves your library to
meaning that clobbering and rebuilding from scratch will result in the
library missing from
/system/lib, and probably an unbootable
image. That's an unfortunate limitation of the
current build system. Don't clobber; do
make -j $N and
Verify the process is using libraries from
when present by reading
/proc/$PID/maps. If it's not, you may need
to disable SELinux, like so:
$ adb root $ adb shell setenforce 0 # restart the process with adb shell kill $PID # if it is a system service, or may be adb shell stop; adb shell start.
Better stack traces
AddressSanitizer uses a fast, frame-pointer-based unwinder to record a stack trace for every memory allocation and deallocation event in the program. Most of Android is built without frame pointers. As a result, you will often get only one or two meaningful frames. To fix this, either rebuild the library with ASan (recommended!), or with:
ASAN_OPTIONS=fast_unwind_on_malloc=0 in the process
environment. The latter can be very CPU-intensive, depending on
Initially, ASan reports contain references to offsets in binaries and shared libraries. There are two ways to obtain source file and line information:
- Ensure llvm-symbolizer binary is present in
/system/bin. Llvm-symbolizer is built from sources in:
- Filter the report
The second approach can provide more data (i.e. file:line locations) because of the availability of symbolized libraries on the host.
AddressSanitizer in the apps
AddressSanitizer cannot see into Java code, but it can detect bugs in the JNI
libraries. For that, you'll need to build the executable with ASan, which in
this case is
/system/bin/app_process(32|64). This will
enable ASan in all apps on the device at the same time, which is a
bit stressful, but nothing that a 2GB RAM device cannot handle.
Add the usual
the app_process build rule in
app_process__asan target in the same file for now (if it is
still there at the time you read
this). Edit the Zygote record in
system/core/rootdir/init.zygote(32|64).rc to add the
setenv LD_LIBRARY_PATH /system/lib/asan:/system/lib setenv ASAN_OPTIONS allow_user_segv_handler=true
Build, adb sync, fastboot flash boot, reboot.
Using the wrap property
The approach in the previous section puts AddressSanitizer into every application in the system (actually, into every descendant of the Zygote process). It is possible to run only one (or several) applications with ASan, trading some memory overhead for slower application startup.
This can be done by starting your app with the “wrap.” property, the same one that’s used to run apps under Valgrind. The following example runs the Gmail app under ASan:
$ adb root $ adb shell setenforce 0 # disable SELinux $ adb shell setprop wrap.com.google.android.gm "asanwrapper"
In this context, asanwrapper rewrites
/system/bin/asan/app_process, which is built with
AddressSanitizer. It also adds
/system/lib/asan at the start of
the dynamic library search path. This way ASan-instrumented
/system/lib/asan are preferred to normal libraries
/system/lib when running with asanwrapper.
Again, if a bug is found, the app will crash, and the report will be printed to the log.
The master branch has support for building the entire Android platform with AddressSanitizer at once.
Run the following commands in the same build tree.
$ make -j42 $ SANITIZE_TARGET=address make -j42
In this mode,
userdata.img contains extra libraries and must be
flashed to the device as well. Use the following command line:
$ fastboot flash userdata && fastboot flashall
At the moment of this writing, modern Nexus and Pixel devices boot to the UI in this mode.
This works by building two sets of shared libraries: normal in
/system/lib (the first make invocation), ASan-instrumented in
/data/asan/lib (the second make invocation). Executables from the
second build overwrite the ones from the first build. ASan-instrumented
executables get a different library search path that includes
/system/lib through the use of
"/system/bin/linker_asan" in PT_INTERP.
The build system clobbers intermediate object directories when the
$SANITIZE_TARGET value has changed. This forces a rebuild of all
targets while preserving installed binaries under
Some targets cannot be built with ASan:
- Statically linked executables.
LOCAL_SANITIZE:=falsewill not be ASan'd for
Executables like these are skipped in the SANITIZE_TARGET build, and the
version from the first make invocation is left in
Libraries like this are simply built without ASan. They can contain some ASan code anyway from the static libraries they depend upon.
AddressSanitizerOnAndroid public project site