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Interfacing to Operating Systems

I'll divide this chapter into two sections:

  • How to Interface to POSIX Operating Systems.
  • How to Interface to the Windows Operating System.

Interface to POSIX Operating Systems

On POSIX, the presence of the C run-time library is an unavoidable fact for which reason it makes a lot of sense to directly call such C run-time functions.

Sample POSIX "Hello World" Application

On POSIX, it is really very easy to create the Hello world program:

declare i32 @puts(i8* nocapture) nounwind

@.hello = private unnamed_addr constant [13 x i8] c"hello world\0A\00"

define i32 @main(i32 %argc, i8** %argv) {
    %1 = getelementptr [13 x i8], [13 x i8]* @.hello, i32 0, i32 0
    call i32 @puts(i8* %1)
    ret i32 0
}

How to Interface to the Windows Operating System

On Windows, the C run-time library is mostly considered of relevance to the C and C++ languages only, so you have a plethora (thousands) of standard system interfaces that any client application may use.

Sample Windows "Hello World" Application

Hello world on Windows is nowhere as straightforward as on POSIX:

.. literalinclude:: listings/windows.ll
    :language: llvm