1 <html devsite> 2 <head> 3 <title>AddressSanitizer</title> 4 <meta name="project_path" value="/_project.yaml" /> 5 <meta name="book_path" value="/_book.yaml" /> 6 </head> 7 <body> 8 <!-- 9 Copyright 2017 The Android Open Source Project 10 11 Licensed under the Apache License, Version 2.0 (the "License"); 12 you may not use this file except in compliance with the License. 13 You may obtain a copy of the License at 14 15 http://www.apache.org/licenses/LICENSE-2.0 16 17 Unless required by applicable law or agreed to in writing, software 18 distributed under the License is distributed on an "AS IS" BASIS, 19 WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 20 See the License for the specific language governing permissions and 21 limitations under the License. 22 --> 23 24 25 26 <p>AddressSanitizer (ASan) is a fast compiler-based tool for detecting memory bugs 27 in native code. It is comparable to Valgrind (Memcheck tool), but, unlike it, 28 ASan:</p> 29 30 <ul> 31 <li> + detects overflows on stack and global objects 32 <li> - does not detect uninitialized reads and memory leaks 33 <li> + is much faster (two-three times slowdown compared to Valgrinds 20-100x) 34 <li> + has less memory overhead 35 </ul> 36 37 <p>This document describes how to build and run parts of the Android platform with 38 AddressSanitizer. If you are looking to build a standalone (i.e. SDK/NDK) 39 application with AddressSanitizer, see the <a 40 href="https://github.com/google/sanitizers/wiki/AddressSanitizerOnAndroid">AddressSanitizerOnAndroid</a> 41 public project site instead.</p> 42 43 <p>AddressSanitizer consists of a compiler (<code>external/clang</code>) and a runtime library 44 (<code>external/compiler-rt/lib/asan</code>).</p> 45 46 <p class="note"><strong>Note</strong>: Use the current master 47 branch to gain access to the <a href="#sanitize_target">SANITIZE_TARGET</a> 48 feature and the ability to build the entire Android platform with 49 AddressSanitizer at once. Otherwise, you are limited to using 50 <code>LOCAL_SANITIZE</code>.</p> 51 52 <h2 id=building_with_clang>Building with Clang</h2> 53 54 <p>As a first step to building an ASan-instrumented binary, make sure that your 55 code builds with Clang. This is done by default on the master branch, so there should be nothing 56 you need to do. If you believe that the module you'd like to test is being built with GCC, 57 you can switch to Clang by adding <code>LOCAL_CLANG:=true</code> 58 to the build rules. Clang may find bugs in your code that GCC missed.</p> 59 60 <h2 id=building_executables_with_addresssanitizer>Building executables with AddressSanitizer</h2> 61 62 <p>Add <code>LOCAL_SANITIZE:=address</code> to the build rule of the 63 executable.</p> 64 65 <pre class="devsite-click-to-copy"> 66 LOCAL_SANITIZE:=address 67 </pre> 68 69 <p>When a bug is detected, ASan prints a verbose report both to the standard 70 output and to <code>logcat</code> and then crashes the process.</p> 71 72 <h2 id=building_shared_libraries_with_addresssanitizer>Building shared libraries with AddressSanitizer</h2> 73 74 <p>Due to the way ASan works, a library built with ASan cannot be used by an 75 executable that's built without ASan.</p> 76 77 <p class="note"><strong>Note</strong>: In runtime situations where an ASan library is 78 loaded into an incorrect process, you will see unresolved symbol messages 79 starting with <code>_asan</code> or <code>_sanitizer</code>.</p> 80 81 <p>To sanitize a shared library that is used in multiple executables, not all of 82 which are built with ASan, you'll need two copies of the library. The 83 recommended way to do this is to add the following to <code>Android.mk</code> 84 for the module in question:</p> 85 86 <pre class="devsite-click-to-copy"> 87 LOCAL_SANITIZE:=address 88 LOCAL_MODULE_RELATIVE_PATH := asan 89 </pre> 90 91 <p>This puts the library in <code>/system/lib/asan</code> instead of 92 <code>/system/lib</code>. Then, run your executable with: 93 <code>LD_LIBRARY_PATH=/system/lib/asan</code></p> 94 95 <p>For system daemons, add the following to the appropriate section of 96 <code>/init.rc</code> or <code>/init.$device$.rc</code>.</p> 97 98 <pre class="devsite-click-to-copy"> 99 setenv LD_LIBRARY_PATH /system/lib/asan 100 </pre> 101 102 <p class="warning"><strong>Warning</strong>: The <code>LOCAL_MODULE_RELATIVE_PATH</code> 103 setting <strong>moves</strong> your library to <code>/system/lib/asan</code>, 104 meaning that clobbering and rebuilding from scratch will result in the 105 library missing from <code>/system/lib</code>, and probably an unbootable 106 image. That's an unfortunate limitation of the 107 current build system. Don't clobber; do <code>make -j $N</code> and <code>adb 108 sync</code>.</p> 109 110 <p>Verify the process is using libraries from <code>/system/lib/asan</code> 111 when present by reading <code>/proc/$PID/maps</code>. If it's not, you may need 112 to disable SELinux, like so:</p> 113 114 <pre class="devsite-click-to-copy"> 115 <code class="devsite-terminal">adb root</code> 116 <code class="devsite-terminal">adb shell setenforce 0</code> 117 # restart the process with adb shell kill $PID 118 # if it is a system service, or may be adb shell stop; adb shell start. 119 </pre> 120 121 <h2 id=better_stack_traces>Better stack traces</h2> 122 123 <p>AddressSanitizer uses a fast, frame-pointer-based unwinder to record a stack 124 trace for every memory allocation and deallocation event in the program. Most 125 of Android is built without frame pointers. As a result, you will often get 126 only one or two meaningful frames. To fix this, either rebuild the library with 127 ASan (recommended!), or with:</p> 128 129 <pre class="devsite-click-to-copy"> 130 LOCAL_CFLAGS:=-fno-omit-frame-pointer 131 LOCAL_ARM_MODE:=arm 132 </pre> 133 134 <p>Or set <code>ASAN_OPTIONS=fast_unwind_on_malloc=0</code> in the process 135 environment. The latter can be very CPU-intensive, depending on 136 the load.</p> 137 138 <h2 id=symbolization>Symbolization</h2> 139 140 <p>Initially, ASan reports contain references to offsets in binaries and shared 141 libraries. There are two ways to obtain source file and line information:</p> 142 143 <ul> 144 <li>Ensure llvm-symbolizer binary is present in <code>/system/bin</code>. 145 Llvm-symbolizer is built from sources in: 146 <code>third_party/llvm/tools/llvm-symbolizer</code> <li>Filter the report 147 through the <code>external/compiler-rt/lib/asan/scripts/symbolize.py</code> 148 script. 149 </ul> 150 151 <p>The second approach can provide more data (i.e. file:line locations) because of 152 the availability of symbolized libraries on the host.</p> 153 154 <h2 id=addresssanitizer_in_the_apps>AddressSanitizer in the apps</h2> 155 156 <p>AddressSanitizer cannot see into Java code, but it can detect bugs in the JNI 157 libraries. For that, you'll need to build the executable with ASan, which in 158 this case is <code>/system/bin/app_process(<em>32|64</em>)</code>. This will 159 enable ASan in all apps on the device at the same time, which is a 160 bit stressful, but nothing that a 2GB RAM device cannot handle.</p> 161 162 <p>Add the usual <code>LOCAL_SANITIZE:=address</code> to 163 the app_process build rule in <code>frameworks/base/cmds/app_process</code>. Ignore 164 the <code>app_process__asan</code> target in the same file for now (if it is 165 still there at the time you read 166 this). Edit the Zygote record in 167 <code>system/core/rootdir/init.zygote(<em>32|64</em>).rc</code> to add the 168 following lines:</p> 169 170 <pre class="devsite-click-to-copy"> 171 setenv LD_LIBRARY_PATH /system/lib/asan:/system/lib 172 setenv ASAN_OPTIONS 173 allow_user_segv_handler=true 174 </pre> 175 176 <p>Build, adb sync, fastboot flash boot, reboot.</p> 177 178 <h2 id=using_the_wrap_property>Using the wrap property</h2> 179 180 <p>The approach in the previous section puts AddressSanitizer into every 181 application in the system (actually, into every descendant of the Zygote 182 process). It is possible to run only one (or several) applications with ASan, 183 trading some memory overhead for slower application startup.</p> 184 185 <p>This can be done by starting your app with the wrap. property, the same one 186 thats used to run apps under Valgrind. The following example runs the Gmail app 187 under ASan:</p> 188 189 <pre class="devsite-click-to-copy"> 190 <code class="devsite-terminal">adb root</code> 191 <code class="devsite-terminal">adb shell setenforce 0 # disable SELinux</code> 192 <code class="devsite-terminal">adb shell setprop wrap.com.google.android.gm "asanwrapper"</code> 193 </pre> 194 195 <p>In this context, asanwrapper rewrites <code>/system/bin/app_process</code> 196 to <code>/system/bin/asan/app_process</code>, which is built with 197 AddressSanitizer. It also adds <code>/system/lib/asan</code> at the start of 198 the dynamic library search path. This way ASan-instrumented 199 libraries from <code>/system/lib/asan</code> are preferred to normal libraries 200 in <code>/system/lib</code> when running with asanwrapper.</p> 201 202 <p>Again, if a bug is found, the app will crash, and the report will be printed to 203 the log.</p> 204 205 <h2 id=sanitize_target>SANITIZE_TARGET</h2> 206 207 <p>The master branch has support for building the entire Android platform with 208 AddressSanitizer at once.</p> 209 210 <p>Run the following commands in the same build tree.</p> 211 212 <pre class="devsite-click-to-copy"> 213 <code class="devsite-terminal">make -j42</code> 214 <code class="devsite-terminal">SANITIZE_TARGET=address make -j42</code> 215 </pre> 216 217 <p>In this mode, <code>userdata.img</code> contains extra libraries and must be 218 flashed to the device as well. Use the following command line:</p> 219 220 <pre class="devsite-terminal devsite-click-to-copy"> 221 fastboot flash userdata && fastboot flashall 222 </pre> 223 224 <p>At the moment of this writing, modern Nexus and Pixel devices boot to the UI in this mode.</p> 225 226 <p>This works by building two sets of shared libraries: normal in 227 <code>/system/lib</code> (the first make invocation), ASan-instrumented in 228 <code>/data/asan/lib</code> (the second make invocation). Executables from the 229 second build overwrite the ones from the first build. ASan-instrumented 230 executables get a different library search path that includes 231 <code>/data/asan/lib</code> before <code>/system/lib</code> through the use of 232 "/system/bin/linker_asan" in PT_INTERP.</p> 233 234 <p>The build system clobbers intermediate object directories when the 235 <code>$SANITIZE_TARGET</code> value has changed. This forces a rebuild of all 236 targets while preserving installed binaries under <code>/system/lib</code>.</p> 237 238 <p>Some targets cannot be built with ASan:</p> 239 240 <ul> 241 <li>Statically linked executables. 242 <li><code>LOCAL_CLANG:=false</code> targets 243 <li><code>LOCAL_SANITIZE:=false</code> will not be ASan'd for <code>SANITIZE_TARGET=address</code> 244 </ul> 245 246 <p>Executables like these are skipped in the SANITIZE_TARGET build, and the 247 version from the first make invocation is left in <code>/system/bin</code>.</p> 248 249 <p>Libraries like this are simply built without ASan. They can contain some ASan 250 code anyway from the static libraries they depend upon.</p> 251 252 <h2 id=supporting_documentation>Supporting documentation</h2> 253 254 <p><a href="https://github.com/google/sanitizers/wiki/AddressSanitizerOnAndroid">AddressSanitizerOnAndroid</a> public project site</p> 255 <p><a href="https://www.chromium.org/developers/testing/addresssanitizer">AddressSanitizer and Chromium</a></p> 256 <p><a href="https://github.com/google/sanitizers">Other Google Sanitizers</a></p> 257 258 </body> 259 </html> 260
