[DTrace-devel] [PATCH v2 6/7] tcp: support non-libctf environments

[Kris Van Hees]

Commit 0fa93b3ac ("tcp: new provider") and commit c08a5fcf2
("tcp provider: support tcp:::accept-established in absence of skb") both
introduced code that uses ctf_func_type_info() without a pre-processor
conditional to also support the case when libctf is not present on the
system.

When libctf is not present, it is assumed that the system is quite old
and therefore is running an older kernel.  Use of libdtrace-ctf (which
has been deprecated in favour of libctf) on systems with recent kernels
is not supported and may lead to unexpected results.

Signed-off-by: Kris Van Hees <kris.van.hees at oracle.com>
---
 libdtrace/dt_prov_tcp.c | 27 ++++++++++++++++-----------
 1 file changed, 16 insertions(+), 11 deletions(-)

diff --git a/libdtrace/dt_prov_tcp.c b/libdtrace/dt_prov_tcp.c
index 44ed2bc9..c3d5553e 100644
--- a/libdtrace/dt_prov_tcp.c
+++ b/libdtrace/dt_prov_tcp.c
@@ -160,17 +160,19 @@ static int populate(dtrace_hdl_t *dtp)
  */
 static int trampoline(dt_pcb_t *pcb, uint_t exitlbl)
 {
-	dtrace_hdl_t	*dtp = pcb->pcb_hdl;
 	dt_irlist_t	*dlp = &pcb->pcb_ir;
 	dt_probe_t	*prp = pcb->pcb_probe;
 	dt_probe_t	*uprp = pcb->pcb_parent_probe;
 	int		direction, have_iphdr;
 	int		skarg = 0, skbarg = 1, tcparg = 0;
-	int		skarg_maybe_null, have_skb = 1;
+	int		skarg_maybe_null = 0, have_skb = 1;
 	int		skstate = 0;
+#ifdef HAVE_LIBCTF
+	dtrace_hdl_t	*dtp = pcb->pcb_hdl;
 	dtrace_typeinfo_t sym;
 	ctf_funcinfo_t	fi;
 	int		rc;
+#endif
 
 	/*
 	 * We construct the tcp::: probe arguments as follows:
@@ -262,6 +264,7 @@ static int trampoline(dt_pcb_t *pcb, uint_t exitlbl)
 
 	if (strcmp(prp->desc->prb, "accept-established") == 0) {
 		direction = NET_PROBE_INBOUND;
+#ifdef HAVE_LIBCTF
 		have_iphdr = 1;
 		/* on older (5.4) kernels, tcp_init_transfer() only has 2
 		 * args, i.e. no struct skb * third argument.
@@ -274,11 +277,14 @@ static int trampoline(dt_pcb_t *pcb, uint_t exitlbl)
 		    fi.ctc_argc > 2) {
 			/* skb in arg2 not arg1 */
 			skbarg = 2;
-			skarg_maybe_null = 0;
 		} else {
 			have_skb = 0;
 			have_iphdr = 0;
 		}
+#else
+		have_skb = 0;
+		have_iphdr = 0;
+#endif
 		/* ensure arg1 is BPF_SOCK_OPS_PASSIVE_ESTABLISHED_CB */
 		emit(dlp, BPF_LOAD(BPF_DW, BPF_REG_6, BPF_REG_7, DMST_ARG(1)));
 		emit(dlp, BPF_BRANCH_IMM(BPF_JNE, BPF_REG_6,
@@ -291,20 +297,17 @@ static int trampoline(dt_pcb_t *pcb, uint_t exitlbl)
 		if (strcmp(uprp->desc->fun, "tcp_v4_send_reset") == 0 ||
 		    strcmp(uprp->desc->fun, "tcp_v6_send_reset") == 0)
 			skarg_maybe_null = 1;
-		else
-			skarg_maybe_null = 0;
 	} else if (strcmp(prp->desc->prb, "connect-established") == 0) {
 		direction = NET_PROBE_INBOUND;
 		have_iphdr = 1;
-		skarg_maybe_null = 0;
 	} else if (strcmp(prp->desc->prb, "connect-refused") == 0) {
 		direction = NET_PROBE_INBOUND;
 		have_iphdr = 1;
-		skarg_maybe_null = 0;
 		skstate = BPF_TCP_SYN_SENT;
 	} else {
 		direction = NET_PROBE_OUTBOUND;
 		if (strcmp(uprp->desc->fun, "ip_send_unicast_reply") == 0) {
+#ifdef HAVE_LIBCTF
 			/* Newer kernels pass the original socket as second
 			 * arg to ip_send_unicast_reply(); if that function
 			 * has an extra (> 9) argument we know we have to
@@ -329,6 +332,11 @@ static int trampoline(dt_pcb_t *pcb, uint_t exitlbl)
 				skbarg = 1;
 				tcparg = 5;
 			}
+#else
+			skarg = 0;
+			skbarg = 1;
+			tcparg = 5;
+#endif
 			have_iphdr = 1;
 			tcparg = 6;
 			skarg_maybe_null = 1;
@@ -340,11 +348,8 @@ static int trampoline(dt_pcb_t *pcb, uint_t exitlbl)
 		} else if (strcmp(prp->desc->prb, "connect-request") == 0) {
 			skstate = BPF_TCP_SYN_SENT;
 			have_iphdr = 0;
-			skarg_maybe_null = 0;
-		} else {
+		} else
 			have_iphdr = 0;
-			skarg_maybe_null = 0;
-		}
 	}
 
 	/* first save sk to args[3]; this avoids overwriting it when we
-- 
2.51.0