Compiler development articles

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Warning: As of 2021-May-21. the current compiler version is 3.2.2, so it is possible some of the details listed below may have changed.

The current FPC version under developement is 2.5.1. Compiler internals are documented at the evolving FPC internals page.


How to start

FPC internals

Language related articles

Coding style

Porting Free Pascal

Testing FPC

Enable new style smartlinking (FreeBSD, Linux)

  • in i_*.pas add tf_smartlink_sections to the flags field of the platform description record for your OS/CPU combo (in my case i_bsd.pas, the system_i386_freebsd_info record)
  • in ogelf.pas scroll down to nearly the bottom, and add af_smartlink_sections to the flags field of as_i386_elf32_info
  • run "(g)make all OPT='-Aas -k--gc-sections' at the toplevel to build using new smartlinking routines.

C++ linking

Note that FPC doesn't have negative VMT offsets due to GNU LD limitations.

The fundament of above C++ <-> OPas lies in COM interfaces: (quote from Rudy Velthuis)

"Well, all compilers must be able to create COM interfaces. Since in C++, these are simply pure abstract classes, and Delphi must have the same layout, for many reasons, they are all compatible. In fact, a pure abstract class pointer points to a structure of which the first entry is a VMT. This is also how interfaces are built"

Processor dependent

See also platform list.

Passing Pascal Types to C Routines


PIC information


PPC Calling conventions

Internal Linker

Internal Linker