Core dump information when code is optimized

Core dump information when code is optimized

[Lennyk]

Hi,

When I compile only with -O1 flag - my core dump information does not 
show line number or offset (when a segmentation fault has occurred).
Only when I add the -g flag does the core dump contain line number 
information - but the executable's size grows significantly!

Is there a way to get this information with core dump - but maintain the 
optimized sized executable?

Thanks!

Re: Core dump information when code is optimized

[Joel Brobecker]

> Is there a way to get this information with core dump - but maintain the  
> optimized sized executable?

The -O flags are completely independent from debugging information.
In order to do symbolic debugging, GDB needs debugging information,
which is why using the -g switch helps. There might be a way to produce
only line number information if that's what you need, but I don't know
offhand. Check the compiler/linker docs. Regardless, the extra info
will cause the size of your executable to grow, as you have discovered.

-- 
Joel

Re: Core dump information when code is optimized

[Michael Snyder]

Lennyk wrote:
> Hi,
> 
> When I compile only with -O1 flag - my core dump information does not 
> show line number or offset (when a segmentation fault has occurred).
> Only when I add the -g flag does the core dump contain line number 
> information - but the executable's size grows significantly!
> 
> Is there a way to get this information with core dump - but maintain the 
> optimized sized executable?

It is -g that matters, not -O.

-g generates line info.  This info goes into your executable, but it
does not increase your memory footprint -- only the size of the file.
In other words this line info is not copied into memory at runtime.

Which means that it also does not appear in the corefile, so your
corefile should not get significantly bigger.

Re: Core dump information when code is optimized

[Lennyk]

Thanks!

In the meantime I found how to separate the debug and symbol information 
from the binary executable - using objcopy:

1) Copy only the debug & symbol information from the binary to another file:
    objcopy --only-keep-debug <your_binary_filename> <output_file>
2) Strip the original binary file from its debug & symbol information:
    objcopy --strip-debug <your_binary_filename>
3) Link between the stripped binary and the debug & symbol information 
file created in step (1):
    objcopy --add-gnu-debuglink=<file_with_debug_info> <stripped_binary>

That's it! now the binary executable is optimized in size - and the core 
dump generates debug & symbol information from the created output file 
(in step (1)).

Enjoy,
Lenny.

Michael Snyder wrote:
> Lennyk wrote:
>> Hi,
>>
>> When I compile only with -O1 flag - my core dump information does not 
>> show line number or offset (when a segmentation fault has occurred).
>> Only when I add the -g flag does the core dump contain line number 
>> information - but the executable's size grows significantly!
>>
>> Is there a way to get this information with core dump - but maintain 
>> the optimized sized executable?
>
> It is -g that matters, not -O.
>
> -g generates line info.  This info goes into your executable, but it
> does not increase your memory footprint -- only the size of the file.
> In other words this line info is not copied into memory at runtime.
>
> Which means that it also does not appear in the corefile, so your
> corefile should not get significantly bigger.
>
>