Clang -Wcast-function-type-mismatch warning causing build failure

[ajkhoury]

A -Wcast-function-type-mismatch warning is generated when compiling examples using Clang on Windows:

.../xed/wkit/examples/xed-util-disas-pecoff.cpp:87:8: error: cast from 'FARPROC' (aka 'long long (*)()') to 'fptr_t' (aka 'int (*)(void *)') converts to incompatible function type [-Werror,-Wcast-function-type-mismatch]
   87 |    p = (fptr_t) GetProcAddress(
      |        ^~~~~~~~~~~~~~~~~~~~~~~~
   88 |                    GetModuleHandle(TEXT("kernel32.dll")), 
      |                    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
   89 |                    function_name);
      |                    ~~~~~~~~~~~~~~
1 error generated.

This causes a compiler error due to -Werror being set by default. I've opened a PR with the appropriate fix which adds a void pointer cast before casting to fptr_t which effectively ignores this warning.

see #351

[kkhalail]

Hi, can you provide the build cmd that caused this issue (flag combinations)?

[ajkhoury]

Hi, can you provide the build cmd that caused this issue (flag combinations)?

Building from mbuild with this command:

python3 ./contrib/xed/mfile.py --debug --opt=noopt --no-encoder --limit-strings --static --jobs=8 --cc="C:/Program Files/Microsoft Visual Studio/2022/Professional/VC/Tools/Llvm/x64/bin/clang.exe" --cxx="C:/Program Files/Microsoft Visual Studio/2022/Professional/VC/Tools/Llvm/x64/bin/clang++.exe" --extra-flags=-Wno-cast-function-type-mismatch --compiler=clang --ar="C:/Program Files/Microsoft Visual Studio/2022/Professional/VC/Tools/Llvm/x64/bin/llvm-ar.exe" --build-dir=./contrib/lib/xed examples

Which mbuild generates the compile command for xed-util-disas-pecoff.cpp as such:

[COMMAND     ] C:/Program Files/Microsoft Visual Studio/2022/Professional/VC/Tools/Llvm/x64/bin/clang++.exe -I./contrib/lib/xed/wkit/examples -I./contrib/lib/xed/wkit/include    -g    -m64  -Wno-cast-function-type-mismatch -Wall -Wunused -Werror -Wno-long-long -Wno-unknown-pragmas -fmessage-length=0 -pipe -fno-exceptions -Wformat-security -Wformat -fomit-frame-pointer -Wextra -Wno-error=type-limits -fstack-protector -Wno-unused-function -DXED_VERSION="v2025.06.08" -DXED_AVX -DXED_SUPPORTS_LZCNT_TZCNT -DXED_AMD_ENABLED -DXED_VIA_ENABLED -DXED_SUPPORTS_AVX512 -DXED_MPX -DXED_CET -DXED_APX -DXED_SUPPORTS_SHA -DXED_DECODER  -c -o ./contrib/lib/xed/wkit/examples/obj/xed-util-disas-pecoff.o ./contrib/lib/xed/wkit/examples/xed-util-disas-pecoff.cpp
[EXIT_STATUS ] 1
[STDERR] 
./contrib/lib/xed/wkit/examples/xed-util-disas-pecoff.cpp:87:8: error: cast from 'FARPROC' (aka 'long long (*)()') to 'fptr_t' (aka 'int (*)(void *)') converts to incompatible function type [-Werror,-Wcast-function-type-mismatch]
   87 |    p = (fptr_t) GetProcAddress(
      |        ^~~~~~~~~~~~~~~~~~~~~~~~
   88 |                    GetModuleHandle(TEXT("kernel32.dll")), 
      |                    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
   89 |                    function_name);
      |                    ~~~~~~~~~~~~~~
1 error generated.
ABORT: XED EXAMPLES build failed

[kkhalail]

Hi, which version of clang are you using, because the versions that we use do not acknowledge -Wno-cast-function-type-mismatch for instance

[ajkhoury]

Hi, this is clang version 19.1.7.

Same issue here, the -Wno-cast-function-type-mismatch option has no effect, -Wcast-function-type-mismatch is still emitted.