net: skbuff: move the fields BPF cares about directly next to the offset marker

To avoid more possible BPF dependencies with moving bitfields
around keep the fields BPF cares about right next to the offset
marker.

Signed-off-by: Jakub Kicinski <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Martin KaFai Lau <[email protected]>

Author: kuba-moo

include/linux/skbuff.h

@@ -947,15 +947,15 @@ struct sk_buff {
 	/* private: */
 	__u8			__mono_tc_offset[0];
 	/* public: */
-	__u8			remcsum_offload:1;
-	__u8			csum_complete_sw:1;
-	__u8			csum_level:2;
-	__u8			dst_pending_confirm:1;
 	__u8			mono_delivery_time:1;	/* See SKB_MONO_DELIVERY_TIME_MASK */
 #ifdef CONFIG_NET_CLS_ACT
-	__u8			tc_skip_classify:1;
 	__u8			tc_at_ingress:1;	/* See TC_AT_INGRESS_MASK */
+	__u8			tc_skip_classify:1;
 #endif
+	__u8			remcsum_offload:1;
+	__u8			csum_complete_sw:1;
+	__u8			csum_level:2;
+	__u8			dst_pending_confirm:1;
 
 	__u8			l4_hash:1;
 	__u8			sw_hash:1;
@@ -1072,11 +1072,11 @@ struct sk_buff {
  * around, you also must adapt these constants.
  */
 #ifdef __BIG_ENDIAN_BITFIELD
-#define TC_AT_INGRESS_MASK		(1 << 0)
-#define SKB_MONO_DELIVERY_TIME_MASK	(1 << 2)
+#define SKB_MONO_DELIVERY_TIME_MASK	(1 << 7)
+#define TC_AT_INGRESS_MASK		(1 << 6)
 #else
-#define TC_AT_INGRESS_MASK		(1 << 7)
-#define SKB_MONO_DELIVERY_TIME_MASK	(1 << 5)
+#define SKB_MONO_DELIVERY_TIME_MASK	(1 << 0)
+#define TC_AT_INGRESS_MASK		(1 << 1)
 #endif
 #define SKB_BF_MONO_TC_OFFSET		offsetof(struct sk_buff, __mono_tc_offset)
 

tools/testing/selftests/bpf/prog_tests/ctx_rewrite.c

@@ -69,15 +69,15 @@ static struct test_case test_cases[] = {
 	{
 		N(SCHED_CLS, struct __sk_buff, tstamp),
 		.read  = "r11 = *(u8 *)($ctx + sk_buff::__mono_tc_offset);"
-			 "w11 &= 160;"
-			 "if w11 != 0xa0 goto pc+2;"
+			 "w11 &= 3;"
+			 "if w11 != 0x3 goto pc+2;"
 			 "$dst = 0;"
 			 "goto pc+1;"
 			 "$dst = *(u64 *)($ctx + sk_buff::tstamp);",
 		.write = "r11 = *(u8 *)($ctx + sk_buff::__mono_tc_offset);"
-			 "if w11 & 0x80 goto pc+1;"
+			 "if w11 & 0x2 goto pc+1;"
 			 "goto pc+2;"
-			 "w11 &= -33;"
+			 "w11 &= -2;"
 			 "*(u8 *)($ctx + sk_buff::__mono_tc_offset) = r11;"
 			 "*(u64 *)($ctx + sk_buff::tstamp) = $src;",
 	},