Keith Packard has been putting in a lot of work over the past few months on PicoLibc, his lightweight libc replacement, which is specifically aimed at memory-limited embedded systems. Keith has been steadily increasing the functionality of PicoLibc and has attracted some additional contributors along the way. One of those contributors, Jonathan McDowell in Belfast, has just added the hooks for compiling xtensa-lx106-elf binaries. Jonathan notes that it has been tested on an ESP8266 with the 2.2.1 + 3.0.1 Espressif NONOS SDKs + GCC 9.2.1 from Debian.
Over at CNX Software, Siji Sunny recently put together a (non-ESP specific) description of how to configure, compile and build code using PicoLibc under Linux, so it should now be possible (with Jonathan’s additions) to cross-compile for the ESP8266 using that handy guide. In the meantime, Keith is continuing with additional work on integration of the ESP8266 and ESP32 targets.