From af117e303f79e84bd96c385101694aa3028bbc48 Mon Sep 17 00:00:00 2001
From: "copilot-swe-agent[bot]" <198982749+Copilot@users.noreply.github.com>
Date: Sun, 1 Mar 2026 11:08:27 +0000
Subject: [PATCH 1/2] Initial plan


From 16b22c3eb8b904d34ba159e9c80a164b9d3e58e9 Mon Sep 17 00:00:00 2001
From: "copilot-swe-agent[bot]" <198982749+Copilot@users.noreply.github.com>
Date: Sun, 1 Mar 2026 11:10:54 +0000
Subject: [PATCH 2/2] Fix hardcoded cpu=0 in libbpf.c: use
 get_first_online_cpu() for probe attachment

Co-authored-by: ekyooo <46103109+ekyooo@users.noreply.github.com>
---
 src/cc/libbpf.c | 25 +++++++++++++++++++++++--
 1 file changed, 23 insertions(+), 2 deletions(-)

diff --git a/src/cc/libbpf.c b/src/cc/libbpf.c
index 246d0b25d0fb..7bfd1c986074 100644
--- a/src/cc/libbpf.c
+++ b/src/cc/libbpf.c
@@ -1080,6 +1080,27 @@ static int bpf_get_retprobe_bit(const char *event_type)
   return errno ? -1 : ret;
 }
 
+/*
+ * Returns the first online CPU by parsing /sys/devices/system/cpu/online.
+ * The file contains a sorted list of ranges (e.g. "0-3", "1,3-5").
+ * Reading the first integer with fscanf stops at the first non-digit
+ * (hyphen or comma), which always gives the lowest-numbered online CPU.
+ * Falls back to CPU 0 if the file cannot be read or parsed.
+ */
+static int get_first_online_cpu(void)
+{
+  FILE *fp;
+  int cpu = 0;
+
+  fp = fopen("/sys/devices/system/cpu/online", "r");
+  if (!fp)
+    return 0;
+  if (fscanf(fp, "%d", &cpu) != 1)
+    cpu = 0;
+  fclose(fp);
+  return cpu;
+}
+
 /*
  * Kernel API with e12f03d ("perf/core: Implement the 'perf_kprobe' PMU") allows
  * creating [k,u]probe with perf_event_open, which makes it easier to clean up
@@ -1092,7 +1113,7 @@ static int bpf_try_perf_event_open_with_probe(const char *name, uint64_t offs,
   struct perf_event_attr attr = {};
   int type = bpf_find_probe_type(event_type);
   int is_return_bit = bpf_get_retprobe_bit(event_type);
-  int cpu = 0;
+  int cpu = get_first_online_cpu();
 
   if (type < 0 || is_return_bit < 0)
     return -1;
@@ -1160,7 +1181,7 @@ static const char *get_tracefs_path()
 static int bpf_attach_tracing_event(int progfd, const char *event_path, int pid,
                                     int *pfd)
 {
-  int efd, cpu = 0;
+  int efd, cpu = get_first_online_cpu();
   ssize_t bytes;
   char buf[PATH_MAX];
   struct perf_event_attr attr = {};