Re: [PATCH] kbuild: mark prepare0 as PHONY to fix external module build

On Tue, Jan 15, 2019 at 7:45 PM Alexey Kardashevskiy [off-list ref] wrote:

On 15/01/2019 18:19, Masahiro Yamada wrote:

quoted

Commit c3ff2a5193fa ("powerpc/32: add stack protector support")
caused kernel panic on PowerPC if an external module is used with
CONFIG_STACKPROTECTOR because the 'prepare' target was not executed
for the external module build.

Commit e07db28eea38 ("kbuild: fix single target build for external
module") turned it into a build error because the 'prepare' target is
now executed but the 'prepare0' target is missing for the external
module build.

External module on arm/arm64 with CONFIG_STACKPROTECTOR_PER_TASK is
also broken in the same way.

Move 'PHONY += prepare0' to the common place. Make is fine with missing
rule for phony targets.

I minimize the change so it can be easily backported to 4.20.x

To fix v4.20 for external modules of PowerPC, please backport
e07db28eea38 ("kbuild: fix single target build for external module"),
and then this commit.

Link: https://bugzilla.kernel.org/show_bug.cgi?id=201891
Fixes: e07db28eea38 ("kbuild: fix single target build for external module")
Fixes: c3ff2a5193fa ("powerpc/32: add stack protector support")
Fixes: 189af4657186 ("ARM: smp: add support for per-task stack canaries")
Fixes: 0a1213fa7432 ("arm64: enable per-task stack canaries")
Cc: linux-stable <redacted> # v4.20
Reported-by: Samuel Holland <samuel@sholland.org>
Reported-by: Alexey Kardashevskiy <redacted>
Signed-off-by: Masahiro Yamada <redacted>

Tested-by: Alexey Kardashevskiy <redacted>

Thanks for fixing this! Out of curiosity - how does this work?
arch/powerpc/Makefile's stack_protector_prepare still depends on
prepare0 which is still defined only if KBUILD_EXTMOD=="" but somehow it
does not bother ./Makefile? Thanks,

Missing phony targets are ignored.


I do not know if it is officially documented,
but GNU Make works like that.

Is the following test code helpful?


[Test Makefile]

prepare: prepare0
        @echo hello world

.PHONY: prepare prepare0


[Result]
$ make
hello world



-- 
Best Regards
Masahiro Yamada