Building GLFW with MinGW64 gcc -- entry-symbol warnings & linker errors - gcc

Question

This is on a fairly fresh vanilla Win7 64-bit installation with the latest MinGW64, in a clean (freshly extracted) GLFW 2.7.5 source directory calling their make win32-msys command.
[A] Building the libs
#1 -- Warning at gcc -c -I. -I.. -Wall -mwin32 -O2 -o win32_init.o win32_init.c:
win32_init.c: In function '_glfwPlatformTerminate':
win32_init.c:353:27: warning: cast to pointer from integer of different size [-Wint-to-pointer-cast]
#2 -- Warning at gcc -c -I. -I.. -Wall -mwin32 -O2 -mdll -DGLFW_BUILD_DLL -D_GLFW_NO_DLOAD_GDI32 -D_GLFW_NO_DLOAD_WINMM -o win32_init_dll.o win32_init.c:
win32_init.c: In function '_glfwPlatformTerminate':
win32_init.c:353:27: warning: cast to pointer from integer of different size [-Wint-to-pointer-cast]
But the relevant output files do get created in .\lib\win32: glfw.dll, libglfwdll.a and libglfw.a. However I worry those might be corrupted, since it's impossible for me to link to them via gcc later on -- same problem as the last one in this post described further down.
[B] Building the examples
#3 -- Warning at triangle.exe, pong3d.exe, splitview.exe, mipmaps.exe, gears.exe, boing.exe, wave.exe, heightmap.exe:
c:/mingw64/x86_64-w64-mingw32/bin/ld.exe: warning: cannot find entry symbol _mainCRTStartup; defaulting to 0000000000401000
Not so however for listmodes.exe, mthello.exe, mtbench.exe and particles.exe which build fine. Indeed those 4 are the only ones running properly here afterwards, the others just exit immediately without outputs or errors (naturally, since there is no valid entry point for them).
[C] Building the tests
Warning at accuracy.exe, dynamic.exe:
c:/mingw64/x86_64-w64-mingw32/bin/ld.exe: warning: cannot find entry symbol _mainCRTStartup; defaulting to 0000000000401000
No such problem for defaults.exe. For dynamic.exe it then proceeds with the following errors:
C:\Users\roxor\AppData\Local\Temp\cc8hsorn.o:dynamic.c:(.text.startup+0x1c): undefined reference to `__imp_glfwGetVersion'
C:\Users\roxor\AppData\Local\Temp\cc8hsorn.o:dynamic.c:(.text.startup+0x62): undefined reference to `__imp_glfwInit'
C:\Users\roxor\AppData\Local\Temp\cc8hsorn.o:dynamic.c:(.text.startup+0xcf): undefined reference to `__imp_glfwOpenWindow'
C:\Users\roxor\AppData\Local\Temp\cc8hsorn.o:dynamic.c:(.text.startup+0x10b): undefined reference to `__imp_glfwSetWindowTitle'
C:\Users\roxor\AppData\Local\Temp\cc8hsorn.o:dynamic.c:(.text.startup+0x118): undefined reference to `__imp_glfwSetWindowSizeCallback'
C:\Users\roxor\AppData\Local\Temp\cc8hsorn.o:dynamic.c:(.text.startup+0x123): undefined reference to `__imp_glfwSwapInterval'
C:\Users\roxor\AppData\Local\Temp\cc8hsorn.o:dynamic.c:(.text.startup+0x14a): undefined reference to `__imp_glfwGetWindowParam'
C:\Users\roxor\AppData\Local\Temp\cc8hsorn.o:dynamic.c:(.text.startup+0x151): undefined reference to `__imp_glfwSwapBuffers'
C:\Users\roxor\AppData\Local\Temp\cc8hsorn.o:dynamic.c:(.text.startup+0x174): undefined reference to `__imp_glfwTerminate'
collect2: ld returned 1 exit status
make[1]: *** [dynamic.exe] Error 1
make[1]: Leaving directory `/c/glfw64/tests'
make: *** [win32-msys] Error 2
Now this latter one is the test program for loading the DLL. You might think that's simply missing the necessary libs (.a and .dll) in the correct places, but do note at this very point I DID have all the necessary includes and libs (from an earlier GLFW make that was exactly the same as the above, same versions, same warnings, same output files) in the correct places:
libglfwdll.a in \MinGW64\x86_64-w64-mingw32\lib (next to libglu32.a, libopengl32.a)
glfw.h in \MinGW64\x86_64-w64-mingw32\include\GL (next to gl.h, glaux.h, glu.h)
glfw.dll in \windows and \windows\system32 (next to opengl32.dll, glu32.dll)

Answer 1

Problem A is harmless but I've added an additional cast to remove the warning. Problems B and C are due to two bugs in GLFW. They have now been fixed, in part thanks to this thread. Thanks for posting it to the GLFW bug tracker and so bringing them to my attention. The fixes will be included in the 2.7.6 release. Until then, you can grab trunk from the GLFW Subversion repository.
Problem C was tricky enough to solve that someone may find a summary useful.
Proper linking for 32-bit requires a .def file with __stdcall decorated symbols, but this file cannot be used for 64-bit. The solution was to have GCC generate the correct .def file for the given architecture.
This is done by linking the DLL twice. First it's linked as exporting __stdcall decorated symbols (the default) and generating the .def file (using -Wl,--output-def,file.def) and then it's linked again without decorations (using --kill-at) to produce the final DLL. This generated .def file can then be used as usual with dlltool to generate the import library.
The most useful resource I found whilst researching this was Stdcall and DLL tools of MSVC and MinGW, which among other things outlines this method.

Answer 2

I got the same error too.
Solved by change the file glfw-2.7.5\tests\Makefile.win32.mingw:12 from
SOLIB = ../lib/win32/libglfwdll.a
to
SOLIB = ../lib/win32/glfw.dll

Answer 3

I ran into the exact same problem and while researching the errors and warning I found a fix for the 'cannot find entry symbol error' warning:
In examples/Makefile.win32.msys and tests/Makefile.win32.msys change the line
WINDOWS = -mwindows -e _mainCRTStartup
to
WINDOWS = -mwindows
Kabie's fix helps with the dynamic linking error
I'm not 100% sure this is a correct solution as I don't completely understand the reason for the alternate entry point name in the first place but at least the tests seem to work and the examples run.