Commit ec97a76f authored by Dave Marchevsky's avatar Dave Marchevsky Committed by Alexei Starovoitov
Browse files

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: default avatarDave Marchevsky <davemarchevsky@fb.com>
Cc: David Vernet <void@manifault.com>
Cc: Tejun Heo <tj@kernel.org>
Acked-by: default avatarDavid Vernet <void@manifault.com>
Link: https://lore.kernel.org/r/20230303005500.1614874-1-davemarchevsky@fb.com


Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
parent c501bf55

tools/testing/selftests/bpf/Makefile

+1 −1
Original line number Diff line number Diff line
@@ -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

tools/testing/selftests/bpf/progs/rbtree.c

+1 −1
Original line number Diff line number Diff line
@@ -75,7 +75,7 @@ SEC("tc") 
long rbtree_add_and_remove(void *ctx)

{

	struct bpf_rb_node *res = NULL;

	struct node_data *n, *m;

	struct node_data *n, *m = NULL;



	n = bpf_obj_new(typeof(*n));

	if (!n)

tools/testing/selftests/bpf/progs/rbtree_fail.c

+5 −2
Original line number Diff line number Diff line
@@ -232,7 +232,10 @@ long rbtree_api_first_release_unlock_escape(void *ctx) 


	bpf_spin_lock(&glock);

	res = bpf_rbtree_first(&groot);

	if (res)

	if (!res) {

		bpf_spin_unlock(&glock);

		return 1;

	}

	n = container_of(res, struct node_data, node);

	bpf_spin_unlock(&glock);

tools/testing/selftests/bpf/progs/test_kfunc_dynptr_param.c

+1 −1
Original line number Diff line number Diff line
@@ -48,7 +48,7 @@ SEC("?lsm.s/bpf") 
__failure __msg("arg#0 expected pointer to stack or dynptr_ptr")

int BPF_PROG(not_ptr_to_stack, int cmd, union bpf_attr *attr, unsigned int size)

{

	unsigned long val;

	unsigned long val = 0;



	return bpf_verify_pkcs7_signature((struct bpf_dynptr *)val,

					  (struct bpf_dynptr *)val, NULL);

tools/testing/selftests/bpf/progs/test_sk_lookup_kern.c

+1 −1
Original line number Diff line number Diff line
@@ -23,8 +23,8 @@ static struct bpf_sock_tuple *get_tuple(void *data, __u64 nh_off, 
					bool *ipv4)

{

	struct bpf_sock_tuple *result;

	__u64 ihl_len = 0;

	__u8 proto = 0;

	__u64 ihl_len;



	if (eth_proto == bpf_htons(ETH_P_IP)) {

		struct iphdr *iph = (struct iphdr *)(data + nh_off);