libbpf: Add uprobe syscall feature detection

Adding uprobe syscall feature detection that will be used
in following changes.

Signed-off-by: Jiri Olsa <jolsa@kernel.org>

Author: olsajiri

tools/lib/bpf/features.c

@@ -506,6 +506,25 @@ static int probe_kern_arg_ctx_tag(int token_fd)
 	return probe_fd(prog_fd);
 }
 
+#ifdef __x86_64__
+#ifndef __NR_uprobe
+#define __NR_uprobe 336
+#endif
+static int probe_uprobe_syscall(int token_fd)
+{
+	/*
+	 * When not executed from executed kernel provided trampoline,
+	 * the uprobe syscall returns ENXIO error.
+	 */
+	return syscall(__NR_uprobe) == -1 && errno == ENXIO;
+}
+#else
+static int probe_uprobe_syscall(int token_fd)
+{
+	return 0;
+}
+#endif
+
 typedef int (*feature_probe_fn)(int /* token_fd */);
 
 static struct kern_feature_cache feature_cache;
@@ -581,6 +600,9 @@ static struct kern_feature_desc {
 	[FEAT_BTF_QMARK_DATASEC] = {
 		"BTF DATASEC names starting from '?'", probe_kern_btf_qmark_datasec,
 	},
+	[FEAT_UPROBE_SYSCALL] = {
+		"Kernel supports uprobe syscall", probe_uprobe_syscall,
+	},
 };
 
 bool feat_supported(struct kern_feature_cache *cache, enum kern_feature_id feat_id)

tools/lib/bpf/libbpf_internal.h

@@ -392,6 +392,8 @@ enum kern_feature_id {
 	FEAT_ARG_CTX_TAG,
 	/* Kernel supports '?' at the front of datasec names */
 	FEAT_BTF_QMARK_DATASEC,
+	/* Kernel supports uprobe syscall */
+	FEAT_UPROBE_SYSCALL,
 	__FEAT_CNT,
 };