Sean Silva | 93ca021 | 2012-12-13 01:10:46 +0000 | [diff] [blame] | 1 | ================ |
| 2 | AddressSanitizer |
| 3 | ================ |
| 4 | |
| 5 | .. contents:: |
| 6 | :local: |
| 7 | |
| 8 | Introduction |
| 9 | ============ |
| 10 | |
Dmitri Gribenko | 97555a1 | 2012-12-15 21:10:51 +0000 | [diff] [blame] | 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: |
Sean Silva | 93ca021 | 2012-12-13 01:10:46 +0000 | [diff] [blame] | 14 | |
Dmitri Gribenko | 97555a1 | 2012-12-15 21:10:51 +0000 | [diff] [blame] | 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 |
Sean Silva | 93ca021 | 2012-12-13 01:10:46 +0000 | [diff] [blame] | 19 | |
| 20 | Typical slowdown introduced by AddressSanitizer is **2x**. |
| 21 | |
| 22 | How to build |
| 23 | ============ |
| 24 | |
Dmitri Gribenko | 97555a1 | 2012-12-15 21:10:51 +0000 | [diff] [blame] | 25 | Follow the `clang build instructions <../get_started.html>`_. CMake build is |
| 26 | supported. |
Sean Silva | 93ca021 | 2012-12-13 01:10:46 +0000 | [diff] [blame] | 27 | |
| 28 | Usage |
| 29 | ===== |
| 30 | |
Dmitri Gribenko | 97555a1 | 2012-12-15 21:10:51 +0000 | [diff] [blame] | 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``). |
Sean Silva | 93ca021 | 2012-12-13 01:10:46 +0000 | [diff] [blame] | 40 | |
Dmitri Gribenko | 97555a1 | 2012-12-15 21:10:51 +0000 | [diff] [blame] | 41 | .. code-block:: console |
Sean Silva | 93ca021 | 2012-12-13 01:10:46 +0000 | [diff] [blame] | 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 | |
Sean Silva | 93ca021 | 2012-12-13 01:10:46 +0000 | [diff] [blame] | 50 | # Compile and link |
| 51 | % clang -O1 -g -fsanitize=address -fno-omit-frame-pointer example_UseAfterFree.cc |
| 52 | |
Dmitri Gribenko | 97555a1 | 2012-12-15 21:10:51 +0000 | [diff] [blame] | 53 | or: |
Sean Silva | 93ca021 | 2012-12-13 01:10:46 +0000 | [diff] [blame] | 54 | |
Dmitri Gribenko | 97555a1 | 2012-12-15 21:10:51 +0000 | [diff] [blame] | 55 | .. code-block:: console |
Sean Silva | 93ca021 | 2012-12-13 01:10:46 +0000 | [diff] [blame] | 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 | |
Dmitri Gribenko | 97555a1 | 2012-12-15 21:10:51 +0000 | [diff] [blame] | 62 | If a bug is detected, the program will print an error message to stderr and |
| 63 | exit with a non-zero exit code. Currently, AddressSanitizer does not symbolize |
| 64 | its output, so you may need to use a separate script to symbolize the result |
| 65 | offline (this will be fixed in future). |
Sean Silva | 93ca021 | 2012-12-13 01:10:46 +0000 | [diff] [blame] | 66 | |
Dmitri Gribenko | 97555a1 | 2012-12-15 21:10:51 +0000 | [diff] [blame] | 67 | .. code-block:: console |
Sean Silva | 93ca021 | 2012-12-13 01:10:46 +0000 | [diff] [blame] | 68 | |
| 69 | % ./a.out 2> log |
| 70 | % projects/compiler-rt/lib/asan/scripts/asan_symbolize.py / < log | c++filt |
| 71 | ==9442== ERROR: AddressSanitizer heap-use-after-free on address 0x7f7ddab8c084 at pc 0x403c8c bp 0x7fff87fb82d0 sp 0x7fff87fb82c8 |
| 72 | READ of size 4 at 0x7f7ddab8c084 thread T0 |
| 73 | #0 0x403c8c in main example_UseAfterFree.cc:4 |
| 74 | #1 0x7f7ddabcac4d in __libc_start_main ??:0 |
| 75 | 0x7f7ddab8c084 is located 4 bytes inside of 400-byte region [0x7f7ddab8c080,0x7f7ddab8c210) |
| 76 | freed by thread T0 here: |
| 77 | #0 0x404704 in operator delete[](void*) ??:0 |
| 78 | #1 0x403c53 in main example_UseAfterFree.cc:4 |
| 79 | #2 0x7f7ddabcac4d in __libc_start_main ??:0 |
| 80 | previously allocated by thread T0 here: |
| 81 | #0 0x404544 in operator new[](unsigned long) ??:0 |
| 82 | #1 0x403c43 in main example_UseAfterFree.cc:2 |
| 83 | #2 0x7f7ddabcac4d in __libc_start_main ??:0 |
| 84 | ==9442== ABORTING |
| 85 | |
| 86 | AddressSanitizer exits on the first detected error. This is by design. |
| 87 | One reason: it makes the generated code smaller and faster (both by |
| 88 | ~5%). Another reason: this makes fixing bugs unavoidable. With Valgrind, |
| 89 | it is often the case that users treat Valgrind warnings as false |
| 90 | positives (which they are not) and don't fix them. |
| 91 | |
Dmitri Gribenko | 97555a1 | 2012-12-15 21:10:51 +0000 | [diff] [blame] | 92 | ``__has_feature(address_sanitizer)`` |
Sean Silva | 93ca021 | 2012-12-13 01:10:46 +0000 | [diff] [blame] | 93 | ------------------------------------ |
| 94 | |
Dmitri Gribenko | 97555a1 | 2012-12-15 21:10:51 +0000 | [diff] [blame] | 95 | In some cases one may need to execute different code depending on whether |
| 96 | AddressSanitizer is enabled. |
| 97 | :ref:`\_\_has\_feature <langext-__has_feature-__has_extension>` can be used for |
| 98 | this purpose. |
Sean Silva | 93ca021 | 2012-12-13 01:10:46 +0000 | [diff] [blame] | 99 | |
Dmitri Gribenko | 97555a1 | 2012-12-15 21:10:51 +0000 | [diff] [blame] | 100 | .. code-block:: c |
Sean Silva | 93ca021 | 2012-12-13 01:10:46 +0000 | [diff] [blame] | 101 | |
| 102 | #if defined(__has_feature) |
Dmitri Gribenko | 97555a1 | 2012-12-15 21:10:51 +0000 | [diff] [blame] | 103 | # if __has_feature(address_sanitizer) |
| 104 | // code that builds only under AddressSanitizer |
| 105 | # endif |
Sean Silva | 93ca021 | 2012-12-13 01:10:46 +0000 | [diff] [blame] | 106 | #endif |
| 107 | |
Kostya Serebryany | 85aee96 | 2013-02-26 06:58:27 +0000 | [diff] [blame] | 108 | ``__attribute__((no_sanitize_address))`` |
Dmitri Gribenko | 97555a1 | 2012-12-15 21:10:51 +0000 | [diff] [blame] | 109 | ----------------------------------------------- |
Sean Silva | 93ca021 | 2012-12-13 01:10:46 +0000 | [diff] [blame] | 110 | |
Dmitri Gribenko | 97555a1 | 2012-12-15 21:10:51 +0000 | [diff] [blame] | 111 | Some code should not be instrumented by AddressSanitizer. One may use the |
| 112 | function attribute |
Kostya Serebryany | 85aee96 | 2013-02-26 06:58:27 +0000 | [diff] [blame] | 113 | :ref:`no_sanitize_address <langext-address_sanitizer>` |
| 114 | (or a deprecated synonym `no_address_safety_analysis`) |
Dmitri Gribenko | 97555a1 | 2012-12-15 21:10:51 +0000 | [diff] [blame] | 115 | to disable instrumentation of a particular function. This attribute may not be |
| 116 | supported by other compilers, so we suggest to use it together with |
| 117 | ``__has_feature(address_sanitizer)``. Note: currently, this attribute will be |
| 118 | lost if the function is inlined. |
Sean Silva | 93ca021 | 2012-12-13 01:10:46 +0000 | [diff] [blame] | 119 | |
| 120 | Supported Platforms |
| 121 | =================== |
| 122 | |
| 123 | AddressSanitizer is supported on |
| 124 | |
Dmitri Gribenko | 97555a1 | 2012-12-15 21:10:51 +0000 | [diff] [blame] | 125 | * Linux i386/x86\_64 (tested on Ubuntu 10.04 and 12.04); |
| 126 | * MacOS 10.6, 10.7 and 10.8 (i386/x86\_64). |
Sean Silva | 93ca021 | 2012-12-13 01:10:46 +0000 | [diff] [blame] | 127 | |
| 128 | Support for Linux ARM (and Android ARM) is in progress (it may work, but |
| 129 | is not guaranteed too). |
| 130 | |
| 131 | Limitations |
| 132 | =========== |
| 133 | |
Dmitri Gribenko | 97555a1 | 2012-12-15 21:10:51 +0000 | [diff] [blame] | 134 | * AddressSanitizer uses more real memory than a native run. Exact overhead |
| 135 | depends on the allocations sizes. The smaller the allocations you make the |
| 136 | bigger the overhead is. |
| 137 | * AddressSanitizer uses more stack memory. We have seen up to 3x increase. |
| 138 | * On 64-bit platforms AddressSanitizer maps (but not reserves) 16+ Terabytes of |
| 139 | virtual address space. This means that tools like ``ulimit`` may not work as |
| 140 | usually expected. |
| 141 | * Static linking is not supported. |
Sean Silva | 93ca021 | 2012-12-13 01:10:46 +0000 | [diff] [blame] | 142 | |
| 143 | Current Status |
| 144 | ============== |
| 145 | |
Dmitri Gribenko | 97555a1 | 2012-12-15 21:10:51 +0000 | [diff] [blame] | 146 | AddressSanitizer is fully functional on supported platforms starting from LLVM |
| 147 | 3.1. The test suite is integrated into CMake build and can be run with ``make |
| 148 | check-asan`` command. |
Sean Silva | 93ca021 | 2012-12-13 01:10:46 +0000 | [diff] [blame] | 149 | |
| 150 | More Information |
| 151 | ================ |
| 152 | |
Dmitri Gribenko | 97555a1 | 2012-12-15 21:10:51 +0000 | [diff] [blame] | 153 | `http://code.google.com/p/address-sanitizer <http://code.google.com/p/address-sanitizer/>`_ |
| 154 | |