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

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Message-Id: <20230818090119.477441-5-danieltimlee@gmail.com>
Date: Fri, 18 Aug 2023 18:01:14 +0900
From: "Daniel T. Lee" <danieltimlee@...il.com>
To: Alexei Starovoitov <ast@...nel.org>,
	Daniel Borkmann <daniel@...earbox.net>,
	Andrii Nakryiko <andrii@...nel.org>
Cc: Martin KaFai Lau <martin.lau@...ux.dev>,
	Song Liu <song@...nel.org>,
	Yonghong Song <yonghong.song@...ux.dev>,
	John Fastabend <john.fastabend@...il.com>,
	KP Singh <kpsingh@...nel.org>,
	Stanislav Fomichev <sdf@...gle.com>,
	Hao Luo <haoluo@...gle.com>,
	Jiri Olsa <jolsa@...nel.org>,
	Jens Axboe <axboe@...nel.dk>,
	Johannes Thumshirn <johannes.thumshirn@....com>,
	netdev@...r.kernel.org,
	bpf@...r.kernel.org
Subject: [bpf-next 4/9] samples/bpf: fix symbol mismatch by compiler optimization

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@...il.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