Linker/loader errors (unresolved function name symbols) in openr.c and writer.c

Question

Compiled Arduino source and, at end of the build, got the unresolved symbols (function entry point names) for openr.c and writer.c

The invocation arguments used were consistent with the _open_r() and _write_r() function definitions, and they compile without errors.

Any suggestions on why this error came up, or even what openr.c and writer.c do are welcomed.

^{/home/digysol/arduino-1.8.0/hardware/tools/arm/bin/../lib/gcc/arm-none-eabi/4.8.4/../../../../arm-none-eabi/lib/armv7e-m/fpu/libc.a(lib_a-openr.o): In function "_open_r": openr.c:(.text._open_r+0x10):
        undefined reference to "_open"}

^{/home/digysol/arduino-1.8.0/hardware/tools/arm/bin/../lib/gcc/arm-none-eabi/4.8.4/../../../../arm-none-eabi/lib/armv7e-m/fpu/libc.a(lib_a-writer.o): In function "_write_r": writer.c:(.text._write_r+0x10):
        undefined reference to "_write"}

^{collect2: error: ld returned 1 exit status}

Answer 1

undefined reference to "_open" I look at this and it automatically tells me it's a missing library.

The libc.a binary looks like it's trying to use it. So maybe libc.a is having trouble building with missing params, see a relevant question.