[PATCH] perf trace: sys_enter_openat.c fix libbpf 1.0+ compatibility

[Leo Yan]

Avoid use of tools/perf/include/bpf/bpf.h and use the more regular BPF
headers.

With fixing:

  # ./perf trace -e examples/bpf/sys_enter_openat.c
  0.000 irqbalance/1025 syscalls:sys_enter_openat(AT_FDCWD, "", O_RDONLY)
  1.596 irqbalance/1025 syscalls:sys_enter_openat(AT_FDCWD, "", O_RDONLY)
  1.832 irqbalance/1025 syscalls:sys_enter_openat(AT_FDCWD, "", O_RDONLY)
  1.864 irqbalance/1025 syscalls:sys_enter_openat(AT_FDCWD, "", O_RDONLY)

Signed-off-by: Leo Yan <leo.yan@xxxxxxxxxx>
---
 tools/perf/examples/bpf/sys_enter_openat.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/tools/perf/examples/bpf/sys_enter_openat.c b/tools/perf/examples/bpf/sys_enter_openat.c
index c4481c390d23..8edfa7c147d1 100644
--- a/tools/perf/examples/bpf/sys_enter_openat.c
+++ b/tools/perf/examples/bpf/sys_enter_openat.c
@@ -14,7 +14,9 @@
  * the return value.
  */
 
-#include <bpf/bpf.h>
+#include <linux/bpf.h>
+#include <linux/limits.h>
+#include <bpf/bpf_helpers.h>
 
 struct syscall_enter_openat_args {
 	unsigned long long unused;
@@ -25,9 +27,10 @@ struct syscall_enter_openat_args {
 	long		   mode;
 };
 
-int syscall_enter(openat)(struct syscall_enter_openat_args *args)
+SEC("syscalls:sys_enter_openat")
+int syscall_enter_openat(struct syscall_enter_openat_args *args)
 {
 	return 1;
 }
 
-license(GPL);
+char _license[] SEC("license") = "GPL";