[bpf-next 4/9] samples/bpf: fix symbol mismatch by compiler optimization

["Daniel T. Lee" <danieltimlee@gmail.com>]

Currently, multiple kprobe programs are suffering from symbol mismatch
due to compiler optimization. These optimizations might induce
additional suffix to the symbol name such as '.isra' or '.constprop'.

    # egrep ' finish_task_switch| __netif_receive_skb_core' /proc/kallsyms
    ffffffff81135e50 t finish_task_switch.isra.0
    ffffffff81dd36d0 t __netif_receive_skb_core.constprop.0
    ffffffff8205cc0e t finish_task_switch.isra.0.cold
    ffffffff820b1aba t __netif_receive_skb_core.constprop.0.cold

To avoid this, this commit replaces the original kprobe section to
kprobe.multi in order to match symbol with wildcard characters. Here,
asterisk is used for avoiding symbol mismatch.

Signed-off-by: Daniel T. Lee <danieltimlee@gmail.com>
---
 samples/bpf/offwaketime.bpf.c | 2 +-
 samples/bpf/tracex1.bpf.c     | 3 ++-
 2 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/samples/bpf/offwaketime.bpf.c b/samples/bpf/offwaketime.bpf.c
index 8e5105811178..3200a0f44969 100644
--- a/samples/bpf/offwaketime.bpf.c
+++ b/samples/bpf/offwaketime.bpf.c
@@ -118,7 +118,7 @@ int oncpu(struct trace_event_raw_sched_switch *ctx)
 	/* record previous thread sleep time */
 	u32 pid = ctx->prev_pid;
 #else
-SEC("kprobe/finish_task_switch")
+SEC("kprobe.multi/finish_task_switch*")
 int oncpu(struct pt_regs *ctx)
 {
 	struct task_struct *p = (void *) PT_REGS_PARM1(ctx);
diff --git a/samples/bpf/tracex1.bpf.c b/samples/bpf/tracex1.bpf.c
index bb78bdbffa87..f3be14a03964 100644
--- a/samples/bpf/tracex1.bpf.c
+++ b/samples/bpf/tracex1.bpf.c
@@ -22,11 +22,12 @@
  * Number of arguments and their positions can change, etc.
  * In such case this bpf+kprobe example will no longer be meaningful
  */
-SEC("kprobe/__netif_receive_skb_core")
+SEC("kprobe.multi/__netif_receive_skb_core*")
 int bpf_prog1(struct pt_regs *ctx)
 {
 	/* attaches to kprobe __netif_receive_skb_core,
 	 * looks for packets on loobpack device and prints them
+	 * (wildcard is used for avoiding symbol mismatch due to optimization)
 	 */
 	char devname[IFNAMSIZ];
 	struct net_device *dev;
-- 
2.34.1