Here is how you can build a user-space application for uClinux.

On the host activate the development environment (refer to Installing and Activating Cross Development Environment):

$ . ./ACTIVATE.sh

Develop source files for whatever application you would like to run on the uClinux target. For instance:

$ vi test.c
#include <stdio.h>

int main(int argc, char *argv[])
{
    printf("Hello %s\n", argv[1]);
    return 1;
}

Build the application for the uClinux target, and copy the binary to the directory exported via NFS:

$ ${CROSS_COMPILE_APPS}gcc -o test test.c
$ cp test /home/yur/nfs/

Run the application binary on the target. One easy way to do that is to have an NFS share mounted on the target, which immediately provides access to the host development directory:

/ # mount -o nolock 192.168.1.41:/home/yur/nfs /mnt/nfs
/ # /mnt/nfs/test "STM32H7-EVAL uclinux"
Hello STM32H7-EVAL uclinux
/ #