Avoid some strlen work, primarily via strnlen

* admin/merge-gnulib (GNULIB_MODULES): Add strnlen.
* lib-src/etags.c (find_entries):
* src/emacs.c (main):
* src/nsmenu.m (parseKeyEquiv:):
* src/nsterm.m (ns_xlfd_to_fontname):
* src/term.c (vfatal):
Prefer !*X to !strlen (X).
* lib-src/etags.c (pfnote, add_regex):
* lib-src/pop.c (pop_open):
* lib-src/update-game-score.c (main):
* lwlib/lwlib.c (lw_separator_p):
* src/doprnt.c (doprnt):
* src/emacs.c (main):
* src/inotify.c (inotifyevent_to_event):
* src/keyboard.c (menu_separator_name_p, parse_tool_bar_item):
* src/sysdep.c (get_current_dir_name_or_unreachable):
* src/xdisp.c (store_mode_line_string):
Use strnlen to avoid unnecessary work with strlen.
* lib-src/etags.c (Prolog_functions, prolog_pr)
(Erlang_functions, erlang_func):
Prefer ptrdiff_t to size_t when either will do.
(prolog_pr, erlang_func): New arg LASTLEN, to avoid
unnecessary strlen call. All callers changed.
* lib/gnulib.mk.in, m4/gnulib-comp.m4: Regenerate.
* lib/strnlen.c, m4/strnlen.m4: New files, copied from Gnulib.
* lwlib/lwlib.c (lw_separator_p):
* src/json.c (json_has_prefix):
Use strncmp to avoid unecessary work with strlen + memcmp.
* src/process.c (set_socket_option): Use SBYTES instead of strlen.

20 files changed, 174 insertions, 127 deletions

diff --git a/admin/merge-gnulib b/admin/merge-gnulib
index 78e74882f3d..6cf29589f71 100755
--- a/admin/merge-gnulib
+++ b/admin/merge-gnulib
@@ -40,7 +40,7 @@ GNULIB_MODULES='
   manywarnings memmem-simple memrchr minmax mkostemp mktime nstrftime
   pipe2 pselect pthread_sigmask putenv qcopy-acl readlink readlinkat regex
   sig2str socklen stat-time std-gnu11 stdalign stddef stdio
-  stpcpy strtoimax symlink sys_stat sys_time
+  stpcpy strnlen strtoimax symlink sys_stat sys_time
   tempname time time_r time_rz timegm timer-time timespec-add timespec-sub
   update-copyright unlocked-io utimens
   vla warnings
diff --git a/lib-src/etags.c b/lib-src/etags.c
index 442b622cceb..036c485d0bb 100644
--- a/lib-src/etags.c
+++ b/lib-src/etags.c
@@ -1811,7 +1811,7 @@ find_entries (FILE *inf)
         }
       *cp = '\0';
 
-      if (strlen (lp) > 0)
+      if (*lp)
         {
           lang = get_language_from_interpreter (lp);
           if (lang != NULL && lang->function != NULL)
@@ -2012,7 +2012,7 @@ pfnote (char *name, bool is_func, char *linestart, int linelen, int lno,
   np->left = np->right = NULL;
   if (CTAGS && !cxref_style)
     {
-      if (strlen (linestart) < 50)
+      if (strnlen (linestart, 50) < 50)
         np->regex = concat (linestart, "$", "");
       else
         np->regex = savenstr (linestart, 50);
@@ -5883,20 +5883,15 @@ HTML_labels (FILE *inf)
  * Original code by Sunichirou Sugou (1989)
  * Rewritten by Anders Lindgren (1996)
  */
-static size_t prolog_pr (char *, char *);
+static ptrdiff_t prolog_pr (char *, char *, ptrdiff_t);
 static void prolog_skip_comment (linebuffer *, FILE *);
 static size_t prolog_atom (char *, size_t);
 
 static void
 Prolog_functions (FILE *inf)
 {
-  char *cp, *last;
-  size_t len;
-  size_t allocated;
-
-  allocated = 0;
-  len = 0;
-  last = NULL;
+  char *cp, *last = NULL;
+  ptrdiff_t lastlen = 0, allocated = 0;
 
   LOOP_ON_INPUT_LINES (inf, lb, cp)
     {
@@ -5906,17 +5901,22 @@ Prolog_functions (FILE *inf)
         continue;
       else if (cp[0] == '/' && cp[1] == '*')    /* comment. */
         prolog_skip_comment (&lb, inf);
-      else if ((len = prolog_pr (cp, last)) > 0)
+      else
         {
-          /* Predicate or rule.  Store the function name so that we
-             only generate a tag for the first clause.  */
-          if (last == NULL)
-            last = xnew (len + 1, char);
-          else if (len + 1 > allocated)
-            xrnew (last, len + 1, char);
-          allocated = len + 1;
-          memcpy (last, cp, len);
-          last[len] = '\0';
+          ptrdiff_t len = prolog_pr (cp, last, lastlen);
+          if (0 < len)
+            {
+              /* Store the predicate name to avoid generating duplicate
+                 tags later.  */
+              if (allocated <= len)
+                {
+                  xrnew (last, len + 1, char);
+                  allocated = len + 1;
+                }
+              memcpy (last, cp, len);
+              last[len] = '\0';
+              lastlen = len;
+            }
         }
     }
   free (last);
@@ -5949,33 +5949,25 @@ prolog_skip_comment (linebuffer *plb, FILE *inf)
  * Return the size of the name of the predicate or rule, or 0 if no
  * header was found.
  */
-static size_t
-prolog_pr (char *s, char *last)
-
-                                /* Name of last clause. */
+static ptrdiff_t
+prolog_pr (char *s, char *last, ptrdiff_t lastlen)
 {
-  size_t pos;
-  size_t len;
-
-  pos = prolog_atom (s, 0);
-  if (! pos)
+  ptrdiff_t len = prolog_atom (s, 0);
+  if (len == 0)
     return 0;
+  ptrdiff_t pos = skip_spaces (s + len) - s;
 
-  len = pos;
-  pos = skip_spaces (s + pos) - s;
-
+  /* Save only the first clause.  */
   if ((s[pos] == '.'
        || (s[pos] == '(' && (pos += 1))
        || (s[pos] == ':' && s[pos + 1] == '-' && (pos += 2)))
-      && (last == NULL          /* save only the first clause */
-          || len != strlen (last)
-          || !strneq (s, last, len)))
-        {
-          make_tag (s, len, true, s, pos, lineno, linecharno);
-          return len;
-        }
-  else
-    return 0;
+      && ! (lastlen == len && memcmp (s, last, len) == 0))
+    {
+      make_tag (s, len, true, s, pos, lineno, linecharno);
+      return len;
+    }
+
+  return 0;
 }
 
 /*
@@ -6043,21 +6035,15 @@ prolog_atom (char *s, size_t pos)
  * Assumes that Erlang functions start at column 0.
  * Original code by Anders Lindgren (1996)
  */
-static int erlang_func (char *, char *, int *);
+static int erlang_func (char *, char *, ptrdiff_t, ptrdiff_t *);
 static void erlang_attribute (char *);
 static int erlang_atom (char *);
 
 static void
 Erlang_functions (FILE *inf)
 {
-  char *cp, *last;
-  int len;
-  int allocated;
-  int name_offset = 0;
-
-  allocated = 0;
-  len = 0;
-  last = NULL;
+  char *cp, *last = NULL;
+  ptrdiff_t lastlen = 0, allocated = 0;
 
   LOOP_ON_INPUT_LINES (inf, lb, cp)
     {
@@ -6078,19 +6064,23 @@ Erlang_functions (FILE *inf)
               last = NULL;
             }
         }
-      else if ((len = erlang_func (cp, last, &name_offset)) > 0)
+      else
         {
-          /*
-           * Function.  Store the function name so that we only
-           * generates a tag for the first clause.
-           */
-          if (last == NULL)
-            last = xnew (len + 1, char);
-          else if (len + 1 > allocated)
-            xrnew (last, len + 1, char);
-          allocated = len + 1;
-          memcpy (last, cp + name_offset, len);
-          last[len] = '\0';
+          ptrdiff_t name_offset;
+          ptrdiff_t len = erlang_func (cp, last, lastlen, &name_offset);
+          if (0 < len)
+            {
+              /* Store the function name to avoid generating duplicate
+                 tags later.  */
+              if (allocated <= len)
+                {
+                  xrnew (last, len + 1, char);
+                  allocated = len + 1;
+                }
+              memcpy (last, cp + name_offset, len);
+              last[len] = '\0';
+              lastlen = len;
+            }
         }
     }
   free (last);
@@ -6108,40 +6098,27 @@ Erlang_functions (FILE *inf)
  * was found.
  */
 static int
-erlang_func (char *s, char *last, int *name_offset)
-
-                                /* Name of last clause. */
+erlang_func (char *s, char *last, ptrdiff_t lastlen, ptrdiff_t *name_offset)
 {
-  int pos;
-  int len;
   char *name = s;
-
-  pos = erlang_atom (s);
-  if (pos < 1)
+  ptrdiff_t len = erlang_atom (s);
+  if (len == 0)
     return 0;
-
-  len = pos;
-  pos = skip_spaces (s + pos) - s;
+  ptrdiff_t pos = skip_spaces (s + len) - s;
 
   /* If the name is quoted, the quotes are not part of the name. */
-  if (len > 2 && name[0] == '\'' && name[len - 1] == '\'')
-    {
-      *name_offset = 1;
-      name++;
-      len -= 2;
-    }
-  else
-    *name_offset = 0;
+  bool quoted = 2 < len && name[0] == '\'' && name[len - 1] == '\'';
+  name += quoted;
+  len -= 2 * quoted;
 
   /* Save only the first clause. */
   if (s[pos++] == '('
-      && (last == NULL
-          || len != (int)strlen (last)
-          || !strneq (name, last, len)))
-        {
-          make_tag (name, len, true, s, pos, lineno, linecharno);
-          return len;
-        }
+      && ! (lastlen == len && memcmp (name, last, len) == 0))
+    {
+      make_tag (s, len, true, s, pos, lineno, linecharno);
+      *name_offset = quoted;
+      return len;
+    }
 
   return 0;
 }
@@ -6363,7 +6340,7 @@ add_regex (char *regexp_pattern, language *lang)
     single_line = false;        /* dot does not match newline */
 
 
-  if (strlen (regexp_pattern) < 3)
+  if (strnlen (regexp_pattern, 3) < 3)
     {
       error ("null regexp");
       return;
diff --git a/lib-src/pop.c b/lib-src/pop.c
index c14808d6d37..e4bd6c04965 100644
--- a/lib-src/pop.c
+++ b/lib-src/pop.c
@@ -285,7 +285,7 @@ pop_open (char *host, char *username, char *password, int flags)
   /*
    * I really shouldn't use the pop_error variable like this, but....
    */
-  if (strlen (username) > ERROR_MAX - 6)
+  if (strnlen (username, ERROR_MAX - 6 + 1) == ERROR_MAX - 6 + 1)
     {
       pop_close (server);
       strcpy (pop_error,
@@ -299,7 +299,7 @@ pop_open (char *host, char *username, char *password, int flags)
       return (0);
     }
 
-  if (strlen (password) > ERROR_MAX - 6)
+  if (strnlen (password, ERROR_MAX - 6 + 1) == ERROR_MAX - 6 + 1)
     {
       pop_close (server);
       strcpy (pop_error,
diff --git a/lib-src/update-game-score.c b/lib-src/update-game-score.c
index 8a6f46b38e7..782425186e8 100644
--- a/lib-src/update-game-score.c
+++ b/lib-src/update-game-score.c
@@ -240,7 +240,7 @@ main (int argc, char **argv)
   if (! user)
     lose_syserr ("Couldn't determine user id");
   data = argv[optind + 2];
-  if (strlen (data) > MAX_DATA_LEN)
+  if (strnlen (data, MAX_DATA_LEN + 1) == MAX_DATA_LEN + 1)
     data[MAX_DATA_LEN] = '\0';
   nl = strchr (data, '\n');
   if (nl)
diff --git a/lib/gnulib.mk.in b/lib/gnulib.mk.in
index b9a32d9dbc1..b4d510bd62e 100644
--- a/lib/gnulib.mk.in
+++ b/lib/gnulib.mk.in
@@ -136,6 +136,7 @@
 #  stddef \
 #  stdio \
 #  stpcpy \
+#  strnlen \
 #  strtoimax \
 #  symlink \
 #  sys_stat \
@@ -1075,7 +1076,6 @@ gl_GNULIB_ENABLED_getdtablesize = @gl_GNULIB_ENABLED_getdtablesize@
 gl_GNULIB_ENABLED_getgroups = @gl_GNULIB_ENABLED_getgroups@
 gl_GNULIB_ENABLED_malloca = @gl_GNULIB_ENABLED_malloca@
 gl_GNULIB_ENABLED_open = @gl_GNULIB_ENABLED_open@
-gl_GNULIB_ENABLED_pathmax = @gl_GNULIB_ENABLED_pathmax@
 gl_GNULIB_ENABLED_strtoll = @gl_GNULIB_ENABLED_strtoll@
 gl_LIBOBJS = @gl_LIBOBJS@
 gl_LTLIBOBJS = @gl_LTLIBOBJS@
@@ -1110,7 +1110,6 @@ pdfdir = @pdfdir@
 prefix = @prefix@
 program_transform_name = @program_transform_name@
 psdir = @psdir@
-runstatedir = @runstatedir@
 sbindir = @sbindir@
 sharedstatedir = @sharedstatedir@
 srcdir = @srcdir@
@@ -2811,6 +2810,17 @@ EXTRA_DIST += string.in.h
 endif
 ## end   gnulib module string
 
+## begin gnulib module strnlen
+ifeq (,$(OMIT_GNULIB_MODULE_strnlen))
+
+
+EXTRA_DIST += strnlen.c
+
+EXTRA_libgnu_a_SOURCES += strnlen.c
+
+endif
+## end   gnulib module strnlen
+
 ## begin gnulib module strtoimax
 ifeq (,$(OMIT_GNULIB_MODULE_strtoimax))
 
diff --git a/lib/strnlen.c b/lib/strnlen.c
new file mode 100644
index 00000000000..9fb663509a0
--- /dev/null
+++ b/lib/strnlen.c
@@ -0,0 +1,30 @@
+/* Find the length of STRING, but scan at most MAXLEN characters.
+   Copyright (C) 2005-2007, 2009-2019 Free Software Foundation, Inc.
+   Written by Simon Josefsson.
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3, or (at your option)
+   any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program; if not, see <https://www.gnu.org/licenses/>.  */
+
+#include <config.h>
+
+#include <string.h>
+
+/* Find the length of STRING, but scan at most MAXLEN characters.
+   If no '\0' terminator is found in that many characters, return MAXLEN.  */
+
+size_t
+strnlen (const char *string, size_t maxlen)
+{
+  const char *end = memchr (string, '\0', maxlen);
+  return end ? (size_t) (end - string) : maxlen;
+}
diff --git a/lwlib/lwlib.c b/lwlib/lwlib.c
index 8142d92f077..f37c1058792 100644
--- a/lwlib/lwlib.c
+++ b/lwlib/lwlib.c
@@ -1233,8 +1233,7 @@ lw_separator_p (const char *label, enum menu_separator *type, int motif_p)
 {
   int separator_p = 0;
 
-  if (strlen (label) >= 3
-      && memcmp (label, "--:", 3) == 0)
+  if (strncmp (label, "--:",  3) == 0)
     {
       static struct separator_table
       {
@@ -1276,7 +1275,7 @@ lw_separator_p (const char *label, enum menu_separator *type, int motif_p)
             break;
           }
     }
-  else if (strlen (label) > 3
+  else if (strnlen (label, 4) == 4
            && memcmp (label, "--", 2) == 0
            && label[2] != '-')
     {
diff --git a/m4/gnulib-comp.m4 b/m4/gnulib-comp.m4
index cb6dce15ccf..7e724fe3c4e 100644
--- a/m4/gnulib-comp.m4
+++ b/m4/gnulib-comp.m4
@@ -154,6 +154,7 @@ AC_DEFUN([gl_EARLY],
   # Code from module stdlib:
   # Code from module stpcpy:
   # Code from module string:
+  # Code from module strnlen:
   # Code from module strtoimax:
   # Code from module strtoll:
   # Code from module symlink:
@@ -403,6 +404,12 @@ AC_DEFUN([gl_INIT],
   fi
   gl_STRING_MODULE_INDICATOR([stpcpy])
   gl_HEADER_STRING_H
+  gl_FUNC_STRNLEN
+  if test $HAVE_DECL_STRNLEN = 0 || test $REPLACE_STRNLEN = 1; then
+    AC_LIBOBJ([strnlen])
+    gl_PREREQ_STRNLEN
+  fi
+  gl_STRING_MODULE_INDICATOR([strnlen])
   gl_FUNC_STRTOIMAX
   if test $HAVE_DECL_STRTOIMAX = 0 || test $REPLACE_STRTOIMAX = 1; then
     AC_LIBOBJ([strtoimax])
@@ -1003,6 +1010,7 @@ AC_DEFUN([gl_FILE_LIST], [
   lib/str-two-way.h
   lib/strftime.h
   lib/string.in.h
+  lib/strnlen.c
   lib/strtoimax.c
   lib/strtol.c
   lib/strtoll.c
@@ -1131,6 +1139,7 @@ AC_DEFUN([gl_FILE_LIST], [
   m4/stdlib_h.m4
   m4/stpcpy.m4
   m4/string_h.m4
+  m4/strnlen.m4
   m4/strtoimax.m4
   m4/strtoll.m4
   m4/symlink.m4
diff --git a/m4/strnlen.m4 b/m4/strnlen.m4
new file mode 100644
index 00000000000..c283c3ece9f
--- /dev/null
+++ b/m4/strnlen.m4
@@ -0,0 +1,30 @@
+# strnlen.m4 serial 13
+dnl Copyright (C) 2002-2003, 2005-2007, 2009-2019 Free Software Foundation,
+dnl Inc.
+dnl This file is free software; the Free Software Foundation
+dnl gives unlimited permission to copy and/or distribute it,
+dnl with or without modifications, as long as this notice is preserved.
+
+AC_DEFUN([gl_FUNC_STRNLEN],
+[
+  AC_REQUIRE([gl_HEADER_STRING_H_DEFAULTS])
+
+  dnl Persuade glibc <string.h> to declare strnlen().
+  AC_REQUIRE([AC_USE_SYSTEM_EXTENSIONS])
+
+  AC_CHECK_DECLS_ONCE([strnlen])
+  if test $ac_cv_have_decl_strnlen = no; then
+    HAVE_DECL_STRNLEN=0
+  else
+    m4_pushdef([AC_LIBOBJ], [:])
+    dnl Note: AC_FUNC_STRNLEN does AC_LIBOBJ([strnlen]).
+    AC_FUNC_STRNLEN
+    m4_popdef([AC_LIBOBJ])
+    if test $ac_cv_func_strnlen_working = no; then
+      REPLACE_STRNLEN=1
+    fi
+  fi
+])
+
+# Prerequisites of lib/strnlen.c.
+AC_DEFUN([gl_PREREQ_STRNLEN], [:])
diff --git a/src/doprnt.c b/src/doprnt.c
index 5fb70634048..64bb368ee3e 100644
--- a/src/doprnt.c
+++ b/src/doprnt.c
@@ -357,8 +357,8 @@ doprnt (char *buffer, ptrdiff_t bufsize, const char *format,
               if (fmtcpy[1] != 's')
                 minlen = atoi (&fmtcpy[1]);
               string = va_arg (ap, char *);
-              tem = strlen (string);
-              if (STRING_BYTES_BOUND < tem)
+              tem = strnlen (string, STRING_BYTES_BOUND + 1);
+              if (tem == STRING_BYTES_BOUND + 1)
                 error ("String for %%s or %%S format is too long");
               width = strwidth (string, tem);
               goto doit1;
diff --git a/src/emacs.c b/src/emacs.c
index 1ddd10b8051..231acc0ef32 100644
--- a/src/emacs.c
+++ b/src/emacs.c
@@ -1520,8 +1520,8 @@ Using an Emacs configured with --with-x-toolkit=lucid does not have this problem
               }
 
             /* In exec'd: parse special dname into pipe and name info. */
-            if (!dname_arg || !strchr (dname_arg, '\n')
-                || strlen (dname_arg) < 1 || strlen (dname_arg) > 70)
+            if (!dname_arg || !*dname_arg || strnlen (dname_arg, 71) == 71
+                || !strchr (dname_arg, '\n'))
           {
             fprintf (stderr, "emacs daemon: daemon name absent or too long\n");
             exit (EXIT_CANNOT_INVOKE);
diff --git a/src/inotify.c b/src/inotify.c
index 9a7dbb8f413..e8891aefc7a 100644
--- a/src/inotify.c
+++ b/src/inotify.c
@@ -181,8 +181,7 @@ inotifyevent_to_event (Lisp_Object watch, struct inotify_event const *ev)
 
   if (ev->len > 0)
     {
-      size_t const len = strlen (ev->name);
-      name = make_unibyte_string (ev->name, min (len, ev->len));
+      name = make_unibyte_string (ev->name, strnlen (ev->name, ev->len));
       name = DECODE_FILE (name);
     }
   else
diff --git a/src/json.c b/src/json.c
index e2a4424463b..23234c767d8 100644
--- a/src/json.c
+++ b/src/json.c
@@ -197,9 +197,7 @@ init_json (void)
 static bool
 json_has_prefix (const char *string, const char *prefix)
 {
-  size_t string_len = strlen (string);
-  size_t prefix_len = strlen (prefix);
-  return string_len >= prefix_len && memcmp (string, prefix, prefix_len) == 0;
+  return strncmp (string, prefix, strlen (prefix)) == 0;
 }
 
 /* Return whether STRING ends with SUFFIX.  */
diff --git a/src/keyboard.c b/src/keyboard.c
index 0d7f124f5f3..56916e0cb4e 100644
--- a/src/keyboard.c
+++ b/src/keyboard.c
@@ -7331,7 +7331,7 @@ menu_separator_name_p (const char *label)
 {
   if (!label)
     return 0;
-  else if (strlen (label) > 3
+  else if (strnlen (label, 4) == 4
            && memcmp (label, "--", 2) == 0
            && label[2] != '-')
     {
@@ -8248,13 +8248,13 @@ parse_tool_bar_item (Lisp_Object key, Lisp_Object item)
       Lisp_Object tcapt = PROP (TOOL_BAR_ITEM_CAPTION);
       const char *label = SYMBOLP (tkey) ? SSDATA (SYMBOL_NAME (tkey)) : "";
       const char *capt = STRINGP (tcapt) ? SSDATA (tcapt) : "";
-      ptrdiff_t max_lbl =
-        2 * max (0, min (tool_bar_max_label_size, STRING_BYTES_BOUND / 2));
-      char *buf = xmalloc (max_lbl + 1);
+      ptrdiff_t max_lbl_size =
+        2 * max (0, min (tool_bar_max_label_size, STRING_BYTES_BOUND / 2)) + 1;
+      char *buf = xmalloc (max_lbl_size);
       Lisp_Object new_lbl;
-      ptrdiff_t caption_len = strlen (capt);
+      ptrdiff_t caption_len = strnlen (capt, max_lbl_size);
 
-      if (caption_len <= max_lbl && capt[0] != '\0')
+      if (0 < caption_len && caption_len < max_lbl_size)
         {
           strcpy (buf, capt);
           while (caption_len > 0 && buf[caption_len - 1] == '.')
@@ -8263,7 +8263,8 @@ parse_tool_bar_item (Lisp_Object key, Lisp_Object item)
           label = capt = buf;
         }
 
-      if (strlen (label) <= max_lbl && label[0] != '\0')
+      ptrdiff_t label_len = strnlen (label, max_lbl_size);
+      if (0 < label_len && label_len < max_lbl_size)
         {
           ptrdiff_t j;
           if (label != buf)
diff --git a/src/nsmenu.m b/src/nsmenu.m
index 3fe06cda02a..817f8cff184 100644
--- a/src/nsmenu.m
+++ b/src/nsmenu.m
@@ -611,7 +611,7 @@ ns_activate_menubar (struct frame *f)
   const char *tpos = key;
   keyEquivModMask = NSEventModifierFlagCommand;
 
-  if (!key || !strlen (key))
+  if (!key || !*key)
     return @"";
 
   while (*tpos == ' ' || *tpos == '(')
diff --git a/src/nsterm.m b/src/nsterm.m
index 0ab03b46df1..8d46a49cc5e 100644
--- a/src/nsterm.m
+++ b/src/nsterm.m
@@ -9298,7 +9298,7 @@ ns_xlfd_to_fontname (const char *xlfd)
     sscanf (xlfd, "-%*[^-]-%179[^-]-", name);
 
   /* stopgap for malformed XLFD input */
-  if (strlen (name) == 0)
+  if (!*name)
     strcpy (name, "Monaco");
 
   /* undo hack in ns_fontname_to_xlfd, converting '$' to '-', '_' to ' '
diff --git a/src/process.c b/src/process.c
index 6717ccb4187..15d87cf6015 100644
--- a/src/process.c
+++ b/src/process.c
@@ -2857,11 +2857,7 @@ set_socket_option (int s, Lisp_Object opt, Lisp_Object val)
            This should work on all systems.   KFS. 2003-09-23.  */
         memset (devname, 0, sizeof devname);
         if (STRINGP (val))
-          {
-            char *arg = SSDATA (val);
-            int len = min (strlen (arg), IFNAMSIZ);
-            memcpy (devname, arg, len);
-          }
+          memcpy (devname, SDATA (val), min (SBYTES (val), IFNAMSIZ));
         else if (!NILP (val))
           error ("Bad option value for %s", name);
         ret = setsockopt (s, sopt->optlevel, sopt->optnum,
diff --git a/src/sysdep.c b/src/sysdep.c
index 0910b69f8bc..b702bae5818 100644
--- a/src/sysdep.c
+++ b/src/sysdep.c
@@ -281,7 +281,7 @@ get_current_dir_name_or_unreachable (void)
       pwd = get_current_dir_name ();
       if (pwd)
         {
-          if (strlen (pwd) < dirsize_max)
+          if (strnlen (pwd, dirsize_max) < dirsize_max)
             return pwd;
           free (pwd);
           errno = ERANGE;
@@ -298,7 +298,7 @@ get_current_dir_name_or_unreachable (void)
      sometimes a nicer name, and using it may avoid a fatal error if a
      parent directory is searchable but not readable.  */
   if (pwd
-      && (pwdlen = strlen (pwd)) < bufsize_max
+      && (pwdlen = strnlen (pwd, bufsize_max)) < bufsize_max
       && IS_DIRECTORY_SEP (pwd[pwdlen && IS_DEVICE_SEP (pwd[1]) ? 2 : 0])
       && stat (pwd, &pwdstat) == 0
       && stat (".", &dotstat) == 0
diff --git a/src/term.c b/src/term.c
index ce06e1cd4e5..8b5a710d80a 100644
--- a/src/term.c
+++ b/src/term.c
@@ -4400,7 +4400,7 @@ vfatal (const char *str, va_list ap)
 {
   fprintf (stderr, "emacs: ");
   vfprintf (stderr, str, ap);
-  if (!(strlen (str) > 0 && str[strlen (str) - 1] == '\n'))
+  if (! (str[0] && str[strlen (str) - 1] == '\n'))
     fprintf (stderr, "\n");
   exit (1);
 }
diff --git a/src/xdisp.c b/src/xdisp.c
index 25e8932945e..9f63ef4b180 100644
--- a/src/xdisp.c
+++ b/src/xdisp.c
@@ -24341,9 +24341,7 @@ store_mode_line_string (const char *string, Lisp_Object lisp_string,
 
   if (string != NULL)
     {
-      len = strlen (string);
-      if (precision > 0 && len > precision)
-        len = precision;
+      len = strnlen (string, precision <= 0 ? SIZE_MAX : precision);
       lisp_string = make_string (string, len);
       if (NILP (props))
         props = mode_line_string_face_prop;