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Activate AddressSanitizer in Qt6

Jazzco 5 Reputation points
2025-07-03T10:44:22.05+00:00

Hi all,

I'm developing in Qt c++ under Windows and try to use AddressSanitizer within QtCreator. According to this blog from 2021 (https://devblogs.microsoft.com/cppblog/address-sanitizer-for-msvc-now-generally-available/) it should be possible.

When I add the -fsanitize=address flag and build a debug version it crashes with a null-pointer violation. Stack trace is:

.  0  Id: 302c.447c Suspend: 1 Teb: 00000047`9202c000 Unfrozen
Child-SP          RetAddr               Call Site
(Inline Function) --------`--------     clang_rt_asan_dynamic_x86_64!__asan::QuickCheckForUnpoisonedRegion(void)+0x3b [D:\a\_work\1\s\src\vctools\asan\llvm\compiler-rt\lib\asan\asan_interceptors_memintrinsics.h @ 59]
00000047`922fdfc0 00007ffb`768c5621     clang_rt_asan_dynamic_x86_64!__asan_wrap_strlen(char * s = 0x00007ffa`77f97678 "llvm-symbolizer.exe")+0x136 [D:\a\_work\1\s\src\vctools\asan\llvm\compiler-rt\lib\sanitizer_common\sanitizer_common_interceptors.inc @ 425]
00000047`922fe850 00007ffb`741ef915     ntdll!RtlInitAnsiStringEx+0x21
00000047`922fe880 00007ffa`77f2c13a     KERNELBASE!GetFileAttributesA+0x25
00000047`922fe8d0 00007ffa`77f25aee     clang_rt_asan_dynamic_x86_64!__sanitizer::FileExists(char * filename = <Value unavailable error>)+0xa [D:\a\_work\1\s\src\vctools\asan\llvm\compiler-rt\lib\sanitizer_common\sanitizer_win.cpp @ 105]
00000047`922fe900 00007ffa`77f37c56     clang_rt_asan_dynamic_x86_64!__sanitizer::FindPathToBinary(char * name = 0x00007ffa`77f97678 "llvm-symbolizer.exe")+0xe [D:\a\_work\1\s\src\vctools\asan\llvm\compiler-rt\lib\sanitizer_common\sanitizer_file.cpp @ 207]
00000047`922fe970 00007ffa`77f37ff0     clang_rt_asan_dynamic_x86_64!__sanitizer::ChooseSymbolizerTools(struct __sanitizer::IntrusiveList<__sanitizer::SymbolizerTool> * list = 0x00000047`922fe9c0, class __sanitizer::LowLevelAllocator * allocator = 0x00007ffa`789a8068)+0x146 [D:\a\_work\1\s\src\vctools\asan\llvm\compiler-rt\lib\sanitizer_common\sanitizer_symbolizer_win.cpp @ 268]
00000047`922fe9a0 00007ffa`77f35a10     clang_rt_asan_dynamic_x86_64!__sanitizer::Symbolizer::PlatformInit(void)+0x30 [D:\a\_work\1\s\src\vctools\asan\llvm\compiler-rt\lib\sanitizer_common\sanitizer_symbolizer_win.cpp @ 291]
00000047`922fea10 00007ffa`77f772b3     clang_rt_asan_dynamic_x86_64!__sanitizer::Symbolizer::GetOrInit(void)+0x30 [D:\a\_work\1\s\src\vctools\asan\llvm\compiler-rt\lib\sanitizer_common\sanitizer_symbolizer_libcdep.cpp @ 24]
00000047`922fea50 00007ffa`77f77113     clang_rt_asan_dynamic_x86_64!__asan::AsanInitInternal(void)+0x183 [D:\a\_work\1\s\src\vctools\asan\llvm\compiler-rt\lib\asan\asan_rtl.cpp @ 575]
00000047`922feab0 00007ffb`73e5e716     clang_rt_asan_dynamic_x86_64!__asan::AsanInitFromRtl(void)+0x33 [D:\a\_work\1\s\src\vctools\asan\llvm\compiler-rt\lib\asan\asan_rtl.cpp @ 588]
00000047`922feae0 00007ffa`77f8d176     ucrtbase!initterm+0x36
00000047`922feb10 00007ffa`77f8d2e7     clang_rt_asan_dynamic_x86_64!dllmain_crt_process_attach(struct HINSTANCE__ * instance = 0x00007ffa`77f20000, void * reserved = 0x00000047`922ff500)+0x9a [D:\a\_work\1\s\src\vctools\crt\vcstartup\src\startup\dll_dllmain.cpp @ 66]
00000047`922feb40 00007ffb`76852983     clang_rt_asan_dynamic_x86_64!dllmain_dispatch(struct HINSTANCE__ * instance = 0x00007ffa`77f20000, unsigned long reason = 1, void * reserved = 0x00000047`922ff500)+0x6f [D:\a\_work\1\s\src\vctools\crt\vcstartup\src\startup\dll_dllmain.cpp @ 276]
00000047`922feba0 00007ffb`7685193c     ntdll!RtlDeactivateActivationContext+0xdd3
00000047`922fee80 00007ffb`7681bc7a     ntdll!RtlDeleteElementGenericTableAvlEx+0x4fc
00000047`922fef90 00007ffb`7681bca6     ntdll!LdrGetProcedureAddressForCaller+0xb1a
00000047`922fefd0 00007ffb`768456ac     ntdll!LdrGetProcedureAddressForCaller+0xb46
00000047`922ff010 00007ffb`76843864     ntdll!EtwEventWriteNoRegistration+0x266c
00000047`922ff3e0 00007ffb`7684364e     ntdll!EtwEventWriteNoRegistration+0x824
00000047`922ff460 00007ffb`76815fce     ntdll!EtwEventWriteNoRegistration+0x60e
00000047`922ff4b0 00000000`00000000     ntdll!LdrInitializeThunk+0xe

Any ideas what I miss?

Regards

Jazzco

Developer technologies | C++
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  1. Varsha Dundigalla(INFOSYS LIMITED) 155 Reputation points Microsoft External Staff
    2025-07-08T05:03:27.08+00:00

    Thank you for reaching out. Please find the answer below

    Fixing AddressSanitizer Crashes in Qt on Windows

    1. Use Clang-cl with MSVC Toolchain
    • Required for ASan compatibility on Windows.
    • Ensure you're using Clang-cl, not MSVC's cl.exe.
    1. Enable AddressSanitizer
    • Add the following flags:
      • -fsanitize=address to both CXXFLAGS and LDFLAGS.
    1. Symbolization Support
    • Set the path to the symbolizer:
      • Either set ASAN_SYMBOLIZER_PATH to the ___location of llvm-symbolizer.exe
      • Or ensure llvm-symbolizer.exe is in your system PATH.
    1. Rebuild Everything
    • Rebuild Qt and all its dependencies with -fsanitize=address.
    • Mixing sanitized and unsanitized binaries can cause issues.
    1. Use Release CRT
    • Link against the Release C Runtime (/MD), not Debug (/MDd).
    • Debug CRT is incompatible with ASan and may cause false positives or crashes.

    Ensures AddressSanitizer works reliably in your Qt application.

    This setup avoids null-pointer crashes and keeps AddressSanitizer working correctly.

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