From: Denis Ovsienko <denis@ovsienko.info>
Date: Sat, 29 Mar 2025 14:03:15 +0000 (+0000)
Subject: Mind all-zeroes IPv6 netmask tetras in gen_hostop6().
X-Git-Url: https://git.tcpdump.org/libpcap/commitdiff_plain/8788f6815528c8e39964354523e38c79c4c06af0

Mind all-zeroes IPv6 netmask tetras in gen_hostop6().

Produce as few comparison blocks as possible: skip all zero 32-bit
parts, generate one always-true comparison only if it is the only
comparison block.

Now the unoptimized filter program for "ip6 dst net ::/0" has only one
always-true comparison, longer IPv6 netmasks have none and are the same
as the optimized version.
---

diff --git a/gencode.c b/gencode.c
index 74780cdc..0f6866f8 100644
--- a/gencode.c
+++ b/gencode.c
@@ -4472,14 +4472,19 @@ gen_hostop6(compiler_state_t *cstate, struct in6_addr *addr,
 	/* this order is important */
 	memcpy(a, addr, sizeof(a));
 	memcpy(m, mask, sizeof(m));
-	b1 = gen_mcmp(cstate, OR_LINKPL, offset + 12, BPF_W, ntohl(a[3]), ntohl(m[3]));
-	b0 = gen_mcmp(cstate, OR_LINKPL, offset + 8, BPF_W, ntohl(a[2]), ntohl(m[2]));
-	gen_and(b0, b1);
-	b0 = gen_mcmp(cstate, OR_LINKPL, offset + 4, BPF_W, ntohl(a[1]), ntohl(m[1]));
-	gen_and(b0, b1);
-	b0 = gen_mcmp(cstate, OR_LINKPL, offset + 0, BPF_W, ntohl(a[0]), ntohl(m[0]));
-	gen_and(b0, b1);
-	return b1;
+	b1 = NULL;
+	for (int i = 3; i >= 0; i--) {
+		// Same as the Q_IP case in gen_host().
+		if (m[i] == 0 && a[i] == 0)
+			continue;
+		b0 = gen_mcmp(cstate, OR_LINKPL, offset + 4 * i, BPF_W,
+		    ntohl(a[i]), ntohl(m[i]));
+		if (b1)
+			gen_and(b0, b1);
+		else
+			b1 = b0;
+	}
+	return b1 ? b1 : gen_true(cstate);
 }
 #endif
 
diff --git a/testprogs/TESTrun b/testprogs/TESTrun
index 12704fc1..d671042f 100755
--- a/testprogs/TESTrun
+++ b/testprogs/TESTrun
@@ -11625,17 +11625,11 @@ my @accept_blocks = (
 		unopt => '
 			(000) ldb      [0]
 			(001) and      #0xf0
-			(002) jeq      #0x60            jt 3	jf 12
+			(002) jeq      #0x60            jt 3	jf 6
 			(003) ld       #0x0
-			(004) jeq      #0x0             jt 5	jf 12
-			(005) ld       #0x0
-			(006) jeq      #0x0             jt 7	jf 12
-			(007) ld       #0x0
-			(008) jeq      #0x0             jt 9	jf 12
-			(009) ld       #0x0
-			(010) jeq      #0x0             jt 11	jf 12
-			(011) ret      #262144
-			(012) ret      #0
+			(004) jeq      #0x0             jt 5	jf 6
+			(005) ret      #262144
+			(006) ret      #0
 			',
 	}, # ip6_dst_net_0
 	{
@@ -11643,7 +11637,7 @@ my @accept_blocks = (
 		skip => skip_config_undef ('INET6'),
 		DLT => 'RAW',
 		aliases => ['ip6 dst net ff00::/8'],
-		opt => '
+		unopt => '
 			(000) ldb      [0]
 			(001) and      #0xf0
 			(002) jeq      #0x60            jt 3	jf 7
@@ -11653,29 +11647,13 @@ my @accept_blocks = (
 			(006) ret      #262144
 			(007) ret      #0
 			',
-		unopt => '
-			(000) ldb      [0]
-			(001) and      #0xf0
-			(002) jeq      #0x60            jt 3	jf 13
-			(003) ld       [24]
-			(004) and      #0xff000000
-			(005) jeq      #0xff000000      jt 6	jf 13
-			(006) ld       #0x0
-			(007) jeq      #0x0             jt 8	jf 13
-			(008) ld       #0x0
-			(009) jeq      #0x0             jt 10	jf 13
-			(010) ld       #0x0
-			(011) jeq      #0x0             jt 12	jf 13
-			(012) ret      #262144
-			(013) ret      #0
-			',
 	}, # ip6_dst_net_8
 	{
 		name => 'ip6_dst_net_40',
 		skip => skip_config_undef ('INET6'),
 		DLT => 'RAW',
 		aliases => ['ip6 dst net ff11:2233:4400::/40'],
-		opt => '
+		unopt => '
 			(000) ldb      [0]
 			(001) and      #0xf0
 			(002) jeq      #0x60            jt 3	jf 9
@@ -11687,29 +11665,13 @@ my @accept_blocks = (
 			(008) ret      #262144
 			(009) ret      #0
 			',
-		unopt => '
-			(000) ldb      [0]
-			(001) and      #0xf0
-			(002) jeq      #0x60            jt 3	jf 13
-			(003) ld       [24]
-			(004) jeq      #0xff112233      jt 5	jf 13
-			(005) ld       [28]
-			(006) and      #0xff000000
-			(007) jeq      #0x44000000      jt 8	jf 13
-			(008) ld       #0x0
-			(009) jeq      #0x0             jt 10	jf 13
-			(010) ld       #0x0
-			(011) jeq      #0x0             jt 12	jf 13
-			(012) ret      #262144
-			(013) ret      #0
-			',
 	}, # ip6_dst_net_40
 	{
 		name => 'ip6_dst_net_80',
 		skip => skip_config_undef ('INET6'),
 		DLT => 'RAW',
 		aliases => ['ip6 dst net ff11:2233:4455:6677:8899::/80'],
-		opt => '
+		unopt => '
 			(000) ldb      [0]
 			(001) and      #0xf0
 			(002) jeq      #0x60            jt 3	jf 11
@@ -11723,22 +11685,6 @@ my @accept_blocks = (
 			(010) ret      #262144
 			(011) ret      #0
 			',
-		unopt => '
-			(000) ldb      [0]
-			(001) and      #0xf0
-			(002) jeq      #0x60            jt 3	jf 13
-			(003) ld       [24]
-			(004) jeq      #0xff112233      jt 5	jf 13
-			(005) ld       [28]
-			(006) jeq      #0x44556677      jt 7	jf 13
-			(007) ld       [32]
-			(008) and      #0xffff0000
-			(009) jeq      #0x88990000      jt 10	jf 13
-			(010) ld       #0x0
-			(011) jeq      #0x0             jt 12	jf 13
-			(012) ret      #262144
-			(013) ret      #0
-			',
 	}, # ip6_dst_net_80
 	{
 		name => 'ip6_dst_net_120',