How to access the keys or values of Python GDB Value

Question

I have a struct in GDB and want to run a script which examines this struct. In Python GDB you can easily access the struct via

(gdb) python mystruct = gdb.parse_and_eval("mystruct")

Now I got this variable called mystruct which is a GDB.Value object. And I can access all the members of the struct by simply using this object as a dictionary (likemystruct['member']).

The problem is, that my script doesn't know which members a certain struct has. So I wanted to get the keys (or even the values) from this GDB.Value object. But neither mystruct.values() nor mystruct.keys() is working here.

Is there no possibility to access this information? I think it's highly unlikely that you can't access this information, but I didn't found it anywhere. A dir(mystruct) showed me that there also is no keys or values function. I can see all the members by printing the mystruct, but isn't there a way to get the members in python?

Answer 1

From GDB documentation:

You can get the type of mystruct like so:

tp = mystruct.type

and iterate over the fields via tp.fields()

No evil workarounds required ;-)

Update: GDB 7.4 has just been released. From the announcement:

Type objects for struct and union types now allow access to the fields using standard Python dictionary (mapping) methods.

Answer 2

Evil workaround:

python print eval("dict(" + str(mystruct)[1:-2] + ")")

I don't know if this is generalisable. As a demo, I wrote a minimal example test.cpp

#include <iostream>

struct mystruct
{
  int i;
  double x;
} mystruct_1;

int main ()
{
  mystruct_1.i = 2;
  mystruct_1.x = 1.242;
  std::cout << "Blarz";
  std::cout << std::endl;
}

Now I run g++ -g test.cpp -o test as usual and fire up gdb test. Here is a example session transcript:

(gdb) break main
Breakpoint 1 at 0x400898: file test.cpp, line 11.
(gdb) run
Starting program: ...

Breakpoint 1, main () at test.cpp:11
11        mystruct_1.i = 2;
(gdb) step
12        mystruct_1.x = 1.242;
(gdb) step
13        std::cout << "Blarz";
(gdb) python mystruct = gdb.parse_and_eval("mystruct_1")
(gdb) python print mystruct
{i = 2, x = 1.242}
(gdb) python print eval("dict(" + str(mystruct)[1:-2] + ")")
{'i': 2, 'x': 1.24}
(gdb) python print eval("dict(" + str(mystruct)[1:-2] + ")").keys()
['i', 'x']