[Cortex-M3] Things to try in order to shrink image size

Hi,

I need to reduce a image size to a minimum. The project is a CANBUS Bootstrap that must fit under 4KB and be written in C.

I'm using MicroLIB, Link-Time Code Generation, -O3, ZI init.

What other compiler/assembler/linker settings could I possibly apply in order to shrink the image?

Thanks.