[Buildroot] Kernel compilation, tools/endian.h, and HOSTCFLAGS

[Arguin, Christopher P UTAS]

Hello all,

I'm basically leaving this here for the next person who runs into it...

Ever since we started using buildroot we've had a failure during the kernel compilation. This is using a Linux 3.19 kernel targeting an x86_64 board:

    HOSTCC  Documentation/watchdog/src/watchdog-test
    HOSTLD  Documentation/vDSO/vdso_standalone_test_x86
  Documentation/mic/mpssd/mpssd.c:44:26: fatal error: tools/endian.h: No such file or directory
  compilation terminated.

We've been working around this, but I finally decided to tackle it.

tools/endian.h is part of the kernel distribution, and should be included because of this line in Documentation/mic/mpssd/Makefile:
   HOSTCFLAGS += -I$(objtree)/usr/include -I$(srctree)/tools/include

I finally discovered that during compilation buildroot invokes the kernel's make with HOSTCFLAGS="". If I remove that, the build succeeds. Add that, and the build fails with this error. It seems as if setting HOSTCFLAGS prevents the kernel from adding to it, although I don't understand that mechanism yet. Setting HOSTCFLAGS="-Wall" also fails, so the easy way out won't work.

Interestingly, back in 2008 it looks like there was a buildroot patch to stop setting HOSTCFLAGS for Linux 2.6 for the same basic reason (http://lists.busybox.net/pipermail/buildroot/2008-October/023217.html), but I don't think that patch made it into the code base. I don't see many other references in the history or the mailing list. 

The latest version of the Documentation/mic/mpssd/Makefile is wrapped in an "ifndef CROSS_COMPILE" which prevents the issue, although not really fixing it. Changing the makefile to set HOST_EXTRACFLAGS is the fix I went with, but I'm not really sure if that is correct either.

-- 
Christopher Arguin - Software Architect - ISR Systems
UTC AEROSPACE SYSTEMS
7 Technology Park Drive, Westford, MA 01886
Tel: +1 978 490 2278  Mobile: +1 978 495 2542  Fax: +1 978 490 2806
christopher.arguin at utas.utc.com  www.utcaerospacesystems.com

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