[lttng-dev] Request change name of function lookup_enum in libbabeltrace to make GDB use this lib

Mathieu Desnoyers mathieu.desnoyers at efficios.com
Thu Dec 20 09:16:43 EST 2012 

* Hui Zhu (teawater at gmail.com) wrote:
> On Tue, Dec 11, 2012 at 11:18 PM, Hui Zhu <teawater at gmail.com> wrote:
> > On Mon, Dec 10, 2012 at 10:05 PM, Mathieu Desnoyers
> > <mathieu.desnoyers at efficios.com> wrote:
> >> * Hui Zhu (teawater at gmail.com) wrote:
> >>> On Thu, Dec 6, 2012 at 11:57 PM, Pedro Alves <palves at redhat.com> wrote:
> >>> > On 12/05/2012 12:08 PM, Mathieu Desnoyers wrote:
> >>> >> * Hui Zhu (teawater at gmail.com) wrote:
> >>> >>> Hi,
> >>> >>>
> >>> >>> I am working on add CTF support to GDB.  You can see my patch review threads in:
> >>> >>> http://sourceware.org/ml/gdb-patches/2012-11/msg00552.html
> >>> >>> http://sourceware.org/ml/gdb-patches/2012-11/msg00554.html
> >>> >>> http://sourceware.org/ml/gdb-patches/2012-11/msg00553.html
> >>> >>> http://sourceware.org/ml/gdb-patches/2012-11/msg00555.html
> >>> >>> http://sourceware.org/ml/gdb-patches/2012-11/msg00556.html
> >>> >>>
> >>> >>> To make GDB support CTF read, I use libbabeltrace with GDB.  You can
> >>> >>> see the patch in
> >>> >>> http://sourceware.org/ml/gdb-patches/2012-11/msg00555.html.
> >>> >>> I have a issue is  libbabeltrace have a function called lookup_enum
> >>> >>> that is same with a GDB function.
> >>> >>> I change the function name of GDB to handle this issue in my patch.
> >>> >>>
> >>> >>> But Tom said let libbabeltrace to change function name is better.
> >>> >>> So I send this mail to ask do you mind change the function name of
> >>> >>> lookup_enum?   If you can change the function name that will be really
> >>> >>> helpful for us.  Thanks a lot.
> >>> >>> And I post a patch about change the function name in libbabeltrace.
> >>> >>
> >>> >> I'm CCing Julien Desfossez on this one. From what I see,
> >>> >> include/babeltrace/types.h is not included into the system, so it should
> >>> >> not be considered to be a public header of libbabeltrace.
> >>> >
> >>> > I've just built and installed babeltrace 1.0.0 (where's the mainline repository,
> >>> > BTW?), and indeed, I'm not seeing the types.h file anywhere in the
> >>> > installed tree:
> >>> >
> >>> > $ ~/src/babeltrace/install/include> find
> >>> > .
> >>> > ./babeltrace
> >>> > ./babeltrace/trace-handle.h
> >>> > ./babeltrace/list.h
> >>> > ./babeltrace/babeltrace.h
> >>> > ./babeltrace/context.h
> >>> > ./babeltrace/iterator.h
> >>> > ./babeltrace/ctf
> >>> > ./babeltrace/ctf/callbacks.h
> >>> > ./babeltrace/ctf/events.h
> >>> > ./babeltrace/ctf/iterator.h
> >>> > ./babeltrace/format.h
> >>> > ./babeltrace/clock-types.h
> >>> >
> >>> > The GDB patch is including types.h explicitly:
> >>> >
> >>> > +#ifdef HAVE_LIBBABELTRACE
> >>> > +#include <babeltrace/babeltrace.h>
> >>> > +#include <babeltrace/types.h>
> >>> > +#include <babeltrace/ctf/events.h>
> >>> > +#include <babeltrace/ctf/iterator.h>
> >>> >
> >>> > So indeed, Hui, you'll need to make sure your patch works against an
> >>> > installed babeltrace, making sure it does not pick up headers
> >>> > from babeltrace's source directory.  If there's really no reason to
> >>> > include that types.h header (since it seems you don't really need any
> >>> > function declared in that file), maybe there's actually nothing for
> >>> > babeltrace to do.
> >>>
> >>> Oops, sorry for I miss something.
> >>> I use include babeltrace/types.h because I use function
> >>> get_int_signedness that defined inside it.
> >>
> >> Can you use:
> >>
> >> include/babeltrace/ctf/events.h: bt_ctf_get_int_signedness() instead ?
> >>
> >> This one is within an exported header,
> >>
> >> Thanks,
> >>
> >> Mathieu
> >
> > Great! My part is OK now.  Thanks for your help.
> >
> > Best,
> > Hui
> >
> 
> Hi Mathieu.,
> 
> I am so sorry that I still have issue with the function name of lookup_enum.
> What I met is a crash when try to use libbabeltrace in GDB:
> #0  0x00000000005d0cfc in block_static_block (block=0x7ffff6e5ee3e) at
> ../../gdb/gdb/block.c:343
> #1  0x00000000005d42ae in lookup_symbol_aux_local (name=0xf70c70
> "\240!\224\001", block=0x7ffff6e5ee3e,
>     domain=STRUCT_DOMAIN, language=language_c) at ../../gdb/gdb/symtab.c:1429
> #2  0x00000000005d40b5 in lookup_symbol_aux (name=0xf70c70
> "\240!\224\001", block=0x7ffff6e5ee3e, domain=STRUCT_DOMAIN,
>     language=language_c, is_a_field_of_this=0x0) at ../../gdb/gdb/symtab.c:1345
> #3  0x00000000005d3cae in lookup_symbol_in_language (name=0xf70c70
> "\240!\224\001", block=0x7ffff6e5ee3e,
>     domain=STRUCT_DOMAIN, lang=language_c, is_a_field_of_this=0x0) at
> ../../gdb/gdb/symtab.c:1231
> #4  0x00000000005d3cff in lookup_symbol (name=0xf70c70
> "\240!\224\001", block=0x7ffff6e5ee3e, domain=STRUCT_DOMAIN,
>     is_a_field_of_this=0x0) at ../../gdb/gdb/symtab.c:1246
> #5  0x000000000062f372 in lookup_enum (name=0xf70c70 "\240!\224\001",
> block=0x7ffff6e5ee3e)
>     at ../../gdb/gdb/gdbtypes.c:1287
> #6  0x00007ffff6e479b5 in ctf_read_event (ppos=0xf6cca8,
> stream=0xf6cc10) at ../../../babeltrace/formats/ctf/ctf.c:434
> #7  0x00007ffff7071204 in stream_read_event (sin=<optimized out>) at
> ../../babeltrace/lib/iterator.c:65
> #8  0x00007ffff7071eb3 in bt_iter_init (iter=0x13ec820, ctx=0xf4b8b0,
> begin_pos=0x7fffffffdad0, end_pos=<optimized out>)
>     at ../../babeltrace/lib/iterator.c:703
> #9  0x00007ffff6e4a6ac in bt_ctf_iter_create (ctx=0xf4b8b0,
> begin_pos=0x7fffffffdad0, end_pos=0x0)
>     at ../../../babeltrace/formats/ctf/iterator.c:53
> #10 0x000000000050d4b1 in bt_ctf_open (dirname=0xd98c1b
> "/home/teawater/gdb/ctf/kernel/") at ../../gdb/gdb/ctf.c:1289
> 
> You can see that when function ctf_read_event of libbabeltrace try to
> call function lookup_enum.  It call the function of GDB.  Then it got
> crash.
> 
> So could you help me with it?

Hrm, since lookup_enum() and other similar functions are internal to
babeltrace, we should probably define them as:

__attribute__((visibility("hidden")))

so they don't override other libraries' symbols.

Can you try doing this modification to babeltrace and see if it helps ?
If it does, then we'll consider doing that across our code-base.

Thanks,

Mathieu


> 
> Thanks,
> Hui
> 
> >>
> >>>
> >>> Thanks,
> >>> Hui
> >>>
> >>>
> >>> >
> >>> >> Julien, is there an publically exposed babeltrace API that performs
> >>> >> something similar to the internal lookup_enum() ?
> >>> >>
> >>> >> Hui, are you using other functions from include/babeltrace/types.h ?
> >>> >
> >>> > --
> >>> > Pedro Alves
> >>> >
> >>
> >> --
> >> Mathieu Desnoyers
> >> Operating System Efficiency R&D Consultant
> >> EfficiOS Inc.
> >> http://www.efficios.com

-- 
Mathieu Desnoyers
Operating System Efficiency R&D Consultant
EfficiOS Inc.
http://www.efficios.com

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