1<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" 2 "http://www.w3.org/TR/html4/strict.dtd"> 3<!-- Material used from: HTML 4.01 specs: http://www.w3.org/TR/html401/ --> 4<html> 5<head> 6 <META http-equiv="Content-Type" content="text/html; charset=ISO-8859-1"> 7 <title>AddressSanitizer, a fast memory error detector</title> 8 <link type="text/css" rel="stylesheet" href="../menu.css"> 9 <link type="text/css" rel="stylesheet" href="../content.css"> 10 <style type="text/css"> 11 td { 12 vertical-align: top; 13 } 14 </style> 15</head> 16<body> 17 18<!--#include virtual="../menu.html.incl"--> 19 20<div id="content"> 21 22<h1>AddressSanitizer</h1> 23<ul> 24 <li> <a href="#intro">Introduction</a> 25 <li> <a href="#howtobuild">How to Build</a> 26 <li> <a href="#usage">Usage</a> 27 <ul><li> <a href="#has_feature">__has_feature(address_sanitizer)</a></ul> 28 <ul><li> <a href="#no_address_safety_analysis"> 29 __attribute__((no_address_safety_analysis))</a></ul> 30 <li> <a href="#platforms">Supported Platforms</a> 31 <li> <a href="#limitations">Limitations</a> 32 <li> <a href="#status">Current Status</a> 33 <li> <a href="#moreinfo">More Information</a> 34</ul> 35 36<h2 id="intro">Introduction</h2> 37AddressSanitizer is a fast memory error detector. 38It consists of a compiler instrumentation module and a run-time library. 39The tool can detect the following types of bugs: 40<ul> <li> Out-of-bounds accesses to heap, stack and globals 41 <li> Use-after-free 42 <li> Use-after-return (to some extent) 43 <li> Double-free, invalid free 44</ul> 45Typical slowdown introduced by AddressSanitizer is <b>2x</b>. 46 47<h2 id="howtobuild">How to build</h2> 48Follow the <a href="../get_started.html">clang build instructions</a>. <BR> 49 50<h2 id="usage">Usage</h2> 51Simply compile and link your program with <tt>-faddress-sanitizer</tt> flag. <BR> 52To get a reasonable performance add <tt>-O1</tt> or higher. <BR> 53To get nicer stack traces in error messages add 54<tt>-fno-omit-frame-pointer</tt>. <BR> 55To get perfect stack traces you may need to disable inlining (just use <tt>-O1</tt>) and tail call 56elimination (</tt>-fno-optimize-sibling-calls</tt>). 57 58<pre> 59% cat example_UseAfterFree.cc 60int main(int argc, char **argv) { 61 int *array = new int[100]; 62 delete [] array; 63 return array[argc]; // BOOM 64} 65</pre> 66 67<pre> 68% clang -O1 -g -faddress-sanitizer -fno-omit-frame-pointer example_UseAfterFree.cc 69</pre> 70 71If a bug is detected, the program will print an error message to stderr and exit with a 72non-zero exit code. 73Currently, AddressSanitizer does not symbolize its output, so you may need to use a 74separate script to symbolize the result offline (this will be fixed in future). 75<pre> 76% ./a.out 2> log 77% projects/compiler-rt/lib/asan/scripts/asan_symbolize.py / < log | c++filt 78==9442== ERROR: AddressSanitizer heap-use-after-free on address 0x7f7ddab8c084 at pc 0x403c8c bp 0x7fff87fb82d0 sp 0x7fff87fb82c8 79READ of size 4 at 0x7f7ddab8c084 thread T0 80 #0 0x403c8c in main example_UseAfterFree.cc:4 81 #1 0x7f7ddabcac4d in __libc_start_main ??:0 820x7f7ddab8c084 is located 4 bytes inside of 400-byte region [0x7f7ddab8c080,0x7f7ddab8c210) 83freed by thread T0 here: 84 #0 0x404704 in operator delete[](void*) ??:0 85 #1 0x403c53 in main example_UseAfterFree.cc:4 86 #2 0x7f7ddabcac4d in __libc_start_main ??:0 87previously allocated by thread T0 here: 88 #0 0x404544 in operator new[](unsigned long) ??:0 89 #1 0x403c43 in main example_UseAfterFree.cc:2 90 #2 0x7f7ddabcac4d in __libc_start_main ??:0 91==9442== ABORTING 92</pre> 93 94<h3 id="has_feature">__has_feature(address_sanitizer)</h3> 95In some cases one may need to execute different code depending on whether 96AddressSanitizer is enabled. 97<a href="LanguageExtensions.html#__has_feature_extension">__has_feature</a> 98can be used for this purpose. 99<pre> 100#if defined(__has_feature) 101# if __has_feature(address_sanitizer) 102 code that builds only under AddressSanitizer 103# endif 104#endif 105</pre> 106 107<h3 id="no_address_safety_analysis">__attribute__((no_address_safety_analysis))</h3> 108Some code should not be instrumentated by AddressSanitizer. 109One may use the function attribute 110<a href="LanguageExtensions.html#address_sanitizer"> 111 <tt>no_address_safety_analysis</tt></a> 112to disable instrumentation of a particular function. 113This attribute may not be supported by other compilers, so we suggest to 114use it together with <tt>__has_feature(address_sanitizer)</tt>. 115Note: currently, this attribute will be lost if the function is inlined. 116 117<h2 id="platforms">Supported Platforms</h2> 118AddressSanitizer is supported on 119<ul><li>Linux x86_64 (tested on Ubuntu 10.04). 120<li>MacOS 10.6, 10.7 and 10.8 (i386/x86_64). 121</ul> 122Support for Linux i386/ARM is in progress 123(it may work, but is not guaranteed too). 124 125 126<h2 id="limitations">Limitations</h2> 127<ul> 128<li> AddressSanitizer uses more real memory than a native run. 129How much -- depends on the allocations sizes. The smaller the 130allocations you make the bigger the overhead. 131<li> AddressSanitizer uses more stack memory. We have seen up to 3x increase. 132<li> On 64-bit platforms AddressSanitizer maps (but not reserves) 13316+ Terabytes of virtual address space. 134This means that tools like <tt>ulimit</tt> may not work as usually expected. 135<li> Static linking is not supported. 136</ul> 137 138 139<h2 id="status">Current Status</h2> 140AddressSanitizer is fully functional on supported platforms starting from LLVM 3.1. 141The test suite is integrated into CMake build (can be run with "make 142check-asan" command). 143 144<h2 id="moreinfo">More Information</h2> 145<a href="http://code.google.com/p/address-sanitizer/">http://code.google.com/p/address-sanitizer</a>. 146 147 148</div> 149</body> 150</html> 151