selftests/bpf: Add CFLAGS per source file and runner

This patch adds support to specify CFLAGS per source file and per test
runner.

Signed-off-by: Cupertino Miranda <cupertino.miranda@oracle.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: Yonghong Song <yonghong.song@linux.dev>
Link: https://lore.kernel.org/bpf/20240507122220.207820-2-cupertino.miranda@oracle.com

Author: cupermir

tools/testing/selftests/bpf/Makefile

@@ -81,11 +81,11 @@ TEST_INST_SUBDIRS += bpf_gcc
 # The following tests contain C code that, although technically legal,
 # triggers GCC warnings that cannot be disabled: declaration of
 # anonymous struct types in function parameter lists.
-progs/btf_dump_test_case_bitfields.c-CFLAGS := -Wno-error
-progs/btf_dump_test_case_namespacing.c-CFLAGS := -Wno-error
-progs/btf_dump_test_case_packing.c-CFLAGS := -Wno-error
-progs/btf_dump_test_case_padding.c-CFLAGS := -Wno-error
-progs/btf_dump_test_case_syntax.c-CFLAGS := -Wno-error
+progs/btf_dump_test_case_bitfields.c-bpf_gcc-CFLAGS := -Wno-error
+progs/btf_dump_test_case_namespacing.c-bpf_gcc-CFLAGS := -Wno-error
+progs/btf_dump_test_case_packing.c-bpf_gcc-CFLAGS := -Wno-error
+progs/btf_dump_test_case_padding.c-bpf_gcc-CFLAGS := -Wno-error
+progs/btf_dump_test_case_syntax.c-bpf_gcc-CFLAGS := -Wno-error
 endif
 
 ifneq ($(CLANG_CPUV4),)
@@ -470,7 +470,7 @@ LINKED_BPF_SRCS := $(patsubst %.bpf.o,%.c,$(foreach skel,$(LINKED_SKELS),$($(ske
 # $eval()) and pass control to DEFINE_TEST_RUNNER_RULES.
 # Parameters:
 # $1 - test runner base binary name (e.g., test_progs)
-# $2 - test runner extra "flavor" (e.g., no_alu32, cpuv4, gcc-bpf, etc)
+# $2 - test runner extra "flavor" (e.g., no_alu32, cpuv4, bpf_gcc, etc)
 define DEFINE_TEST_RUNNER
 
 TRUNNER_OUTPUT := $(OUTPUT)$(if $2,/)$2
@@ -498,7 +498,7 @@ endef
 # Using TRUNNER_XXX variables, provided by callers of DEFINE_TEST_RUNNER and
 # set up by DEFINE_TEST_RUNNER itself, create test runner build rules with:
 # $1 - test runner base binary name (e.g., test_progs)
-# $2 - test runner extra "flavor" (e.g., no_alu32, cpuv4, gcc-bpf, etc)
+# $2 - test runner extra "flavor" (e.g., no_alu32, cpuv4, bpf_gcc, etc)
 define DEFINE_TEST_RUNNER_RULES
 
 ifeq ($($(TRUNNER_OUTPUT)-dir),)
@@ -521,7 +521,8 @@ $(TRUNNER_BPF_OBJS): $(TRUNNER_OUTPUT)/%.bpf.o:				\
 		     | $(TRUNNER_OUTPUT) $$(BPFOBJ)
 	$$(call $(TRUNNER_BPF_BUILD_RULE),$$<,$$@,			\
 					  $(TRUNNER_BPF_CFLAGS)         \
-					  $$($$<-CFLAGS))
+					  $$($$<-CFLAGS)		\
+					  $$($$<-$2-CFLAGS))
 
 $(TRUNNER_BPF_SKELS): %.skel.h: %.bpf.o $(BPFTOOL) | $(TRUNNER_OUTPUT)
 	$$(call msg,GEN-SKEL,$(TRUNNER_BINARY),$$@)