[fpc-devel] Re: Episode 4. Addressing and it's limits Part Two

Hans-Peter Diettrich DrDiettrich1 at aol.com
Thu Feb 9 08:37:25 CET 2012

steve smithers schrieb:

> The bit that provides code for VM/SP as opposed to say MVS, is the RTL,
> so if I want to open a file, there is a routine in the RTL called OpenFile
> (or whatever) that issues the VM code for open.  This lives in System.pp
> or Sysfile.pp or whatever it's called in the RTL/VMSP sub-directory
> Now, in order for the compiler to function it needs access to a certain
> level of base functionality in the VM/SP RTL.

The RTL is compiled before the compiler, so that it can be used inside 
the compiler. This is required for cross-compilation, where the compiler 
has to use the file access routines of the *host* system, and is 
compiled into code for the host system.

The RTL may contain assembler code for the target machine, if you don't 
trust your own compiler to generate appropriate code.


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