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selftests/bpf: Fix test_kmods KDIR to honor O= and distro kernels

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test_kmods/Makefile always pointed KDIR at the kernel source tree root,
ignoring O= and KBUILD_OUTPUT. On distro kernels where the source tree has
not been built, the Makefile had no fallback and would fail
unconditionally.

When O= or KBUILD_OUTPUT is set and points at a prepared kernel build
directory (one containing Module.symvers), pass it through so kbuild can
locate the correct build infrastructure (scripts, Kconfig, etc.). Note
that the module artifacts themselves still land in the M= directory,
which is test_kmods/; O= only controls where kbuild finds its build
infrastructure. Fall back to /lib/modules/$(uname -r)/build when neither
an explicit valid build directory nor an in-tree Module.symvers is
present.

A selftests-only O= value (one that does not contain Module.symvers, e.g.
a private output directory) is intentionally not treated as a kernel
build directory. Without this guard, a user invoking
"make -C tools/testing/selftests/bpf O=/tmp/out" would have test_kmods
try to use /tmp/out as the kernel build dir and fail.

The parent bpf/Makefile resolves O= and KBUILD_OUTPUT to absolute paths
before invoking the test_kmods sub-make. Without this, $(abspath ...)
inside test_kmods/Makefile would resolve relative paths against the
sub-make's CWD (test_kmods/) rather than the user's invocation directory.

When O= is passed to kbuild, also pass KBUILD_OUTPUT=$(KMOD_O_VALID)
explicitly. The parent invocation lifts KBUILD_OUTPUT into MAKEFLAGS as
a command-line variable, which would otherwise suppress kbuild's own
"KBUILD_OUTPUT := $(O)" assignment and cause it to use the inherited
KBUILD_OUTPUT instead of the validated O=.

Guard both all and clean against a missing KDIR so the step is silently
skipped rather than fatal. Make the parent Makefile's cp conditional so it
does not abort when modules were not built.

Signed-off-by: Ricardo B. Marlière <rbm@suse.com>
Link: https://lore.kernel.org/r/20260602-selftests-bpf_misconfig-v12-2-27f898b3ba26@suse.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
Ricardo B. Marlière 2026-06-02 10:02:51 -03:00 committed by Alexei Starovoitov
parent a6850fa388
commit 9779193e87
2 changed files with 33 additions and 7 deletions
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10
tools/testing/selftests/bpf/Makefile
View File

@ -296,13 +296,15 @@ $(OUTPUT)/sign-file: ../../../../scripts/sign-file.c
# subst() turns the rule into a pattern matching rule
$(addprefix test_kmods/,$(subst .ko,%ko,$(TEST_KMODS))): $(VMLINUX_BTF) $(RESOLVE_BTFIDS) $(wildcard test_kmods/Makefile test_kmods/*.[ch])
$(Q)$(RM) test_kmods/*.ko test_kmods/*.mod.o # force re-compilation
$(Q)$(MAKE) $(submake_extras) -C test_kmods \
RESOLVE_BTFIDS=$(RESOLVE_BTFIDS) \
$(Q)$(MAKE) $(submake_extras) -C test_kmods \
$(if $(O),O=$(abspath $(O))) \
$(if $(KBUILD_OUTPUT),KBUILD_OUTPUT=$(abspath $(KBUILD_OUTPUT)))\
RESOLVE_BTFIDS=$(RESOLVE_BTFIDS) \
EXTRA_CFLAGS='' EXTRA_LDFLAGS=''
$(TEST_KMOD_TARGETS): $(addprefix test_kmods/,$(TEST_KMODS))
$(call msg,MOD,,$@)
$(Q)cp test_kmods/$(@F) $@
$(Q)$(if $(PERMISSIVE),if [ -f test_kmods/$(@F) ]; then )cp test_kmods/$(@F) $@$(if $(PERMISSIVE),; fi)
DEFAULT_BPFTOOL := $(HOST_SCRATCH_DIR)/sbin/bpftool
@ -718,7 +720,7 @@ $(TRUNNER_LIB_OBJS): $(TRUNNER_OUTPUT)/%.o:$(TOOLSDIR)/lib/%.c
$(TRUNNER_BINARY)-extras: $(TRUNNER_EXTRA_FILES) | $(TRUNNER_OUTPUT)
ifneq ($2:$(OUTPUT),:$(shell pwd))
$$(call msg,EXT-COPY,$(TRUNNER_BINARY),$(TRUNNER_EXTRA_FILES))
$(Q)rsync -aq $$^ $(TRUNNER_OUTPUT)/
$(Q)rsync -aq $(if $(PERMISSIVE),--ignore-missing-args) $$^ $(TRUNNER_OUTPUT)/
endif
# some X.test.o files have runtime dependencies on Y.bpf.o files

30
tools/testing/selftests/bpf/test_kmods/Makefile
View File

@ -1,5 +1,16 @@
TEST_KMOD_DIR := $(realpath $(dir $(abspath $(lastword $(MAKEFILE_LIST)))))
KDIR ?= $(abspath $(TEST_KMOD_DIR)/../../../../..)
SRCTREE_KDIR := $(abspath $(TEST_KMOD_DIR)/../../../../..)
# Honor O=/KBUILD_OUTPUT only if they point at a prepared kernel build
# directory (one containing Module.symvers); otherwise treat the value as a
# selftests-only output directory and fall back to in-tree or distro headers.
# The parent bpf/Makefile resolves O=/KBUILD_OUTPUT to absolute paths before
# invoking this sub-make so relative paths still anchor to the user's
# invocation directory.
KMOD_O := $(or $(O),$(KBUILD_OUTPUT))
KMOD_O_VALID := $(if $(KMOD_O),$(if $(wildcard $(KMOD_O)/Module.symvers),$(KMOD_O)))
KDIR ?= $(if $(KMOD_O_VALID),$(SRCTREE_KDIR), \
$(if $(wildcard $(SRCTREE_KDIR)/Module.symvers),$(SRCTREE_KDIR), \
/lib/modules/$(shell uname -r)/build))
ifeq ($(V),1)
Q =
@ -14,8 +25,21 @@ $(foreach m,$(MODULES),$(eval obj-m += $(m:.ko=.o)))
CFLAGS_bpf_testmod.o = -I$(src)
# When BPF_STRICT_BUILD != 0, a missing KDIR is fatal (the default).
# When permissive, skip silently.
PERMISSIVE := $(filter 0,$(BPF_STRICT_BUILD))
all:
$(Q)$(MAKE) -C $(KDIR) M=$(TEST_KMOD_DIR) modules
ifeq ($(PERMISSIVE),)
$(Q)$(MAKE) -C $(KDIR) $(if $(KMOD_O_VALID),O=$(KMOD_O_VALID) KBUILD_OUTPUT=$(KMOD_O_VALID),KBUILD_OUTPUT=) \
M=$(TEST_KMOD_DIR) modules
else ifneq ("$(wildcard $(KDIR))", "")
$(Q)$(MAKE) -C $(KDIR) $(if $(KMOD_O_VALID),O=$(KMOD_O_VALID) KBUILD_OUTPUT=$(KMOD_O_VALID),KBUILD_OUTPUT=) \
M=$(TEST_KMOD_DIR) modules
endif
clean:
$(Q)$(MAKE) -C $(KDIR) M=$(TEST_KMOD_DIR) clean
ifneq ("$(wildcard $(KDIR))", "")
$(Q)$(MAKE) -C $(KDIR) $(if $(KMOD_O_VALID),O=$(KMOD_O_VALID) KBUILD_OUTPUT=$(KMOD_O_VALID),KBUILD_OUTPUT=) \
M=$(TEST_KMOD_DIR) clean
endif