Enable Gnulib substitute on Android systems with defective strnlen

* configure.ac (AC_FUNC_STRNLEN): Detect a bug where strnlen is
liable to integer overflows if addition of the search limit to
the string would also overflow.

* src/xdisp.c (store_mode_line_string): Remove stopgap measure.

2 files changed, 25 insertions, 12 deletions

diff --git a/configure.ac b/configure.ac
index f0437d6f8cb..909f5786c9a 100644
--- a/configure.ac
+++ b/configure.ac
@@ -1611,6 +1611,30 @@ AC_DEFUN([gl_TYPE_OFF64_T],
   [HAVE_OFF64_T=1
    AC_SUBST([HAVE_OFF64_T])])
 
+# `strnlen' cannot accept nlen greater than the size of the object S
+# on Android 2.2 and earlier.
+m4_define([ORIGINAL_AC_FUNC_STRNLEN], m4_defn([AC_FUNC_STRNLEN]))
+AC_DEFUN([AC_FUNC_STRNLEN], [
+AC_REQUIRE([AC_USE_SYSTEM_EXTENSIONS])dnl
+AC_REQUIRE([AC_CANONICAL_HOST])dnl
+AC_CACHE_CHECK([for strnlen capable of accepting large limits],
+  [emacs_cv_func_strnlen_working],
+  [AC_RUN_IFELSE([AC_LANG_PROGRAM([AC_INCLUDES_DEFAULT], [[
+  volatile size_t (*strnlen_pointer) (const char *s, size_t) = &strnlen;
+  if ((*strnlen_pointer) ("", -1) != 0)
+    return 1;
+  return 0;
+]])],[emacs_cv_func_strnlen_working=yes],
+     [emacs_cv_func_strnlen_working=no],
+     [# Guess no on Android 21 and earlier, yes elsewhere.
+      AS_IF([test -n "$ANDROID_SDK" && test "$ANDROID_SDK" -lt 22],
+        [emacs_cv_func_strnlen_working=no],
+        [emacs_cv_func_strnlen_working='guessing yes'])])])
+AS_IF([test "$emacs_cv_func_strnlen_working" != "no"],
+  [ORIGINAL_AC_FUNC_STRNLEN],
+  [ac_cv_func_strnlen_working=no
+   AC_LIBOBJ([strnlen])])])
+
 # Initialize gnulib right after choosing the compiler.
 dnl Amongst other things, this sets AR and ARFLAGS.
 gl_EARLY
diff --git a/src/xdisp.c b/src/xdisp.c
index 566c4b211d6..8c7e8e5cb43 100644
--- a/src/xdisp.c
+++ b/src/xdisp.c
@@ -28065,18 +28065,7 @@ store_mode_line_string (const char *string, Lisp_Object lisp_string,
 
   if (string != NULL)
     {
-#if defined HAVE_ANDROID && !defined ANDROID_STUBIFY    \
-  && __ANDROID_API__ < 22
-      /* Circumvent a bug in memchr preventing strnlen from returning
-         valid values when a large limit is specified.
-
-         https://issuetracker.google.com/issues/37020957 */
-      if (precision <= 0 || ((uintptr_t) string
-                             > (UINTPTR_MAX - precision)))
-        len = strlen (string);
-      else
-#endif /* HAVE_ANDROID && !ANDROID_STUBIFY && __ANDROID_API__ < 22 */
-        len = strnlen (string, precision <= 0 ? SIZE_MAX : precision);
+      len = strnlen (string, precision <= 0 ? SIZE_MAX : precision);
       lisp_string = make_string (string, len);
       if (NILP (props))
         props = mode_line_string_face_prop;