On 5/12/23 3:33 AM, Quentin Monnet wrote:
From: Alexander Lobakin <alobakin@xxxxx>
When building bpftool with !CONFIG_PERF_EVENTS:
skeleton/pid_iter.bpf.c:47:14: error: incomplete definition of type 'struct bpf_perf_link'
perf_link = container_of(link, struct bpf_perf_link, link);
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
tools/bpf/bpftool/bootstrap/libbpf/include/bpf/bpf_helpers.h:74:22: note: expanded from macro 'container_of'
((type *)(__mptr - offsetof(type, member))); \
^~~~~~~~~~~~~~~~~~~~~~
tools/bpf/bpftool/bootstrap/libbpf/include/bpf/bpf_helpers.h:68:60: note: expanded from macro 'offsetof'
#define offsetof(TYPE, MEMBER) ((unsigned long)&((TYPE *)0)->MEMBER)
~~~~~~~~~~~^
skeleton/pid_iter.bpf.c:44:9: note: forward declaration of 'struct bpf_perf_link'
struct bpf_perf_link *perf_link;
^
&bpf_perf_link is being defined and used only under the ifdef.
Define struct bpf_perf_link___local with the `preserve_access_index`
attribute inside the pid_iter BPF prog to allow compiling on any
configs. CO-RE will substitute it with the real struct bpf_perf_link
accesses later on.
container_of() is not CO-REd, but it is a noop for
'container_of() is not CO-REd' is incorrect.
#define container_of(ptr, type, member) \
({ \
void *__mptr = (void *)(ptr); \
((type *)(__mptr - offsetof(type, member))); \
})
offsetof() will do necessary CO-RE relocation if the field is specified
with preserve_access_index attribute. So container_of will actually
do CO-RE relocation as well.
bpf_perf_link <-> bpf_link and the local copy is a full mirror of
the original structure.
Fixes: cbdaf71f7e65 ("bpftool: Add bpf_cookie to link output")
Suggested-by: Andrii Nakryiko <andrii@xxxxxxxxxx>
Signed-off-by: Alexander Lobakin <alobakin@xxxxx>
Signed-off-by: Quentin Monnet <quentin@xxxxxxxxxxxxx>
---
tools/bpf/bpftool/skeleton/pid_iter.bpf.c | 9 +++++++--
1 file changed, 7 insertions(+), 2 deletions(-)
diff --git a/tools/bpf/bpftool/skeleton/pid_iter.bpf.c b/tools/bpf/bpftool/skeleton/pid_iter.bpf.c
index e2af8e5fb29e..3a4c4f7d83d8 100644
--- a/tools/bpf/bpftool/skeleton/pid_iter.bpf.c
+++ b/tools/bpf/bpftool/skeleton/pid_iter.bpf.c
@@ -15,6 +15,11 @@ enum bpf_obj_type {
BPF_OBJ_BTF,
};
+struct bpf_perf_link___local {
+ struct bpf_link link;
+ struct file *perf_file;
+} __attribute__((preserve_access_index));
+
struct perf_event___local {
u64 bpf_cookie;
} __attribute__((preserve_access_index));
@@ -45,10 +50,10 @@ static __always_inline __u32 get_obj_id(void *ent, enum bpf_obj_type type)
/* could be used only with BPF_LINK_TYPE_PERF_EVENT links */
static __u64 get_bpf_cookie(struct bpf_link *link)
{
+ struct bpf_perf_link___local *perf_link;
struct perf_event___local *event;
- struct bpf_perf_link *perf_link;
- perf_link = container_of(link, struct bpf_perf_link, link);
+ perf_link = container_of(link, struct bpf_perf_link___local, link);
event = BPF_CORE_READ(perf_link, perf_file, private_data);
return BPF_CORE_READ(event, bpf_cookie);
}
