RE: userspace probe breakage with gcc 4.8 due to inablility to locate semaphore variable

[Mayuresh Kulkarni <mkulkarni at kcg dot com>]

>> [...]
>> I had a userspace probe (details below) and this worked fine with stap
>> 1.6 and gcc 4.6.  After upgrading to gcc 4.8, this has stopped
>> working. (I believe this to be the only change, everything else on the
>> box is the same) [...] But, stap -g -vvvvv with the following probe
>> fails with failure to find foo_bar_semaphore

> If you use relatively recent <sys/sdt.h> with semaphores (i.e., your C program #defines _SDT_HAS_SEMAPHORES), you also need to run "/usr/bin/dtrace -G ..." to create an object file
> that contains that semaphore.  That .o needs to be linked into your executable.

> -FChe

Thanks for the reply. I will keep it in mind when we update to 2.7.

Meanwhile, in my setup, I have found out that the runtime box has native gcc 4.4 And the regression is because the build uses gcc 4.8 (which uses dwarf4 by default ) while till gcc 4.6, dwarf2 was the default.  So the combination of [ build with 4.6, run on box with 4.4 ] used to work but does not work if built with 4.8. If I explicitly build the binary with -g -gdwarf-2 , then things are fine.

Unfortunately, I cannot muck with the build settings. Might there be  a way of telling systemtap at runtime that the binary being probed uses dwarf4?

Thanks,
Mayuresh
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