SDCC Library Licenses

The great majority of SDCC run-time libraries are licensed under the GPLv2+LE which allows linking of sdcc run time libraries with both free and non-free (proprietary, closed source) applications.

Possibly non-free pic headers and library

The exception are PIC device libraries and header files which are derived from Microchip header (.inc) and linker script (.lkr) files. Microchip claims copyright on those, which might or might not be a valid claim (see https://debian-legal.debian.narkive.com/gGuSWDyP/are-register-names-and-locations-under-copyright for a discussion). Microchip requires that "The header files should state that they are only to be used with authentic Microchip devices" which would make them incompatible with the GPL. PIC device libraries and header files are located at non-free/lib and non-free/include directories respectively. SDCC should be run with the --use-non-free command line option in order to include possibly non-free header files and libraries.