Working with the installed Nios® II software build tools for Eclipse (Nios® II SBT):
\libhal_bsp.a(alt_putchar.o): In function `alt_putchar': alt_putchar.c:(.text+0xc): undefined reference to `null' alt_putchar.c:(.text+0x1c): undefined reference to `null' alt_putchar.c:(.text+0x28): undefined reference to `ALT_MODULE_CLASS_null_write'
Using Nios® II SBT from Quartus Prime Pro 18.1.1 Build 263 is more useful:
This problem is scheduled to be fixed in a future Intel® Quartus® Prime software release as mentioned in the shared KDB as follow and you can use the workaround mentioned here:
Can you please elaborate more how can I help you?