1 ================ 2 AddressSanitizer 3 ================ 4 5 .. contents:: 6 :local: 7 8 Introduction 9 ============ 10 11 AddressSanitizer is a fast memory error detector. It consists of a compiler 12 instrumentation module and a run-time library. The tool can detect the 13 following types of bugs: 14 15 * Out-of-bounds accesses to heap, stack and globals 16 * Use-after-free 17 * Use-after-return (to some extent) 18 * Double-free, invalid free 19 * Memory leaks (experimental) 20 21 Typical slowdown introduced by AddressSanitizer is **2x**. 22 23 How to build 24 ============ 25 26 Build LLVM/Clang with `CMake <http://llvm.org/docs/CMake.html>`_. 27 28 Usage 29 ===== 30 31 Simply compile and link your program with ``-fsanitize=address`` flag. The 32 AddressSanitizer run-time library should be linked to the final executable, so 33 make sure to use ``clang`` (not ``ld``) for the final link step. When linking 34 shared libraries, the AddressSanitizer run-time is not linked, so 35 ``-Wl,-z,defs`` may cause link errors (don't use it with AddressSanitizer). To 36 get a reasonable performance add ``-O1`` or higher. To get nicer stack traces 37 in error messages add ``-fno-omit-frame-pointer``. To get perfect stack traces 38 you may need to disable inlining (just use ``-O1``) and tail call elimination 39 (``-fno-optimize-sibling-calls``). 40 41 .. code-block:: console 42 43 % cat example_UseAfterFree.cc 44 int main(int argc, char **argv) { 45 int *array = new int[100]; 46 delete [] array; 47 return array[argc]; // BOOM 48 } 49 50 # Compile and link 51 % clang -O1 -g -fsanitize=address -fno-omit-frame-pointer example_UseAfterFree.cc 52 53 or: 54 55 .. code-block:: console 56 57 # Compile 58 % clang -O1 -g -fsanitize=address -fno-omit-frame-pointer -c example_UseAfterFree.cc 59 # Link 60 % clang -g -fsanitize=address example_UseAfterFree.o 61 62 If a bug is detected, the program will print an error message to stderr and 63 exit with a non-zero exit code. AddressSanitizer exits on the first detected error. 64 This is by design: 65 66 * This approach allows AddressSanitizer to produce faster and smaller generated code 67 (both by ~5%). 68 * Fixing bugs becomes unavoidable. AddressSanitizer does not produce 69 false alarms. Once a memory corruption occurs, the program is in an inconsistent 70 state, which could lead to confusing results and potentially misleading 71 subsequent reports. 72 73 If your process is sandboxed and you are running on OS X 10.10 or earlier, you 74 will need to set ``DYLD_INSERT_LIBRARIES`` environment variable and point it to 75 the ASan library that is packaged with the compiler used to build the 76 executable. (You can find the library by searching for dynamic libraries with 77 ``asan`` in their name.) If the environment variable is not set, the process will 78 try to re-exec. Also keep in mind that when moving the executable to another machine, 79 the ASan library will also need to be copied over. 80 81 Symbolizing the Reports 82 ========================= 83 84 To make AddressSanitizer symbolize its output 85 you need to set the ``ASAN_SYMBOLIZER_PATH`` environment variable to point to 86 the ``llvm-symbolizer`` binary (or make sure ``llvm-symbolizer`` is in your 87 ``$PATH``): 88 89 .. code-block:: console 90 91 % ASAN_SYMBOLIZER_PATH=/usr/local/bin/llvm-symbolizer ./a.out 92 ==9442== ERROR: AddressSanitizer heap-use-after-free on address 0x7f7ddab8c084 at pc 0x403c8c bp 0x7fff87fb82d0 sp 0x7fff87fb82c8 93 READ of size 4 at 0x7f7ddab8c084 thread T0 94 #0 0x403c8c in main example_UseAfterFree.cc:4 95 #1 0x7f7ddabcac4d in __libc_start_main ??:0 96 0x7f7ddab8c084 is located 4 bytes inside of 400-byte region [0x7f7ddab8c080,0x7f7ddab8c210) 97 freed by thread T0 here: 98 #0 0x404704 in operator delete[](void*) ??:0 99 #1 0x403c53 in main example_UseAfterFree.cc:4 100 #2 0x7f7ddabcac4d in __libc_start_main ??:0 101 previously allocated by thread T0 here: 102 #0 0x404544 in operator new[](unsigned long) ??:0 103 #1 0x403c43 in main example_UseAfterFree.cc:2 104 #2 0x7f7ddabcac4d in __libc_start_main ??:0 105 ==9442== ABORTING 106 107 If that does not work for you (e.g. your process is sandboxed), you can use a 108 separate script to symbolize the result offline (online symbolization can be 109 force disabled by setting ``ASAN_OPTIONS=symbolize=0``): 110 111 .. code-block:: console 112 113 % ASAN_OPTIONS=symbolize=0 ./a.out 2> log 114 % projects/compiler-rt/lib/asan/scripts/asan_symbolize.py / < log | c++filt 115 ==9442== ERROR: AddressSanitizer heap-use-after-free on address 0x7f7ddab8c084 at pc 0x403c8c bp 0x7fff87fb82d0 sp 0x7fff87fb82c8 116 READ of size 4 at 0x7f7ddab8c084 thread T0 117 #0 0x403c8c in main example_UseAfterFree.cc:4 118 #1 0x7f7ddabcac4d in __libc_start_main ??:0 119 ... 120 121 Note that on OS X you may need to run ``dsymutil`` on your binary to have the 122 file\:line info in the AddressSanitizer reports. 123 124 Additional Checks 125 ================= 126 127 Initialization order checking 128 ----------------------------- 129 130 AddressSanitizer can optionally detect dynamic initialization order problems, 131 when initialization of globals defined in one translation unit uses 132 globals defined in another translation unit. To enable this check at runtime, 133 you should set environment variable 134 ``ASAN_OPTIONS=check_initialization_order=1``. 135 136 Note that this option is not supported on OS X. 137 138 Memory leak detection 139 --------------------- 140 141 For more information on leak detector in AddressSanitizer, see 142 :doc:`LeakSanitizer`. The leak detection is turned on by default on Linux; 143 however, it is not yet supported on other platforms. 144 145 Issue Suppression 146 ================= 147 148 AddressSanitizer is not expected to produce false positives. If you see one, 149 look again; most likely it is a true positive! 150 151 Suppressing Reports in External Libraries 152 ----------------------------------------- 153 Runtime interposition allows AddressSanitizer to find bugs in code that is 154 not being recompiled. If you run into an issue in external libraries, we 155 recommend immediately reporting it to the library maintainer so that it 156 gets addressed. However, you can use the following suppression mechanism 157 to unblock yourself and continue on with the testing. This suppression 158 mechanism should only be used for suppressing issues in external code; it 159 does not work on code recompiled with AddressSanitizer. To suppress errors 160 in external libraries, set the ``ASAN_OPTIONS`` environment variable to point 161 to a suppression file. You can either specify the full path to the file or the 162 path of the file relative to the location of your executable. 163 164 .. code-block:: bash 165 166 ASAN_OPTIONS=suppressions=MyASan.supp 167 168 Use the following format to specify the names of the functions or libraries 169 you want to suppress. You can see these in the error report. Remember that 170 the narrower the scope of the suppression, the more bugs you will be able to 171 catch. 172 173 .. code-block:: bash 174 175 interceptor_via_fun:NameOfCFunctionToSuppress 176 interceptor_via_fun:-[ClassName objCMethodToSuppress:] 177 interceptor_via_lib:NameOfTheLibraryToSuppress 178 179 Conditional Compilation with ``__has_feature(address_sanitizer)`` 180 ----------------------------------------------------------------- 181 182 In some cases one may need to execute different code depending on whether 183 AddressSanitizer is enabled. 184 :ref:`\_\_has\_feature <langext-__has_feature-__has_extension>` can be used for 185 this purpose. 186 187 .. code-block:: c 188 189 #if defined(__has_feature) 190 # if __has_feature(address_sanitizer) 191 // code that builds only under AddressSanitizer 192 # endif 193 #endif 194 195 Disabling Instrumentation with ``__attribute__((no_sanitize("address")))`` 196 -------------------------------------------------------------------------- 197 198 Some code should not be instrumented by AddressSanitizer. One may use the 199 function attribute ``__attribute__((no_sanitize("address")))`` (which has 200 deprecated synonyms `no_sanitize_address` and `no_address_safety_analysis`) to 201 disable instrumentation of a particular function. This attribute may not be 202 supported by other compilers, so we suggest to use it together with 203 ``__has_feature(address_sanitizer)``. 204 205 Suppressing Errors in Recompiled Code (Blacklist) 206 ------------------------------------------------- 207 208 AddressSanitizer supports ``src`` and ``fun`` entity types in 209 :doc:`SanitizerSpecialCaseList`, that can be used to suppress error reports 210 in the specified source files or functions. Additionally, AddressSanitizer 211 introduces ``global`` and ``type`` entity types that can be used to 212 suppress error reports for out-of-bound access to globals with certain 213 names and types (you may only specify class or struct types). 214 215 You may use an ``init`` category to suppress reports about initialization-order 216 problems happening in certain source files or with certain global variables. 217 218 .. code-block:: bash 219 220 # Suppress error reports for code in a file or in a function: 221 src:bad_file.cpp 222 # Ignore all functions with names containing MyFooBar: 223 fun:*MyFooBar* 224 # Disable out-of-bound checks for global: 225 global:bad_array 226 # Disable out-of-bound checks for global instances of a given class ... 227 type:Namespace::BadClassName 228 # ... or a given struct. Use wildcard to deal with anonymous namespace. 229 type:Namespace2::*::BadStructName 230 # Disable initialization-order checks for globals: 231 global:bad_init_global=init 232 type:*BadInitClassSubstring*=init 233 src:bad/init/files/*=init 234 235 Limitations 236 =========== 237 238 * AddressSanitizer uses more real memory than a native run. Exact overhead 239 depends on the allocations sizes. The smaller the allocations you make the 240 bigger the overhead is. 241 * AddressSanitizer uses more stack memory. We have seen up to 3x increase. 242 * On 64-bit platforms AddressSanitizer maps (but not reserves) 16+ Terabytes of 243 virtual address space. This means that tools like ``ulimit`` may not work as 244 usually expected. 245 * Static linking is not supported. 246 247 Supported Platforms 248 =================== 249 250 AddressSanitizer is supported on: 251 252 * Linux i386/x86\_64 (tested on Ubuntu 12.04) 253 * OS X 10.7 - 10.11 (i386/x86\_64) 254 * iOS Simulator 255 * Android ARM 256 * FreeBSD i386/x86\_64 (tested on FreeBSD 11-current) 257 258 Ports to various other platforms are in progress. 259 260 Current Status 261 ============== 262 263 AddressSanitizer is fully functional on supported platforms starting from LLVM 264 3.1. The test suite is integrated into CMake build and can be run with ``make 265 check-asan`` command. 266 267 More Information 268 ================ 269 270 `<https://github.com/google/sanitizers/wiki/AddressSanitizer>`_ 271
