Auto-dependencies generated for %.test.o files refer to skels using filenames as opposed to full paths. This requires make to be able to link this name to an actual path, because not all generated skels are put in the working directory. In the original patch [1], this was mitigated by this target: $(notdir %.skel.h): $(TRUNNER_OUTPUT)/%.skel.h @true This turned out to be insufficient. First, %.lskel.h and %.subskel.h were missed, because a typical selftests/bpf build could find these files in the working directory. This error was detected by an out-of-tree build [2]. Second, even with missing rules added, this target causes unnecessary rebuilds in the out-of-tree case, as X.skel.h is searched for in the working directory, and not in the $(OUTPUT). Using vpath directive [3] is a better solution. Instead of introducing a separate target (X.skel.h in addition to $(TRUNNER_OUTPUT)/X.skel.h), make is instructed to search for skels in the output, which allows make to correctly detect that skel has already been generated. [1]: https://lore.kernel.org/bpf/VJihUTnvtwEgv_mOnpfy7EgD9D2MPNoHO-MlANeLIzLJPGhDeyOuGKIYyKgk0O6KPjfM-MuhtvPwZcngN8WFqbTnTRyCSMc2aMZ1ODm1T_g=@pm.me/ [2]: https://lore.kernel.org/bpf/CIjrhJwoIqMc2IhuppVqh4ZtJGbx8kC8rc9PHhAIU6RccnWT4I04F_EIr4GxQwxZe89McuGJlCnUk9UbkdvWtSJjAsd7mHmnTy9F8K2TLZM=@pm.me/ [3]: https://www.gnu.org/software/make/manual/html_node/Selective-Search.html Reported-by: Björn Töpel <bjorn@xxxxxxxxxx> Signed-off-by: Ihor Solodrai <ihor.solodrai@xxxxx> --- tools/testing/selftests/bpf/Makefile | 9 +++++---- 1 file changed, 5 insertions(+), 4 deletions(-) diff --git a/tools/testing/selftests/bpf/Makefile b/tools/testing/selftests/bpf/Makefile index df75f1beb731..365740f24d2e 100644 --- a/tools/testing/selftests/bpf/Makefile +++ b/tools/testing/selftests/bpf/Makefile @@ -622,10 +622,11 @@ $(TRUNNER_BPF_SKELS_LINKED): $(TRUNNER_OUTPUT)/%: $$$$(%-deps) $(BPFTOOL) | $(TR # When the compiler generates a %.d file, only skel basenames (not # full paths) are specified as prerequisites for corresponding %.o -# file. This target makes %.skel.h basename dependent on full paths, -# linking generated %.d dependency with actual %.skel.h files. -$(notdir %.skel.h): $(TRUNNER_OUTPUT)/%.skel.h - @true +# file. vpath directives below instruct make to search for skel files +# in TRUNNER_OUTPUT, if they are not present in the working directory. +vpath %.skel.h $(TRUNNER_OUTPUT) +vpath %.lskel.h $(TRUNNER_OUTPUT) +vpath %.subskel.h $(TRUNNER_OUTPUT) endif -- 2.34.1
