mirror/libbpf
1
0
Fork 0
mirror of https://github.com/netdata/libbpf.git synced 2026-03-21 00:39:07 +08:00
Code Issues Packages Projects Releases Wiki Activity

libbpf: Add debug messaging in dedup equivalence/identity matching

Browse Source 
We have seen a number of issues like [1]; failures to deduplicate
key kernel data structures like task_struct.  These are often hard
to debug from pahole even with verbose output, especially when
identity/equivalence checks fail deep in a nested struct comparison.

Here we add debug messages of the form

libbpf: STRUCT 'task_struct' size=2560 vlen=194 cand_id[54222] canon_id[102820] shallow-equal but not equiv for field#23 'sched_class': 0

These will be emitted during dedup from pahole when --verbose/-V
is specified.  This greatly helps identify exactly where dedup
failures are experienced.

[1] https://lore.kernel.org/bpf/b8e8b560-bce5-414b-846d-0da6d22a9983@oracle.com/

Changes since v1:

- updated debug messages to refer to shallow-equal, added ids (Andrii)

Signed-off-by: Alan Maguire <alan.maguire@oracle.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20251203191507.55565-1-alan.maguire@oracle.com
This commit is contained in:
Alan Maguire
2025-12-03 19:15:07 +00:00
committed by Andrii Nakryiko
parent 7ac4e3a670
commit 8ffe064aed
1 changed files with 24 additions and 5 deletions
Download Patch File Download Diff File Expand all files Collapse all files

29
src/btf.c
View File

@@ -4431,11 +4431,14 @@ static bool btf_dedup_identical_types(struct btf_dedup *d, __u32 id1, __u32 id2,
struct btf_type *t1, *t2;
int k1, k2;
recur:
if (depth <= 0)
return false;
t1 = btf_type_by_id(d->btf, id1);
t2 = btf_type_by_id(d->btf, id2);
if (depth <= 0) {
pr_debug("Reached depth limit for identical type comparison for '%s'/'%s'\n",
btf__name_by_offset(d->btf, t1->name_off),
btf__name_by_offset(d->btf, t2->name_off));
return false;
}
k1 = btf_kind(t1);
k2 = btf_kind(t2);
@@ -4497,8 +4500,16 @@ recur:
for (i = 0, n = btf_vlen(t1); i < n; i++, m1++, m2++) {
if (m1->type == m2->type)
continue;
if (!btf_dedup_identical_types(d, m1->type, m2->type, depth - 1))
if (!btf_dedup_identical_types(d, m1->type, m2->type, depth - 1)) {
if (t1->name_off) {
pr_debug("%s '%s' size=%d vlen=%d id1[%u] id2[%u] shallow-equal but not identical for field#%d '%s'\n",
k1 == BTF_KIND_STRUCT ? "STRUCT" : "UNION",
btf__name_by_offset(d->btf, t1->name_off),
t1->size, btf_vlen(t1), id1, id2, i,
btf__name_by_offset(d->btf, m1->name_off));
}
return false;
}
}
return true;
}
@@ -4739,8 +4750,16 @@ static int btf_dedup_is_equiv(struct btf_dedup *d, __u32 cand_id,
canon_m = btf_members(canon_type);
for (i = 0; i < vlen; i++) {
eq = btf_dedup_is_equiv(d, cand_m->type, canon_m->type);
if (eq <= 0)
if (eq <= 0) {
if (cand_type->name_off) {
pr_debug("%s '%s' size=%d vlen=%d cand_id[%u] canon_id[%u] shallow-equal but not equiv for field#%d '%s': %d\n",
cand_kind == BTF_KIND_STRUCT ? "STRUCT" : "UNION",
btf__name_by_offset(d->btf, cand_type->name_off),
cand_type->size, vlen, cand_id, canon_id, i,
btf__name_by_offset(d->btf, cand_m->name_off), eq);
}
return eq;
}
cand_m++;
canon_m++;
}