(gdb) p/x equivalent in gdb python script?

Question

the main structure is

struct my_struct 
{
   int x; 
   void* md_template;
   void* md_capture_buff;
   ....
};

When i am doing

(gdb) p ((struct my_struct *)dev_base->next->priv)

The output is like this

$1 = {
 x= 15 '\017'
 md_template = ,
 md_capture_buff =
}

And when i am doing it with p/x:

(gdb) p/x ((struct my_struct *)dev_base->next->priv)

The output is like this

$1 = {
 x= 0xf;
 md_template =0x410027001a50 ,
 md_capture_buff = 0x41002c0c5490
}

In gdb-python:

python val = gdb.parse_and_eval('((struct my_struct *)dev_base->next->priv)')

python print val

The output is:

$1 = {
 x= 15 '\017'
 md_template = ,
 md_capture_buff =
}

So how to write equivalent to p/x in gdb-python? or how to get the address of 'md_capture_buff' in python script as python val = gdb.parse_and_eval('((struct my_struct *)dev_base->next->priv)').address is not prining the address?

Tom Tromey · Accepted Answer · 2013-06-05 13:41:04Z

0

You probably have "set print address" off. I wouldn't do this. It's arguably a bug that the str operator is respecting this setting.

There isn't a good way to reproduce "p/x" other than just invoking it directly. See gdb.execute.

You can get the value of any field using []. Like

val = something['fieldname']

It's usually better, IMO, to use the API rather than parse_and_eval. That is, you can cast, look up fields, etc, directly from Python.

answered Jun 5, 2013 at 13:41

Tom Tromey

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3 Comments

Baijnath Jaiswal Over a year ago

@tromey, Thanks. But while traversing a structure if an array occurs as a member, then how to print the values of whole array in hex (more readable form). it is possible only with p/x. but we can not use gdb.execute('p/x <array>') in the middle of traversal. I want to implement this in this script stackoverflow.com/questions/16787289/… . Please let me know if there is a way to do this. can we control printing arrays as the pointers are done in this script ?

hesham_EE Over a year ago

I'm trying to avoid parse_and_eval() but I'm not sure how to read a structure pointer directly without it. What API can I use to avoid using parse_and_eval(), assuming the OP's question?

Tom Tromey Over a year ago

There are a number of methods on gdb.Value that you'd use. You can use dereference to dereference a pointer, use ["fieldname"] to get a field from a structure (or a pointer-to-structure -- so often you don't even need dereference), and use cast to change the type.

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