Re: [powerpc:next-test 54/220] arch/powerpc/kernel/vdso32/vgettimeofday.c:13:5: warning: no previous prototype for function '__c_kernel_clock_gettime64'

kernel test robot [off-list ref] writes:

tree:   https://git.kernel.org/pub/scm/linux/kernel/git/powerpc/linux.git next-test
head:   4e4ed87981c764498942c52004c620bb8f104eac
commit: d0e3fc69d00d1f50d22d6b6acfc555ccda80ad1e [54/220] powerpc/vdso: Provide __kernel_clock_gettime64() on vdso32
config: powerpc64-randconfig-r011-20201204 (attached as .config)
compiler: clang version 12.0.0 (https://github.com/llvm/llvm-project 32c501dd88b62787d3a5ffda7aabcf4650dbe3cd)
reproduce (this is a W=1 build):
        wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
        chmod +x ~/bin/make.cross
        # install powerpc64 cross compiling tool for clang build
        # apt-get install binutils-powerpc64-linux-gnu
        # https://git.kernel.org/pub/scm/linux/kernel/git/powerpc/linux.git/commit/?id=d0e3fc69d00d1f50d22d6b6acfc555ccda80ad1e
        git remote add powerpc https://git.kernel.org/pub/scm/linux/kernel/git/powerpc/linux.git
        git fetch --no-tags powerpc next-test
        git checkout d0e3fc69d00d1f50d22d6b6acfc555ccda80ad1e
        # save the attached .config to linux build tree
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross ARCH=powerpc64 

If you fix the issue, kindly add following tag as appropriate
Reported-by: kernel test robot <redacted>

All warnings (new ones prefixed by >>):

   arch/powerpc/kernel/vdso32/vgettimeofday.c:7:5: error: conflicting types for '__c_kernel_clock_gettime'
   int __c_kernel_clock_gettime(clockid_t clock, struct old_timespec32 *ts,
       ^

We're building vdso32, which is 32-bit code, we pass -m32:

  clang -Wp,-MMD,arch/powerpc/kernel/vdso32/.vgettimeofday.o.d -nostdinc -isystem /usr/lib/llvm-11/lib/clang/11.0.0/include -I/linux/arch/powerpc/include -I./arch/powerpc/include/generated -I/linux/include -I./include -I/linux/arch/powerpc/include/uapi -I./arch/powerpc/include/generated/uapi -I/linux/include/uapi -I./include/generated/uapi -include /linux/include/linux/kconfig.h -include /linux/include/linux/compiler_types.h -D__KERNEL__ -I /linux/arch/powerpc -DHAVE_AS_ATHIGH=1 -Qunused-arguments -Wall -Wundef -Werror=strict-prototypes -Wno-trigraphs -fno-strict-aliasing -fno-common -fshort-wchar -fno-PIE -Werror=implicit-function-declaration -Werror=implicit-int -Werror=return-type -Wno-format-security -std=gnu89 --target=powerpc64le-linux-gnu --prefix=/usr/bin/powerpc64le-linux-gnu- --gcc-toolchain=/usr -no-integrated-as -Werror=unknown-warning-option -mlittle-endian -m64 -msoft-float -pipe -mcpu=power8 -mtune=power9 -mno-altivec -mno-vsx -mno-spe -fno-asynchronous-unwind-tables -Wa,-mpower4 -Wa,-many -mlittle-endian -fno-delete-null-pointer-checks -Wno-frame-address -Wno-address-of-packed-member -Os -Wframe-larger-than=2048 -fno-stack-protector -Wno-format-invalid-specifier -Wno-gnu -mno-global-merge -Wno-unused-const-variable -fomit-frame-pointer -Wdeclaration-after-statement -Wvla -Wno-pointer-sign -Wno-array-bounds -fno-strict-overflow -fno-stack-check -Werror=date-time -Werror=incompatible-pointer-types -fmacro-prefix-map=/linux/= -Wno-initializer-overrides -Wno-format -Wno-sign-compare -Wno-format-zero-length -Wno-pointer-to-enum-cast -Wno-tautological-constant-out-of-range-compare -D_TASK_CPU=304 -shared -fno-common -fno-builtin -nostdlib -Wl,-soname=linux-vdso32.so.1 -Wl,--hash-style=both -include /linux/lib/vdso/gettimeofday.c -fno-stack-protector -DDISABLE_BRANCH_PROFILING -ffreestanding -fasynchronous-unwind-tables   -I /linux/arch/powerpc/kernel/vdso32 -I ./arch/powerpc/kernel/vdso32    -DKBUILD_MODFILE='"arch/powerpc/kernel/vdso32/vgettimeofday"' -DKBUILD_BASENAME='"vgettimeofday"' -DKBUILD_MODNAME='"vgettimeofday"' -m32 -c -o arch/powerpc/kernel/vdso32/vgettimeofday.o /linux/arch/powerpc/kernel/vdso32/vgettimeofday.c

   arch/powerpc/include/asm/vdso/gettimeofday.h:183:5: note: previous declaration is here
   int __c_kernel_clock_gettime(clockid_t clock, struct __kernel_timespec *ts,
       ^

But this is inside an #ifdef __powerpc64__ block:

182 #ifdef __powerpc64__
183 int __c_kernel_clock_gettime(clockid_t clock, struct __kernel_timespec *ts,
184                              const struct vdso_data *vd);


So is clang defining __powerpc64__ even for 32-bit code?

And the answer appears to be yes:

  $ clang --version
  Ubuntu clang version 11.0.0-2
  Target: powerpc64le-unknown-linux-gnu

  $ clang -m32 -dM -E - < /dev/null | grep powerpc
  #define __powerpc64__ 1
  #define __powerpc__ 1

Compare to gcc:

  $ gcc --version
  gcc (Ubuntu 10.2.0-13ubuntu1) 10.2.0
  
  $ gcc -m32 -dM -E - < /dev/null | grep powerpc
  #define __powerpc__ 1
  #define powerpc 1
  #define __powerpc 1


Which is fairly problematic, because we use the presence/absence of
__powerpc64__ to determine if we're building 64-bit/32-bit code in
several places.

Not sure what the best approach for fixing that is.

cheers