linux build failure seen building 32bit user space support on ppc64el

[Matthias Klose]

linux build failure seen building 32bit user space support on ppc64el, using the toolchain from ubuntu-toolchain-r/ppa on trusty. complete build log at
https://launchpad.net/ubuntu/+archive/test-rebuild-20150317-security/+build/7070318

  VDSO32A arch/powerpc/kernel/vdso32/gettimeofday.o
/build/buildd/linux-3.13.0/arch/powerpc/kernel/vdso32/gettimeofday.S: Assembler messages:
/build/buildd/linux-3.13.0/arch/powerpc/kernel/vdso32/gettimeofday.S:42: Error: syntax error; found `@', expected `,'
/build/buildd/linux-3.13.0/arch/powerpc/kernel/vdso32/gettimeofday.S:42: Error: junk at end of line: `@local'
/build/buildd/linux-3.13.0/arch/powerpc/kernel/vdso32/gettimeofday.S:48: Error: syntax error; found `@', expected `,'
/build/buildd/linux-3.13.0/arch/powerpc/kernel/vdso32/gettimeofday.S:48: Error: junk at end of line: `@local'
/build/buildd/linux-3.13.0/arch/powerpc/kernel/vdso32/gettimeofday.S:83: Error: syntax error; found `@', expected `,'
/build/buildd/linux-3.13.0/arch/powerpc/kernel/vdso32/gettimeofday.S:83: Error: junk at end of line: `@local'
/build/buildd/linux-3.13.0/arch/powerpc/kernel/vdso32/gettimeofday.S:87: Error: syntax error; found `@', expected `,'
/build/buildd/linux-3.13.0/arch/powerpc/kernel/vdso32/gettimeofday.S:87: Error: junk at end of line: `@local'
/build/buildd/linux-3.13.0/arch/powerpc/kernel/vdso32/gettimeofday.S:195: Error: syntax error; found `@', expected `,'
/build/buildd/linux-3.13.0/arch/powerpc/kernel/vdso32/gettimeofday.S:195: Error: junk at end of line: `@local'
make[4]: *** [arch/powerpc/kernel/vdso32/gettimeofday.o] Error 1
make[3]: *** [arch/powerpc/kernel/vdso32] Error 2
make[3]: *** Waiting for unfinished jobs....

yeah, thanks for non-verbose build logs !!!

doing it the hard way, you see that this file was (and wants to be) compiled with -m32, and I assume with gcc finally dropping the multilib configurations for ppc64el, the kernel configury decides that it can do without -m32.

but why in the first place is this needed? there is no powerpcle user space.

I assume this issue is latent in all releases.

[Matthias Klose (doko)]

arch/powerpc/Makefile has:

HAS_BIARCH := $(call cc-option-yn, -m32)

but in vivid:

$ gcc-4.8 -m32 -c foo.c
foo.c:1:0: error: -m32 not supported in this configuration
$ gcc-4.9 -m32 -c foo.c
foo.c:1:0: error: -m32 not supported in this configuration
$ gcc-5 -m32 -c foo.c
foo.c:1:0: error: -m32 not supported in this configuration

and the vdso32 stuff seems to be built unconditionally.

[Alan Modra (amodra)]

It does seem a bit pointless to be building a 32-bit vdso on powerpc64le where you know there is no 32-bit user runtime.

Now if some other part of the kernel needs to be compiled 32-bit, then it would appear that gcc will need to be configured with
--enable-targets=powerpcle-linux --disable-multilib.

[Michael Ellerman (michael-ellerman)]

We'll aim to fix this in the kernel. It's a long-held assumption in the 64-bit code that 32-bit also exists, so teasing it all apart will take some work, all mechanical but time consuming. In the short term it might be best to just re-enable 32-bit in the toolchain.

[Matthias Klose (doko)]

configured the compiler as suggested for my trusty tests, so that I don't see this build failure anymore in trusty.