kcov: refactor common handle ID into kcov_common_handle_id

Store common handle IDs in "struct kcov_common_handle_id", which consumes
no space in non-KCOV builds.

This cleanup removes #ifdef boilerplate code from subsystems that
integrate with KCOV (in particular in usbip_common.h and skbuff.h, see the
diffstat).

This should also make it easier to add KCOV remote coverage to more
subsystems in the future.

Link: https://lore.kernel.org/20260430-kcov-refactor-common-handle-v1-1-23a0c7a0ba38@google.com
Signed-off-by: Jann Horn <jannh@google.com>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Reviewed-by: Dmitry Vyukov <dvyukov@google.com>
Acked-by: Jakub Kicinski <kuba@kernel.org>
Cc: Alexander Potapenko <glider@google.com>
Cc: Andrey Konovalov <andreyknvl@gmail.com>
Cc: Eugenio Pérez <eperezma@redhat.com>
Cc: Hongren (Zenithal) Zheng <i@zenithal.me>
Cc: Jann Horn <jannh@google.com>
Cc: Jason Wang <jasowang@redhat.com>
Cc: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Valentina Manea <valentina.manea.m@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

3 files changed, 15 insertions, 17 deletions

diff --git a/include/linux/kcov.h b/include/linux/kcov.h
index 0143358874b0..cdb72b3859d8 100644
--- a/include/linux/kcov.h
+++ b/include/linux/kcov.h
@@ -43,11 +43,11 @@ do {						\
 /* See Documentation/dev-tools/kcov.rst for usage details. */
 void kcov_remote_start(u64 handle);
 void kcov_remote_stop(void);
-u64 kcov_common_handle(void);
+struct kcov_common_handle_id kcov_common_handle(void);
 
-static inline void kcov_remote_start_common(u64 id)
+static inline void kcov_remote_start_common(struct kcov_common_handle_id id)
 {
-	kcov_remote_start(kcov_remote_handle(KCOV_SUBSYSTEM_COMMON, id));
+	kcov_remote_start(kcov_remote_handle(KCOV_SUBSYSTEM_COMMON, id.val));
 }
 
 static inline void kcov_remote_start_usb(u64 id)
@@ -99,11 +99,11 @@ static inline void kcov_prepare_switch(struct task_struct *t) {}
 static inline void kcov_finish_switch(struct task_struct *t) {}
 static inline void kcov_remote_start(u64 handle) {}
 static inline void kcov_remote_stop(void) {}
-static inline u64 kcov_common_handle(void)
+static inline struct kcov_common_handle_id kcov_common_handle(void)
 {
-	return 0;
+	return (struct kcov_common_handle_id){};
 }
-static inline void kcov_remote_start_common(u64 id) {}
+static inline void kcov_remote_start_common(struct kcov_common_handle_id id) {}
 static inline void kcov_remote_start_usb(u64 id) {}
 static inline void kcov_remote_start_usb_softirq(u64 id) {}
 static inline void kcov_remote_stop_softirq(void) {}
diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 2bcf78a4de7b..a3fe418f7ced 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -1082,9 +1082,7 @@ struct sk_buff {
 	__u16			network_header;
 	__u16			mac_header;
 
-#ifdef CONFIG_KCOV
-	u64			kcov_handle;
-#endif
+	struct kcov_common_handle_id kcov_handle;
 
 	); /* end headers group */
 
@@ -5437,20 +5435,14 @@ static inline void skb_reset_csum_not_inet(struct sk_buff *skb)
 }
 
 static inline void skb_set_kcov_handle(struct sk_buff *skb,
-				       const u64 kcov_handle)
+				       struct kcov_common_handle_id kcov_handle)
 {
-#ifdef CONFIG_KCOV
 	skb->kcov_handle = kcov_handle;
-#endif
 }
 
-static inline u64 skb_get_kcov_handle(struct sk_buff *skb)
+static inline struct kcov_common_handle_id skb_get_kcov_handle(struct sk_buff *skb)
 {
-#ifdef CONFIG_KCOV
 	return skb->kcov_handle;
-#else
-	return 0;
-#endif
 }
 
 static inline void skb_mark_for_recycle(struct sk_buff *skb)
diff --git a/include/linux/types.h b/include/linux/types.h
index 608050dbca6a..93166b0b0617 100644
--- a/include/linux/types.h
+++ b/include/linux/types.h
@@ -224,6 +224,12 @@ struct ustat {
 	char			f_fpack[6];
 };
 
+struct kcov_common_handle_id {
+#ifdef CONFIG_KCOV
+	u64 val;
+#endif
+};
+
 /**
  * struct callback_head - callback structure for use with RCU and task_work
  * @next: next update requests in a list