Is there anyway to write registers/memory without specify core-file

I am debugging on a RTOS. The core file generation is impossible.
However, I can use the gdb to load my compiled elf file onto
simulator. But it seems the memory can not be accessed on "target
sim".

I have a simple need: Load symbol file, load registers, load some
memory. This is quite like the load of core-file. But my register
content and memory are raw data, not assembled in a core-file.

Who can help me out?