FPC Subtarget Support
As of version 3.3.1, medio 2023, FPC has support for subtargets.
What are subtargets
A subtarget is a named set of configuration options for the compiler which is applied during compilation and installation of the RTL, Packages and utils. The compiler itself can also be compiled with a subtarget if you so desire.
This named set of configuration options is supplied as a configuration file much like the default configuration file (fpc.cfg). This file is read in addition to the regular configuration file, and must have a fixed name.
For example, to create a subtarget 'myfeature', you must create a configuration file called fpc-myfeature.cfg. The configuration name must be lowercase in the filename.
When compiling, you can select a subtarget on the command-line using the -t compiler option:
fpc -tmyfeature
Only 1 subtarget can be specified, if you specify a second, you will get an error.
If so desired, you can combine subtargets into a new subtarget with the help of the #INCLUDE directive.
In the subtarget definition file, you can put any options that you would specify on the command-line or in a configuration file.
For example:
-dUNICODERTL -Municodestrings
This configuration will always be loaded, also in the case when you specify -n. So in case of the following command-line
fpc -n -tmyfeature
will not load fpc.cfg, but will load fpc-myfeature.cfg.
When you specify a subtarget, besides loading the configuration file, the compiler does 3 other things:
- The $fpctarget macro will become CPU-OS-SUBTARGETNAME. For example
x86_64-linux-myfeature
- It will define a macro FPC_SUBTARGET_SUBTARGETNAME , for example:
FPC_SUBTARGET_MYFEATURE
- It will define a macro FPC_SUBTARGET with value SUBTARGETNAME , for example:
FPC_SUBTARGET=myfeature
Because the $fpctarget macro changes value when you specify a subtarget, this has an effect on the search path:
The default configuration file uses this macro to specify the unit path. As a result, the compiler will search in a different directory for units.
For example for linux 64-bit, if you specify -tmyfeature Instead of looking for units in the default
/usr/local/lib/fpc/3.3.1/x86_64-linux
instead, it will search in directory
/usr/local/lib/fpc/3.3.1/x86_64-linux-myfeature
Using subtargets
Using subtargets in Makefiles
To compile the FPC RTL and packages for a subtarget, you can specify the SUB_TARGET define
make SUB_TARGET=myfeature clean all
This has 2 effects:
- The compiler is called with -tmyfeature
- When doing an install, the subtarget name will be appended to the installation directory.
make SUB_TARGET=myfeature install
will (on Linux) install into
/usr/local/lib/fpc/3.3.1/x86_64-linux-myfeature
Using subtargets in fpcmake
The default fpcmake makefile generator creates now by default makefiles that understand the SUB_TARGET option.
Using subtargets with fpmake
The fpmake tool also understands the subtarget concept, you can set the subtarget with the -s option.
The Free Pascal rtl/packages use the subtarget concept to create the unicode RTL (where string=unicodestring) in parallel to the regular single-byte RTL (where string=ansistring or shortstring)
