[PATCH 2/3] powerpc: Adjust adding stack protector flags to KBUILD_CLAGS for clang

[Nathan Chancellor <nathan@kernel.org>]

After fixing the HAVE_STACKPROTECTER checks for clang's in-progress
per-task stack protector support [1], the build fails during prepare0
because '-mstack-protector-guard-offset' has not been added to
KBUILD_CFLAGS yet but the other '-mstack-protector-guard' flags have.

  clang: error: '-mstack-protector-guard=tls' is used without '-mstack-protector-guard-offset', and there is no default
  clang: error: '-mstack-protector-guard=tls' is used without '-mstack-protector-guard-offset', and there is no default
  make[4]: *** [scripts/Makefile.build:229: scripts/mod/empty.o] Error 1
  make[4]: *** [scripts/Makefile.build:102: scripts/mod/devicetable-offsets.s] Error 1

Mirror other architectures and add all '-mstack-protector-guard' flags
to KBUILD_CFLAGS atomically during stack_protector_prepare, which
resolves the issue and allows clang's implementation to fully work with
the kernel.

Link: https://github.com/llvm/llvm-project/pull/110928 [1]
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
---
 arch/powerpc/Makefile | 15 ++++++---------
 1 file changed, 6 insertions(+), 9 deletions(-)

diff --git a/arch/powerpc/Makefile b/arch/powerpc/Makefile
index bbfe4a1f06ef9db9b2f2e48e02096b1e0500a14b..8f9e387c4c7dd06d8756dca3eac808cc344a937d 100644
--- a/arch/powerpc/Makefile
+++ b/arch/powerpc/Makefile
@@ -100,13 +100,6 @@ KBUILD_AFLAGS	+= -m$(BITS)
 KBUILD_LDFLAGS	+= -m elf$(BITS)$(LDEMULATION)
 endif
 
-cflags-$(CONFIG_STACKPROTECTOR)	+= -mstack-protector-guard=tls
-ifdef CONFIG_PPC64
-cflags-$(CONFIG_STACKPROTECTOR)	+= -mstack-protector-guard-reg=r13
-else
-cflags-$(CONFIG_STACKPROTECTOR)	+= -mstack-protector-guard-reg=r2
-endif
-
 LDFLAGS_vmlinux-y := -Bstatic
 LDFLAGS_vmlinux-$(CONFIG_RELOCATABLE) := -pie
 LDFLAGS_vmlinux-$(CONFIG_RELOCATABLE) += -z notext
@@ -402,9 +395,13 @@ prepare: stack_protector_prepare
 PHONY += stack_protector_prepare
 stack_protector_prepare: prepare0
 ifdef CONFIG_PPC64
-	$(eval KBUILD_CFLAGS += -mstack-protector-guard-offset=$(shell awk '{if ($$2 == "PACA_CANARY") print $$3;}' include/generated/asm-offsets.h))
+	$(eval KBUILD_CFLAGS += -mstack-protector-guard=tls \
+				-mstack-protector-guard-reg=r13 \
+				-mstack-protector-guard-offset=$(shell awk '{if ($$2 == "PACA_CANARY") print $$3;}' include/generated/asm-offsets.h))
 else
-	$(eval KBUILD_CFLAGS += -mstack-protector-guard-offset=$(shell awk '{if ($$2 == "TASK_CANARY") print $$3;}' include/generated/asm-offsets.h))
+	$(eval KBUILD_CFLAGS += -mstack-protector-guard=tls \
+				-mstack-protector-guard-reg=r2 \
+				-mstack-protector-guard-offset=$(shell awk '{if ($$2 == "TASK_CANARY") print $$3;}' include/generated/asm-offsets.h))
 endif
 endif
 

-- 
2.47.0