libbpf: Make DECLARE_LIBBPF_OPTS macro strictly a variable declaration

LIBBPF_OPTS is implemented as a mix of field declaration and memset
+ assignment. This makes it neither variable declaration nor purely
statements, which is a problem, because you can't mix it with either
other variable declarations nor other function statements, because C90
compiler mode emits warning on mixing all that together.

This patch changes LIBBPF_OPTS into a strictly declaration of variable
and solves this problem, as can be seen in case of bpftool, which
previously would emit compiler warning, if done this way (LIBBPF_OPTS as
part of function variables declaration block).

This patch also renames LIBBPF_OPTS into DECLARE_LIBBPF_OPTS to follow
kernel convention for similar macros more closely.

v1->v2:
- rename LIBBPF_OPTS into DECLARE_LIBBPF_OPTS (Jakub Sitnicki).

Signed-off-by: Andrii Nakryiko <andriin@fb.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Toke Høiland-Jørgensen <toke@redhat.com>
Link: https://lore.kernel.org/bpf/20191022172100.3281465-1-andriin@fb.com

diff --git a/tools/bpf/bpftool/prog.c b/tools/bpf/bpftool/prog.c
index 27da96a..4535c86 100644 (file)
--- a/tools/bpf/bpftool/prog.c
+++ b/tools/bpf/bpftool/prog.c
@@ -1091,8 +1091,11 @@ free_data_in:
 
 static int load_with_options(int argc, char **argv, bool first_prog_only)
 {
-       struct bpf_object_load_attr load_attr = { 0 };
        enum bpf_prog_type common_prog_type = BPF_PROG_TYPE_UNSPEC;
+       DECLARE_LIBBPF_OPTS(bpf_object_open_opts, open_opts,
+               .relaxed_maps = relaxed_maps,
+       );
+       struct bpf_object_load_attr load_attr = { 0 };
        enum bpf_attach_type expected_attach_type;
        struct map_replace *map_replace = NULL;
        struct bpf_program *prog = NULL, *pos;
@@ -1106,9 +1109,6 @@ static int load_with_options(int argc, char **argv, bool first_prog_only)
        const char *file;
        int idx, err;
 
-       LIBBPF_OPTS(bpf_object_open_opts, open_opts,
-               .relaxed_maps = relaxed_maps,
-       );
 
        if (!REQ_ARGS(2))
                return -1;

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 803219d..8b4d765 100644 (file)
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -3678,7 +3678,7 @@ out:
 static struct bpf_object *
 __bpf_object__open_xattr(struct bpf_object_open_attr *attr, int flags)
 {
-       LIBBPF_OPTS(bpf_object_open_opts, opts,
+       DECLARE_LIBBPF_OPTS(bpf_object_open_opts, opts,
                .relaxed_maps = flags & MAPS_RELAX_COMPAT,
        );
 
@@ -3730,7 +3730,7 @@ struct bpf_object *
 bpf_object__open_buffer(const void *obj_buf, size_t obj_buf_sz,
                        const char *name)
 {
-       LIBBPF_OPTS(bpf_object_open_opts, opts,
+       DECLARE_LIBBPF_OPTS(bpf_object_open_opts, opts,
                .object_name = name,
                /* wrong default, but backwards-compatible */
                .relaxed_maps = true,

diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h
index 0fdf086..c63e2ff 100644 (file)
--- a/tools/lib/bpf/libbpf.h
+++ b/tools/lib/bpf/libbpf.h
@@ -75,14 +75,19 @@ struct bpf_object_open_attr {
  * have all the padding bytes initialized to zero. It's not guaranteed though,
  * when copying literal, that compiler won't copy garbage in literal's padding
  * bytes, but that's the best way I've found and it seems to work in practice.
+ *
+ * Macro declares opts struct of given type and name, zero-initializes,
+ * including any extra padding, it with memset() and then assigns initial
+ * values provided by users in struct initializer-syntax as varargs.
  */
-#define LIBBPF_OPTS(TYPE, NAME, ...)                                       \
-       struct TYPE NAME;                                                   \
-       memset(&NAME, 0, sizeof(struct TYPE));                              \
-       NAME = (struct TYPE) {                                              \
-               .sz = sizeof(struct TYPE),                                  \
-               __VA_ARGS__                                                 \
-       }
+#define DECLARE_LIBBPF_OPTS(TYPE, NAME, ...)                               \
+       struct TYPE NAME = ({                                               \
+               memset(&NAME, 0, sizeof(struct TYPE));                      \
+               (struct TYPE) {                                             \
+                       .sz = sizeof(struct TYPE),                          \
+                       __VA_ARGS__                                         \
+               };                                                          \
+       })
 
 struct bpf_object_open_opts {
        /* size of this struct, for forward/backward compatiblity */

diff --git a/tools/testing/selftests/bpf/prog_tests/attach_probe.c b/tools/testing/selftests/bpf/prog_tests/attach_probe.c
index 0ee1ce1..a83111a 100644 (file)
--- a/tools/testing/selftests/bpf/prog_tests/attach_probe.c
+++ b/tools/testing/selftests/bpf/prog_tests/attach_probe.c
@@ -50,7 +50,7 @@ void test_attach_probe(void)
        const int kprobe_idx = 0, kretprobe_idx = 1;
        const int uprobe_idx = 2, uretprobe_idx = 3;
        const char *obj_name = "attach_probe";
-       LIBBPF_OPTS(bpf_object_open_opts, open_opts,
+       DECLARE_LIBBPF_OPTS(bpf_object_open_opts, open_opts,
                .object_name = obj_name,
                .relaxed_maps = true,
        );

diff --git a/tools/testing/selftests/bpf/prog_tests/core_reloc.c b/tools/testing/selftests/bpf/prog_tests/core_reloc.c
index 523dca8..09dfa75 100644 (file)
--- a/tools/testing/selftests/bpf/prog_tests/core_reloc.c
+++ b/tools/testing/selftests/bpf/prog_tests/core_reloc.c
@@ -377,7 +377,7 @@ void test_core_reloc(void)
                if (!test__start_subtest(test_case->case_name))
                        continue;
 
-               LIBBPF_OPTS(bpf_object_open_opts, opts,
+               DECLARE_LIBBPF_OPTS(bpf_object_open_opts, opts,
                        .relaxed_core_relocs = test_case->relaxed_core_relocs,
                );
 

diff --git a/tools/testing/selftests/bpf/prog_tests/reference_tracking.c b/tools/testing/selftests/bpf/prog_tests/reference_tracking.c
index 4493ba2..fc0d7f4 100644 (file)
--- a/tools/testing/selftests/bpf/prog_tests/reference_tracking.c
+++ b/tools/testing/selftests/bpf/prog_tests/reference_tracking.c
@@ -5,7 +5,7 @@ void test_reference_tracking(void)
 {
        const char *file = "test_sk_lookup_kern.o";
        const char *obj_name = "ref_track";
-       LIBBPF_OPTS(bpf_object_open_opts, open_opts,
+       DECLARE_LIBBPF_OPTS(bpf_object_open_opts, open_opts,
                .object_name = obj_name,
                .relaxed_maps = true,
        );