Re: Re. How to setup a breakpoint on constructor

[Michael Stout <stout at evolution dot com>]

I didn't modify the linetable_entry structure, but just changed the 
signature of find_line_common from

/* Given a line table and a line number, return the index into the line
  table for the pc of the nearest line whose number is >= the specified 
one.
  Return -1 if none is found.  The value is >= 0 if it is an index.

  Set *EXACT_MATCH nonzero if the value returned is an exact match.  */

static int find_line_common (struct linetable *l, int lineno,
         int *exact_match)

to
static int
find_line_common (struct linetable *l, int lineno,
         int *exact_match,int **returned_entries);

The current signature is just plain wrong or at best misleading  since 
there can be multiple linetable
entries that share a common linenumber.  The same is true for 
find_line_pc.  The first change I would
recommend is renaming find_line_common to find_first_line_common and 
implementing it using
a correct version of find_line_common. 

Mike



David Lecomber wrote:

> Hi Michael,
>
> I tried the same -- and am happily using a GDB with working constructors
> - and (bonus) working breakpoints for compilers that generate different
> versions of the same function in the same executable - eg. Intel's
> compiler which has specific optimizations depending on what's under the
> hood.
>
> http://sources.redhat.com/ml/gdb-patches/2004-10/msg00241.html
>
> The general consensus back then to my solution was "ok, it works, but it
> ain't how we'd like to fix it".  Looks like we've both come up with
> broadly the same.  
>
> We're still waiting for the "Right Thing" [TM] to appear... sigh.. not
> sure who's thinking about this one at the moment.
>
> d.
>
>
>
> On Wed, 2005-03-09 at 14:34 -0800, Michael Stout wrote:
>  
>
> > I've hacked my gdb sources to get breakpoints to work on constructors.  
> > Well it seems to work.
> > see
> >
> > http://sources.redhat.com/ml/gdb/2004-07/msg00162.html
> >
> > and
> >
> > http://sources.redhat.com/ml/gdb/2004-07/msg00163.html
> >
> > which explains  the issue with multiple copies of the constructor
> >
> > Here is my analysis from someone who is completely unfamiliar with gdb:
> > There are two essential problems
> >
> > 1) gdb assumes there is a one-to-one mapping between a 
> > file-linenumber-symbol-table and file:linenumber entered by
> > the user. 
> >
> > a) find_line_common in symtab.c currently only returns one index into 
> > the linnumber-symbol-table where it should
> > be able to return multiple line numbers.
> > b) the same is true for find_line_symtab
> > c) decode_all_digits in linespec.c calls fine_line_symtab needs to 
> > handle the multiple values returned by find_line_symtab
> >
> > 2) gdb assumes a one-to-one mapping between a breakpoint number and a 
> > breakpoint address.  I hacked my fix by
> > using the breakpoint::releated_breakpoint but I don't think this is not 
> > a good fix.
> >
> >
> > To fix this requires a load of changes.  I'm willing to start submitting 
> > patches to get this to work, but I need to have someone
> > look over my shoulder.  The first step would be to modify modify 
> > find_line_common to return multiple indexes.
> >
> > Here is a simple sample program that illustrates the problem
> >
> > class gobo
> > {
> > public:
> >    gobo();
> >    int i;
> > };
> >
> > gobo ::gobo()
> > {
> >    i = 4;
> > }
> >
> > int main(int argc,int **argv)
> > {
> >    gobo flagger;
> > }
> >
> > g++ -g -o foo foo.cpp (g++ 3.3.5 debian)
> > gdb foo
> > break foo.cpp:10
> > run
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >