[binutils] Problems about utilizing BFD in a symbolic debugger

[binutils] Problems about utilizing BFD in a symbolic debugger

[Rui Hong]

Hi everyone,


Glad to join the binutils community.

I'm using C to make a symbolic debugger inside a software simulator for RISCV/ELF(DWARF) executable and starting to use binutils-bfd to implement features about symbol/DWARF handling.
Using BFD doc/bfd.h, I've found BFD functions like bfd_find_nearest_line, bfd_canonicalize_symtab to implement features on "symbol-->address-->line", such as command 'b main / b func_name', or showing correct file and line after 'b *0x40000040' command.
But I do not find any other BFD functions on "line-->address", to implement command like 'b main.c:14'.
And the symbol table in ELF or what the bfd_canonicalize_symtab returns seems to be a rather simple symbol table with no variable in the source file, which makes it harder to get a variable's location to implement command like 'p var1'(do I really have to parse DWARF manually?)


I really need advice or some code examples anywhere(I'm looking into GDB source code right now, but it's quite complex. Even a rough location of the code would be helpful)


To sum my questions:
1. how can I map file:line to actual address using BFD?

2. how to build a complete symbol table with variables and their locations in it using BFD?
3. how to get the original complete line number table from .debug_line section using BFD?


Any advice, code example or location of code would be helpful!



Kind regards,
Rui

Re: [binutils] Problems about utilizing BFD in a symbolic debugger

[Nick Clifton]

Hi Rui,

> Glad to join the binutils community.

And it is very nice to have you join us.

> Using BFD doc/bfd.h, I've found BFD functions like bfd_find_nearest_line, bfd_canonicalize_symtab to implement features on "symbol-->address-->line", such as command 'b main / b func_name', or showing correct file and line after 'b *0x40000040' command.
> But I do not find any other BFD functions on "line-->address", to implement command like 'b main.c:14'.

There aren't any!  The BFD library does not have code to implement
source line to address mapping.  It only handles the other way around
(is address to source line).  So unfortunately you are going to need
to delve into the GDB code to solve this problem.


> And the symbol table in ELF or what the bfd_canonicalize_symtab returns seems to be a rather simple symbol table with no variable in the source file,

True - and again this is because the BFD library does not implement
this kind of mapping, so there is no need to contain this information
in the symbol table.


Cheers
   Nick