Re. How to setup a breakpoint on constructor

[Michael Stout]

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
>>
>>
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