[DTrace-devel] [PATCH v2 dtrace 2/3] fbt: revert to kprobe impl if we cannot find BTF for fprobe function

[Alan Maguire]

When using fprobes, it is possible the to-be-probed function does not
have a BTF representation.  If this occurs, revert to using the kprobe
implementation.

Signed-off-by: Alan Maguire <alan.maguire at oracle.com>
---
 libdtrace/dt_bpf.h      | 5 +++++
 libdtrace/dt_prov_fbt.c | 8 +++++++-
 2 files changed, 12 insertions(+), 1 deletion(-)

diff --git a/libdtrace/dt_bpf.h b/libdtrace/dt_bpf.h
index 5716d232..dc4eb64d 100644
--- a/libdtrace/dt_bpf.h
+++ b/libdtrace/dt_bpf.h
@@ -32,6 +32,11 @@ extern "C" {
 					(dtp)->dt_bpffeatures |= (feat); \
 				} while (0)
 
+#define BPF_UNSET_FEATURE(dtp, feat) \
+				do { \
+					(dtp)->dt_bpffeatures ^= (feat); \
+				} while (0)
+
 #define DT_CONST_PRID			1
 #define DT_CONST_ARGC			2
 #define DT_CONST_STBSZ			3
diff --git a/libdtrace/dt_prov_fbt.c b/libdtrace/dt_prov_fbt.c
index 0ba0fb71..15ffa137 100644
--- a/libdtrace/dt_prov_fbt.c
+++ b/libdtrace/dt_prov_fbt.c
@@ -232,8 +232,14 @@ static int fprobe_probe_info(dtrace_hdl_t *dtp, const dt_probe_t *prp,
 
 	btf_id = dt_btf_lookup_name_kind(dtp, dmp->dm_btf, desc->fun,
 					 BTF_KIND_FUNC);
-	if (btf_id <= 0)
+	if (btf_id <= 0) {
+		if (btf_id == -ENOENT) {
+			dt_dprintf("fbt: cannot use fprobes, reverting to kprobes\n");
+			BPF_UNSET_FEATURE(dtp, BPF_FEAT_FENTRY);
+			prp->prov->impl = &dt_fbt_kprobe;
+		}
 		goto done;
+	}
 
 	dt_tp_set_event_id(prp, btf_id);
 
-- 
2.43.5