[PATCH 2/3] powerpc/vdso: Don't pass 64-bit ABI cflags to 32-bit VDSO

[Michael Ellerman <mpe@ellerman.id.au>]

When building the 32-bit VDSO, we are building 32-bit code as part of
a 64-bit kernel build. That requires us to tweak the cflags to trick
the compiler into building 32-bit code for us. The main way we do that
is by passing -m32, but there are other options that affect code
generation and ABI selection.

In particular when building vgettimeofday.c, we end up passing
-mcall-aixdesc because it's in KBUILD_CFLAGS, which causes the
compiler to generate function descriptors, and dot symbols, eg:

  $ nm arch/powerpc/kernel/vdso32/vgettimeofday.o
  000005d0 T .__c_kernel_clock_getres
  00000024 D __c_kernel_clock_getres
  ...

We get away with that at the moment because we also use the DOTSYM
macro, and that is also incorrectly prepending a '.' in 32-bit VDSO
code due to a separate bug.

But we shouldn't be generating function descriptors for this file,
there's no 32-bit ABI that includes function descriptors, so the
resulting object file is some frankenstein and it's surprising that it
even links.

So filter out all the ABI-related options we add to CFLAGS for 64-bit
builds, so that they're not used when building 32-bit code. With that
we only see regular text symbols:

  $ nm arch/powerpc/kernel/vdso32/vgettimeofday.o                                                                                                                                     michael@alpine1-p1
  000005d0 T __c_kernel_clock_getres
  00000000 T __c_kernel_clock_gettime
  00000200 T __c_kernel_clock_gettime64
  00000410 T __c_kernel_gettimeofday
  00000650 T __c_kernel_time

Fixes: ab037dd87a2f ("powerpc/vdso: Switch VDSO to generic C implementation.")
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
---
 arch/powerpc/kernel/vdso32/Makefile | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/powerpc/kernel/vdso32/Makefile b/arch/powerpc/kernel/vdso32/Makefile
index 6616f4e794d0..9cb6f524854b 100644
--- a/arch/powerpc/kernel/vdso32/Makefile
+++ b/arch/powerpc/kernel/vdso32/Makefile
@@ -27,7 +27,7 @@ endif
 CC32FLAGS :=
 ifdef CONFIG_PPC64
 CC32FLAGS += -m32
-KBUILD_CFLAGS := $(filter-out -mcmodel=medium,$(KBUILD_CFLAGS))
+KBUILD_CFLAGS := $(filter-out -mcmodel=medium -mabi=elfv1 -mabi=elfv2 -mcall-aixdesc,$(KBUILD_CFLAGS))
 endif
 
 targets := $(obj-vdso32) vdso32.so.dbg
-- 
2.25.1