Re: bfd Mach-O DWARF debugging support

[Iain Sandoe <idsandoe at googlemail dot com>]

Hi Albert,

On 8 Apr 2012, at 11:07, Albert Zeyer wrote:

> It seems that the binary references to `.o` files.

Yes and I believe that we have partial support already in gdb, but  
maybe not elsewhere in binutils (Tristan would know better).

however...

> That is also where
> `dsymutil` is collecting its debug info from.

.. the reason for dsymutil's existence is that when you do "gcc foo.c - 
g -o foo" the intermediate object files are temporary - deleted at the  
end of the compile - so that they cannot be found later for debug etc.

dsymutil intercepts them before they are removed and copies the debug  
info.

if you build every source with "-c" and then link separately this  
problem might not arise (providing you keep the .o files where they  
were built).

if you are doing a single file with a c/l like about - one thing you  
can try is to add "-save-temps" so that the intermediate object is  
saved.

(or dsymutil, of course)

however, AFAIR, Apple's gcc automatically invokes dsymutil when "-g*"  
is on the c/l for Darwin >= 9 (osx 10.5) or if -g-dwarf* is explicitly  
stated.

FSF GCC also does the same (and for a wider range of languages).

> Apples GDB and other Apple tools read this referenced debug info.
> Maybe libbfd should too?

I am sure that there are (possibly large) gaps in our support.
It would be very nice if we had complete support for this -- patches  
welcome!
(darwin has only a small group of volunteers, the more the merrier!)

cheers
Iain

> Regards,
> Albert
>
>
> On Fri, Apr 6, 2012 at 5:13 AM, Albert Zeyer <albzey@googlemail.com>  
> wrote:
> > Hi,
> >
> > I was wondering about the current state of the Mach-O DWARF debugging
> > support. I saw some patches recently which implemented
> > `bfd_mach_o_find_nearest_line` (that is mostly what I am interested
> > in).
> >
> > I have a binary which was build via `gcc -gdwarf-2` (Apples GCC).
> >
> > I tried binutils-2.22.52 but it doesn't really work for me. I tried  
> > to
> > debug it a bit. Some things I can say so far:
> >
> > * `objdump -g` doesn't output anything regarding debugging info.
> > * In bfd/dwarf2.c, in find_line(), _bfd_dwarf2_slurp_debug_info  
> > returns false.
> > * In _bfd_dwarf2_slurp_debug_info(), find_debug_info returns false.
> > * `objdump -h` doesn't list any debug section.
> >
> > When I use `dsymutil` to generate a dSYM from my binary,
> > `bfd_mach_o_find_nearest_line` works.
> >
> > Can somebody give some hints wether it should work or about the  
> > current state?
> >
> > Regards,
> > Albert