ELF File format for ARM compilers (for my own debugger)

I'm interested in debugging Cortex-M3 microcontrollers, especially STM32. I know it may soud silly (there are many debuggers to use) but I'd like to build my own debugger (software and hardware including STM32 devices programmer). GCC ARM compiler generates *.elf file which is used by debuggers. I found official ELF file specification in the Internet but it seems it lacks important information which i search for. For example, the specification does not say anything about such information as what flash memory adressess are assigned to particular lines of source C code (which i suppose are used by the debugger to highlight the current line of source code being executed) or all the variables names used in your program (including local and global ones). Is it possible to find better specification of the ELF file ?