[PATCHv4 bpf-next 1/5] libbpf: Add uprobe syscall feature detection

[Jiri Olsa <jolsa@kernel.org>]

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

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
---
 tools/lib/bpf/features.c        | 24 ++++++++++++++++++++++++
 tools/lib/bpf/libbpf_internal.h |  2 ++
 2 files changed, 26 insertions(+)

diff --git a/tools/lib/bpf/features.c b/tools/lib/bpf/features.c
index 2fa434f09cce..adcad221c601 100644
--- a/tools/lib/bpf/features.c
+++ b/tools/lib/bpf/features.c
@@ -568,6 +568,27 @@ static int probe_ldimm64_full_range_off(int token_fd)
 	return 1;
 }
 
+#ifdef __x86_64__
+
+#ifndef __NR_uprobe
+#define __NR_uprobe 336
+#endif
+
+static int probe_uprobe_syscall(int token_fd)
+{
+	/*
+	 * If kernel supports uprobe() syscall, it will return -ENXIO when called
+	 * from the outside of a kernel-generated uprobe trampoline.
+	 */
+	return syscall(__NR_uprobe) < 0 && 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;
@@ -646,6 +667,9 @@ static struct kern_feature_desc {
 	[FEAT_LDIMM64_FULL_RANGE_OFF] = {
 		"full range LDIMM64 support", probe_ldimm64_full_range_off,
 	},
+	[FEAT_UPROBE_SYSCALL] = {
+		"kernel supports uprobe syscall", probe_uprobe_syscall,
+	},
 };
 
 bool feat_supported(struct kern_feature_cache *cache, enum kern_feature_id feat_id)
diff --git a/tools/lib/bpf/libbpf_internal.h b/tools/lib/bpf/libbpf_internal.h
index 974147e8a8aa..4bcb6ca69bb1 100644
--- a/tools/lib/bpf/libbpf_internal.h
+++ b/tools/lib/bpf/libbpf_internal.h
@@ -394,6 +394,8 @@ enum kern_feature_id {
 	FEAT_BTF_QMARK_DATASEC,
 	/* Kernel supports LDIMM64 imm offsets past 512 MiB. */
 	FEAT_LDIMM64_FULL_RANGE_OFF,
+	/* Kernel supports uprobe syscall */
+	FEAT_UPROBE_SYSCALL,
 	__FEAT_CNT,
 };
 
-- 
2.53.0