GCC compiles for RISC-V 32-bit (Double-Float). See https://github.com/lupyuen/nuttx-rust-app

gcc-compiler.log

$ make --trace
...
## GCC compiles `hello_main.c` to `hello.o`
## for RISC-V 32-bit (Double-Float)
riscv64-unknown-elf-gcc \
  -march=rv32imafdc \
  -mabi=ilp32d \
  -c \
  -fno-common \
  -Wall \
  -Wstrict-prototypes \
  -Wshadow \
  -Wundef \
  -Wno-attributes \
  -Wno-unknown-pragmas \
  -Wno-psabi \
  -Os \
  -fno-strict-aliasing \
  -fomit-frame-pointer \
  -ffunction-sections \
  -fdata-sections \
  -g \
  -isystem nuttx/include \
  -D__NuttX__ \
  -DNDEBUG  \
  -pipe \
  -I "apps/include" \
  -Dmain=hello_main \
  hello_main.c \
  -o hello_main.c...apps.examples.hello.o