tests: Rework mocking facility

Using the linker's --wrap feature has the downside that it only covers
references across object files: If foo.c defines a() and b(), with b
calling a, --wrap=a does nothing to that call.

Instead, use objcopy to mark a weak and global so it can be overridden
by another implementation, but only for files originating in src/.

That way mocks - implemented in tests/ - become the source of truth.

TEST=Had such an issue with get_log_level() in a follow-up commit, and
the mock now takes over. Also, all existing unit tests still pass.

Change-Id: I99c6d6e44ecfc73366bf464d9c51c7da3f8db388
Signed-off-by: Patrick Georgi <pgeorgi@google.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/55360
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Jakub Czapiga <jacz@semihalf.com>
diff --git a/tests/Makefile.inc b/tests/Makefile.inc
index 3473ef7..15ea670 100644
--- a/tests/Makefile.inc
+++ b/tests/Makefile.inc
@@ -17,6 +17,7 @@
 CMOCKA_LIB := $(cmockaobj)/src/libcmocka.so
 
 CMAKE:= cmake
+OBJCOPY?= objcopy
 
 TEST_DEFAULT_CONFIG = $(top)/configs/config.emulation_qemu_x86_i440fx
 TEST_DOTCONFIG = $(testobj)/.config
@@ -114,18 +115,21 @@
 
 $($(1)-objs): TEST_CFLAGS += -I$$(dir $$($(1)-config-file)) \
 	-D__$$(shell echo $$($(1)-stage) | tr '[:lower:]' '[:upper:]')__
+$($(1)-srcobjs): OBJCOPY_FLAGS += $$(foreach mock,$$($(1)-mocks),--globalize-symbol=$$(mock) --weaken-symbol=$$(mock))
 $($(1)-objs): $(testobj)/$(1)/%.o: $$$$*.c $$($(1)-config-file)
 	mkdir -p $$(dir $$@)
 	$(HOSTCC) $(HOSTCFLAGS) $$(TEST_CFLAGS) $($(1)-cflags)  -MMD \
-		-MT $$@ -c $$< -o $$@
+		-MT $$@ -c $$< -o $$@.orig
+	$(OBJCOPY) $$@.orig $$(OBJCOPY_FLAGS) $$@
 
-$($(1)-bin): TEST_LDFLAGS+= $$(foreach mock,$$($(1)-mocks),-Wl,--wrap=$$(mock))
 $($(1)-bin): $($(1)-objs) $(CMOCKA_LIB)
 	$(HOSTCC) $$^ $($(1)-cflags) $$(TEST_LDFLAGS) -o $$@
 
 endef
 
 $(foreach test, $(alltests), \
+	$(eval $(test)-srcobjs:=$(addprefix $(testobj)/$(test)/, \
+		$(patsubst %.c,%.o,$(filter src/%,$($(test)-srcs))))) \
 	$(eval $(test)-objs:=$(addprefix $(testobj)/$(test)/, \
 		$(patsubst %.c,%.o,$($(test)-srcs)))))
 $(foreach test, $(alltests), \