diff --git a/.gitignore b/.gitignore
index 006bf00df1..38e63c8ee3 100644
--- a/.gitignore
+++ b/.gitignore
@@ -76,7 +76,6 @@
 /git-init-db
 /git-interpret-trailers
 /git-instaweb
-/git-legacy-difftool
 /git-log
 /git-ls-files
 /git-ls-remote
diff --git a/Makefile b/Makefile
index 2053cb0458..3c2f3f03fc 100644
--- a/Makefile
+++ b/Makefile
@@ -527,7 +527,7 @@ SCRIPT_LIB += git-sh-setup
 SCRIPT_LIB += git-sh-i18n
 
 SCRIPT_PERL += git-add--interactive.perl
-SCRIPT_PERL += git-legacy-difftool.perl
+SCRIPT_PERL += git-difftool.perl
 SCRIPT_PERL += git-archimport.perl
 SCRIPT_PERL += git-cvsexportcommit.perl
 SCRIPT_PERL += git-cvsimport.perl
@@ -889,7 +889,6 @@ BUILTIN_OBJS += builtin/diff-files.o
 BUILTIN_OBJS += builtin/diff-index.o
 BUILTIN_OBJS += builtin/diff-tree.o
 BUILTIN_OBJS += builtin/diff.o
-BUILTIN_OBJS += builtin/difftool.o
 BUILTIN_OBJS += builtin/fast-export.o
 BUILTIN_OBJS += builtin/fetch-pack.o
 BUILTIN_OBJS += builtin/fetch.o
diff --git a/builtin.h b/builtin.h
index 9e4a89816d..6442c9bd6e 100644
--- a/builtin.h
+++ b/builtin.h
@@ -60,7 +60,6 @@ extern int cmd_diff_files(int argc, const char **argv, const char *prefix);
 extern int cmd_diff_index(int argc, const char **argv, const char *prefix);
 extern int cmd_diff(int argc, const char **argv, const char *prefix);
 extern int cmd_diff_tree(int argc, const char **argv, const char *prefix);
-extern int cmd_difftool(int argc, const char **argv, const char *prefix);
 extern int cmd_fast_export(int argc, const char **argv, const char *prefix);
 extern int cmd_fetch(int argc, const char **argv, const char *prefix);
 extern int cmd_fetch_pack(int argc, const char **argv, const char *prefix);
diff --git a/builtin/difftool.c b/builtin/difftool.c
deleted file mode 100644
index 9b336f713c..0000000000
--- a/builtin/difftool.c
+++ /dev/null
@@ -1,733 +0,0 @@
-/*
- * "git difftool" builtin command
- *
- * This is a wrapper around the GIT_EXTERNAL_DIFF-compatible
- * git-difftool--helper script.
- *
- * This script exports GIT_EXTERNAL_DIFF and GIT_PAGER for use by git.
- * The GIT_DIFF* variables are exported for use by git-difftool--helper.
- *
- * Any arguments that are unknown to this script are forwarded to 'git diff'.
- *
- * Copyright (C) 2016 Johannes Schindelin
- */
-#include "cache.h"
-#include "builtin.h"
-#include "run-command.h"
-#include "exec_cmd.h"
-#include "parse-options.h"
-#include "argv-array.h"
-#include "strbuf.h"
-#include "lockfile.h"
-#include "dir.h"
-
-static char *diff_gui_tool;
-static int trust_exit_code;
-
-static const char *const builtin_difftool_usage[] = {
-	N_("git difftool [<options>] [<commit> [<commit>]] [--] [<path>...]"),
-	NULL
-};
-
-static int difftool_config(const char *var, const char *value, void *cb)
-{
-	if (!strcmp(var, "diff.guitool")) {
-		diff_gui_tool = xstrdup(value);
-		return 0;
-	}
-
-	if (!strcmp(var, "difftool.trustexitcode")) {
-		trust_exit_code = git_config_bool(var, value);
-		return 0;
-	}
-
-	return git_default_config(var, value, cb);
-}
-
-static int print_tool_help(void)
-{
-	const char *argv[] = { "mergetool", "--tool-help=diff", NULL };
-	return run_command_v_opt(argv, RUN_GIT_CMD);
-}
-
-static int parse_index_info(char *p, int *mode1, int *mode2,
-			    struct object_id *oid1, struct object_id *oid2,
-			    char *status)
-{
-	if (*p != ':')
-		return error("expected ':', got '%c'", *p);
-	*mode1 = (int)strtol(p + 1, &p, 8);
-	if (*p != ' ')
-		return error("expected ' ', got '%c'", *p);
-	*mode2 = (int)strtol(p + 1, &p, 8);
-	if (*p != ' ')
-		return error("expected ' ', got '%c'", *p);
-	if (get_oid_hex(++p, oid1))
-		return error("expected object ID, got '%s'", p + 1);
-	p += GIT_SHA1_HEXSZ;
-	if (*p != ' ')
-		return error("expected ' ', got '%c'", *p);
-	if (get_oid_hex(++p, oid2))
-		return error("expected object ID, got '%s'", p + 1);
-	p += GIT_SHA1_HEXSZ;
-	if (*p != ' ')
-		return error("expected ' ', got '%c'", *p);
-	*status = *++p;
-	if (!*status)
-		return error("missing status");
-	if (p[1])
-		return error("unexpected trailer: '%s'", p + 1);
-	return 0;
-}
-
-/*
- * Remove any trailing slash from $workdir
- * before starting to avoid double slashes in symlink targets.
- */
-static void add_path(struct strbuf *buf, size_t base_len, const char *path)
-{
-	strbuf_setlen(buf, base_len);
-	if (buf->len && buf->buf[buf->len - 1] != '/')
-		strbuf_addch(buf, '/');
-	strbuf_addstr(buf, path);
-}
-
-/*
- * Determine whether we can simply reuse the file in the worktree.
- */
-static int use_wt_file(const char *workdir, const char *name,
-		       struct object_id *oid)
-{
-	struct strbuf buf = STRBUF_INIT;
-	struct stat st;
-	int use = 0;
-
-	strbuf_addstr(&buf, workdir);
-	add_path(&buf, buf.len, name);
-
-	if (!lstat(buf.buf, &st) && !S_ISLNK(st.st_mode)) {
-		struct object_id wt_oid;
-		int fd = open(buf.buf, O_RDONLY);
-
-		if (fd >= 0 &&
-		    !index_fd(wt_oid.hash, fd, &st, OBJ_BLOB, name, 0)) {
-			if (is_null_oid(oid)) {
-				oidcpy(oid, &wt_oid);
-				use = 1;
-			} else if (!oidcmp(oid, &wt_oid))
-				use = 1;
-		}
-	}
-
-	strbuf_release(&buf);
-
-	return use;
-}
-
-struct working_tree_entry {
-	struct hashmap_entry entry;
-	char path[FLEX_ARRAY];
-};
-
-static int working_tree_entry_cmp(struct working_tree_entry *a,
-				  struct working_tree_entry *b, void *keydata)
-{
-	return strcmp(a->path, b->path);
-}
-
-/*
- * The `left` and `right` entries hold paths for the symlinks hashmap,
- * and a SHA-1 surrounded by brief text for submodules.
- */
-struct pair_entry {
-	struct hashmap_entry entry;
-	char left[PATH_MAX], right[PATH_MAX];
-	const char path[FLEX_ARRAY];
-};
-
-static int pair_cmp(struct pair_entry *a, struct pair_entry *b, void *keydata)
-{
-	return strcmp(a->path, b->path);
-}
-
-static void add_left_or_right(struct hashmap *map, const char *path,
-			      const char *content, int is_right)
-{
-	struct pair_entry *e, *existing;
-
-	FLEX_ALLOC_STR(e, path, path);
-	hashmap_entry_init(e, strhash(path));
-	existing = hashmap_get(map, e, NULL);
-	if (existing) {
-		free(e);
-		e = existing;
-	} else {
-		e->left[0] = e->right[0] = '\0';
-		hashmap_add(map, e);
-	}
-	strlcpy(is_right ? e->right : e->left, content, PATH_MAX);
-}
-
-struct path_entry {
-	struct hashmap_entry entry;
-	char path[FLEX_ARRAY];
-};
-
-static int path_entry_cmp(struct path_entry *a, struct path_entry *b, void *key)
-{
-	return strcmp(a->path, key ? key : b->path);
-}
-
-static void changed_files(struct hashmap *result, const char *index_path,
-			  const char *workdir)
-{
-	struct child_process update_index = CHILD_PROCESS_INIT;
-	struct child_process diff_files = CHILD_PROCESS_INIT;
-	struct strbuf index_env = STRBUF_INIT, buf = STRBUF_INIT;
-	const char *git_dir = absolute_path(get_git_dir()), *env[] = {
-		NULL, NULL
-	};
-	FILE *fp;
-
-	strbuf_addf(&index_env, "GIT_INDEX_FILE=%s", index_path);
-	env[0] = index_env.buf;
-
-	argv_array_pushl(&update_index.args,
-			 "--git-dir", git_dir, "--work-tree", workdir,
-			 "update-index", "--really-refresh", "-q",
-			 "--unmerged", NULL);
-	update_index.no_stdin = 1;
-	update_index.no_stdout = 1;
-	update_index.no_stderr = 1;
-	update_index.git_cmd = 1;
-	update_index.use_shell = 0;
-	update_index.clean_on_exit = 1;
-	update_index.dir = workdir;
-	update_index.env = env;
-	/* Ignore any errors of update-index */
-	run_command(&update_index);
-
-	argv_array_pushl(&diff_files.args,
-			 "--git-dir", git_dir, "--work-tree", workdir,
-			 "diff-files", "--name-only", "-z", NULL);
-	diff_files.no_stdin = 1;
-	diff_files.git_cmd = 1;
-	diff_files.use_shell = 0;
-	diff_files.clean_on_exit = 1;
-	diff_files.out = -1;
-	diff_files.dir = workdir;
-	diff_files.env = env;
-	if (start_command(&diff_files))
-		die("could not obtain raw diff");
-	fp = xfdopen(diff_files.out, "r");
-	while (!strbuf_getline_nul(&buf, fp)) {
-		struct path_entry *entry;
-		FLEX_ALLOC_STR(entry, path, buf.buf);
-		hashmap_entry_init(entry, strhash(buf.buf));
-		hashmap_add(result, entry);
-	}
-	if (finish_command(&diff_files))
-		die("diff-files did not exit properly");
-	strbuf_release(&index_env);
-	strbuf_release(&buf);
-}
-
-static NORETURN void exit_cleanup(const char *tmpdir, int exit_code)
-{
-	struct strbuf buf = STRBUF_INIT;
-	strbuf_addstr(&buf, tmpdir);
-	remove_dir_recursively(&buf, 0);
-	if (exit_code)
-		warning(_("failed: %d"), exit_code);
-	exit(exit_code);
-}
-
-static int ensure_leading_directories(char *path)
-{
-	switch (safe_create_leading_directories(path)) {
-		case SCLD_OK:
-		case SCLD_EXISTS:
-			return 0;
-		default:
-			return error(_("could not create leading directories "
-				       "of '%s'"), path);
-	}
-}
-
-static int run_dir_diff(const char *extcmd, int symlinks, const char *prefix,
-			int argc, const char **argv)
-{
-	char tmpdir[PATH_MAX];
-	struct strbuf info = STRBUF_INIT, lpath = STRBUF_INIT;
-	struct strbuf rpath = STRBUF_INIT, buf = STRBUF_INIT;
-	struct strbuf ldir = STRBUF_INIT, rdir = STRBUF_INIT;
-	struct strbuf wtdir = STRBUF_INIT;
-	size_t ldir_len, rdir_len, wtdir_len;
-	struct cache_entry *ce = xcalloc(1, sizeof(ce) + PATH_MAX + 1);
-	const char *workdir, *tmp;
-	int ret = 0, i;
-	FILE *fp;
-	struct hashmap working_tree_dups, submodules, symlinks2;
-	struct hashmap_iter iter;
-	struct pair_entry *entry;
-	enum object_type type;
-	unsigned long size;
-	struct index_state wtindex;
-	struct checkout lstate, rstate;
-	int rc, flags = RUN_GIT_CMD, err = 0;
-	struct child_process child = CHILD_PROCESS_INIT;
-	const char *helper_argv[] = { "difftool--helper", NULL, NULL, NULL };
-	struct hashmap wt_modified, tmp_modified;
-	int indices_loaded = 0;
-
-	workdir = get_git_work_tree();
-
-	/* Setup temp directories */
-	tmp = getenv("TMPDIR");
-	xsnprintf(tmpdir, sizeof(tmpdir), "%s/git-difftool.XXXXXX", tmp ? tmp : "/tmp");
-	if (!mkdtemp(tmpdir))
-		return error("could not create '%s'", tmpdir);
-	strbuf_addf(&ldir, "%s/left/", tmpdir);
-	strbuf_addf(&rdir, "%s/right/", tmpdir);
-	strbuf_addstr(&wtdir, workdir);
-	if (!wtdir.len || !is_dir_sep(wtdir.buf[wtdir.len - 1]))
-		strbuf_addch(&wtdir, '/');
-	mkdir(ldir.buf, 0700);
-	mkdir(rdir.buf, 0700);
-
-	memset(&wtindex, 0, sizeof(wtindex));
-
-	memset(&lstate, 0, sizeof(lstate));
-	lstate.base_dir = ldir.buf;
-	lstate.base_dir_len = ldir.len;
-	lstate.force = 1;
-	memset(&rstate, 0, sizeof(rstate));
-	rstate.base_dir = rdir.buf;
-	rstate.base_dir_len = rdir.len;
-	rstate.force = 1;
-
-	ldir_len = ldir.len;
-	rdir_len = rdir.len;
-	wtdir_len = wtdir.len;
-
-	hashmap_init(&working_tree_dups,
-		     (hashmap_cmp_fn)working_tree_entry_cmp, 0);
-	hashmap_init(&submodules, (hashmap_cmp_fn)pair_cmp, 0);
-	hashmap_init(&symlinks2, (hashmap_cmp_fn)pair_cmp, 0);
-
-	child.no_stdin = 1;
-	child.git_cmd = 1;
-	child.use_shell = 0;
-	child.clean_on_exit = 1;
-	child.dir = prefix;
-	child.out = -1;
-	argv_array_pushl(&child.args, "diff", "--raw", "--no-abbrev", "-z",
-			 NULL);
-	for (i = 0; i < argc; i++)
-		argv_array_push(&child.args, argv[i]);
-	if (start_command(&child))
-		die("could not obtain raw diff");
-	fp = xfdopen(child.out, "r");
-
-	/* Build index info for left and right sides of the diff */
-	i = 0;
-	while (!strbuf_getline_nul(&info, fp)) {
-		int lmode, rmode;
-		struct object_id loid, roid;
-		char status;
-		const char *src_path, *dst_path;
-		size_t src_path_len, dst_path_len;
-
-		if (starts_with(info.buf, "::"))
-			die(N_("combined diff formats('-c' and '--cc') are "
-			       "not supported in\n"
-			       "directory diff mode('-d' and '--dir-diff')."));
-
-		if (parse_index_info(info.buf, &lmode, &rmode, &loid, &roid,
-				     &status))
-			break;
-		if (strbuf_getline_nul(&lpath, fp))
-			break;
-		src_path = lpath.buf;
-		src_path_len = lpath.len;
-
-		i++;
-		if (status != 'C' && status != 'R') {
-			dst_path = src_path;
-			dst_path_len = src_path_len;
-		} else {
-			if (strbuf_getline_nul(&rpath, fp))
-				break;
-			dst_path = rpath.buf;
-			dst_path_len = rpath.len;
-		}
-
-		if (S_ISGITLINK(lmode) || S_ISGITLINK(rmode)) {
-			strbuf_reset(&buf);
-			strbuf_addf(&buf, "Subproject commit %s",
-				    oid_to_hex(&loid));
-			add_left_or_right(&submodules, src_path, buf.buf, 0);
-			strbuf_reset(&buf);
-			strbuf_addf(&buf, "Subproject commit %s",
-				    oid_to_hex(&roid));
-			if (!oidcmp(&loid, &roid))
-				strbuf_addstr(&buf, "-dirty");
-			add_left_or_right(&submodules, dst_path, buf.buf, 1);
-			continue;
-		}
-
-		if (S_ISLNK(lmode)) {
-			char *content = read_sha1_file(loid.hash, &type, &size);
-			add_left_or_right(&symlinks2, src_path, content, 0);
-			free(content);
-		}
-
-		if (S_ISLNK(rmode)) {
-			char *content = read_sha1_file(roid.hash, &type, &size);
-			add_left_or_right(&symlinks2, dst_path, content, 1);
-			free(content);
-		}
-
-		if (lmode && status != 'C') {
-			ce->ce_mode = lmode;
-			oidcpy(&ce->oid, &loid);
-			strcpy(ce->name, src_path);
-			ce->ce_namelen = src_path_len;
-			if (checkout_entry(ce, &lstate, NULL))
-				return error("could not write '%s'", src_path);
-		}
-
-		if (rmode) {
-			struct working_tree_entry *entry;
-
-			/* Avoid duplicate working_tree entries */
-			FLEX_ALLOC_STR(entry, path, dst_path);
-			hashmap_entry_init(entry, strhash(dst_path));
-			if (hashmap_get(&working_tree_dups, entry, NULL)) {
-				free(entry);
-				continue;
-			}
-			hashmap_add(&working_tree_dups, entry);
-
-			if (!use_wt_file(workdir, dst_path, &roid)) {
-				ce->ce_mode = rmode;
-				oidcpy(&ce->oid, &roid);
-				strcpy(ce->name, dst_path);
-				ce->ce_namelen = dst_path_len;
-				if (checkout_entry(ce, &rstate, NULL))
-					return error("could not write '%s'",
-						     dst_path);
-			} else if (!is_null_oid(&roid)) {
-				/*
-				 * Changes in the working tree need special
-				 * treatment since they are not part of the
-				 * index.
-				 */
-				struct cache_entry *ce2 =
-					make_cache_entry(rmode, roid.hash,
-							 dst_path, 0, 0);
-
-				add_index_entry(&wtindex, ce2,
-						ADD_CACHE_JUST_APPEND);
-
-				add_path(&rdir, rdir_len, dst_path);
-				if (ensure_leading_directories(rdir.buf))
-					return error("could not create "
-						     "directory for '%s'",
-						     dst_path);
-				add_path(&wtdir, wtdir_len, dst_path);
-				if (symlinks) {
-					if (symlink(wtdir.buf, rdir.buf)) {
-						ret = error_errno("could not symlink '%s' to '%s'", wtdir.buf, rdir.buf);
-						goto finish;
-					}
-				} else {
-					struct stat st;
-					if (stat(wtdir.buf, &st))
-						st.st_mode = 0644;
-					if (copy_file(rdir.buf, wtdir.buf,
-						      st.st_mode)) {
-						ret = error("could not copy '%s' to '%s'", wtdir.buf, rdir.buf);
-						goto finish;
-					}
-				}
-			}
-		}
-	}
-
-	if (finish_command(&child)) {
-		ret = error("error occurred running diff --raw");
-		goto finish;
-	}
-
-	if (!i)
-		return 0;
-
-	/*
-	 * Changes to submodules require special treatment.This loop writes a
-	 * temporary file to both the left and right directories to show the
-	 * change in the recorded SHA1 for the submodule.
-	 */
-	hashmap_iter_init(&submodules, &iter);
-	while ((entry = hashmap_iter_next(&iter))) {
-		if (*entry->left) {
-			add_path(&ldir, ldir_len, entry->path);
-			ensure_leading_directories(ldir.buf);
-			write_file(ldir.buf, "%s", entry->left);
-		}
-		if (*entry->right) {
-			add_path(&rdir, rdir_len, entry->path);
-			ensure_leading_directories(rdir.buf);
-			write_file(rdir.buf, "%s", entry->right);
-		}
-	}
-
-	/*
-	 * Symbolic links require special treatment.The standard "git diff"
-	 * shows only the link itself, not the contents of the link target.
-	 * This loop replicates that behavior.
-	 */
-	hashmap_iter_init(&symlinks2, &iter);
-	while ((entry = hashmap_iter_next(&iter))) {
-		if (*entry->left) {
-			add_path(&ldir, ldir_len, entry->path);
-			ensure_leading_directories(ldir.buf);
-			write_file(ldir.buf, "%s", entry->left);
-		}
-		if (*entry->right) {
-			add_path(&rdir, rdir_len, entry->path);
-			ensure_leading_directories(rdir.buf);
-			write_file(rdir.buf, "%s", entry->right);
-		}
-	}
-
-	strbuf_release(&buf);
-
-	strbuf_setlen(&ldir, ldir_len);
-	helper_argv[1] = ldir.buf;
-	strbuf_setlen(&rdir, rdir_len);
-	helper_argv[2] = rdir.buf;
-
-	if (extcmd) {
-		helper_argv[0] = extcmd;
-		flags = 0;
-	} else
-		setenv("GIT_DIFFTOOL_DIRDIFF", "true", 1);
-	rc = run_command_v_opt(helper_argv, flags);
-
-	/*
-	 * If the diff includes working copy files and those
-	 * files were modified during the diff, then the changes
-	 * should be copied back to the working tree.
-	 * Do not copy back files when symlinks are used and the
-	 * external tool did not replace the original link with a file.
-	 *
-	 * These hashes are loaded lazily since they aren't needed
-	 * in the common case of --symlinks and the difftool updating
-	 * files through the symlink.
-	 */
-	hashmap_init(&wt_modified, (hashmap_cmp_fn)path_entry_cmp,
-		     wtindex.cache_nr);
-	hashmap_init(&tmp_modified, (hashmap_cmp_fn)path_entry_cmp,
-		     wtindex.cache_nr);
-
-	for (i = 0; i < wtindex.cache_nr; i++) {
-		struct hashmap_entry dummy;
-		const char *name = wtindex.cache[i]->name;
-		struct stat st;
-
-		add_path(&rdir, rdir_len, name);
-		if (lstat(rdir.buf, &st))
-			continue;
-
-		if ((symlinks && S_ISLNK(st.st_mode)) || !S_ISREG(st.st_mode))
-			continue;
-
-		if (!indices_loaded) {
-			static struct lock_file lock;
-			strbuf_reset(&buf);
-			strbuf_addf(&buf, "%s/wtindex", tmpdir);
-			if (hold_lock_file_for_update(&lock, buf.buf, 0) < 0 ||
-			    write_locked_index(&wtindex, &lock, COMMIT_LOCK)) {
-				ret = error("could not write %s", buf.buf);
-				rollback_lock_file(&lock);
-				goto finish;
-			}
-			changed_files(&wt_modified, buf.buf, workdir);
-			strbuf_setlen(&rdir, rdir_len);
-			changed_files(&tmp_modified, buf.buf, rdir.buf);
-			add_path(&rdir, rdir_len, name);
-			indices_loaded = 1;
-		}
-
-		hashmap_entry_init(&dummy, strhash(name));
-		if (hashmap_get(&tmp_modified, &dummy, name)) {
-			add_path(&wtdir, wtdir_len, name);
-			if (hashmap_get(&wt_modified, &dummy, name)) {
-				warning(_("both files modified: '%s' and '%s'."),
-					wtdir.buf, rdir.buf);
-				warning(_("working tree file has been left."));
-				warning("");
-				err = 1;
-			} else if (unlink(wtdir.buf) ||
-				   copy_file(wtdir.buf, rdir.buf, st.st_mode))
-				warning_errno(_("could not copy '%s' to '%s'"),
-					      rdir.buf, wtdir.buf);
-		}
-	}
-
-	if (err) {
-		warning(_("temporary files exist in '%s'."), tmpdir);
-		warning(_("you may want to cleanup or recover these."));
-		exit(1);
-	} else
-		exit_cleanup(tmpdir, rc);
-
-finish:
-	free(ce);
-	strbuf_release(&ldir);
-	strbuf_release(&rdir);
-	strbuf_release(&wtdir);
-	strbuf_release(&buf);
-
-	return ret;
-}
-
-static int run_file_diff(int prompt, const char *prefix,
-			 int argc, const char **argv)
-{
-	struct argv_array args = ARGV_ARRAY_INIT;
-	const char *env[] = {
-		"GIT_PAGER=", "GIT_EXTERNAL_DIFF=git-difftool--helper", NULL,
-		NULL
-	};
-	int ret = 0, i;
-
-	if (prompt > 0)
-		env[2] = "GIT_DIFFTOOL_PROMPT=true";
-	else if (!prompt)
-		env[2] = "GIT_DIFFTOOL_NO_PROMPT=true";
-
-
-	argv_array_push(&args, "diff");
-	for (i = 0; i < argc; i++)
-		argv_array_push(&args, argv[i]);
-	ret = run_command_v_opt_cd_env(args.argv, RUN_GIT_CMD, prefix, env);
-	exit(ret);
-}
-
-/*
- * NEEDSWORK: this function can go once the legacy-difftool Perl script is
- * retired.
- *
- * We intentionally avoid reading the config directly here, to avoid messing up
- * the GIT_* environment variables when we need to fall back to exec()ing the
- * Perl script.
- */
-static int use_builtin_difftool(void) {
-	struct child_process cp = CHILD_PROCESS_INIT;
-	struct strbuf out = STRBUF_INIT;
-	int ret;
-
-	argv_array_pushl(&cp.args,
-			 "config", "--bool", "difftool.usebuiltin", NULL);
-	cp.git_cmd = 1;
-	if (capture_command(&cp, &out, 6))
-		return 0;
-	strbuf_trim(&out);
-	ret = !strcmp("true", out.buf);
-	strbuf_release(&out);
-	return ret;
-}
-
-int cmd_difftool(int argc, const char **argv, const char *prefix)
-{
-	int use_gui_tool = 0, dir_diff = 0, prompt = -1, symlinks = 0,
-	    tool_help = 0;
-	static char *difftool_cmd = NULL, *extcmd = NULL;
-	struct option builtin_difftool_options[] = {
-		OPT_BOOL('g', "gui", &use_gui_tool,
-			 N_("use `diff.guitool` instead of `diff.tool`")),
-		OPT_BOOL('d', "dir-diff", &dir_diff,
-			 N_("perform a full-directory diff")),
-		{ OPTION_SET_INT, 'y', "no-prompt", &prompt, NULL,
-			N_("do not prompt before launching a diff tool"),
-			PARSE_OPT_NOARG | PARSE_OPT_NONEG, NULL, 0},
-		{ OPTION_SET_INT, 0, "prompt", &prompt, NULL, NULL,
-			PARSE_OPT_NOARG | PARSE_OPT_NONEG | PARSE_OPT_HIDDEN,
-			NULL, 1 },
-		OPT_BOOL(0, "symlinks", &symlinks,
-			 N_("use symlinks in dir-diff mode")),
-		OPT_STRING('t', "tool", &difftool_cmd, N_("<tool>"),
-			   N_("use the specified diff tool")),
-		OPT_BOOL(0, "tool-help", &tool_help,
-			 N_("print a list of diff tools that may be used with "
-			    "`--tool`")),
-		OPT_BOOL(0, "trust-exit-code", &trust_exit_code,
-			 N_("make 'git-difftool' exit when an invoked diff "
-			    "tool returns a non - zero exit code")),
-		OPT_STRING('x', "extcmd", &extcmd, N_("<command>"),
-			   N_("specify a custom command for viewing diffs")),
-		OPT_END()
-	};
-
-	/*
-	 * NEEDSWORK: Once the builtin difftool has been tested enough
-	 * and git-legacy-difftool.perl is retired to contrib/, this preamble
-	 * can be removed.
-	 */
-	if (!use_builtin_difftool()) {
-		const char *path = mkpath("%s/git-legacy-difftool",
-					  git_exec_path());
-
-		if (sane_execvp(path, (char **)argv) < 0)
-			die_errno("could not exec %s", path);
-
-		return 0;
-	}
-	prefix = setup_git_directory();
-	trace_repo_setup(prefix);
-	setup_work_tree();
-	/* NEEDSWORK: once we no longer spawn anything, remove this */
-	setenv(GIT_DIR_ENVIRONMENT, absolute_path(get_git_dir()), 1);
-	setenv(GIT_WORK_TREE_ENVIRONMENT, absolute_path(get_git_work_tree()), 1);
-
-	git_config(difftool_config, NULL);
-	symlinks = has_symlinks;
-
-	argc = parse_options(argc, argv, prefix, builtin_difftool_options,
-			     builtin_difftool_usage, PARSE_OPT_KEEP_UNKNOWN |
-			     PARSE_OPT_KEEP_DASHDASH);
-
-	if (tool_help)
-		return print_tool_help();
-
-	if (use_gui_tool && diff_gui_tool && *diff_gui_tool)
-		setenv("GIT_DIFF_TOOL", diff_gui_tool, 1);
-	else if (difftool_cmd) {
-		if (*difftool_cmd)
-			setenv("GIT_DIFF_TOOL", difftool_cmd, 1);
-		else
-			die(_("no <tool> given for --tool=<tool>"));
-	}
-
-	if (extcmd) {
-		if (*extcmd)
-			setenv("GIT_DIFFTOOL_EXTCMD", extcmd, 1);
-		else
-			die(_("no <cmd> given for --extcmd=<cmd>"));
-	}
-
-	setenv("GIT_DIFFTOOL_TRUST_EXIT_CODE",
-	       trust_exit_code ? "true" : "false", 1);
-
-	/*
-	 * In directory diff mode, 'git-difftool--helper' is called once
-	 * to compare the a / b directories. In file diff mode, 'git diff'
-	 * will invoke a separate instance of 'git-difftool--helper' for
-	 * each file that changed.
-	 */
-	if (dir_diff)
-		return run_dir_diff(extcmd, symlinks, prefix, argc, argv);
-	return run_file_diff(prompt, prefix, argc, argv);
-}
diff --git a/exec_cmd.c b/exec_cmd.c
index de35da4300..bfd5e3e10d 100644
--- a/exec_cmd.c
+++ b/exec_cmd.c
@@ -65,7 +65,6 @@ void git_set_argv_exec_path(const char *exec_path)
 const char *git_exec_path(void)
 {
 	const char *env;
-	static char *system_exec_path;
 
 	if (argv_exec_path)
 		return argv_exec_path;
@@ -75,9 +74,7 @@ const char *git_exec_path(void)
 		return env;
 	}
 
-	if (!system_exec_path)
-		system_exec_path = system_path(GIT_EXEC_PATH);
-	return system_exec_path;
+	return system_path(GIT_EXEC_PATH);
 }
 
 static void add_path(struct strbuf *out, const char *path)
diff --git a/git-legacy-difftool.perl b/git-difftool.perl
similarity index 100%
rename from git-legacy-difftool.perl
rename to git-difftool.perl
diff --git a/git.c b/git.c
index eee36fd911..124d026bdb 100644
--- a/git.c
+++ b/git.c
@@ -424,12 +424,6 @@ static struct cmd_struct commands[] = {
 	{ "diff-files", cmd_diff_files, RUN_SETUP | NEED_WORK_TREE },
 	{ "diff-index", cmd_diff_index, RUN_SETUP },
 	{ "diff-tree", cmd_diff_tree, RUN_SETUP },
-	/*
-	 * NEEDSWORK: Once the redirection to git-legacy-difftool.perl in
-	 * builtin/difftool.c has been removed, this entry should be changed to
-	 * RUN_SETUP | NEED_WORK_TREE
-	 */
-	{ "difftool", cmd_difftool },
 	{ "fast-export", cmd_fast_export, RUN_SETUP },
 	{ "fetch", cmd_fetch, RUN_SETUP },
 	{ "fetch-pack", cmd_fetch_pack, RUN_SETUP },
diff --git a/t/t7800-difftool.sh b/t/t7800-difftool.sh
index f205b2d031..e0f81bdb22 100755
--- a/t/t7800-difftool.sh
+++ b/t/t7800-difftool.sh
@@ -23,22 +23,6 @@ prompt_given ()
 	test "$prompt" = "Launch 'test-tool' [Y/n]? branch"
 }
 
-for use_builtin_difftool in false true
-do
-
-test_expect_success 'verify we are running the correct difftool' '
-	if test true = '$use_builtin_difftool'
-	then
-		test_must_fail ok=129 git difftool -h >help &&
-		grep "g, --gui" help
-	else
-		git difftool -h >help &&
-		grep "g|--gui" help
-	fi
-'
-
-# NEEDSWORK: lose all the PERL prereqs once legacy-difftool is retired.
-
 # Create a file on master and change it on branch
 test_expect_success PERL 'setup' '
 	echo master >file &&
@@ -582,17 +566,4 @@ test_expect_success PERL,SYMLINKS 'difftool --dir-diff symlinked directories' '
 	)
 '
 
-test true != $use_builtin_difftool || break
-
-test_expect_success 'tear down for re-run' '
-	rm -rf * .[a-z]* &&
-	git init
-'
-
-# run as builtin difftool now
-GIT_CONFIG_PARAMETERS="'difftool.usebuiltin=true'"
-export GIT_CONFIG_PARAMETERS
-
-done
-
 test_done