[RFC PATCH kernel] powerpc/stack_protector: Fix external modules building

c3ff2a519 "powerpc/32: add stack protector support" addes stack protector
support so now powerpc's "prepare" target depends on prepare0 (via
stack_protector_prepare target).

It works fine until we try build an external module where it fails with:
Run: 'make -j128 SYSSRC=/home/aik/p/kernel SYSOUT=/home/aik/pbuild/kernel-le-pseries/ ARCH=powerpc'
make[1]: Entering directory '/home/aik/p/kernel'
make[2]: Entering directory '/home/aik/pbuild/kernel-le-pseries'
make[2]: *** No rule to make target 'prepare0', needed by 'stack_protector_prepare'.  Stop.

The reason for that is that the main Linux Makefile defines "prepare0"
only if KBUILD_EXTMOD=="".

This hacks powerpc's Makefile to make external modules build again.

Fixes: c3ff2a519 "powerpc/32: add stack protector support"
Signed-off-by: Alexey Kardashevskiy <redacted>
---


It has been suggested that there is a better way of fixing this hence RFC.


---
 arch/powerpc/Makefile | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/arch/powerpc/Makefile b/arch/powerpc/Makefile
index 488c9ed..0492f62 100644
--- a/arch/powerpc/Makefile
+++ b/arch/powerpc/Makefile

@@ -419,7 +419,11 @@ archheaders:
 ifdef CONFIG_STACKPROTECTOR
 prepare: stack_protector_prepare
 
+ifeq ($(KBUILD_EXTMOD),)
 stack_protector_prepare: prepare0
+else
+stack_protector_prepare:
+endif
 ifdef CONFIG_PPC64
 	$(eval KBUILD_CFLAGS += -mstack-protector-guard-offset=$(shell awk '{if ($$2 == "PACA_CANARY") print $$3;}' include/generated/asm-offsets.h))
 else

-- 
2.17.1

On Thu, Jan 10, 2019 at 2:44 PM Alexey Kardashevskiy [off-list ref] wrote:

Honestly, I think this is ugly.

Do you want me to send an alternative solution?

 ifdef CONFIG_PPC64
        $(eval KBUILD_CFLAGS += -mstack-protector-guard-offset=$(shell awk '{if ($$2 == "PACA_CANARY") print $$3;}' include/generated/asm-offsets.h))
 else
--
2.17.1

-- 
Best Regards
Masahiro Yamada

On 11/01/2019 14:08, Masahiro Yamada wrote:

On Thu, Jan 10, 2019 at 2:44 PM Alexey Kardashevskiy [off-list ref] wrote:

quoted

c3ff2a519 "powerpc/32: add stack protector support" addes stack protector
support so now powerpc's "prepare" target depends on prepare0 (via
stack_protector_prepare target).

It works fine until we try build an external module where it fails with:
Run: 'make -j128 SYSSRC=/home/aik/p/kernel SYSOUT=/home/aik/pbuild/kernel-le-pseries/ ARCH=powerpc'
make[1]: Entering directory '/home/aik/p/kernel'
make[2]: Entering directory '/home/aik/pbuild/kernel-le-pseries'
make[2]: *** No rule to make target 'prepare0', needed by 'stack_protector_prepare'.  Stop.

The reason for that is that the main Linux Makefile defines "prepare0"
only if KBUILD_EXTMOD=="".

This hacks powerpc's Makefile to make external modules build again.

Fixes: c3ff2a519 "powerpc/32: add stack protector support"
Signed-off-by: Alexey Kardashevskiy <redacted>
---


It has been suggested that there is a better way of fixing this hence RFC.


---
 arch/powerpc/Makefile | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/arch/powerpc/Makefile b/arch/powerpc/Makefile
index 488c9ed..0492f62 100644
--- a/arch/powerpc/Makefile
+++ b/arch/powerpc/Makefile

@@ -419,7 +419,11 @@ archheaders:
 ifdef CONFIG_STACKPROTECTOR
 prepare: stack_protector_prepare

+ifeq ($(KBUILD_EXTMOD),)
 stack_protector_prepare: prepare0
+else
+stack_protector_prepare:
+endif

Honestly, I think this is ugly.

Do you want me to send an alternative solution?

YES! Thanks :)

quoted

 ifdef CONFIG_PPC64
        $(eval KBUILD_CFLAGS += -mstack-protector-guard-offset=$(shell awk '{if ($$2 == "PACA_CANARY") print $$3;}' include/generated/asm-offsets.h))
 else
--
2.17.1

-- 
Alexey

Masahiro Yamada [off-list ref] writes:

On Thu, Jan 10, 2019 at 2:44 PM Alexey Kardashevskiy [off-list ref] wrote:

...

quoted

diff --git a/arch/powerpc/Makefile b/arch/powerpc/Makefile
index 488c9ed..0492f62 100644
--- a/arch/powerpc/Makefile
+++ b/arch/powerpc/Makefile

@@ -419,7 +419,11 @@ archheaders:
 ifdef CONFIG_STACKPROTECTOR
 prepare: stack_protector_prepare

+ifeq ($(KBUILD_EXTMOD),)
 stack_protector_prepare: prepare0
+else
+stack_protector_prepare:
+endif

Honestly, I think this is ugly.

Yes I would call it a hack :)

Do you want me to send an alternative solution?

I don't grok how external modules are built well enough to work out what
the right solution is. So if you can come up with something better that
would be awesome.

cheers