[PATCH] powerpc/vdso: Drop -DCC_USING_PATCHABLE_FUNCTION_ENTRY from 32-bit flags with clang

After commit 73cdf24e81e4 ("powerpc64: make clang cross-build
friendly"), building 64-bit little endian + CONFIG_COMPAT=y with clang
results in many warnings along the lines of:

  $ cat arch/powerpc/configs/compat.config
  CONFIG_COMPAT=y

  $ make -skj"$(nproc)" ARCH=powerpc LLVM=1 ppc64le_defconfig compat.config arch/powerpc/kernel/vdso/
  ...
  In file included from <built-in>:4:
  In file included from lib/vdso/gettimeofday.c:6:
  In file included from include/vdso/datapage.h:15:
  In file included from include/vdso/cache.h:5:
  arch/powerpc/include/asm/cache.h:77:8: warning: unknown attribute 'patchable_function_entry' ignored [-Wunknown-attributes]
     77 | static inline u32 l1_icache_bytes(void)
        |        ^~~~~~
  include/linux/compiler_types.h:235:58: note: expanded from macro 'inline'
    235 | #define inline inline __gnu_inline __inline_maybe_unused notrace
        |                                                          ^~~~~~~
  include/linux/compiler_types.h:215:34: note: expanded from macro 'notrace'
    215 | #define notrace                 __attribute__((patchable_function_entry(0, 0)))
        |                                                ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  ...

arch/powerpc/Makefile adds -DCC_USING_PATCHABLE_FUNCTION_ENTRY to
KBUILD_CPPFLAGS, which is inherited by the 32-bit vDSO. However, the
32-bit little endian target does not support
'-fpatchable-function-entry', resulting in the warnings above.

Remove -DCC_USING_PATCHABLE_FUNCTION_ENTRY from the 32-bit vDSO flags
when building with clang to avoid the warnings.

Fixes: 73cdf24e81e4 ("powerpc64: make clang cross-build friendly")
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
---
 arch/powerpc/kernel/vdso/Makefile | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/arch/powerpc/kernel/vdso/Makefile b/arch/powerpc/kernel/vdso/Makefile
index 8834dfe9d727..368759f81708 100644
--- a/arch/powerpc/kernel/vdso/Makefile
+++ b/arch/powerpc/kernel/vdso/Makefile

@@ -62,6 +62,12 @@ CC32FLAGSREMOVE += -fno-stack-clash-protection
 # 32-bit one. clang validates the values passed to these arguments during
 # parsing, even when -fno-stack-protector is passed afterwards.
 CC32FLAGSREMOVE += -mstack-protector-guard%
+# ftrace is disabled for the vdso but arch/powerpc/Makefile adds this define to
+# KBUILD_CPPFLAGS, which enables use of the 'patchable_function_entry'
+# attribute in the 'inline' define via 'notrace'. This attribute is not
+# supported for the powerpcle target, resulting in many instances of
+# -Wunknown-attributes.
+CC32FLAGSREMOVE += -DCC_USING_PATCHABLE_FUNCTION_ENTRY
 endif
 LD32FLAGS := -Wl,-soname=linux-vdso32.so.1
 AS32FLAGS := -D__VDSO32__

---
base-commit: 35e4f2a17eb40288f9bcdb09549fa04a63a96279
change-id: 20260311-ppc-vdso-drop-cc-using-pfe-define-clang-46d6f5041544

Best regards,
--  
Nathan Chancellor [off-list ref]