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

Mathieu Desnoyers mathieu.desnoyers at efficios.com
Mon Jan 7 16:18:55 EST 2013 

* Hui Zhu (teawater at gmail.com) wrote:
> On Thu, Dec 20, 2012 at 10:16 PM, Mathieu Desnoyers
> <mathieu.desnoyers at efficios.com> wrote:
> > * 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
> >
> >
> 
> This is what I got when I add it to lookup_enum:
> make[2]: Entering directory `/home/teawater/gdb/ctf/bb/converter'
>   CCLD   babeltrace
> ../formats/ctf/.libs/libbabeltrace-ctf.so: undefined reference to `lookup_enum'
> collect2: ld returned 1 exit status
> make[2]: *** [babeltrace] Error 1
> make[2]: Leaving directory `/home/teawater/gdb/ctf/bb/converter'
> make[1]: *** [all-recursive] Error 1
> make[1]: Leaving directory `/home/teawater/gdb/ctf/bb'
> make: *** [all] Error 2

OK. So those symbols are used by other .so within our own code-base, but
not exported. We'll need to namespace them.

Julien will prepare a patch.

Thanks!

Mathieu

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

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