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gerrit-public.fairphone.software / platform / external / clang / 460e7a25da073a1cc2bec995bde66877f30ca4f5 / . / docs / AddressSanitizer.html
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Kostya Serebryany7a31d7b2011-11-28 22:34:10 +0000[diff] [blame]20<div id="content">
21
Kostya Serebryanyce98c9b2011-11-28 20:51:02 +0000[diff] [blame]22<h1>AddressSanitizer</h1>
23<ul>
Kostya Serebryanycef57e52012-04-23 09:05:50 +0000[diff] [blame]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>
Kostya Serebryanyce98c9b2011-11-28 20:51:02 +0000[diff] [blame]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:
Kostya Serebryany2e173222011-12-12 23:22:31 +0000[diff] [blame]40<ul> <li> Out-of-bounds accesses to heap, stack and globals
Kostya Serebryanyce98c9b2011-11-28 20:51:02 +0000[diff] [blame]41 <li> Use-after-free
42 <li> Use-after-return (to some extent)
Kostya Serebryany2e173222011-12-12 23:22:31 +0000[diff] [blame]43 <li> Double-free, invalid free
Kostya Serebryanyce98c9b2011-11-28 20:51:02 +0000[diff] [blame]44</ul>
45Typical slowdown introduced by AddressSanitizer is <b>2x</b>.
46
Kostya Serebryany2e173222011-12-12 23:22:31 +0000[diff] [blame]47<h2 id="howtobuild">How to build</h2>
Kostya Serebryanyabc31ca2012-03-15 16:20:29 +0000[diff] [blame]48Follow the <a href="../get_started.html">clang build instructions</a>. <BR>
Kostya Serebryany2e173222011-12-12 23:22:31 +0000[diff] [blame]49
Benjamin Kramer665a8dc2012-01-15 15:26:07 +0000[diff] [blame]50<h2 id="usage">Usage</h2>
Kostya Serebryany2e173222011-12-12 23:22:31 +0000[diff] [blame]51Simply compile and link your program with <tt>-faddress-sanitizer</tt> flag. <BR>
Kostya Serebryany460e7a22012-10-19 07:00:46 +0000[diff] [blame^]52The AddressSanitizer run-time library should be linked to the final executable,
53so make sure to use <tt>clang</tt> (not <tt>ld</tt>) for the final link step.<BR>
54When linking shared libraries, the AddressSanitizer run-time is not linked,
55so <tt>-Wl,-z,defs</tt> may cause link errors (don't use it with AddressSanitizer). <BR>
56
Kostya Serebryany2e173222011-12-12 23:22:31 +0000[diff] [blame]57To get a reasonable performance add <tt>-O1</tt> or higher. <BR>
Kostya Serebryanye683fd92012-01-06 17:35:27 +0000[diff] [blame]58To get nicer stack traces in error messages add
59<tt>-fno-omit-frame-pointer</tt>. <BR>
Kostya Serebryanyf5249f52012-01-23 18:50:23 +0000[diff] [blame]60To get perfect stack traces you may need to disable inlining (just use <tt>-O1</tt>) and tail call
61elimination (</tt>-fno-optimize-sibling-calls</tt>).
Kostya Serebryany2e173222011-12-12 23:22:31 +0000[diff] [blame]62
63<pre>
64% cat example_UseAfterFree.cc
65int main(int argc, char **argv) {
66 int *array = new int[100];
67 delete [] array;
68 return array[argc]; // BOOM
69}
70</pre>
71
72<pre>
Kostya Serebryany460e7a22012-10-19 07:00:46 +0000[diff] [blame^]73# Compile and link
Kostya Serebryanye683fd92012-01-06 17:35:27 +0000[diff] [blame]74% clang -O1 -g -faddress-sanitizer -fno-omit-frame-pointer example_UseAfterFree.cc
Kostya Serebryany2e173222011-12-12 23:22:31 +0000[diff] [blame]75</pre>
Kostya Serebryany460e7a22012-10-19 07:00:46 +0000[diff] [blame^]76OR
77<pre>
78# Compile
79% clang -O1 -g -faddress-sanitizer -fno-omit-frame-pointer -c example_UseAfterFree.cc
80# Link
81% clang -g -faddress-sanitizer example_UseAfterFree.o
82</pre>
Kostya Serebryany2e173222011-12-12 23:22:31 +0000[diff] [blame]83
84If a bug is detected, the program will print an error message to stderr and exit with a
Kostya Serebryanyb8769932011-12-02 00:24:42 +0000[diff] [blame]85non-zero exit code.
Kostya Serebryany2e173222011-12-12 23:22:31 +0000[diff] [blame]86Currently, AddressSanitizer does not symbolize its output, so you may need to use a
87separate script to symbolize the result offline (this will be fixed in future).
88<pre>
89% ./a.out 2> log
90% projects/compiler-rt/lib/asan/scripts/asan_symbolize.py / < log | c++filt
91==9442== ERROR: AddressSanitizer heap-use-after-free on address 0x7f7ddab8c084 at pc 0x403c8c bp 0x7fff87fb82d0 sp 0x7fff87fb82c8
92READ of size 4 at 0x7f7ddab8c084 thread T0
93 #0 0x403c8c in main example_UseAfterFree.cc:4
94 #1 0x7f7ddabcac4d in __libc_start_main ??:0
950x7f7ddab8c084 is located 4 bytes inside of 400-byte region [0x7f7ddab8c080,0x7f7ddab8c210)
96freed by thread T0 here:
97 #0 0x404704 in operator delete[](void*) ??:0
98 #1 0x403c53 in main example_UseAfterFree.cc:4
99 #2 0x7f7ddabcac4d in __libc_start_main ??:0
100previously allocated by thread T0 here:
101 #0 0x404544 in operator new[](unsigned long) ??:0
102 #1 0x403c43 in main example_UseAfterFree.cc:2
103 #2 0x7f7ddabcac4d in __libc_start_main ??:0
104==9442== ABORTING
105</pre>
Kostya Serebryanyce98c9b2011-11-28 20:51:02 +0000[diff] [blame]106
107<h3 id="has_feature">__has_feature(address_sanitizer)</h3>
108In some cases one may need to execute different code depending on whether
109AddressSanitizer is enabled.
110<a href="LanguageExtensions.html#__has_feature_extension">__has_feature</a>
111can be used for this purpose.
112<pre>
Kostya Serebryanyf45f2342012-07-02 11:00:33 +0000[diff] [blame]113#if defined(__has_feature)
114# if __has_feature(address_sanitizer)
115 code that builds only under AddressSanitizer
116# endif
Kostya Serebryanyce98c9b2011-11-28 20:51:02 +0000[diff] [blame]117#endif
118</pre>
119
Kostya Serebryanycef57e52012-04-23 09:05:50 +0000[diff] [blame]120<h3 id="no_address_safety_analysis">__attribute__((no_address_safety_analysis))</h3>
121Some code should not be instrumentated by AddressSanitizer.
122One may use the function attribute
123<a href="LanguageExtensions.html#address_sanitizer">
124 <tt>no_address_safety_analysis</tt></a>
125to disable instrumentation of a particular function.
Kostya Serebryanyf45f2342012-07-02 11:00:33 +0000[diff] [blame]126This attribute may not be supported by other compilers, so we suggest to
127use it together with <tt>__has_feature(address_sanitizer)</tt>.
Kostya Serebryanycef57e52012-04-23 09:05:50 +0000[diff] [blame]128Note: currently, this attribute will be lost if the function is inlined.
129
Kostya Serebryanyce98c9b2011-11-28 20:51:02 +0000[diff] [blame]130<h2 id="platforms">Supported Platforms</h2>
Kostya Serebryany2e173222011-12-12 23:22:31 +0000[diff] [blame]131AddressSanitizer is supported on
Kostya Serebryany460e7a22012-10-19 07:00:46 +0000[diff] [blame^]132<ul><li>Linux i386/x86_64 (tested on Ubuntu 10.04 and 12.04).
Alexey Samsonova8ee4412012-09-06 09:49:03 +0000[diff] [blame]133<li>MacOS 10.6, 10.7 and 10.8 (i386/x86_64).
Kostya Serebryanyce98c9b2011-11-28 20:51:02 +0000[diff] [blame]134</ul>
Kostya Serebryany460e7a22012-10-19 07:00:46 +0000[diff] [blame^]135Support for Linux ARM (and Android ARM) is in progress
Kostya Serebryanyabc31ca2012-03-15 16:20:29 +0000[diff] [blame]136(it may work, but is not guaranteed too).
137
Kostya Serebryanyce98c9b2011-11-28 20:51:02 +0000[diff] [blame]138
139<h2 id="limitations">Limitations</h2>
140<ul>
Kostya Serebryanycef57e52012-04-23 09:05:50 +0000[diff] [blame]141<li> AddressSanitizer uses more real memory than a native run.
142How much -- depends on the allocations sizes. The smaller the
143allocations you make the bigger the overhead.
144<li> AddressSanitizer uses more stack memory. We have seen up to 3x increase.
145<li> On 64-bit platforms AddressSanitizer maps (but not reserves)
14616+ Terabytes of virtual address space.
147This means that tools like <tt>ulimit</tt> may not work as usually expected.
148<li> Static linking is not supported.
Kostya Serebryanyce98c9b2011-11-28 20:51:02 +0000[diff] [blame]149</ul>
150
151
152<h2 id="status">Current Status</h2>
Kostya Serebryany219cd6c2012-04-23 10:15:18 +0000[diff] [blame]153AddressSanitizer is fully functional on supported platforms starting from LLVM 3.1.
Alexey Samsonova8ee4412012-09-06 09:49:03 +0000[diff] [blame]154The test suite is integrated into CMake build (can be run with "make
155check-asan" command).
Kostya Serebryany2e173222011-12-12 23:22:31 +0000[diff] [blame]156
157<h2 id="moreinfo">More Information</h2>
Kostya Serebryanyce98c9b2011-11-28 20:51:02 +0000[diff] [blame]158<a href="http://code.google.com/p/address-sanitizer/">http://code.google.com/p/address-sanitizer</a>.
159
160
Kostya Serebryany7a31d7b2011-11-28 22:34:10 +0000[diff] [blame]161</div>
Kostya Serebryanyce98c9b2011-11-28 20:51:02 +0000[diff] [blame]162</body>
163</html>