A few BPF selftests perform type punning and they may break strict aliasing rules, which are exploited by both GCC and clang by default while optimizing. This can lead to broken compiled programs. This patch disables strict aliasing for these particular tests, by mean of the -fno-strict-aliasing command line option. This will make sure these tests are optimized properly even if some strict aliasing rule gets violated. After this patch, GCC is able to build all the selftests without warning about potential strict aliasing issue. bpf@vger discussion on strict aliasing and BPF selftests: https://lore.kernel.org/bpf/bae1205a-b6e5-4e46-8e20-520d7c327f7a@xxxxxxxxx/T/#t Tested in bpf-next master. No regressions. Signed-off-by: Jose E. Marchesi <jose.marchesi@xxxxxxxxxx> Cc: Yonghong Song <yhs@xxxxxxxx> Cc: Eduard Zingerman <eddyz87@xxxxxxxxx> Cc: david.faust@xxxxxxxxxx Cc: cupertino.miranda@xxxxxxxxxx --- tools/testing/selftests/bpf/Makefile | 13 +++++++++++++ 1 file changed, 13 insertions(+) diff --git a/tools/testing/selftests/bpf/Makefile b/tools/testing/selftests/bpf/Makefile index 1a3654bcb5dd..79253a376fc8 100644 --- a/tools/testing/selftests/bpf/Makefile +++ b/tools/testing/selftests/bpf/Makefile @@ -41,6 +41,19 @@ CFLAGS += -g $(OPT_FLAGS) -rdynamic \ LDFLAGS += $(SAN_LDFLAGS) LDLIBS += $(LIBELF_LIBS) -lz -lrt -lpthread +# The following tests perform type punning and they may break strict +# aliasing rules, which are exploited by both GCC and clang by default +# while optimizing. This can lead to broken programs. +progs/bind4_prog.c-CFLAGS := -fno-strict-aliasing +progs/bind6_prog.c-CFLAGS := -fno-strict-aliasing +progs/dynptr_fail.c-CFLAGS := -fno-strict-aliasing +progs/linked_list_fail.c-CFLAGS := -fno-strict-aliasing +progs/map_kptr_fail.c-CFLAGS := -fno-strict-aliasing +progs/syscall.c-CFLAGS := -fno-strict-aliasing +progs/test_pkt_md_access.c-CFLAGS := -fno-strict-aliasing +progs/test_sk_lookup.c-CFLAGS := -fno-strict-aliasing +progs/timer_crash.c-CFLAGS := -fno-strict-aliasing + ifneq ($(LLVM),) # Silence some warnings when compiled with clang CFLAGS += -Wno-unused-command-line-argument -- 2.30.2
