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The [**`/fsanitize=address`**](../build/reference/fsanitize.md) compiler option instruments memory references in your code to catch memory safety errors at runtime. The instrumentation hooks loads, stores, scopes, `alloca`, and CRT functions. It can detect hidden bugs such as out-of-bounds, use-after-free, use-after-scope, and so on. For a non-exhaustive list of errors detected at runtime, see [AddressSanitizer error examples](./asan-error-examples.md).
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The [**`/fsanitize=address`**](../build/reference/fsanitize.md) compiler option instruments memory references in your code to catch memory safety errors at runtime. The instrumentation hooks loads, stores, scopes, `alloca`, and CRT functions. It can detect hidden bugs such as out-of-bounds, use-after-free, use-after-scope, and so on. For a nonexhaustive list of errors detected at runtime, see [AddressSanitizer error examples](./asan-error-examples.md).
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**`/fsanitize=address`** is compatible with all existing C++ or C optimization levels (for example, **`/Od`**, **`/O1`**, **`/O2`**, **`/O2 /GL`**, and profile guided optimization). The code produced with this option works with static and dynamic CRTs (for example, **`/MD`**, **`/MDd`**, **`/MT`**, and **`/MTd`**). This compiler option can be used to create an .EXE or .DLL targeting x86 or x64. Debug information is required for optimal formatting of call stacks.
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@@ -82,7 +82,7 @@ These libraries are added to the default library list when you specify **`/fsani
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|**`/MTd`**|*`clang_rt.fuzzer_MTd-{arch}`*|
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|**`/MDd`**|*`clang_rt.fuzzer_MDd-{arch}`*|
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LibFuzzer libraries that omit the **`main`** function are also available. It's your responsibility to define **`main`** and to call **`LLVMFuzzerInitialize`** and **`LLVMFuzzerTestOneInput`** when you use these libraries. To use one of these libraries, specify [`/NODEFAULTLIB`](../build/reference/nodefaultlib-ignore-libraries.md) and explicitly link with the library below that corresponds to your runtime and architecture:
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LibFuzzer libraries that omit the **`main`** function are also available. It's your responsibility to define **`main`** and to call **`LLVMFuzzerInitialize`** and **`LLVMFuzzerTestOneInput`** when you use these libraries. To use one of these libraries, specify [`/NODEFAULTLIB`](../build/reference/nodefaultlib-ignore-libraries.md) and explicitly link with the following library that corresponds to your runtime and architecture:
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| Runtime option | LibFuzzer no_main library |
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|--|--|
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1. Compile using the [`/fsanitize-address-use-after-return`](../build/reference/fsanitize.md) option.
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2. Before executing your program, run `set ASAN_OPTIONS=detect_stack_use_after_return=1` to set the runtime check option.
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The **`/fsanitize-address-use-after-return`** option causes the compiler to generate code to use a dual stack frame in the heap when locals are considered "address taken". This code is *much slower* than just using **`/fsanitize=address`** alone. For more information and an example, see [Error: `stack-use-after-return`](error-stack-use-after-return.md).
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The **`/fsanitize-address-use-after-return`** option causes the compiler to generate code to use a dual stack frame in the heap when locals are considered "address taken." This code is *much slower* than just using **`/fsanitize=address`** alone. For more information and an example, see [Error: `stack-use-after-return`](error-stack-use-after-return.md).
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The dual stack frame in the heap remains after the return from the function that created it. Consider an example where the address of a local, allocated to a slot in the heap, is used after the return. The shadow bytes associated with the fake heap frame contain the value 0xF9. That 0xF9 means a stack-use-after-return error when the runtime reports the error.
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@@ -110,18 +110,32 @@ Stack frames are allocated in the heap and remain after functions return. The ru
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### `/INFERASANLIBS[:NO]` linker option
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The **`/fsanitize=address`** compiler option marks objects to specify the AddressSanitizer library to link into your executable. The libraries have names that begin with *`clang_rt.asan*`*. The [`/INFERASANLIBS`](../build/reference/inferasanlibs.md) linker option (on by default) links these libraries from their default locations automatically. Here are the libraries chosen and automatically linked in:
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The **`/fsanitize=address`** compiler option marks objects to specify which AddressSanitizer library to link into your executable. The libraries have names that begin with *`clang_rt.asan*`*. The [`/INFERASANLIBS`](../build/reference/inferasanlibs.md) linker option (on by default) links these libraries from their default locations automatically. Here are the libraries chosen and automatically linked in.
> In the following table, *`{arch}`* is either *`i386`* or *`x86_64`*.
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> These libraries use Clang conventions for architecture names. MSVC conventions are normally `x86` and `x64` rather than `i386` and `x86_64`. They refer to the same architectures.
| `/MT` or `/MTd` | *`clang_rt.asan_dynamic-{arch}`*, *`clang_rt.asan_static_runtime_thunk-{arch}`* | *`clang_rt.asan_dynamic-{arch}`*
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| `/MD` or `/MDd` | *`clang_rt.asan_dynamic-{arch}`*, *`clang_rt.asan_dynamic_runtime_thunk-{arch}`* | *`clang_rt.asan_dynamic-{arch}`*
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The linker option [`/INFERASANLIBS:NO`](../build/reference/inferasanlibs.md) prevents the linker from linking a *`clang_rt.asan*`* library file from the default location. Add the library path in your build scripts if you use this option. Otherwise, the linker reports an unresolved external symbol error.
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**Previous Versions**
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Prior to Visual Studio 17.7 Preview 3, statically linked (**`/MT`** or **`/MTd`**) builds didn't use a DLL dependency. Instead, the AddressSanitizer runtime was statically linked into the user's EXE. DLL projects would then load exports from the user's EXE to access ASan functionality. Also, dynamically linked projects (**`/MD`** or **`/MTd`**) used different libraries and DLLs depending on whether the project was configured for debug or release. For more information about these changes and their motivations, see [MSVC Address Sanitizer – One DLL for all Runtime Configurations](https://devblogs.microsoft.com/cppblog/msvc-address-sanitizer-one-dll-for-all-runtime-configurations/).
|**`/MDd`**| EITHER |*`clang_rt.asan_dbg_dynamic-{arch}`*, *`clang_rt.asan_dbg_dynamic_runtime_thunk-{arch}`*|
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The linker option [`/INFERASANLIBS:NO`](../build/reference/inferasanlibs.md) prevents the linker from linking a *`clang_rt.asan*`* library file from the default location. Add the library path in your build scripts if you use this option. Otherwise, the linker reports an unresolved external symbol error.
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|**`/MDd`**| Either |*`clang_rt.asan_dbg_dynamic-{arch}`*, *`clang_rt.asan_dbg_dynamic_runtime_thunk-{arch}`*|
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## Visual Studio integration
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|**`/MTd`**|*`libvcasand.lib`*|
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|**`/MDd`**|*`vcasand.lib`*|
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However, if you compile using **`/Zl`** (Omit default library name), you'll need to manually specify the library. If you don't, you'll get an unresolved external symbol link error. Here are some typical examples:
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However, if you compile using **`/Zl`** (Omit default library name), you must manually specify the library. If you don't, you'll get an unresolved external symbol link error. Here are some typical examples:
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```Output
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error LNK2001: unresolved external symbol __you_must_link_with_VCAsan_lib
The AddressSanitizer runtime library intercepts common memory allocation functions and operations to enable inspection of memory accesses. There are several different runtime libraries that support the various types of executables the compiler may generate. The compiler and linker automatically link the appropriate runtime libraries, as long as you pass the [`/fsanitize=address`](../build/reference/fsanitize.md) option at compile time. You can override the default behavior by using the **`/NODEFAULTLIB`** option at link time. For more information, see the section on [linking](./asan-building.md#linker) in the [AddressSanitizer language, build, and debugging reference](./asan-building.md).
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Below is an inventory of runtime libraries for linking to the AddressSanitizer runtime, where *`{arch}`* is either *`i386`* or *`x86_64`*, as of Visual Studio 17.7 Preview 3.
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The list of runtime libraries for linking to the AddressSanitizer runtime as of Visual Studio 17.7 Preview 3, follows. For more information about the `/MT` and `/MD` options, see [/MD, /MT, /LD (Use Run-Time Library)](../build/reference/md-mt-ld-use-run-time-library.md).
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> [!NOTE]
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> These libraries keep the Clang conventions for architecture names. The MSVC conventions are normally x86 and x64 rather than i386 and x86_64. They refer to the same architectures.
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>
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> In the following table, *`{arch}`* is either *`i386`* or *`x86_64`*.
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> These libraries use Clang conventions for architecture names. MSVC conventions are normally `x86` and `x64` rather than `i386` and `x86_64`. They refer to the same architectures.
| MT or MTd | *`clang_rt.asan_dynamic-{arch}`*, *`clang_rt.asan_static_runtime_thunk-{arch}`* | *`clang_rt.asan_dynamic-{arch}`*
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| MD or MDd | *`clang_rt.asan_dynamic-{arch}`*, *`clang_rt.asan_dynamic_runtime_thunk-{arch}`* | *`clang_rt.asan_dynamic-{arch}`*
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| `/MT` or `/MTd` | *`clang_rt.asan_dynamic-{arch}`*, *`clang_rt.asan_static_runtime_thunk-{arch}`* | *`clang_rt.asan_dynamic-{arch}`*
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| `/MD` or `/MDd` | *`clang_rt.asan_dynamic-{arch}`*, *`clang_rt.asan_dynamic_runtime_thunk-{arch}`* | *`clang_rt.asan_dynamic-{arch}`*
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When compiling with `cl /fsanitize=address`, the compiler generates instructions to manage and check the [shadow bytes](./asan-shadow-bytes.md). Your program uses this instrumentation to check memory accesses on the stack, in the heap, or in the global scope. The compiler also produces metadata describing stack and global variables. This metadata enables the runtime to generate precise error diagnostics: function names, lines, and columns in your source code. Combined, the compiler checks and runtime libraries can precisely diagnose many types of [memory safety bugs](./asan-error-examples.md) if they're encountered at run-time.
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### Previous versions
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Prior to Visual Studio 17.7 Preview 3, statically linked (**`/MT`** or **`/MTd`**) builds did not use a DLL dependency and instead fully statically linked in the AddressSanitizer runtime into the user's EXE. DLL projects would then load exports from the user's EXE to access ASan functionality. Additionally, dynamically linked projects (**`/MD`** or **`/MTd`**) used different libraries and DLLs depending on whether the project was configured for debug or release. These changes and their motivations are discussed further on the MSVC Blog:[MSVC Address Sanitizer – One DLL for all Runtime Configurations](https://devblogs.microsoft.com/cppblog/msvc-address-sanitizer-one-dll-for-all-runtime-configurations/).
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Prior to Visual Studio 17.7 Preview 3, statically linked (**`/MT`** or **`/MTd`**) builds didn't use a DLL dependency. Instead, the AddressSanitizer runtime was statically linked into the user's EXE. DLL projects would then load exports from the user's EXE to access ASan functionality. Also, dynamically linked projects (**`/MD`** or **`/MTd`**) used different libraries and DLLs depending on whether the project was configured for debug or release. For more information about these changes and their motivations, see[MSVC Address Sanitizer – One DLL for all Runtime Configurations](https://devblogs.microsoft.com/cppblog/msvc-address-sanitizer-one-dll-for-all-runtime-configurations/).
The AddressSanitizer achieves function interception through many hot-patching techniques. These techniques are [best documented within the source code itself](https://github.com/llvm/llvm-project/blob/1a2eaebc09c6a200f93b8beb37130c8b8aab3934/compiler-rt/lib/interception/interception_win.cpp#L11).
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The AddressSanitizer achieves function interception through many hotpatching techniques. These techniques are [best documented within the source code itself](https://github.com/llvm/llvm-project/blob/1a2eaebc09c6a200f93b8beb37130c8b8aab3934/compiler-rt/lib/interception/interception_win.cpp#L11).
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The runtime libraries intercept many common memory management and memory manipulation functions. For a list, see [AddressSanitizer list of intercepted functions](#intercepted_functions). The allocation interceptors manage metadata and shadow bytes related to each allocation call. Every time a CRT function such as `malloc` or `delete` is called, the interceptors set specific values in the AddressSanitizer shadow-memory region to indicate whether those heap locations are currently accessible and what the bounds of the allocation are. These shadow bytes allow the compiler-generated checks of the [shadow bytes](./asan-shadow-bytes.md) to determine whether a load or store is valid.
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## <aname="intercepted_functions"></a> AddressSanitizer list of intercepted functions (Windows)
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The AddressSanitizer runtime hot-patches many functions to enable memory safety checks at runtime. Here's a non-exhaustive list of the functions that the AddressSanitizer runtime monitors.
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The AddressSanitizer runtime hotpatches many functions to enable memory safety checks at runtime. Here's a non-exhaustive list of the functions that the AddressSanitizer runtime monitors.
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