Assimp 3.1.1 fails to build on big-endian architecture

[richmattes]

I'm trying to build assimp-3.1.1 on the redhat 7 ppc64 architecture. I'm getting the following error:

/builddir/build/BUILD/assimp-3.1.1/code/Bitmap.cpp: In instantiation of 'std::size_t Assimp::Copy(uint8_t*, T&) [with T = short unsigned int; std::size_t = long unsigned int; uint8_t = unsigned char]':
/builddir/build/BUILD/assimp-3.1.1/code/Bitmap.cpp:93:44:   required from here
/builddir/build/BUILD/assimp-3.1.1/code/Bitmap.cpp:85:21: error: lvalue required as unary '&' operand
   std::memcpy(data, &AI_BE(field), sizeof(field)); return sizeof(field);
                     ^
/builddir/build/BUILD/assimp-3.1.1/code/Bitmap.cpp: In instantiation of 'std::size_t Assimp::Copy(uint8_t*, T&) [with T = unsigned int; std::size_t = long unsigned int; uint8_t = unsigned char]':
/builddir/build/BUILD/assimp-3.1.1/code/Bitmap.cpp:94:44:   required from here
/builddir/build/BUILD/assimp-3.1.1/code/Bitmap.cpp:85:21: error: lvalue required as unary '&' operand
/builddir/build/BUILD/assimp-3.1.1/code/Bitmap.cpp: In instantiation of 'std::size_t Assimp::Copy(uint8_t*, T&) [with T = int; std::size_t = long unsigned int; uint8_t = unsigned char]':
/builddir/build/BUILD/assimp-3.1.1/code/Bitmap.cpp:108:42:   required from here
/builddir/build/BUILD/assimp-3.1.1/code/Bitmap.cpp:85:21: error: lvalue required as unary '&' operand
make[2]: *** [code/CMakeFiles/assimp.dir/Bitmap.cpp.o] Error 1
make[2]: *** Waiting for unfinished jobs....

Full build log is here.

It looks like the source of this issue is the in-line use of the AI_BE(t) macro, which on big-endian architectures expands to ByteSwap::Swapped(t). Trying to pass a reference to the expanded statement to memcpy fails with the above error.

I was able to work around the issue by modifying the Copy function in Bitmap.cpp to create a temporary variable that holds the result of AI_BE, and then passing the temporary variable to memcpy.

[umlaeute]

I can confirm the issue (now that i finally got around at packaging assimp-3.1.1 for Debian).

@jpgr87 could you share your workaround?

[umlaeute]

probably something like:

        template<typename T>
        inline std::size_t Copy(uint8_t* data, T& field) {
#ifdef AI_BUILD_BIG_ENDIAN
                T field_swapped=AI_BE(field);
                std::memcpy(data, &field_swapped, sizeof(field)); return sizeof(field);
#else
                std::memcpy(data, &AI_BE(field), sizeof(field)); return sizeof(field);
#endif /* AI_BUILD_BIG_ENDIAN */
        }

or even simpler:

        template<typename T>
        inline std::size_t Copy(uint8_t* data, T& field) {
                T field_=AI_BE(field);
                std::memcpy(data, &field_, sizeof(field)); return sizeof(field);
        }

[richmattes]

My fix is nearly identical to your "even simpler" approach. The patch I'm using can be found here