vdso_standalone_test_x86.c build failure on Linus' tree

[Josh Boyer]

I'm seeing the following build failure on a 32-bit x86 build in Fedora
based on Linux v3.17-2860-gef0625b70dac:

Documentation/vDSO/vdso_standalone_test_x86.o: In function `to_base10':
vdso_standalone_test_x86.c:(.text+0xcc): undefined reference to `__umoddi3'
vdso_standalone_test_x86.c:(.text+0xea): undefined reference to `__udivdi3'
collect2: error: ld returned 1 exit status
scripts/Makefile.host:100: recipe for target
'Documentation/vDSO/vdso_standalone_test_x86' failed
make[2]: *** [Documentation/vDSO/vdso_standalone_test_x86] Error 1
scripts/Makefile.build:404: recipe for target 'Documentation/vDSO' failed
make[1]: *** [Documentation/vDSO] Error 2
make[1]: *** Waiting for unfinished jobs....
Makefile:922: recipe for target 'vmlinux' failed
make: *** [vmlinux] Error 2

Looking at some of the git logs around this, it seems that
vdso_standalone_test_x86.c is 64-bit specific, so I was curious why it
was even being built on a 32-bit build.  Seems this commit:

commit adb19fb66eeebac07fe37d968725bb8906dadb8e
Author: Peter Foley <pefoley2@xxxxxxxxxxx>
Date:   Thu Sep 25 11:23:09 2014 -0700

    Documentation: add makefiles for more targets

    Add a bunch of previously unbuilt source files to the Documentation build
    machinery.

    Signed-off-by: Peter Foley <pefoley2@xxxxxxxxxxx>
    Signed-off-by: Randy Dunlap <rdunlap@xxxxxxxxxxxxx>
    Signed-off-by: Jiri Kosina <jkosina@xxxxxxx>


blindly added it to the build target.

So is vdso_standalone_test_x86.c really 64-bit specific?  If so,
should that commit be reverted (or a hunk of it anyway), should there
be some mechanism to not build it on 32-bit, or should there be some
additional CFLAGS passed?

josh

Full build log here:
http://koji.fedoraproject.org/koji/getfile?taskID=7802438&name=build.log
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