Add a tool to check dependencies.

A follow-up change will tweak linux_shared to run this tool on
libcrypto.so and libssl.so.

Bug: 132
Change-Id: I868551cebdc308829dee3dca12a39395c4a251ee
Reviewed-on: https://boringssl-review.googlesource.com/18407
Reviewed-by: Steven Valdez <svaldez@google.com>

util/check_imported_libraries.go

@@ -0,0 +1,56 @@
+// Copyright (c) 2017, Google Inc.
+//
+// Permission to use, copy, modify, and/or distribute this software for any
+// purpose with or without fee is hereby granted, provided that the above
+// copyright notice and this permission notice appear in all copies.
+//
+// THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+// WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+// MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
+// SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+// WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION
+// OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
+// CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+
+// check_imported_libraries.go checks that each of its arguments only imports a
+// whitelist of allowed libraries. This is used to avoid accidental dependencies
+// on libstdc++.so.
+package main
+
+import (
+	"debug/elf"
+	"fmt"
+	"os"
+)
+
+func checkImportedLibraries(path string) {
+	file, err := elf.Open(path)
+	if err != nil {
+		fmt.Fprintf(os.Stderr, "Error opening %s: %s\n", path, err)
+		os.Exit(1)
+	}
+	defer file.Close()
+
+	libs, err := file.ImportedLibraries()
+	if err != nil {
+		fmt.Fprintf(os.Stderr, "Error reading %s: %s\n", path, err)
+		os.Exit(1)
+	}
+
+	for _, lib := range libs {
+		if lib != "libc.so.6" && lib != "libcrypto.so" && lib != "libpthread.so.0" {
+			fmt.Printf("Invalid dependency for %s: %s\n", path, lib)
+			fmt.Printf("All dependencies:\n")
+			for _, lib := range libs {
+				fmt.Printf("    %s\n", lib)
+			}
+			os.Exit(1)
+		}
+	}
+}
+
+func main() {
+	for _, path := range os.Args[1:] {
+		checkImportedLibraries(path)
+	}
+}