Enable debug-tools for lldb

Question

I'm having trouble using lldb to debug on MacOsX with clang++. I'm using a makefile to compile a projet in C++, and I don't know if the debug option has to be enabled in the compilation command.

Here is an extract of my makefile

FLAGS =-g -Wall -O0
[...]
clang++ $(FLAGS) $^ -o $@

When I try running lldb with this configuration of my makefile, it return an error :

Breakpoint 1: no locations (pending).
WARNING:  Unable to resolve breakpoint to any actual locations.

I suppose I have to enable the debug tools on my makefile, but I haven't found how to do this on internet. I tried with the -g and the -ggdb options, without success.

However, when I try to set a breakpoint differently, it works (but setting a breakpoint on a specific fonction doesn't interest me...) :

breakpoint set -n fonction
Breakpoint 1: [...]

I didn't manage to find answers on internet, so I would be interested in having some help ! Thank you !

Answer 1

It looks like somewhere along the way the debug information is getting lost. One possibility is that your CFLAGS are getting reset before you get to building the .o files you care about, so the .o files don't have debug info. One easy way to check that is run

$ otool -l my_file.o | grep debug_info
  sectname __debug_info

If you don't see that "sectname" output, then your .o file has no debug information.

Run your makefile and look at the build line for my_file.c and make sure there really is a -g option being passed. -ggdb doesn't actually do anything special for clang so -g is all you need...

If the .o file has debug information, then it must be getting lost when you build the final binary.

Mac OS X is a little funny in how it handles debug information. It doesn't write the debug information into the final image, but rather writes a "debug-map" into the executable, and leaves the debug info in the .o file. That debug-map gets stripped when you strip a binary, so if you strip your executable that will remove the link to the debug information. And of course, if you delete the .o files after building, that will also remove the debug information.

Answer 2

I finally installed gdb, and I managed to debug normally. But after reading your post, you make me realize I have maybe delete the .o when compiling. I didn't thought about it, as lldb was able to set break point in some cases (at a specific fonction) but not in other cases (at a specific line).

As I am using a makefile, I forgot to delete the auto delete of all the .o after compiling, and I think that may cause the issue. Now, if I let the .o, that works perfectly. But this is surprising me a lot, as my makefile was the same as my colleague and he was able to debug with gdb without any kind of problem.

Thanks a lot for all your informations.