RE: [PATCH] symtab.c -- Fix off by one allocation bug

["taylor, david" <david dot taylor at emc dot com>]

> From: Joel Brobecker [mailto:brobecker@adacore.com]
> Sent: Monday, June 13, 2016 2:23 PM
> To: taylor, david
> Cc: gdb-patches@sourceware.org
> Subject: Re: [PATCH] symtab.c -- Fix off by one allocation bug
> 
> > This fixes a problem found by valgrind.  Applying this patch caused no
> > regressions on GNU/Linux x86-64 and satisfied valgrind.
> >
> > 	* gdb/symtab.c (symbol_set_names): Fix off by one error in
> > 	allocation.
> 
> Thanks for the patch.
> 
> Can you give a little more detail as to why we need that extra byte, and
> provide that information in the revision log. This kind of information is always
> very precious when doing archelogy.
> 
> Thanks!

Sadly, probably not.

This bug was found awhile ago and at the time we were using STAB
debugging format.  We have since switched to DWARF.  I was having
problems finding the source of a problem we were having and threw
valgrind at it.  I ultimately found the other problem via other methods,
but valgrind found this problem.  I remember staring at the code long
enough to convince myself that valgrind was correct.  And after increasing
it, valgrind was happy.

> > ---
> >  gdb/ChangeLog | 4 ++++
> >  gdb/symtab.c  | 2 +-
> >  2 files changed, 5 insertions(+), 1 deletion(-)
> >
> > diff --git a/gdb/ChangeLog b/gdb/ChangeLog index 9c09269..aaeeb6e
> > 100644
> > --- a/gdb/ChangeLog
> > +++ b/gdb/ChangeLog
> > @@ -1,3 +1,7 @@
> > +2016-06-09  David Taylor  <dtaylor@emc.com>
> > +
> > +	* symtab.c (symbol_set_names): Fix off by one error in allocation.
> > +
> >  2016-06-07  Simon Marchi  <simon.marchi@ericsson.com>
> >
> >  	* mi/mi-interp.c (mi_record_changed): Add missing braces.
> > diff --git a/gdb/symtab.c b/gdb/symtab.c index f7a207a..12e1cf5 100644
> > --- a/gdb/symtab.c
> > +++ b/gdb/symtab.c
> > @@ -1010,7 +1010,7 @@ symbol_set_names (struct general_symbol_info
> *gsymbol,
> >  	    = ((struct demangled_name_entry *)
> >  	       obstack_alloc (&per_bfd->storage_obstack,
> >  			      offsetof (struct demangled_name_entry,
> demangled)
> > -			      + lookup_len + demangled_len + 2));
> > +			      + lookup_len + demangled_len + 3));
> >  	  mangled_ptr = &((*slot)->demangled[demangled_len + 1]);
> >  	  strcpy (mangled_ptr, lookup_name);
> >  	  (*slot)->mangled = mangled_ptr;
> > --
> > 1.9.1
> 
> --
> Joel