Fix find_libraries when no interpreter

Fixed edge case where find_libraries is called on a dynamic
shared object or when the interpreter itself can't be found.

* added unit tests

sqlelf/sql.py

@@ -55,7 +55,17 @@ def execute(
 def find_libraries(binary: lief.Binary) -> Dict[str, str]:
     """Use the interpreter in a binary to determine the path of each linked library"""
     interpreter = binary.interpreter  # type: ignore
-    interpreter_cmd = sh.Command(interpreter)
+    # interpreter can be none/empty if it is a static linked binary
+    # or a dynamic linked binary itself
+    if not interpreter:
+        return {}
+    try:
+        interpreter_cmd = sh.Command(interpreter)
+    except sh.CommandNotFound:
+        # If we can't find the interpreter, we can't resolve the libraries
+        # so we return an empty dictionary
+        # This can happen if we are building binaries wth Nix
+        return {}
     resolution = interpreter_cmd("--list", binary.name)
     result = OrderedDict()
     # TODO: Figure out why `--list` and `ldd` produce different outcomes

tests/test_sql.py

@@ -41,6 +41,20 @@ def test_simple_binary_mocked(Command: sh.Command) -> None:
     assert result["libselinux.so.1"] == "not"
 
 
+def test_find_libraries_no_interpreter() -> None:
+    binary = lief.parse("/bin/ls")
+    binary.interpreter = ""  # type: ignore
+    result = sql.find_libraries(binary)
+    assert len(result) == 0
+
+
+def test_find_libraries_missing_interpreter() -> None:
+    binary = lief.parse("/bin/ls")
+    binary.interpreter = "/nix/store/something/ld-linux.so.2"  # type: ignore
+    result = sql.find_libraries(binary)
+    assert len(result) == 0
+
+
 def test_simple_select_header() -> None:
     # TODO(fzakaria): Figure out a better binary to be doing that we control
     engine = sql.make_sql_engine(["/bin/ls"])