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Date: Wed, 15 Sep 2010 13:43:00 -0000
Message-ID: <AANLkTim24XZssayO6-wvf9WoywRauqXRbUdQi5LjyO9F@mail.gmail.com>
Subject: Python API questions and use cases
From: =?ISO-8859-1?Q?Joel_Borggr=E9n=2DFranck?= <joel.borggren.franck@gmail.com>
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Hi

I'm testing out the new Python API for GDB, and have a couple of use cases
that I don't know how to solve entirely from python. I hope this is the
right mailing list.

In all these cases I'm working on debugging a core.

1) Getting the value of a global

given:

typedef struct foo {
  int bar;
  int baz;
} foo;

foo myGlobalFoo;

in some C file, how do I access the value of myGlobalFoo from python?

The only working solution I have at the moment is to escape to gdb-script
with:

gdb.parse_and_eval("myGlobalFoo")

is this intended?

I know I can iterate over symbols in the symbol table, but I haven't found
a way to go from symbol to value.

2) Casts

given that I know that at address 0xdeadbeef there will be a struct of type
foo how do I get that struct (or a pointer to that struct) as a gdb.Value
object?

Currently i have written a cast function:

def cast(type_string, address):
    """Returns a gdb.Value object with type 'type_string' from memory
    starting at 'address'."""
    return gdb.parse_and_eval("(%s)((void *)%s)" % (type_string, address))

that I think works, but is there some other way?

Another usecase for casts would be if I wanted to mask an address in python,
given:

foo *fooP;

how do I do the equivalent of this in pyhton:

set $check = ((size_t)foo) & 1

I know there is the a cast in the API but that requires that I have a
gdb.Type which I don't know how to get.

I'd be happy to help out adding solutions to these use-cases!

Cheers
Joel