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.
General
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
i386
PowerPC
Internal Linker
Packages
From the Free Pascal wiki, page "Compiler development articles", as the Internet Archive kept it on 2026-01-02, last changed on 2021-06-11. Copyright stays with the author who wrote it, according to the old wiki's Licensing page. If you have concerns about this material, message the admin.