str912fw44 and gcc

I would like to compile free rtos for str912 microcontroller. Why should I use IAR compilers and not GCC? Are there any problems building a toolchain for ARM9 with gcc?

str912fw44 and gcc

There is no reason why you could not use GCC.  There is not a base demo project for you to use in the FreeRTOS download, but you could create your own.  I would suggest using one of the ARM7 GCC projects as a base, I think the FreeRTOS ARM7 and ARM9 ports are the same essentially.