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selftests/bpf: fix bpf_testmod.ko recompilation logic

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bpf_testmod.ko build rule declared dependency on VMLINUX_BTF, but the variable
itself was initialized after the rule was declared, which often caused
bpf_testmod.ko to not be re-compiled. Fix by moving VMLINUX_BTF determination
sooner.

Also enforce bpf_testmod.ko recompilation when we detect that vmlinux image
changed by removing bpf_testmod/bpf_testmod.ko. This is necessary to generate
correct module's split BTF. Without it, Kbuild's module build logic might
determine that nothing changed on the kernel side and thus bpf_testmod.ko
shouldn't be rebuilt, so won't re-generate module BTF, which often leads to
module's BTF with wrong string offsets against vmlinux BTF. Removing .ko file
forces Kbuild to re-build the module.

Reported-by: Alexei Starovoitov <ast@kernel.org>
Fixes: 9f7fa22589 ("selftests/bpf: Add bpf_testmod kernel module for testing")
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/r/20201211015946.4062098-1-andrii@kernel.org
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
Andrii Nakryiko 2020-12-10 17:59:46 -08:00 committed by Alexei Starovoitov
parent 092fde0f86
commit a67079b031
1 changed files with 8 additions and 7 deletions
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15
tools/testing/selftests/bpf/Makefile
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@ -116,6 +116,13 @@ INCLUDE_DIR := $(SCRATCH_DIR)/include
BPFOBJ := $(BUILD_DIR)/libbpf/libbpf.a
RESOLVE_BTFIDS := $(BUILD_DIR)/resolve_btfids/resolve_btfids
VMLINUX_BTF_PATHS ?= $(if $(O),$(O)/vmlinux) \
$(if $(KBUILD_OUTPUT),$(KBUILD_OUTPUT)/vmlinux) \
../../../../vmlinux \
/sys/kernel/btf/vmlinux \
/boot/vmlinux-$(shell uname -r)
VMLINUX_BTF ?= $(abspath $(firstword $(wildcard $(VMLINUX_BTF_PATHS))))
# Define simple and short `make test_progs`, `make test_sysctl`, etc targets
# to build individual tests.
# NOTE: Semicolon at the end is critical to override lib.mk's default static
@ -140,6 +147,7 @@ $(OUTPUT)/urandom_read: urandom_read.c
$(OUTPUT)/bpf_testmod.ko: $(VMLINUX_BTF) $(wildcard bpf_testmod/Makefile bpf_testmod/*.[ch])
$(call msg,MOD,,$@)
$(Q)$(RM) bpf_testmod/bpf_testmod.ko # force re-compilation
$(Q)$(MAKE) $(submake_extras) -C bpf_testmod
$(Q)cp bpf_testmod/bpf_testmod.ko $@
@ -147,13 +155,6 @@ $(OUTPUT)/test_stub.o: test_stub.c $(BPFOBJ)
$(call msg,CC,,$@)
$(Q)$(CC) -c $(CFLAGS) -o $@ $<
VMLINUX_BTF_PATHS ?= $(if $(O),$(O)/vmlinux) \
$(if $(KBUILD_OUTPUT),$(KBUILD_OUTPUT)/vmlinux) \
../../../../vmlinux \
/sys/kernel/btf/vmlinux \
/boot/vmlinux-$(shell uname -r)
VMLINUX_BTF ?= $(abspath $(firstword $(wildcard $(VMLINUX_BTF_PATHS))))
DEFAULT_BPFTOOL := $(SCRATCH_DIR)/sbin/bpftool
$(OUTPUT)/runqslower: $(BPFOBJ) | $(DEFAULT_BPFTOOL)