tools/clang/codesearch: improve codesearch to handle global variables

Contributes to #6469.

To handle global variables:

* Add EntityKindGlobalVariable
* Modify TraverseVarDecl() function logic
* Add a check to ensure StartLine and EndLine are in the same file
* Fix missing #include <cstdint> in json.h

4 files changed, 81 insertions, 0 deletions

diff --git a/pkg/codesearch/testdata/global_vars.c b/pkg/codesearch/testdata/global_vars.c
new file mode 100644
index 000000000..a7f3e76f0
--- /dev/null
+++ b/pkg/codesearch/testdata/global_vars.c
@@ -0,0 +1,18 @@
+// Copyright 2026 syzkaller project authors. All rights reserved.
+// Use of this source code is governed by Apache 2 LICENSE that can be found in the LICENSE file.
+
+#define DEFINE_VAR(name) int name = 1
+#define DEFINE_STATIC_VAR(name) static int name = 2
+
+DEFINE_VAR(macro_var);
+
+DEFINE_STATIC_VAR(static_macro_var);
+
+int global_var = 3;
+static int local_to_file_var = 4;
+
+void some_function(void)
+{
+	int local_var = 5;
+	(void)local_var;
+}
diff --git a/pkg/codesearch/testdata/global_vars.c.json b/pkg/codesearch/testdata/global_vars.c.json
new file mode 100644
index 000000000..89fc1a04b
--- /dev/null
+++ b/pkg/codesearch/testdata/global_vars.c.json
@@ -0,0 +1,61 @@
+{
+	"definitions": [
+		{
+			"name": "some_function",
+			"type": "void (void)",
+			"kind": "function",
+			"body": {
+				"file": "global_vars.c",
+				"start_line": 14,
+				"end_line": 18
+			},
+			"comment": {}
+		},
+		{
+			"name": "global_var",
+			"type": "int",
+			"kind": "global_variable",
+			"body": {
+				"file": "global_vars.c",
+				"start_line": 11,
+				"end_line": 11
+			},
+			"comment": {}
+		},
+		{
+			"name": "local_to_file_var",
+			"type": "int",
+			"kind": "global_variable",
+			"is_static": true,
+			"body": {
+				"file": "global_vars.c",
+				"start_line": 12,
+				"end_line": 12
+			},
+			"comment": {}
+		},
+		{
+			"name": "macro_var",
+			"type": "int",
+			"kind": "global_variable",
+			"body": {
+				"file": "global_vars.c",
+				"start_line": 7,
+				"end_line": 7
+			},
+			"comment": {}
+		},
+		{
+			"name": "static_macro_var",
+			"type": "int",
+			"kind": "global_variable",
+			"is_static": true,
+			"body": {
+				"file": "global_vars.c",
+				"start_line": 9,
+				"end_line": 9
+			},
+			"comment": {}
+		}
+	]
+}
\ No newline at end of file
diff --git a/pkg/codesearch/testdata/query-dir-index-root b/pkg/codesearch/testdata/query-dir-index-root
index 5e72b64c1..7370911ea 100644
--- a/pkg/codesearch/testdata/query-dir-index-root
+++ b/pkg/codesearch/testdata/query-dir-index-root
@@ -4,6 +4,7 @@ directory / subdirs:
  - mm
 
 directory / files:
+ - global_vars.c
  - refs.c
  - source0.c
  - source0.h
diff --git a/pkg/codesearch/testdata/query-dir-index-root2 b/pkg/codesearch/testdata/query-dir-index-root2
index 804bdce54..2b9fdce5d 100644
--- a/pkg/codesearch/testdata/query-dir-index-root2
+++ b/pkg/codesearch/testdata/query-dir-index-root2
@@ -4,6 +4,7 @@ directory /mm/.. subdirs:
  - mm
 
 directory /mm/.. files:
+ - global_vars.c
  - refs.c
  - source0.c
  - source0.h