src/third_party/llvm-project/clang/docs/AddressSanitizer.rst - cobalt - Git at Google

 ================
 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 (runtime flag `ASAN_OPTIONS=detect_stack_use_after_return=1`)
 * Use-after-scope (clang flag `-fsanitize-address-use-after-scope`)
 * Double-free, invalid free
 * Memory leaks (experimental)

 Typical slowdown introduced by AddressSanitizer is **2x**.

 How to build
 ============

 Build LLVM/Clang with `CMake <http://llvm.org/docs/CMake.html>`_.

 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. AddressSanitizer exits on the first detected error.
 This is by design:

 * This approach allows AddressSanitizer to produce faster and smaller generated code
   (both by ~5%).
 * Fixing bugs becomes unavoidable. AddressSanitizer does not produce
   false alarms. Once a memory corruption occurs, the program is in an inconsistent
   state, which could lead to confusing results and potentially misleading
   subsequent reports.

 If your process is sandboxed and you are running on OS X 10.10 or earlier, you
 will need to set ``DYLD_INSERT_LIBRARIES`` environment variable and point it to
 the ASan library that is packaged with the compiler used to build the
 executable. (You can find the library by searching for dynamic libraries with
 ``asan`` in their name.) If the environment variable is not set, the process will
 try to re-exec. Also keep in mind that when moving the executable to another machine,
 the ASan library will also need to be copied over.

 Symbolizing the Reports
 =========================

 To make AddressSanitizer symbolize its output
 you need to set the ``ASAN_SYMBOLIZER_PATH`` environment variable to point to
 the ``llvm-symbolizer`` binary (or make sure ``llvm-symbolizer`` is in your
 ``$PATH``):

 .. code-block:: console

     % ASAN_SYMBOLIZER_PATH=/usr/local/bin/llvm-symbolizer ./a.out
     ==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

 If that does not work for you (e.g. your process is sandboxed), you can use a
 separate script to symbolize the result offline (online symbolization can be
 force disabled by setting ``ASAN_OPTIONS=symbolize=0``):

 .. code-block:: console

     % ASAN_OPTIONS=symbolize=0 ./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
     ...

 Note that on OS X you may need to run ``dsymutil`` on your binary to have the
 file\:line info in the AddressSanitizer reports.

 Additional Checks
 =================

 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``.

 Note that this option is not supported on OS X.

 Memory leak detection
 ---------------------

 For more information on leak detector in AddressSanitizer, see
 :doc:`LeakSanitizer`. The leak detection is turned on by default on Linux,
 and can be enabled using ``ASAN_OPTIONS=detect_leaks=1`` on OS X;
 however, it is not yet supported on other platforms.

 Writable/Executable paging detection
 ------------------------------------

 The W^X detection is disabled by default and can be enabled using
 ``ASAN_OPTIONS=detect_write_exec=1``.

 Issue Suppression
 =================

 AddressSanitizer is not expected to produce false positives. If you see one,
 look again; most likely it is a true positive!

 Suppressing Reports in External Libraries
 -----------------------------------------
 Runtime interposition allows AddressSanitizer to find bugs in code that is
 not being recompiled. If you run into an issue in external libraries, we
 recommend immediately reporting it to the library maintainer so that it
 gets addressed. However, you can use the following suppression mechanism
 to unblock yourself and continue on with the testing. This suppression
 mechanism should only be used for suppressing issues in external code; it
 does not work on code recompiled with AddressSanitizer. To suppress errors
 in external libraries, set the ``ASAN_OPTIONS`` environment variable to point
 to a suppression file. You can either specify the full path to the file or the
 path of the file relative to the location of your executable.

 .. code-block:: bash

     ASAN_OPTIONS=suppressions=MyASan.supp

 Use the following format to specify the names of the functions or libraries
 you want to suppress. You can see these in the error report. Remember that
 the narrower the scope of the suppression, the more bugs you will be able to
 catch.

 .. code-block:: bash

     interceptor_via_fun:NameOfCFunctionToSuppress
     interceptor_via_fun:-[ClassName objCMethodToSuppress:]
     interceptor_via_lib:NameOfTheLibraryToSuppress

 Conditional Compilation with ``__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

 Disabling Instrumentation with ``__attribute__((no_sanitize("address")))``
 --------------------------------------------------------------------------

 Some code should not be instrumented by AddressSanitizer. One may use
 the attribute ``__attribute__((no_sanitize("address")))`` (which has
 deprecated synonyms `no_sanitize_address` and
 `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)``.

 The same attribute used on a global variable prevents AddressSanitizer
 from adding redzones around it and detecting out of bounds accesses.

 Suppressing Errors in Recompiled Code (Blacklist)
 -------------------------------------------------

 AddressSanitizer supports ``src`` and ``fun`` entity types in
 :doc:`SanitizerSpecialCaseList`, that can be used to suppress error reports
 in the specified source files or functions. Additionally, AddressSanitizer
 introduces ``global`` and ``type`` entity types that can be used to
 suppress error reports for out-of-bound access to globals with certain
 names and types (you may only specify class or struct types).

 You may use an ``init`` category to suppress reports about initialization-order
 problems happening in certain source files or with certain global variables.

 .. code-block:: bash

     # Suppress error reports for code in a file or in a function:
     src:bad_file.cpp
     # Ignore all functions with names containing MyFooBar:
     fun:*MyFooBar*
     # Disable out-of-bound checks for global:
     global:bad_array
     # Disable out-of-bound checks for global instances of a given class ...
     type:Namespace::BadClassName
     # ... or a given struct. Use wildcard to deal with anonymous namespace.
     type:Namespace2::*::BadStructName
     # Disable initialization-order checks for globals:
     global:bad_init_global=init
     type:*BadInitClassSubstring*=init
     src:bad/init/files/*=init

 Suppressing memory leaks
 ------------------------

 Memory leak reports produced by :doc:`LeakSanitizer` (if it is run as a part
 of AddressSanitizer) can be suppressed by a separate file passed as

 .. code-block:: bash

     LSAN_OPTIONS=suppressions=MyLSan.supp

 which contains lines of the form `leak:<pattern>`. Memory leak will be
 suppressed if pattern matches any function name, source file name, or
 library name in the symbolized stack trace of the leak report. See
 `full documentation
 <https://github.com/google/sanitizers/wiki/AddressSanitizerLeakSanitizer#suppressions>`_
 for more details.

 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.

 Supported Platforms
 ===================

 AddressSanitizer is supported on:

 * Linux i386/x86\_64 (tested on Ubuntu 12.04)
 * OS X 10.7 - 10.11 (i386/x86\_64)
 * iOS Simulator
 * Android ARM
 * NetBSD i386/x86\_64
 * FreeBSD i386/x86\_64 (tested on FreeBSD 11-current)

 Ports to various other platforms are in progress.

 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
 ================

 `<https://github.com/google/sanitizers/wiki/AddressSanitizer>`_
	================
	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 (runtime flag `ASAN_OPTIONS=detect_stack_use_after_return=1`)
	* Use-after-scope (clang flag `-fsanitize-address-use-after-scope`)
	* Double-free, invalid free
	* Memory leaks (experimental)

	Typical slowdown introduced by AddressSanitizer is 2x.

	How to build
	============

	Build LLVM/Clang with `CMake <http://llvm.org/docs/CMake.html>`_.

	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. AddressSanitizer exits on the first detected error.
	This is by design:

	* This approach allows AddressSanitizer to produce faster and smaller generated code
	(both by ~5%).
	* Fixing bugs becomes unavoidable. AddressSanitizer does not produce
	false alarms. Once a memory corruption occurs, the program is in an inconsistent
	state, which could lead to confusing results and potentially misleading
	subsequent reports.

	If your process is sandboxed and you are running on OS X 10.10 or earlier, you
	will need to set ``DYLD_INSERT_LIBRARIES`` environment variable and point it to
	the ASan library that is packaged with the compiler used to build the
	executable. (You can find the library by searching for dynamic libraries with
	``asan`` in their name.) If the environment variable is not set, the process will
	try to re-exec. Also keep in mind that when moving the executable to another machine,
	the ASan library will also need to be copied over.

	Symbolizing the Reports
	=========================

	To make AddressSanitizer symbolize its output
	you need to set the ``ASAN_SYMBOLIZER_PATH`` environment variable to point to
	the ``llvm-symbolizer`` binary (or make sure ``llvm-symbolizer`` is in your
	``$PATH``):

	.. code-block:: console

	% ASAN_SYMBOLIZER_PATH=/usr/local/bin/llvm-symbolizer ./a.out
	==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

	If that does not work for you (e.g. your process is sandboxed), you can use a
	separate script to symbolize the result offline (online symbolization can be
	force disabled by setting ``ASAN_OPTIONS=symbolize=0``):

	.. code-block:: console

	% ASAN_OPTIONS=symbolize=0 ./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
	...

	Note that on OS X you may need to run ``dsymutil`` on your binary to have the
	file\:line info in the AddressSanitizer reports.

	Additional Checks
	=================

	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``.

	Note that this option is not supported on OS X.

	Memory leak detection
	---------------------

	For more information on leak detector in AddressSanitizer, see
	:doc:`LeakSanitizer`. The leak detection is turned on by default on Linux,
	and can be enabled using ``ASAN_OPTIONS=detect_leaks=1`` on OS X;
	however, it is not yet supported on other platforms.

	Writable/Executable paging detection
	------------------------------------

	The W^X detection is disabled by default and can be enabled using
	``ASAN_OPTIONS=detect_write_exec=1``.

	Issue Suppression
	=================

	AddressSanitizer is not expected to produce false positives. If you see one,
	look again; most likely it is a true positive!

	Suppressing Reports in External Libraries
	-----------------------------------------
	Runtime interposition allows AddressSanitizer to find bugs in code that is
	not being recompiled. If you run into an issue in external libraries, we
	recommend immediately reporting it to the library maintainer so that it
	gets addressed. However, you can use the following suppression mechanism
	to unblock yourself and continue on with the testing. This suppression
	mechanism should only be used for suppressing issues in external code; it
	does not work on code recompiled with AddressSanitizer. To suppress errors
	in external libraries, set the ``ASAN_OPTIONS`` environment variable to point
	to a suppression file. You can either specify the full path to the file or the
	path of the file relative to the location of your executable.

	.. code-block:: bash

	ASAN_OPTIONS=suppressions=MyASan.supp

	Use the following format to specify the names of the functions or libraries
	you want to suppress. You can see these in the error report. Remember that
	the narrower the scope of the suppression, the more bugs you will be able to
	catch.

	.. code-block:: bash

	interceptor_via_fun:NameOfCFunctionToSuppress
	interceptor_via_fun:-[ClassName objCMethodToSuppress:]
	interceptor_via_lib:NameOfTheLibraryToSuppress

	Conditional Compilation with ``__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

	Disabling Instrumentation with ``__attribute__((no_sanitize("address")))``
	--------------------------------------------------------------------------

	Some code should not be instrumented by AddressSanitizer. One may use
	the attribute ``__attribute__((no_sanitize("address")))`` (which has
	deprecated synonyms `no_sanitize_address` and
	`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)``.

	The same attribute used on a global variable prevents AddressSanitizer
	from adding redzones around it and detecting out of bounds accesses.

	Suppressing Errors in Recompiled Code (Blacklist)
	-------------------------------------------------

	AddressSanitizer supports ``src`` and ``fun`` entity types in
	:doc:`SanitizerSpecialCaseList`, that can be used to suppress error reports
	in the specified source files or functions. Additionally, AddressSanitizer
	introduces ``global`` and ``type`` entity types that can be used to
	suppress error reports for out-of-bound access to globals with certain
	names and types (you may only specify class or struct types).

	You may use an ``init`` category to suppress reports about initialization-order
	problems happening in certain source files or with certain global variables.

	.. code-block:: bash

	# Suppress error reports for code in a file or in a function:
	src:bad_file.cpp
	# Ignore all functions with names containing MyFooBar:
	fun:MyFooBar
	# Disable out-of-bound checks for global:
	global:bad_array
	# Disable out-of-bound checks for global instances of a given class ...
	type:Namespace::BadClassName
	# ... or a given struct. Use wildcard to deal with anonymous namespace.
	type:Namespace2::*::BadStructName
	# Disable initialization-order checks for globals:
	global:bad_init_global=init
	type:BadInitClassSubstring=init
	src:bad/init/files/*=init

	Suppressing memory leaks
	------------------------

	Memory leak reports produced by :doc:`LeakSanitizer` (if it is run as a part
	of AddressSanitizer) can be suppressed by a separate file passed as

	.. code-block:: bash

	LSAN_OPTIONS=suppressions=MyLSan.supp

	which contains lines of the form `leak:<pattern>`. Memory leak will be
	suppressed if pattern matches any function name, source file name, or
	library name in the symbolized stack trace of the leak report. See
	`full documentation
	<https://github.com/google/sanitizers/wiki/AddressSanitizerLeakSanitizer#suppressions>`_
	for more details.

	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.

	Supported Platforms
	===================

	AddressSanitizer is supported on:

	* Linux i386/x86\_64 (tested on Ubuntu 12.04)
	* OS X 10.7 - 10.11 (i386/x86\_64)
	* iOS Simulator
	* Android ARM
	* NetBSD i386/x86\_64
	* FreeBSD i386/x86\_64 (tested on FreeBSD 11-current)

	Ports to various other platforms are in progress.

	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
	================

	`<https://github.com/google/sanitizers/wiki/AddressSanitizer>`_