[lttng-dev] Debian specific userspace RCU configure override (ARMv7 Beagle Bone Black)

[Thibault, Daniel]

   Recall that building lttng-ust on a Beagle Bone Black (Angstrom GNU/Linux v2012.12 (Core edition) on kernel 3.8.13), the make fails at the CCLD of libringbuffer_la-ring_buffer_frontend.lo with an unexpected (and so far unexplained) group of "Error: selected processor does not support ARM mode 'dmb'" (25 times).

   lttng-modules installs with no trouble once a few minor adjustments are made to the dependencies (turns out the linux-headers package is called kernel-dev on the BBB).  The install is rather disappointing because the factory-supplied kernel has CONFIG_TRACEPOINTS turned off.  All the other required/desirable kernel switches are turned on.

   userspace-rcu is also successfully installed.

   At this point I can only try lttng-tools in its "kernel tracing only" mode.  Once again bootstrap and configure go smoothly.  It reports:

Target architecture: armv7l
Lttng-UST support: Disabled
Python binding: Disabled
All binaries will be built

   I run into trouble quickly, however.  The CC of common/hashtable/rculfhash.lo runs into "Error: selected processor does not support ARM mode 'dmb'" (8 times).  The make aborts at this point.

   How can this be fixed?  I'm open to "forcing" the Makefile at this point, as a stop-gap.

Daniel U. Thibault
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