How to use variable in link script

Hence when you are using a linker script defined symbol in source code you should always
take the address of the symbol, and never attempt to use its value. For example suppose
you want to copy the contents of a section of memory called .ROM into a section called
.FLASH and the linker script contains these declarations:
start_of_ROM
= .ROM;
end_of_ROM
= .ROM + sizeof (.ROM) - 1;
start_of_FLASH = .FLASH;
Then the C source code to perform the copy would be:
extern char start_of_ROM, end_of_ROM, start_of_FLASH;
memcpy (& start_of_FLASH, & start_of_ROM, & end_of_ROM - & start_of_ROM);