GCC symbol table for local variables on stack

Question

Of course, symbol and type information of each variable defined in a C/C++ program is available, otherwise the debuggers could not show them. But how to access this information?

A lot info about the elf is available, but that is about linking an seems to hold only global variables, not local ones on the stack i.e.

In a remote real time system (not under unix), I'd like to be able to peek now and then by copying some memory in a list together with the associated variable name, and later on take a look at them while the RT system goes on.

The best would be that the dump could be introduced at any time for any variable without the need to add some statements in the code upfront.

Answer 1

But how to access this information?

TL;DR: it's complicated.

You would need to build almost a complete debugger. You can watch this space. When the author gets around to step 9, you'll have an example to follow.

I'd like to be able to peek now and then by copying some memory in a list together with the associated variable name, and later on take a look at them while the RT system goes on.

RT systems do not usually lend themselves to easy debugging. The best you could probably do is take a snapshot of the entire (used portion of) the stack, and "fish out" variable values later.

To do that, you'll need to know current values of the stack pointer and instruction pointer, contents of the stack, and load addresses of all ELF objects. And you'll need to re-implement large part of a debugger (or modify existing one).

The easiest approach might be to convert (post-process) the above info into an ELF core, and then use existing debugger of your choice to analyse the values. You can use Google user-space coredumper to see what's involved. See also this answer.