C - How to create a pattern in code segment to recognize it in memory dump?

Question

I dump my RAM (a piece of it - code segment only) in order to find where is which C function being placed. I have no map file and I don't know what boot/init routines exactly do.

I load my program into RAM, then if I dump the RAM, it is very hard to find exactly where is what function. I'd like to use different patterns build in the C source, to recognize them in the memory dump.

I've tryed to start every function with different first variable containing name of function, like:

char this_function_name[]="main";

but it doesn't work, because this string will be placed in the data segment.

I have simple 16-bit RISC CPU and an experimental proprietary compiler (no GCC or any well-known). The system has 16Mb of RAM, shared with other applications (bootloader, downloader). It is almost impossible to find say a unique sequence of N NOPs or smth. like 0xABCD. I would like to find all functions in RAM, so I need unique identificators of functions visible in RAM-dump.

What would be the best pattern for code segment?

Answer 1

If it were me, I'd use the symbol table, e.g. "nm a.out | grep main". Get the real address of any function you want.

If you really have no symbol table, make your own.

struct tab {
    void *addr;
    char name[100];  // For ease of searching, use an array.
} symtab[] = {
    { (void*)main, "main" },
    { (void*)otherfunc, "otherfunc" },
};

Search for the name, and the address will immediately preceed it. Goto address. ;-)

Answer 2

If your compiler has inline asm you can use it to create a pattern. Write some NOP instructions which you can easily recognize by opcodes in memory dump:

MOV r0,r0
MOV r0,r0
MOV r0,r0
MOV r0,r0