diff options
| author | Dave Marchevsky <davemarchevsky@fb.com> | 2023-03-02 16:55:00 -0800 |
|---|---|---|
| committer | Alexei Starovoitov <ast@kernel.org> | 2023-03-02 22:38:50 -0800 |
| commit | ec97a76f113ee0d8fd17178b4e4ffbf0ab9e5452 (patch) | |
| tree | eb6b1bae88f1830bc61af9ed3659ed144173d79d /tools/testing/selftests/bpf/Makefile | |
| parent | c501bf55c88b834adefda870c7c092ec9052a437 (diff) | |
selftests/bpf: Add -Wuninitialized flag to bpf prog flags
Per C99 standard [0], Section 6.7.8, Paragraph 10:
If an object that has automatic storage duration is not initialized
explicitly, its value is indeterminate.
And in the same document, in appendix "J.2 Undefined behavior":
The behavior is undefined in the following circumstances:
[...]
The value of an object with automatic storage duration is used while
it is indeterminate (6.2.4, 6.7.8, 6.8).
This means that use of an uninitialized stack variable is undefined
behavior, and therefore that clang can choose to do a variety of scary
things, such as not generating bytecode for "bunch of useful code" in
the below example:
void some_func()
{
int i;
if (!i)
return;
// bunch of useful code
}
To add insult to injury, if some_func above is a helper function for
some BPF program, clang can choose to not generate an "exit" insn,
causing verifier to fail with "last insn is not an exit or jmp". Going
from that verification failure to the root cause of uninitialized use
is certain to be frustrating.
This patch adds -Wuninitialized to the cflags for selftest BPF progs and
fixes up existing instances of uninitialized use.
[0]: https://www.open-std.org/jtc1/sc22/WG14/www/docs/n1256.pdf
Signed-off-by: Dave Marchevsky <davemarchevsky@fb.com>
Cc: David Vernet <void@manifault.com>
Cc: Tejun Heo <tj@kernel.org>
Acked-by: David Vernet <void@manifault.com>
Link: https://lore.kernel.org/r/20230303005500.1614874-1-davemarchevsky@fb.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Diffstat (limited to 'tools/testing/selftests/bpf/Makefile')
| -rw-r--r-- | tools/testing/selftests/bpf/Makefile | 2 |
1 files changed, 1 insertions, 1 deletions
diff --git a/tools/testing/selftests/bpf/Makefile b/tools/testing/selftests/bpf/Makefile index f40606a85a0f..eab3cf5399f5 100644 --- a/tools/testing/selftests/bpf/Makefile +++ b/tools/testing/selftests/bpf/Makefile @@ -357,7 +357,7 @@ BPF_CFLAGS = -g -Werror -D__TARGET_ARCH_$(SRCARCH) $(MENDIAN) \ -I$(abspath $(OUTPUT)/../usr/include) CLANG_CFLAGS = $(CLANG_SYS_INCLUDES) \ - -Wno-compare-distinct-pointer-types + -Wno-compare-distinct-pointer-types -Wuninitialized $(OUTPUT)/test_l4lb_noinline.o: BPF_CFLAGS += -fno-inline $(OUTPUT)/test_xdp_noinline.o: BPF_CFLAGS += -fno-inline |