GDB <MULTIPLE> breakpoints, source lines

GDB <MULTIPLE> breakpoints, source lines

[Peter Wainwright]

Hi,

I'm the maintainer of DDD.  I have some questions about the intent of
the gdb <MULTIPLE> breakpoints.

"info break" returns several lines for each breakpoint, e.g.

2.1                         y     0x00007f2e2090c4d4 in
VoxelBuffer<char>::buffer_type() const
                                               at ../VoxelBuffer.cc:95
2.2                         y     0x00007f2e2090c540 in
VoxelBuffer<unsigned char>::buffer_type() const at ../VoxelBuffer.cc:95
2.3                         y     0x00007f2e2090c5ac in
VoxelBuffer<short>::buffer_type() const
                                               at ../VoxelBuffer.cc:95

The info page on breakpoints mentions 3 use cases: constructors,
templates, and inlined functions.  In all 3 cases the multiple locations
are generated from a single source line.  However, the "info break"
display shows a source file and line number for each location.

My question is: are there any circumstances in which you can get a
different source file or line for each location?


Thanks,

Peter Wainwright

Re: GDB <MULTIPLE> breakpoints, source lines

[Vladimir Prus]

Peter Wainwright wrote:

> Hi,
> 
> I'm the maintainer of DDD.  I have some questions about the intent of
> the gdb <MULTIPLE> breakpoints.
> 
> "info break" returns several lines for each breakpoint, e.g.
> 
> 2.1                         y     0x00007f2e2090c4d4 in
> VoxelBuffer<char>::buffer_type() const
>                                                at ../VoxelBuffer.cc:95
> 2.2                         y     0x00007f2e2090c540 in
> VoxelBuffer<unsigned char>::buffer_type() const at ../VoxelBuffer.cc:95
> 2.3                         y     0x00007f2e2090c5ac in
> VoxelBuffer<short>::buffer_type() const
>                                                at ../VoxelBuffer.cc:95
> 
> The info page on breakpoints mentions 3 use cases: constructors,
> templates, and inlined functions.  In all 3 cases the multiple locations
> are generated from a single source line.  However, the "info break"
> display shows a source file and line number for each location.
> 
> My question is: are there any circumstances in which you can get a
> different source file or line for each location?

There should be none, except that we had a bug report whereby GDB would
create multiple location breakpoint where each location has the same
line number and file basename, but different directories.

I think you better assume the source location is always the same. You might
consider if you actually want to display individual locations at all --
unless the user is in position to do something with address, that information
is of no use.

- Volodya

Re: GDB <MULTIPLE> breakpoints, source lines

[Peter Wainwright]

On Sat, 2009-02-14 at 13:22 +0300, Vladimir Prus wrote:
> Peter Wainwright wrote:
> 
> > Hi,
> > 
> > I'm the maintainer of DDD.  I have some questions about the intent of
> > the gdb <MULTIPLE> breakpoints.
> > 
> > "info break" returns several lines for each breakpoint, e.g.
> > 
> > 2.1                         y     0x00007f2e2090c4d4 in
> > VoxelBuffer<char>::buffer_type() const
> >                                                at ../VoxelBuffer.cc:95
> > 2.2                         y     0x00007f2e2090c540 in
> > VoxelBuffer<unsigned char>::buffer_type() const at ../VoxelBuffer.cc:95
> > 2.3                         y     0x00007f2e2090c5ac in
> > VoxelBuffer<short>::buffer_type() const
> >                                                at ../VoxelBuffer.cc:95
> > 
> > The info page on breakpoints mentions 3 use cases: constructors,
> > templates, and inlined functions.  In all 3 cases the multiple locations
> > are generated from a single source line.  However, the "info break"
> > display shows a source file and line number for each location.
> > 
> > My question is: are there any circumstances in which you can get a
> > different source file or line for each location?
> 
> There should be none, except that we had a bug report whereby GDB would
> create multiple location breakpoint where each location has the same
> line number and file basename, but different directories.
> 
> I think you better assume the source location is always the same. You might
> consider if you actually want to display individual locations at all --
> unless the user is in position to do something with address, that information
> is of no use.
> 
> - Volodya

Thanks, that makes things a bit simpler.  We do need to parse and record
the information for each location, because DDD displays a "glyph" to
indicate the breakpoint location in the machine code display window.
But at least it seems we can make do with only one glyph for the source
code window.

(I suppose I can imagine cases in which the user might want to
enable/disable the individual locations separately, but that seems to be
a rather obscure case).

Peter

> 
> 

Re: GDB <MULTIPLE> breakpoints, source lines

[Daniel Jacobowitz]

On Sat, Feb 14, 2009 at 01:22:38PM +0300, Vladimir Prus wrote:
> > My question is: are there any circumstances in which you can get a
> > different source file or line for each location?
> 
> There should be none, except that we had a bug report whereby GDB would
> create multiple location breakpoint where each location has the same
> line number and file basename, but different directories.

Do you think we'll ever use these for e.g. breakpoints on overloaded
functions?

-- 
Daniel Jacobowitz
CodeSourcery

Re: GDB <MULTIPLE> breakpoints, source lines

[Pierre Muller]

Daniel Jacobowitz <drow@false.org> a écrit :

> On Sat, Feb 14, 2009 at 01:22:38PM +0300, Vladimir Prus wrote:
>> > My question is: are there any circumstances in which you can get a
>> > different source file or line for each location?
>>
>> There should be none, except that we had a bug report whereby GDB would
>> create multiple location breakpoint where each location has the same
>> line number and file basename, but different directories.
>
> Do you think we'll ever use these for e.g. breakpoints on overloaded
> functions?
I would really like to use them for global overloaded
functions in pascal!
But I didn't yet have time to look into this seriously :(

Pierre Muller
GDB pascal language support maintainer

Re: GDB <MULTIPLE> breakpoints, source lines

[Vladimir Prus]

Daniel Jacobowitz wrote:

> On Sat, Feb 14, 2009 at 01:22:38PM +0300, Vladimir Prus wrote:
>> > My question is: are there any circumstances in which you can get a
>> > different source file or line for each location?
>> 
>> There should be none, except that we had a bug report whereby GDB would
>> create multiple location breakpoint where each location has the same
>> line number and file basename, but different directories.
> 
> Do you think we'll ever use these for e.g. breakpoints on overloaded
> functions?

I don't know. I never had a particular design to set breakpoint on
every overloaded function. In case of constructors/templates/inlined
function you are very likely to have no idea of the address of the instance
you care about. Overloaded functions are basically separate functions that
happen to share a part of the name, so user is much more likely to know
which function he wants to debug.

- Volodya