teaching gdb about new types?

teaching gdb about new types?

[Richard Silverman]

Hello,

This seems as if it should be simple, but I can't find an answer.  I would like to teach gdb about new types relevant to the program being debugged, which are not among the debugging info in the program.  A concrete example: I have a program which uses pthreads from libc.  It calls:

        int pthread_cond_wait(pthread_cond_t *restrict cond,
            pthread_mutex_t *restrict mutex);

... and the argument types are defined in system header files.  But libc.so has no debugging info, so gdb doesn't know about these types, and can't interpret the arguments for me.  How can I teach gdb about these types?

Thanks,

- Richard

Re: teaching gdb about new types?

[Paul Koning]

The simple answer is to get a copy of libc.so with debug symbols, and load that symbol table.  You don't have to replace the library itself to do that.  

	paul

On Apr 29, 2011, at 2:36 PM, Richard Silverman wrote:

> Hello,
> 
> This seems as if it should be simple, but I can't find an answer.  I would like to teach gdb about new types relevant to the program being debugged, which are not among the debugging info in the program.  A concrete example: I have a program which uses pthreads from libc.  It calls:
> 
>       int pthread_cond_wait(pthread_cond_t *restrict cond,
>           pthread_mutex_t *restrict mutex);
> 
> ... and the argument types are defined in system header files.  But libc.so has no debugging info, so gdb doesn't know about these types, and can't interpret the arguments for me.  How can I teach gdb about these types?
> 
> Thanks,
> 
> - Richard

Re: teaching gdb about new types?

[Richard Silverman]

On Fri, 29 Apr 2011, Paul Koning wrote:

> The simple answer is to get a copy of libc.so with debug symbols, and load that symbol table.  You don't have to replace the library itself to do that.
>
> 	paul

I know, thanks; but the host is Solaris, and Oracle doesn't appear to provide this (although I'm pursuing it with them.).  I could also build the OpenSolaris libc and hope they're close enough.  However, it really seems as if one ought to be able to do what I described.

- Richard

> On Apr 29, 2011, at 2:36 PM, Richard Silverman wrote:
>
>> Hello,
>>
>> This seems as if it should be simple, but I can't find an answer.  I would like to teach gdb about new types relevant to the program being debugged, which are not among the debugging info in the program.  A concrete example: I have a program which uses pthreads from libc.  It calls:
>>
>>       int pthread_cond_wait(pthread_cond_t *restrict cond,
>>           pthread_mutex_t *restrict mutex);
>>
>> ... and the argument types are defined in system header files.  But libc.so has no debugging info, so gdb doesn't know about these types, and can't interpret the arguments for me.  How can I teach gdb about these types?
>>
>> Thanks,
>>
>> - Richard
>
>
>

Re: teaching gdb about new types?

[Paul Koning]

If you're worried about types rather than line numbers, I would think that all you'd need is a symbol table that has the right type definitions in it.  If you know what they are supposed to be, you can supply such a symbol table easily enough.  

	paul


On Apr 29, 2011, at 4:42 PM, Richard Silverman wrote:

> On Fri, 29 Apr 2011, Paul Koning wrote:
> 
>> The simple answer is to get a copy of libc.so with debug symbols, and load that symbol table.  You don't have to replace the library itself to do that.
>> 
>> 	paul
> 
> I know, thanks; but the host is Solaris, and Oracle doesn't appear to provide this (although I'm pursuing it with them.).  I could also build the OpenSolaris libc and hope they're close enough.  However, it really seems as if one ought to be able to do what I described.
> 
> - Richard
> 
>> On Apr 29, 2011, at 2:36 PM, Richard Silverman wrote:
>> 
>>> Hello,
>>> 
>>> This seems as if it should be simple, but I can't find an answer.  I would like to teach gdb about new types relevant to the program being debugged, which are not among the debugging info in the program.  A concrete example: I have a program which uses pthreads from libc.  It calls:
>>> 
>>>      int pthread_cond_wait(pthread_cond_t *restrict cond,
>>>          pthread_mutex_t *restrict mutex);
>>> 
>>> ... and the argument types are defined in system header files.  But libc.so has no debugging info, so gdb doesn't know about these types, and can't interpret the arguments for me.  How can I teach gdb about these types?
>>> 
>>> Thanks,
>>> 
>>> - Richard
>> 
>> 
>> 

Re: teaching gdb about new types?

[Richard Silverman]

On Fri, 29 Apr 2011, Paul Koning wrote:

> If you're worried about types rather than line numbers, I would think that all you'd need is a symbol table that has the right type definitions in it.  If you know what they are supposed to be, you can supply such a symbol table easily enough.
>
> 	paul

I tried that -- I created a little file:

----------------------------------------
#include <pthreads.h>

pthread_cond_t p;
pthread_mutex_t m;
----------------------------------------

... and built an object from it.  However, I can't find a way to get gdb to use it while debugging an existing program, that is, to add the type definitions in that object to its existing set.  The commands "symbol-file" and "add-symbol-file" seem likely candidates, but they don't appear to do it.

- Richard

> On Apr 29, 2011, at 4:42 PM, Richard Silverman wrote:
>
>> On Fri, 29 Apr 2011, Paul Koning wrote:
>>
>>> The simple answer is to get a copy of libc.so with debug symbols, and load that symbol table.  You don't have to replace the library itself to do that.
>>>
>>> 	paul
>>
>> I know, thanks; but the host is Solaris, and Oracle doesn't appear to provide this (although I'm pursuing it with them.).  I could also build the OpenSolaris libc and hope they're close enough.  However, it really seems as if one ought to be able to do what I described.
>>
>> - Richard
>>
>>> On Apr 29, 2011, at 2:36 PM, Richard Silverman wrote:
>>>
>>>> Hello,
>>>>
>>>> This seems as if it should be simple, but I can't find an answer.  I would like to teach gdb about new types relevant to the program being debugged, which are not among the debugging info in the program.  A concrete example: I have a program which uses pthreads from libc.  It calls:
>>>>
>>>>      int pthread_cond_wait(pthread_cond_t *restrict cond,
>>>>          pthread_mutex_t *restrict mutex);
>>>>
>>>> ... and the argument types are defined in system header files.  But libc.so has no debugging info, so gdb doesn't know about these types, and can't interpret the arguments for me.  How can I teach gdb about these types?
>>>>
>>>> Thanks,
>>>>
>>>> - Richard
>>>
>>>
>>>
>
>
>

-- 
   Richard Silverman
   res@qoxp.net

Re: teaching gdb about new types?

[Doug Evans]

On Fri, Apr 29, 2011 at 8:02 PM, Richard Silverman <res@qoxp.net> wrote:
> On Fri, 29 Apr 2011, Paul Koning wrote:
>
>> If you're worried about types rather than line numbers, I would think that
>> all you'd need is a symbol table that has the right type definitions in it.
>>  If you know what they are supposed to be, you can supply such a symbol
>> table easily enough.
>>
>>        paul
>
> I tried that -- I created a little file:
>
> ----------------------------------------
> #include <pthreads.h>
>
> pthread_cond_t p;
> pthread_mutex_t m;
> ----------------------------------------
>
> ... and built an object from it.  However, I can't find a way to get gdb to
> use it while debugging an existing program, that is, to add the type
> definitions in that object to its existing set.  The commands "symbol-file"
> and "add-symbol-file" seem likely candidates, but they don't appear to do
> it.

I've used add-symbol-file to accomplish exactly this kind of thing.
Can you elaborate on what didn't work?

Here's a quick example to illustrate.

bash$ cat foo.c
#include <pthread.h>
pthread_cond_t p;
pthread_mutex_t m;
bash$ gcc -g -c foo.c
bash$ gdb hello.x
[...]
(gdb) pty pthread_cond_t
No symbol "pthread_cond_t" in current context.
(gdb) add-symbol-file foo.o 0
add symbol table from file "foo.o" at
	.text_addr = 0x0
(y or n) y
(gdb) pty pthread_cond_t
type = union {
    struct {
	int __lock;
	unsigned int __futex;
	long long unsigned int __total_seq;
	long long unsigned int __wakeup_seq;
	long long unsigned int __woken_seq;
	void *__mutex;
	unsigned int __nwaiters;
	unsigned int __broadcast_seq;
    } __data;
    char __size[48];
    long long int __align;
}
(gdb)