| Message ID | 20191022172100.3281465-1-andriin@fb.com |
|---|---|
| State | Accepted |
| Delegated to: | BPF Maintainers |
| Headers | show |
| Series | [v2,bpf-next] libbpf: make DECLARE_LIBBPF_OPTS macro strictly a variable declaration | expand |
Andrii Nakryiko <andriin@fb.com> writes: > 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> Acked-by: Toke Høiland-Jørgensen <toke@redhat.com> > +#define DECLARE_LIBBPF_OPTS(TYPE, NAME, ...) \ > + struct TYPE NAME = ({ \ > + memset(&NAME, 0, sizeof(struct TYPE)); \ > + (struct TYPE) { \ > + .sz = sizeof(struct TYPE), \ > + __VA_ARGS__ \ > + }; \ > + }) Found a reference with an explanation of why this works, BTW; turns out it's a GCC extension: http://gcc.gnu.org/onlinedocs/gcc/Statement-Exprs.html#Statement-Exprs -Toke
On Tue, Oct 22, 2019 at 10:21:00AM -0700, Andrii Nakryiko wrote: > 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> Applied, thanks!
diff --git a/tools/bpf/bpftool/prog.c b/tools/bpf/bpftool/prog.c index 27da96a797ab..4535c863d2cd 100644 --- a/tools/bpf/bpftool/prog.c +++ b/tools/bpf/bpftool/prog.c @@ -1091,8 +1091,11 @@ static int do_run(int argc, char **argv) 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 803219d6898c..8b4d765c422b 100644 --- a/tools/lib/bpf/libbpf.c +++ b/tools/lib/bpf/libbpf.c @@ -3678,7 +3678,7 @@ __bpf_object__open(const char *path, const void *obj_buf, size_t obj_buf_sz, 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 0fdf086beba7..c63e2ff84abc 100644 --- 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 0ee1ce100a4a..a83111a32d4a 100644 --- 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 523dca82dc82..09dfa75fe948 100644 --- 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 4493ba277bd7..fc0d7f4f02cf 100644 --- 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, );
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> --- tools/bpf/bpftool/prog.c | 8 ++++---- tools/lib/bpf/libbpf.c | 4 ++-- tools/lib/bpf/libbpf.h | 19 ++++++++++++------- .../selftests/bpf/prog_tests/attach_probe.c | 2 +- .../selftests/bpf/prog_tests/core_reloc.c | 2 +- .../bpf/prog_tests/reference_tracking.c | 2 +- 6 files changed, 21 insertions(+), 16 deletions(-)