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libbpf: Make DECLARE_LIBBPF_OPTS macro strictly a variable declaration

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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
This commit is contained in:
Andrii Nakryiko
2019-10-22 10:21:00 -07:00
committed by Andrii Nakryiko
parent 2b0cd55bf5
commit c7b5116f71
2 changed files with 14 additions and 9 deletions
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4
src/libbpf.c
View File

@@ -3678,7 +3678,7 @@ out:
static struct bpf_object * static struct bpf_object *
__bpf_object__open_xattr(struct bpf_object_open_attr *attr, int flags) __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, .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, bpf_object__open_buffer(const void *obj_buf, size_t obj_buf_sz,
const char *name) const char *name)
{ {
LIBBPF_OPTS(bpf_object_open_opts, opts, DECLARE_LIBBPF_OPTS(bpf_object_open_opts, opts,
.object_name = name, .object_name = name,
/* wrong default, but backwards-compatible */ /* wrong default, but backwards-compatible */
.relaxed_maps = true, .relaxed_maps = true,

19
src/libbpf.h
View File

@@ -75,14 +75,19 @@ struct bpf_object_open_attr {
* have all the padding bytes initialized to zero. It's not guaranteed though, * 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 * 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. * 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, ...) \ #define DECLARE_LIBBPF_OPTS(TYPE, NAME, ...) \
struct TYPE NAME; \ struct TYPE NAME = ({ \
memset(&NAME, 0, sizeof(struct TYPE)); \ memset(&NAME, 0, sizeof(struct TYPE)); \
NAME = (struct TYPE) { \ (struct TYPE) { \
.sz = sizeof(struct TYPE), \ .sz = sizeof(struct TYPE), \
__VA_ARGS__ \ __VA_ARGS__ \
} }; \
})
struct bpf_object_open_opts { struct bpf_object_open_opts {
/* size of this struct, for forward/backward compatiblity */ /* size of this struct, for forward/backward compatiblity */