Re: [DynInst_API:] BPatch_image->findFunction() behavior with weak symbols

[German Llort Sanchez <gllort@xxxxxx>]

Hi Tim!

I haven't tried Ben's suggestions yet, but I confirm that I'm using the 
latest release 10.1, and also using the libiberty demangler. Should I 
try the GNU demangler instead?
Thanks!
-- G.

El 2019-07-18 00:09, Tim Haines escribiÃ:
> Hi, German.
>
> Are you using Dyninst-10.1? If not, I would strongly recommend
> upgrading as there was an enhancement to the build system where the
> USE_GNU_DEMANGLER flag was fixed to work correctly. Previously, there
> was an ambiguity about which demangler was compiled into Dyninst:
> either GNU demangler or libiberty.
>
> Thanks.
>
>  - Tim
>
> On Wed, Jul 17, 2019 at 3:45 PM German Llort Sanchez
> <german.llort@xxxxxx> wrote:
>
> > Hi,
> >
> > Just adding a little extra information, but I'm not sure if
> > clarifies
> > anything or opens a second issue. Checking the API of
> > BPatch_function I
> > noticed the method getNames (in plural), with this comment saying
> > that
> > it returns all names of the symbol including those weak. So I
> > figured
> > out that maybe the match returned by findFunction corresponds to
> > the
> > first name in the list, but maybe in the whole list of names all
> > the
> > other decorations appear, so I could check if the one I am
> > expecting for
> > is present in the list.
> >
> > I tried that, dumping the names like this:
> >
> > BPatch_Vector<const char *> names;
> > found_funcs[0]->getNames(names);
> >
> > cerr << "getRoutine: Searching for " << routine << " found " <<
> > found_funcs.size() << " with " << names.size() << " names: ";
> > for (int i=0; i<names.size(); i++)
> > {
> > cerr << names[i] << " ";
> > }
> >
> > And the output looks like this:
> >
> > getRoutine: Searching for MPI_Init found 1 with 4 names: `a `a `a
> > `a
> > getRoutine: Searching for mpi_init found 1 with 16 names: `a `a `a
> > `a `a
> > `a `a `a `a `a `a `a `a `a `a `a
> > getRoutine: Searching for mpi_init_ found 1 with 16 names: `a `a `a
> > `a
> > `a `a `a `a `a `a `a `a `a `a `a `a
> > getRoutine: Searching for mpi_init__ found 1 with 16 names: `a `a
> > `a `a
> > `a `a `a `a `a `a `a `a `a `a `a `a
> > getRoutine: Searching for MPI_INIT found 1 with 16 names: `a `a `a
> > `a `a
> > `a `a `a `a `a `a `a `a `a `aStarting program execution
> >
> > For each symbol that I look for, there's only 1 BPatch_function
> > match,
> > and for each object, there's several names found, but the names
> > look
> > like that (`a).
> >
> > Also note that the getNames method that I'm using from
> > BPatch_function
> > class is this one:
> >
> > bool getNames(BPatch_Vector<const char *> &names);
> >
> > There's another one with strings:
> >
> > bool getNames(std::vector<std::string> &names);
> >
> > But if I try to use the second one, I'm getting this linking error:
> >
> > launcher.cpp:(.text+0x2aa): undefined reference to
> > `BPatch_function::getNames(std::vector<std::string,
> > std::allocator<std::string> >&)'
> >
> > I have the same problem with several other methods that use the
> > string
> > interface.
> >
> > Thanks for your help!
> > -- G.
> >
> > El 2019-07-15 17:22, GermÃn Llort escribiÃ:
> > > Hi,
> > >
> > > We're using BPatch_image->findFunction() to look for MPI symbols
> > in a
> > > binary. When the binary is Fortran code, different compilers may
> > add
> > > different decorations to the MPI functions. For example, for
> > > "MPI_Init", different compilers may end up naming this function
> > like:
> > > - mpi_init (all lowercase)
> > > - mpi_init_ (1 underscore at the end)
> > > - mpi_init__ (2 underscores at the end)
> > > - MPI_INIT (all uppercase)
> > >
> > > And sometimes, all these variants are present.
> > >
> > > When we use findFunction to look for these different names, ,
> > there's
> > > always a match, but in all cases it matches with "mpi_init__" (2
> > > underscores). For example:
> > >
> > > found_funcs.clear();
> > > if (appImage->findFunction ("mpi_init", found_funcs) != NULL)
> > > {
> > > fprintf(stderr, "match %s\n",
> > found_funcs[0]->getName().c_str());
> > > }
> > >
> > > This results in finding "mpi_init__".
> > >
> > > We use this to discover dynamically the name mangling scheme that
> > was
> > > applied by the compiler, and since all these searches end up
> > matching
> > > with the symbol with 2 underscores, it's misleading for us.
> > >
> > > The particularity with these symbols is that they're defined as
> > weak.
> > > Is this the expected behavior of the search when the symbols are
> > weak?
> > > Or maybe we're doing something wrong?
> > >
> > > Thanks!
> > > -- G.
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