Fix 32-bit windows (use stdcall convention)#85
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On 32-bit Windows, OpenGL functions use the stdcall calling convention (APIENTRY/WINAPI), but the @glfunc macro generates ccall without specifying a convention, which defaults to cdecl. With cdecl, the caller adjusts the stack after the call. With stdcall, the callee pops the arguments before returning. When Julia calls a stdcall function assuming cdecl, both sides adjust the stack — corrupting it by the size of the arguments on every call. In a render loop with multiple GL calls per frame (glViewport, glClearColor, glClear, etc.), this quickly leads to EXCEPTION_ACCESS_VIOLATION crashes in unrelated Julia internals. On 64-bit Windows (and all other platforms) there is only one calling convention, so this was never observed there. The fix adds a stdcall convention to both ccall paths (static opengl32.dll symbols and dynamic getprocaddress pointers) when Sys.iswindows() && Sys.WORD_SIZE == 32.
Member
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Thank you! I'm wondering though, didnt Julia stop supporting win32? |
Author
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https://julialang.org/downloads/support/ well it's still listed as a Tier 1 support. There are still many legacy enterprise applications that use 32-bit - believe it or not. That is also what lead me down this windy road :-) |
Member
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Fair enough 🤷 Well, I guess it wont hurt! |
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On 32-bit Windows, OpenGL functions use the stdcall calling convention (APIENTRY/WINAPI), but the @glfunc macro generates ccall without specifying a convention, which defaults to cdecl.
With cdecl, the caller adjusts the stack after the call. With stdcall, the callee pops the arguments before returning. When Julia calls a stdcall function assuming cdecl, both sides adjust the stack — corrupting it by the size of the arguments on every call. In a render loop with multiple GL calls per frame (glViewport, glClearColor, glClear, etc.), this quickly leads to EXCEPTION_ACCESS_VIOLATION crashes in unrelated Julia internals.
On 64-bit Windows (and all other platforms) there is only one calling convention, so this was never observed there.
The fix adds a stdcall convention to both ccall paths (static opengl32.dll symbols and dynamic getprocaddress pointers) when Sys.iswindows() && Sys.WORD_SIZE == 32.