Re: C/C++ calling convention

James Kanze <>
Sat, 28 Aug 2010 15:07:42 -0700 (PDT)
On Aug 27, 7:30 am, Goran Pusic <> wrote:

On Aug 26, 6:34 pm, James Kanze <> wrote:

In fact, I'd go as far as to say that any given system
effectively has a language-agnostic ABI (but they all lean
towards simplicity of C).

That used to be true in the distant past, but not today.

I am sorry, but no. Additional argument to the way I see things: under
e.g. Windows, there's a myriad of OS interfaces that are exposed
through COM (e.g. Telephony API, to name but one example). Nobody in
their right mind is using these interfaces from C, but rather C++.

What does COM have to do with the OS?

IOW, in theory, C language is incidental to OS interfaces. In
practice, much less so. :-)

In theory, we really have to start by defining what we mean by
"OS". I'm an old timer---for me, the OS is the part of the code
which has to be executed in kernel mode: things like COM or the
GUI aren't directly part of the OS. (But the border isn't
clear. Many years ago, all of the networking software was built
above the OS as well. Today, I don't know of a kernel that
doesn't have support for TCP/IP built in.) Given that, the
actual ABI must be in assembler, because C doesn't offer any
means of switching from user mode to kernel mode. However,
neither Windows nor any of the Unix I know publish this
interface; they make available a runtime library which provides
a C level interface to it. So from the user's point of view,
the ABI is defined in C.

Of course, addins like COM, the GUI, a data base... or the C++
standard library, may define the interface in any language they

James Kanze

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