Individual test files may fail to compile when headers or kernel features
required by that test are absent. Currently this aborts the entire build.

Make the per-test compilation non-fatal: remove the output object on
failure and print a SKIP-TEST marker to stderr. Guard the BTFIDS
post-processing step so it is skipped when the object file is absent. The
linker step will later ignore absent objects, allowing the remaining tests
to build and run.

Group cd and CC in a sub-shell so a cd failure cannot leak into the
error-handling branch and operate in the original working directory; use
$@ (absolute path) for $(RM) so it cannot match an unrelated file there.

Replace the $(call msg,...) in the BTFIDS block with a plain printf
(the msg macro expands to @printf, which is a make-recipe construct and
is invalid inside a shell if-then-fi body) and gate the printf on
$(filter 1,$(V)) so verbose mode (V=1) does not double-print the line
that the recipe shell already echoes; non-verbose modes (V unset, V=0,
V=2, ...) still print the BTFIDS marker, matching the convention of the
shared msg macro.

Restrict tolerance to test_progs and its flavors via an inlined
$(if $(filter test_progs%,$1),$(if $(PERMISSIVE),...)) check: runners
with strong cross-object references (e.g. test_maps) would link-fail
with a partial object set, so they keep strict semantics even when
BPF_STRICT_BUILD=0. The check is inlined rather than stored in a helper
variable so $1 is substituted at $(call) time and the per-runner result
is baked into each recipe.

Note on bisectability: this change is gated entirely behind PERMISSIVE
for test_progs%, so default builds (BPF_STRICT_BUILD!=0) compile and
run identically at every commit in the series. Bisecting in PERMISSIVE
mode at this commit still requires the next two patches ("selftests/bpf:
Skip tests whose objects were not built" and "selftests/bpf: Allow
test_progs to link with a partial object set") to avoid the linker
rejecting missing objects and the runtime aborting on NULL function
pointers.

Signed-off-by: Ricardo B. Marlière <rbm@suse.com>
---
 tools/testing/selftests/bpf/Makefile | 15 ++++++++++++---
 1 file changed, 12 insertions(+), 3 deletions(-)

diff --git a/tools/testing/selftests/bpf/Makefile b/tools/testing/selftests/bpf/Makefile
index 09de69a81112..7739799c2566 100644
--- a/tools/testing/selftests/bpf/Makefile
+++ b/tools/testing/selftests/bpf/Makefile
@@ -588,6 +588,12 @@ endef
 # $2 - test runner extra "flavor" (e.g., no_alu32, cpuv4, bpf_gcc, etc)
 define DEFINE_TEST_RUNNER_RULES
 
+# Permissive build behaviour (skip-on-failure compile, partial-link) only
+# applies to test_progs and its flavors; runners that use strong cross-object
+# references (e.g. test_maps) keep strict semantics even when permissive.
+# The check is inlined per-runner so $1 is substituted at $(call) time and
+# the result is baked into each rule's recipe.
+
 ifeq ($($(TRUNNER_OUTPUT)-dir),)
 $(TRUNNER_OUTPUT)-dir := y
 $(TRUNNER_OUTPUT):
@@ -717,11 +723,14 @@ $(TRUNNER_TEST_OBJS): $(TRUNNER_OUTPUT)/%.test.o:			\
 		      $(TRUNNER_TESTS_DIR)/%.c				\
 		      | $(TRUNNER_OUTPUT)/%.test.d
 	$$(call msg,TEST-OBJ,$(TRUNNER_BINARY),$$@)
-	$(Q)cd $$(@D) && $$(CC) -I. $$(CFLAGS) -MMD -MT $$@ -c $(CURDIR)/$$< $$(LDLIBS) -o $$(@F)
+	$(Q)(cd $$(@D) && $$(CC) -I. $$(CFLAGS) -MMD -MT $$@ -c $(CURDIR)/$$< $$(LDLIBS) -o $$(@F)) $(if $(filter test_progs%,$1),$(if $(PERMISSIVE),|| \
+		($(RM) $$@; printf '  %-12s %s\n' 'SKIP-TEST' '$$(notdir $$@)' 1>&2)))
 	$$(if $$(TEST_NEEDS_BTFIDS),						\
-		$$(call msg,BTFIDS,$(TRUNNER_BINARY),$$@)			\
+		$(Q)if [ -f $$@ ]; then						\
+		$(if $(filter 1,$(V)),true,printf '  %-8s%s %s\n' "BTFIDS" " [$(TRUNNER_BINARY)]" "$$(notdir $$@)"); \
 		$(RESOLVE_BTFIDS) --btf $(TRUNNER_OUTPUT)/btf_data.bpf.o $$@;	\
-		$(RESOLVE_BTFIDS) --patch_btfids $$@.BTF_ids $$@)
+		$(RESOLVE_BTFIDS) --patch_btfids $$@.BTF_ids $$@;		\
+		fi)
 
 $(TRUNNER_TEST_OBJS:.o=.d): $(TRUNNER_OUTPUT)/%.test.d:			\
 			    $(TRUNNER_TESTS_DIR)/%.c			\

-- 
2.54.0