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diff --git a/docs/AddressSanitizer.rst b/docs/AddressSanitizer.rst new file mode 100644 index 0000000..89e8644 --- /dev/null +++ b/docs/AddressSanitizer.rst @@ -0,0 +1,163 @@ +================ +AddressSanitizer +================ + +.. contents:: + :local: + +Introduction +============ + +AddressSanitizer is a fast memory error detector. It consists of a compiler +instrumentation module and a run-time library. The tool can detect the +following types of bugs: + +* Out-of-bounds accesses to heap, stack and globals +* Use-after-free +* Use-after-return (to some extent) +* Double-free, invalid free + +Typical slowdown introduced by AddressSanitizer is **2x**. + +How to build +============ + +Follow the `clang build instructions <../get_started.html>`_. CMake build is +supported. + +Usage +===== + +Simply compile and link your program with ``-fsanitize=address`` flag. The +AddressSanitizer run-time library should be linked to the final executable, so +make sure to use ``clang`` (not ``ld``) for the final link step. When linking +shared libraries, the AddressSanitizer run-time is not linked, so +``-Wl,-z,defs`` may cause link errors (don't use it with AddressSanitizer). To +get a reasonable performance add ``-O1`` or higher. To get nicer stack traces +in error messages add ``-fno-omit-frame-pointer``. To get perfect stack traces +you may need to disable inlining (just use ``-O1``) and tail call elimination +(``-fno-optimize-sibling-calls``). + +.. code-block:: console + + % cat example_UseAfterFree.cc + int main(int argc, char **argv) { + int *array = new int[100]; + delete [] array; + return array[argc]; // BOOM + } + + # Compile and link + % clang -O1 -g -fsanitize=address -fno-omit-frame-pointer example_UseAfterFree.cc + +or: + +.. code-block:: console + + # Compile + % clang -O1 -g -fsanitize=address -fno-omit-frame-pointer -c example_UseAfterFree.cc + # Link + % clang -g -fsanitize=address example_UseAfterFree.o + +If a bug is detected, the program will print an error message to stderr and +exit with a non-zero exit code. Currently, AddressSanitizer does not symbolize +its output, so you may need to use a separate script to symbolize the result +offline (this will be fixed in future). + +.. code-block:: console + + % ./a.out 2> log + % projects/compiler-rt/lib/asan/scripts/asan_symbolize.py / < log | c++filt + ==9442== ERROR: AddressSanitizer heap-use-after-free on address 0x7f7ddab8c084 at pc 0x403c8c bp 0x7fff87fb82d0 sp 0x7fff87fb82c8 + READ of size 4 at 0x7f7ddab8c084 thread T0 + #0 0x403c8c in main example_UseAfterFree.cc:4 + #1 0x7f7ddabcac4d in __libc_start_main ??:0 + 0x7f7ddab8c084 is located 4 bytes inside of 400-byte region [0x7f7ddab8c080,0x7f7ddab8c210) + freed by thread T0 here: + #0 0x404704 in operator delete[](void*) ??:0 + #1 0x403c53 in main example_UseAfterFree.cc:4 + #2 0x7f7ddabcac4d in __libc_start_main ??:0 + previously allocated by thread T0 here: + #0 0x404544 in operator new[](unsigned long) ??:0 + #1 0x403c43 in main example_UseAfterFree.cc:2 + #2 0x7f7ddabcac4d in __libc_start_main ??:0 + ==9442== ABORTING + +AddressSanitizer exits on the first detected error. This is by design. +One reason: it makes the generated code smaller and faster (both by +~5%). Another reason: this makes fixing bugs unavoidable. With Valgrind, +it is often the case that users treat Valgrind warnings as false +positives (which they are not) and don't fix them. + +``__has_feature(address_sanitizer)`` +------------------------------------ + +In some cases one may need to execute different code depending on whether +AddressSanitizer is enabled. +:ref:`\_\_has\_feature <langext-__has_feature-__has_extension>` can be used for +this purpose. + +.. code-block:: c + + #if defined(__has_feature) + # if __has_feature(address_sanitizer) + // code that builds only under AddressSanitizer + # endif + #endif + +``__attribute__((no_sanitize_address))`` +----------------------------------------------- + +Some code should not be instrumented by AddressSanitizer. One may use the +function attribute +:ref:`no_sanitize_address <langext-address_sanitizer>` +(or a deprecated synonym `no_address_safety_analysis`) +to disable instrumentation of a particular function. This attribute may not be +supported by other compilers, so we suggest to use it together with +``__has_feature(address_sanitizer)``. Note: currently, this attribute will be +lost if the function is inlined. + +Initialization order checking +----------------------------- + +AddressSanitizer can optionally detect dynamic initialization order problems, +when initialization of globals defined in one translation unit uses +globals defined in another translation unit. To enable this check at runtime, +you should set environment variable +``ASAN_OPTIONS=check_initialization_order=1``. + +Supported Platforms +=================== + +AddressSanitizer is supported on + +* Linux i386/x86\_64 (tested on Ubuntu 10.04 and 12.04); +* MacOS 10.6, 10.7 and 10.8 (i386/x86\_64). + +Support for Linux ARM (and Android ARM) is in progress (it may work, but +is not guaranteed too). + +Limitations +=========== + +* AddressSanitizer uses more real memory than a native run. Exact overhead + depends on the allocations sizes. The smaller the allocations you make the + bigger the overhead is. +* AddressSanitizer uses more stack memory. We have seen up to 3x increase. +* On 64-bit platforms AddressSanitizer maps (but not reserves) 16+ Terabytes of + virtual address space. This means that tools like ``ulimit`` may not work as + usually expected. +* Static linking is not supported. + +Current Status +============== + +AddressSanitizer is fully functional on supported platforms starting from LLVM +3.1. The test suite is integrated into CMake build and can be run with ``make +check-asan`` command. + +More Information +================ + +`http://code.google.com/p/address-sanitizer <http://code.google.com/p/address-sanitizer/>`_ + |
