I just wanted to try to modify the firmware for the picosoc demo in symbiflow-examples. I found the firmware for it in this symbiflow-arch-defs repository.

I installed the toolchain with:
conda install -c litex-hub gcc-riscv32-elf-newlib

But when building I get this error:

riscv32-unknown-elf-gcc -DHX8KDEMO -DCLK_FREQ=25000000 -DNOSPIFLASH -march=rv32im -Wl,-Bstatic,-T,sections.lds,--strip-debug -ffreestanding -nostdlib -mstrict-align -O0 -o firmware_noflash_25.elf start.s firmware.c
cc1: error: requested ABI requires '-march' to subsume the 'D' extension
make: *** [Makefile:22: firmware_noflash_25.elf] Error 1

There is some details about the compiler args on https://www.sifive.com/blog/all-aboard-part-1-compiler-args

I found that I could add -mabi=ilp32 and then it would build. I am not sure if this is the correct fix, but it appears to be working when I synth the verilog and put it on the basys3. At least it includes my new "printf" and it runs as before.

./hex2progmem.py --rom-style initial firmware/firmware_noflash_100.hex  > ~/symbiflow-examples/xc7/picosoc_demo/progmem.v
.....
make
openocd ....

Version info about compiler for completeness:

riscv32-unknown-elf-gcc --version
riscv32-unknown-elf-gcc (9.2.0) 9.2.0