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Re: Python API questions and use cases
- From: Tom Tromey <tromey at redhat dot com>
- To: Joel BorggrÃn-Franck <joel dot borggren dot franck at gmail dot com>
- Cc: gdb at sourceware dot org
- Date: Wed, 15 Sep 2010 11:56:39 -0600
- Subject: Re: Python API questions and use cases
- References: <AANLkTim24XZssayO6-wvf9WoywRauqXRbUdQi5LjyO9F@mail.gmail.com>
>>>>> "Joel" == Joel BorggrÃn-Franck <joel.borggren.franck@gmail.com> writes:
Joel> 1) Getting the value of a global
Joel> foo myGlobalFoo;
Joel> in some C file, how do I access the value of myGlobalFoo from
Joel> python?
Joel> The only working solution I have at the moment is to escape to
Joel> gdb-script with:
Joel> gdb.parse_and_eval("myGlobalFoo")
Joel> is this intended?
This is simplest.
Joel> I know I can iterate over symbols in the symbol table, but I
Joel> haven't found a way to go from symbol to value.
Hmm, we don't seem to expose a way to do that. Sorry about that.
Could you file a bug report for this?
Joel> 2) Casts
Joel> given that I know that at address 0xdeadbeef there will be a
Joel> struct of type foo how do I get that struct (or a pointer to that
Joel> struct) as a gdb.Value object?
Joel> Currently i have written a cast function:
Joel> def cast(type_string, address):
Joel> """Returns a gdb.Value object with type 'type_string' from memory
Joel> starting at 'address'."""
Joel> return gdb.parse_and_eval("(%s)((void *)%s)" % (type_string, address))
Joel> that I think works, but is there some other way?
I think the tricky part is getting a Value holding the appropriate
constant. For that you might not have anything better, at present, than
parse_and_eval. (This is a non-issue if the address is already a
gdb.Value.)
You can get a (simple) type using gdb.lookup_type. So you should be
able to do something like:
address.cast (gdb.lookup_type ('struct foo').pointer())
Joel> Another usecase for casts would be if I wanted to mask an address
Joel> in python, given:
Joel> foo *fooP;
Joel> how do I do the equivalent of this in pyhton:
Joel> set $check = ((size_t)foo) & 1
Simplest is to do it using Python math:
foo = ...
check = long (foo) & 1
Otherwise you can look up size_t:
check = foo.cast (gdb.lookup_type ('size_t')) & 1
If you really want to set a convenience variable, then for the time
being you will have to use parse_and_eval. We don't expose those any
other way.
Tom