Subject: [PATCH bpf-next v2 3/3] net: skbuff: move the fields BPF cares about directly next to the offset marker

From: Jakub Kicinski <[email-masked]>
Date: Mon, 20 Mar 2023 18:41:15 -0700

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-masked]>
--
v2: fix the assembly in tstamp test
---
 include/linux/skbuff.h                         | 18 +++++++++---------
 .../selftests/bpf/prog_tests/ctx_rewrite.c     |  8 ++++----
 2 files changed, 13 insertions(+), 13 deletions(-)

diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 36d31e74db37..6aeb0e7b9511 100644
--- a/include/linux/skbuff.h
+++ b/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)
 
diff --git a/tools/testing/selftests/bpf/prog_tests/ctx_rewrite.c b/tools/testing/selftests/bpf/prog_tests/ctx_rewrite.c
index ae7b6e50e405..4951aa978f33 100644
--- a/tools/testing/selftests/bpf/prog_tests/ctx_rewrite.c
+++ b/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;",
 	},
-- 
2.39.2