[DTrace-devel] [PATCH v4 2/3] libdtrace: BTF->CTF conversion for kernel modules

[Alan Maguire]

We had logic in place to collect BTF in modules and convert vmlinux
BTF to CTF, but were not doing the same for module BTF.  Add support
to do this, and explicitly set parent dict to "shared_ctf".  With
this in place (along with the support to find the appropriate module
CTF) we can successfully print module-specific types such as:

$ dtrace -n 'fbt::ieee80211_rx_napi:entry { print((struct ieee80211_hw *)arg0); }'
dtrace: description 'fbt::ieee80211_rx_napi:entry ' matched 1 probe
CPU     ID                    FUNCTION:NAME
  6 117489          ieee80211_rx_napi:entry 0xffff9fabc2e688e0 = *
                                            (struct ieee80211_hw) {
                                             .conf = (struct ieee80211_conf) {
                                              .listen_interval = (u16)10,
                                              .long_frame_max_tx_count = (u8)4,
                                              .short_frame_max_tx_count = (u8)7,
                                             },
                                             .wiphy = (struct wiphy *)0xffff9fabc2e683c0,
                                             .rate_control_algorithm = (const char *)0xffffffffc1346ae5,
...

Signed-off-by: Alan Maguire <alan.maguire at oracle.com>
---
 libdtrace/dt_btf.c    | 3 ++-
 libdtrace/dt_cg.c     | 1 -
 libdtrace/dt_module.c | 7 ++++++-
 3 files changed, 8 insertions(+), 3 deletions(-)

diff --git a/libdtrace/dt_btf.c b/libdtrace/dt_btf.c
index 9e67fd9d..4e1ed9f6 100644
--- a/libdtrace/dt_btf.c
+++ b/libdtrace/dt_btf.c
@@ -715,6 +715,7 @@ dt_btf_to_ctf(dtrace_hdl_t *dtp, dt_module_t *dmp, dt_btf_t *btf)
 
 		if (strcmp(dmp->dm_name, "vmlinux") == 0)
 			goto out;
+		ctf_parent_name_set(ctf, "shared_ctf");
 	}
 
 	if (!btf)
@@ -867,7 +868,7 @@ dt_btf_lookup_name_kind(dtrace_hdl_t *dtp, dt_btf_t *btf, const char *name,
 	 * shared one.
 	 */
 	 if (!dtp->dt_shared_btf) {
-		  dt_btf_load_module(dtp, dtp->dt_exec);
+		  btf = dt_btf_load_module(dtp, dtp->dt_exec);
 
 		  if (!btf)
 			   btf = dtp->dt_shared_btf;
diff --git a/libdtrace/dt_cg.c b/libdtrace/dt_cg.c
index 2eb2df9c..4206235b 100644
--- a/libdtrace/dt_cg.c
+++ b/libdtrace/dt_cg.c
@@ -2852,7 +2852,6 @@ dt_cg_act_print(dt_pcb_t *pcb, dt_node_t *dnp, dtrace_actkind_t kind)
 		dnerror(addr, D_PRINT_SIZE,
 			"print( ) argument #1 reference has type '%s' with size 0; cannot print( ) it.\n",
 			ctf_type_name(fp, type, n, sizeof(n)));
-
 	pfp = dt_printf_create(dtp, dmp->dm_name);
 
 	/* reserve space for addr/type, data/size */
diff --git a/libdtrace/dt_module.c b/libdtrace/dt_module.c
index 5e608446..d8a539af 100644
--- a/libdtrace/dt_module.c
+++ b/libdtrace/dt_module.c
@@ -962,8 +962,8 @@ dt_kern_module_find_ctf(dtrace_hdl_t *dtp, dt_module_t *dmp)
 			dt_dprintf("Cannot open CTF archive %s: %s; "
 				   "looking for in-module CTF instead.\n",
 				   ctfa_name, ctf_errmsg(dtp->dt_ctferr));
-#endif
 			return;
+#endif
 		}
 
 		if (dtp->dt_ctfa_path == NULL)
@@ -982,6 +982,11 @@ dt_kern_module_find_ctf(dtrace_hdl_t *dtp, dt_module_t *dmp)
 			    "archive: %s; looking for out-of-tree module.\n",
 			    dmp->dm_name, ctf_errmsg(dtp->dt_ctferr));
 		}
+	} else if (dtp->dt_shared_ctf) {
+#ifdef HAVE_LIBCTF
+		/* Have shared CTF via vmlinux BTF; now do BTF->CTF for mod. */
+		dt_kern_module_ctf_from_btf(dtp, dmp);
+#endif
 	}
 
 	if (dmp->dm_ctfp != NULL) {
-- 
2.43.5