On Monday, October 10, 2011, Francesco Zappa Nardelli wrote:
> Dear all
> 
> if I understand correctly, the function
> 
>   VG_(get_datasym_and_offset)(..addr..&name...)
> 
> looks at the debug informations to return the name and the offset of
> the (global) variable stored at addr.
> 
> This works fine on linux, but when I compile my valgrind application
> on macosx 10.6 (valgrind comes from a recent e.g. < 1 month svn) the
> above does not seem to work anymore: name is always null
> (independently of the --dsymutil=yes option -- and yes, I checked that
> my binary has debug informations with gdb).
> 
> I am confused.  I though that in both cases the debug format used was
> DWARF, and I can't understand why it does not work on mac.  Do you
> have any intuition / suggestion?

The problem is that reading of data symbol addresses was never made
to work (properly? at all? I can't remember) for Mach-O.  Hence 
VG_(get_datasym_and_offset) will never return any useful info.
There is a big comment about this about 100 lines after the start of
ML_(read_macho_debug_info) in coregrind/m_debuginfo/readmacho.c.

If you want to become an expert on Mach-O and figure out how to fix
this (or you are one already), that would be great.  The normal
problem is to come up with correct values for di->data_avma and
di->data_svma (and therefore for di->data_bias).  For explanation
of the avma/svma/bias values, see comment at the top of debuginfo.c.

I'm afraid there's no easy (1/2 hour) fix for this, unless maybe
you are a Mach-O guru.

J

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