Why did Microsoft choose stdcall as their API convention?

Question

Is there a good reason?

Are their internal functions (not exported) also stdcall convention?

Declarer

Answer 1

It was an adaptation to the pascal calling convention for 32-bit code. Pascal was the calling convention for 16-bit operating systems like OS/2 and Windows 3. Why pascal was chosen is a bit of a guess, even I was a small pup back then, but it is slightly more efficient. Which mattered back when 640 KB was all you had to work with.

Most Win32 functions aren't true stdcall as it also prescribes how the exported function is decorated before presented to the linker. Like void Mumble(int arg) becomes _Mumble@4. The number after the @ describes the activation frame size. But most Win32 functions are exported without any decoration. Probably to give the programmer a fighting chance to make GetProcAddress() work. I think the decoration was intended to help the linker detect mismatches between the declared API function signature and the actual one. Having a mismatch in the number of passed arguments is an automatic kaboom since the callee will pop more or less arguments off the stack then were passed. Hard to diagnose too. A weakness of stdcall, the cdecl convention doesn't have this problem.

Internal calling is a mixed bag between stdcall, cdecl and thiscall. Can't say I've ever detected a pattern, although single-stepping Windows code isn't something I enjoy doing.

Etesian

the lack of symbol decoration is cause the winapi binaries use .def files for exporting(which strips decoration and/or uses an ordianl), this makes importing via GetProcAddress simple, as there is no symbol decoration – Scat

I do enjoy single-stepping Windows code sometimes, and I can say that most of the time stdcall is used internally as well. – Pickens

Answer 2

Code compiled with stdcall is significantly smaller than code compiled with cdecl (the alternative). At the time the decision was made, smaller code was faster code.

Rarely

Actually I preferred Hans Passant's answer to mine, but whatever. – Rarely

Because you are a Microsoftee(for long time), I chose your answer. – Declarer

Do you have any evidence for that claim? Intuitively I think it should be a wash between stdcall and cdecl and googling doesn't come up with any size comparisons between the two calling conventions. – Engorge

@BjörnLindqvist For the size; a single retn in the callee vs adjusting esp after every call. Larry blogged about this but I can't find it right now... – Terricolous