Cross-module exception issue with pre-compiler define _HAS_EXCEPTIONS=0 used in an application

[siren186]

Hi @obiltschnig

I encountered a very subtle issue. It is about Poco::Exception in PocoFoundation64.dll. In Visual Studio 2019/2022 release_shared x64.
It is very hard to reproduce. Due to the large amount of code, I can't paste it all here, so I’ve only extracted a small portion.

// This is a small portion I extracted from a large amount of code.
int main() {
    std::uint64_t val = 0x1122334455667788;
    
    try {
    	throw Poco::Exception("error"); 
        // If I do not use Poco::XXXXXXException, everything works fine.
        // throw std::exception("error"); // It's OK !!!
    } catch (const Poco::Exception& e) {
    }
    
    std::cout << val; // Now the val is 0x1122334400000000 !!!
    // It's Very Strange !!! It lost low 32 bit.
    return 0;
}

It took me two days to find the real reason.

auto m = sizeof(Poco::Exception);
auto n = sizeof(std::exception);

// m=72, n=24: In PocoFoundation64.dll
// m=64, n=16: In my EXE

It was all caused by _HAS_EXCEPTIONS=0 in my EXE compile options. This macro will change the class size and implementation of std::exception.

// By: _HAS_EXCEPTIONS=1 (default in visual studio)
// sizeof(std::exception) == 24
namespace std { 
    class exception {
    public:
        virtual ~exception() {}
    private:
        char const* _What;
        bool        _DoFree;
    }
}


// By: _HAS_EXCEPTIONS=0
// sizeof(std::exception) == 16
namespace std { 
    class exception {
    public:
        virtual ~exception() {}
    protected:
        const char* _Ptr;
    }
}

I think it's necessary to add some tips in POCO documentation to avoid users wasting unnecessary time on this issue.

---

See alse: nodejs/node-addon-api#85

[aleks-f]

This is cmake build system problem. VS projects have /EHsc

[matejk]

This is cmake build system problem. VS projects have /EHsc

CMake adds /EHsc by default when building on Windows:

C:\PROGRA~2\MICROS~2\2019\ENTERP~1\VC\Tools\MSVC\1429~1.301\bin\HostX64\x86\cl.exe /nologo /TP -DFoundation_EXPORTS -DPOCO_ENABLE_CPP11 -DPOCO_ENABLE_CPP14 -DPOCO_OS_FAMILY_WINDOWS -DUNICODE -DUTF8PROC_STATIC -D_DEBUG -D_UNICODE -IC:\github\build-poco-Desktop_Qt_5_15_2_MSVC2019_32bit-Debug\Foundation -IC:\github\poco\Foundation\include -IC:\github\poco\Foundation\src /DWIN32 /D_WINDOWS /GR /EHsc /Zc:__cplusplus /Zi /Ob0 /Od /RTC1 -std:c++17 -MDd /showIncludes /FoFoundation\CMakeFiles\Foundation.dir\src\ByteOrder.cpp.obj /FdFoundation\CMakeFiles\Foundation.dir\ /FS -c C:\github\poco\Foundation\src\ByteOrder.cpp
The problem is caused by defining _HAS_EXCEPTIONS=0 in the application that is using Poco. The size of std::exception and Poco::Exception inside Poco binaries is correct.

Additional define in the application is the root of the problems, not the way Poco is built.

[matejk]

What can be done in Poco is to verify the value of _HAS_EXCEPTIONS in Poco header files and abort compile if it is set to 0.