Add script to dump the VDSO

Summary: Helper script for debugging facebookexperimental/hermit#16.

Differential Revision: D41565407

fbshipit-source-id: 01cd3121dde671a563a8d2674cc42bfa6bce1226

scripts/dump-vdso.py

@@ -0,0 +1,57 @@
+#!/usr/bin/env python3
+# Copyright (c) Meta Platforms, Inc. and affiliates.
+# All rights reserved.
+#
+# This source code is licensed under the BSD-style license found in the
+# LICENSE file in the root directory of this source tree.
+
+"""
+Dumps VDSO to the given file. This is useful for debugging why Reverie might not
+be able to patch VDSO entries.
+
+Usage: ./dump-vdso.py [filename]
+
+Examples:
+  ./dump-vdso.py | hexdump -C
+  ./dump-vdso.py vdso.so && objdump -d vdso.so
+"""
+
+import argparse
+import ctypes
+import sys
+from typing import List, Optional
+
+
+def dump_vdso() -> Optional[List[ctypes.c_ubyte]]:
+    """
+    Returns a list containing the VDSO.
+    """
+    with open("/proc/self/maps") as f:
+        for line in f:
+            if "[vdso]" in line:
+                start, end = [int(x, 16) for x in line.split(" ")[0].split("-")]
+                length = end - start
+                return (ctypes.c_ubyte * length).from_address(start)
+
+
+def main() -> int:
+    parser = argparse.ArgumentParser(
+        prog="dump-vdso", description="Dumps VDSO to the given file."
+    )
+    parser.add_argument("filename", nargs="?", help="Filename to write to.")
+
+    args = parser.parse_args()
+
+    data = dump_vdso()
+
+    if args.filename:
+        with open(args.filename, "wb") as f:
+            f.write(data)
+    else:
+        sys.stdout.buffer.write(data)
+
+    return 0
+
+
+if __name__ == "__main__":
+    main()