[OE-core] Autoconf problems in OE build of LTP realtime tests

[Gary Robertson]

Dear OE developers,

Linaro Networking Group is building root filesystem images containing  the
LTP test suite, using the current recipe at
openembedded-core/meta/recipes-extended/ltp/ltp_20140422.bb.  This build
uses autoconf to probe mutex feature support for protocol specification,
priority inheritance, and robust mutexes.  The macros used for this can be
found in ltp/testcases/realtime/m4/check.m4 from the LTP git repository.

We are cross-building for the armv7a architecture using the machine
definition found in
meta-linaro/meta-linaro/conf/machine/genericarmv7a.conf.  The development
host platform is an Ubuntu 12.04 x86_64 platform with all software kept
regularly updated from the Ubuntu repositories.

The macros in check.m4 use the AC_TRY_COMPILE function macro to attempt
compilation of POSIX function calls utilizing the features being probed -
such that if the compilation fails the features are deemed to be
unsupported... and if compilation succeeds the features are deemed
supported.

Native compilation of the same code used in the probes, and execution of
the resulting program - shows support for all the probed mutex features on
both the development host as well as the armv7a target platform... that is
when this probe code is built on either the host or target machine and then
executed in that environment... so support is there in both environments.

Despite the presence of this support the AC_TRY_COMPILE macro is indicating
a lack of support for the probed features during the cross-build process.

I am not personally familiar with the detailed function of the autoconf
macros, and I can find no documentation about how OE interacts with those
macros in order to coerce them into configuring for the target machine in a
cross-build environment... so I am hoping the autoconf experts at OE can
shed some light on this and at least provide some clues as to where to look
for the problem and possible resolution.  Any insight you can provide in
this matter would be appreciated.

Gary Robertson

Real-time engineer, Linaro Networking Group
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