For historical reasons, note BSD/OS's use of some values.

See

   https://www.usenix.org/legacy/events/bsdcon02/full_papers/lidl/lidl_html/index.html

for some information on that; we probably won't be implementing those
extensions, but we might want to avoid using the encodings used by them.

diff --git a/pcap/bpf.h b/pcap/bpf.h
index 342712932f6b3a7b9ee067ed5b88d9078c081f16..983a823323e43987a8d6dbbaac6902deb2df1482 100644 (file)
--- a/pcap/bpf.h
+++ b/pcap/bpf.h
@@ -1335,6 +1335,11 @@ struct bpf_program {
  * (and perhaps implement it in the reference BPF implementation
  * and encourage its implementation elsewhere).
  */
+
+/*
+ * The upper 8 bits of the opcode aren't used. BSD/OS used 0x8000.
+ */
+
 /* instruction classes */
 #define BPF_CLASS(code) ((code) & 0x07)
 #define                BPF_LD          0x00
@@ -1351,7 +1356,7 @@ struct bpf_program {
 #define                BPF_W           0x00
 #define                BPF_H           0x08
 #define                BPF_B           0x10
-/*                             0x18    reserved */
+/*                             0x18    reserved; used by BSD/OS */
 #define BPF_MODE(code) ((code) & 0xe0)
 #define                BPF_IMM         0x00
 #define                BPF_ABS         0x20
@@ -1359,8 +1364,8 @@ struct bpf_program {
 #define                BPF_MEM         0x60
 #define                BPF_LEN         0x80
 #define                BPF_MSH         0xa0
-/*                             0xc0    reserved */
-/*                             0xe0    reserved */
+/*                             0xc0    reserved; used by BSD/OS */
+/*                             0xe0    reserved; used by BSD/OS */
 
 /* alu/jmp fields */
 #define BPF_OP(code)   ((code) & 0xf0)
@@ -1386,7 +1391,7 @@ struct bpf_program {
 #define                BPF_JGT         0x20
 #define                BPF_JGE         0x30
 #define                BPF_JSET        0x40
-/*                             0x50    reserved */
+/*                             0x50    reserved; used on BSD/OS */
 /*                             0x60    reserved */
 /*                             0x70    reserved */
 /*                             0x80    reserved */
@@ -1417,6 +1422,7 @@ struct bpf_program {
 /*                             0x30    reserved */
 /*                             0x38    reserved */
 /* #define     BPF_COPX        0x40    NetBSD "coprocessor" extensions */
+/*                                     also used on BSD/OS */
 /*                             0x48    reserved */
 /*                             0x50    reserved */
 /*                             0x58    reserved */
@@ -1432,7 +1438,7 @@ struct bpf_program {
 /*                             0xa8    reserved */
 /*                             0xb0    reserved */
 /*                             0xb8    reserved */
-/*                             0xc0    reserved */
+/*                             0xc0    reserved; used on BSD/OS */
 /*                             0xc8    reserved */
 /*                             0xd0    reserved */
 /*                             0xd8    reserved */