* [PATCH v2 bpf-next] libbpf: make DECLARE_LIBBPF_OPTS macro strictly a variable declaration
@ 2019-10-22 17:21 Andrii Nakryiko
2019-10-22 17:42 ` Toke Høiland-Jørgensen
2019-10-22 19:38 ` Daniel Borkmann
0 siblings, 2 replies; 3+ messages in thread
From: Andrii Nakryiko @ 2019-10-22 17:21 UTC (permalink / raw)
To: bpf, netdev, ast, daniel; +Cc: andrii.nakryiko, kernel-team, Andrii Nakryiko
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(-)
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,
);
--
2.17.1
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCH v2 bpf-next] libbpf: make DECLARE_LIBBPF_OPTS macro strictly a variable declaration
2019-10-22 17:21 [PATCH v2 bpf-next] libbpf: make DECLARE_LIBBPF_OPTS macro strictly a variable declaration Andrii Nakryiko
@ 2019-10-22 17:42 ` Toke Høiland-Jørgensen
2019-10-22 19:38 ` Daniel Borkmann
1 sibling, 0 replies; 3+ messages in thread
From: Toke Høiland-Jørgensen @ 2019-10-22 17:42 UTC (permalink / raw)
To: Andrii Nakryiko, bpf, netdev, ast, daniel
Cc: andrii.nakryiko, kernel-team, Andrii Nakryiko
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
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH v2 bpf-next] libbpf: make DECLARE_LIBBPF_OPTS macro strictly a variable declaration
2019-10-22 17:21 [PATCH v2 bpf-next] libbpf: make DECLARE_LIBBPF_OPTS macro strictly a variable declaration Andrii Nakryiko
2019-10-22 17:42 ` Toke Høiland-Jørgensen
@ 2019-10-22 19:38 ` Daniel Borkmann
1 sibling, 0 replies; 3+ messages in thread
From: Daniel Borkmann @ 2019-10-22 19:38 UTC (permalink / raw)
To: Andrii Nakryiko; +Cc: bpf, netdev, ast, andrii.nakryiko, kernel-team
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!
^ permalink raw reply [flat|nested] 3+ messages in thread
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2019-10-22 17:21 [PATCH v2 bpf-next] libbpf: make DECLARE_LIBBPF_OPTS macro strictly a variable declaration Andrii Nakryiko
2019-10-22 17:42 ` Toke Høiland-Jørgensen
2019-10-22 19:38 ` Daniel Borkmann
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