libc configuration

libc overview

Espressif's RTOS SDK provides libc functions as part of binary libmain.

esp-open-rtos replaces these with a newlib libc compiled from source.

crosstool-NG as used in esp-open-sdk provides a newlib 2.0 implementation. However it isn't thread-safe when used with FreeRTOS' preemptive threading model.

esp-open-rtos libc

For now we supply our own libc in the 'libc' directory. This is newlib 2.2.0 plus xtensa patches and a locking implementation patch. Using newlib 2.2.0 also allows pulling in the "nano" features for smaller malloc and I/O format implementation.

Source: https://github.com/projectgus/newlib-xtensa

Any commits that update the 'libc' directory list the newlib commit that the library was built from, as well as the configure and compile arguments.

Look through the commit history of the libc directory to see the configure/make statements needed to build. (Look at the full commit message to see the arguments.)

To update the headers and libraries already in the esp-open-rtos tree, configure with --prefix=/patho/to/esp-open-rtos/libc and do a 'make install'.

Using system libc

Pass OWN_LIBC=0 to make (see Build Process) to compile & link with the toolchain-provided "system" libc instead of the esp-open-rtos libc.