Re: [PATCH v4 3/4] selftests/livepatch: build the test modules against the kernel in O=

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential
issue to consider:
- [Medium] selftests/livepatch: KDIR fallback ignores builds without
  Module.symvers
--

commit 62f70537bbca33262ec62f1273becbdf534f58fc
Author: Sasha Levin <sashal@kernel.org>

selftests/livepatch: build the test modules against the kernel in O=

This commit selects KDIR from O= or KBUILD_OUTPUT (or the kernel source
tree) before falling back to the running kernel's build directory, and
strips O= and KBUILD_OUTPUT when invoking the kernel Makefile for the
livepatch test modules.

> diff --git a/tools/testing/selftests/livepatch/Makefile b/tools/testing/selftests/livepatch/Makefile
> index a080eb54a215d..97478ef90945c 100644
> --- a/tools/testing/selftests/livepatch/Makefile
> +++ b/tools/testing/selftests/livepatch/Makefile
> @@ -1,5 +1,31 @@
>  # SPDX-License-Identifier: GPL-2.0
>  
> +# The test modules are built against the kernel in KDIR. When KDIR is not
> +# set, use the output directory given with O= or KBUILD_OUTPUT if a kernel
> +# was built there, as with
> +#   make O=/tmp/kselftest TARGETS=livepatch kselftest
> +# otherwise the kernel source tree if the kernel was built in it, as with
> +#   cd tools/testing/selftests/livepatch; make
> +# and otherwise the build directory of the running kernel, which its
> +# devel files provide. A kernel was built in a directory if it has a
> +# Module.symvers.
> +ifndef KDIR
> +KBUILD_DIR := $(firstword $(O) $(KBUILD_OUTPUT))
> +ifneq ($(and $(KBUILD_DIR),$(wildcard $(KBUILD_DIR)/Module.symvers)),)
> +KDIR := $(KBUILD_DIR)
> +else ifneq ($(wildcard ../../../../Module.symvers),)
> +KDIR := ../../../..
> +else
> +KDIR := /lib/modules/$(shell uname -r)/build
> +endif
> +endif

[Severity: Medium]
Does checking only for Module.symvers cause KDIR to fall back to the host's
/lib/modules/$(uname -r)/build when the target kernel in O= or the source
tree was built with CONFIG_MODULES=n or an image-only target (which
produces vmlinux.symvers instead of Module.symvers)?

When that happens and the host has kernel headers with CONFIG_LIVEPATCH=y,
test_modules/Makefile reads the host's include/config/auto.conf and builds
the test modules against the running host kernel instead of skipping them
for the target kernel, which breaks cross-compiled builds or builds where
the in-tree test modules use newer kernel APIs than the host.

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20261110161050.2451750-1-sashal@kernel.org?part=3