From 27a90b14b93d3b2e1efd10764e456af7e2a42991 Mon Sep 17 00:00:00 2001 From: "Jose E. Marchesi" Date: Tue, 30 Jan 2024 12:03:43 +0100 Subject: [PATCH] bpf: Build type-punning BPF selftests with -fno-strict-aliasing 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@linux.dev/T/#t Tested in bpf-next master. No regressions. Signed-off-by: Jose E. Marchesi Signed-off-by: Daniel Borkmann Link: https://lore.kernel.org/bpf/bae1205a-b6e5-4e46-8e20-520d7c327f7a@linux.dev Link: https://lore.kernel.org/bpf/20240130110343.11217-1-jose.marchesi@oracle.com --- 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 1a3654bcb5dd1..79253a376fc89 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