diff --git a/.editorconfig b/.editorconfig
index 6e4eaa8e955341..82e121a41754b5 100644
--- a/.editorconfig
+++ b/.editorconfig
@@ -4,7 +4,11 @@ insert_final_newline = true
 
 # The settings for C (*.c and *.h) files are mirrored in .clang-format.  Keep
 # them in sync.
-[{*.{c,h,sh,bash,perl,pl,pm,txt,adoc},config.mak.*,Makefile,templates/hooks/*.sample}]
+[{*.{c,h,sh,bash,perl,pl,pm,txt,adoc},config.mak.*,Makefile}]
+indent_style = tab
+tab_width = 8
+
+[templates/hooks/*.sample]
 indent_style = tab
 tab_width = 8
 
diff --git a/Documentation/RelNotes/2.54.0.adoc b/Documentation/RelNotes/2.54.0.adoc
index d7c67cbb078aeb..d5e833512ee66a 100644
--- a/Documentation/RelNotes/2.54.0.adoc
+++ b/Documentation/RelNotes/2.54.0.adoc
@@ -88,6 +88,9 @@ UI, Workflows & Features
  * "git repo structure" command learns to report maximum values on
    various aspects of objects it inspects.
 
+ * "git rebase" learns "--trailer" command to drive the
+   interpret-trailers machinery.
+
 
 Performance, Internal Implementation, Development Support etc.
 --------------------------------------------------------------
@@ -193,6 +196,20 @@ Performance, Internal Implementation, Development Support etc.
  * Reduce dependence on the global the_hash_algo and the_repository
    variables of wt-status code path.
 
+  * The way combined list-object filter options are parsed has been
+    revamped.
+
+ * Editorconfig filename patterns were specified incorrectly, making
+   many source files inside subdirectories unaffected, which has been
+   corrected.
+
+ * The run_command() API lost its implicit dependencyon the singleton
+   `the_repository` instance.
+
+ * The unit test helper function was taught to use backslash +
+   mnemonic notation for certain control characters like "\t", instead
+   of octal notation like "\011".
+
 
 Fixes since v2.53
 -----------------
@@ -323,6 +340,10 @@ Fixes since v2.53
  * Plug a few leaks where mmap'ed memory regions are not unmapped.
    (merge a8a69bbb64 jk/unleak-mmap later to maint).
 
+ * A test now uses the symbolic constant $ZERO_OID instead of 40 "0" to
+   work better with SHA-256 as well as SHA-1.
+   (merge 30310f3cc4 ss/t3200-test-zero-oid later to maint).
+
  * Other code cleanup, docfix, build fix, etc.
    (merge d79fff4a11 jk/remote-tracking-ref-leakfix later to maint).
    (merge 7a747f972d dd/t5403-modernise later to maint).
@@ -362,3 +383,5 @@ Fixes since v2.53
    (merge 63c00a677b ss/t9123-setup-inside-test-expect-success later to maint).
    (merge beca0ca4be os/doc-git-custom-commands later to maint).
    (merge 4c223571be ty/patch-ids-document-lazy-eval later to maint).
+   (merge 476365ac85 jc/doc-wholesale-replace-before-next later to maint).
+   (merge 35f220b639 ss/submodule--helper-use-xmalloc later to maint).
diff --git a/Documentation/SubmittingPatches b/Documentation/SubmittingPatches
index 359f5fb74e6991..d570184ec84998 100644
--- a/Documentation/SubmittingPatches
+++ b/Documentation/SubmittingPatches
@@ -56,6 +56,18 @@ feedback before sending a new version, rather than sending an updated
 series immediately after receiving a review. This helps collect broader
 input and avoids unnecessary churn from many rapid iterations.
 
+. These early update iterations are expected to be full replacements,
+  not incremental updates on top of what you posted already.  If you
+  are correcting mistakes you made in the previous iteration that a
+  reviewer noticed and pointed out in their review, you _fix_ that
+  mistake by rewriting your history (e.g., by using "git rebase -i")
+  to pretend that you never made the mistake in the first place.  In
+  other words, this is a chance to pretend to be a perfect developer,
+  and you are expected to take advantage of that.  In the larger
+  picture, nobody is interested in your earlier mistakes.  Just
+  present a logical progression made by a perfect developer who makes
+  no mistakes while working on the topic.
+
 . Polish, refine, and re-send your patches to the list and to the people
   who spent their time to improve your patch.  Go back to step (2).
 
diff --git a/Documentation/git-rebase.adoc b/Documentation/git-rebase.adoc
index e177808004fa81..f6c22d1598978a 100644
--- a/Documentation/git-rebase.adoc
+++ b/Documentation/git-rebase.adoc
@@ -497,6 +497,13 @@ See also INCOMPATIBLE OPTIONS below.
 +
 See also INCOMPATIBLE OPTIONS below.
 
+--trailer=<trailer>::
+	Append the given trailer to every rebased commit message, processed
+	via linkgit:git-interpret-trailers[1]. This option implies
+	`--force-rebase`.
++
+See also INCOMPATIBLE OPTIONS below.
+
 -i::
 --interactive::
 	Make a list of the commits which are about to be rebased.  Let the
@@ -653,6 +660,7 @@ are incompatible with the following options:
  * --[no-]reapply-cherry-picks when used without --keep-base
  * --update-refs
  * --root when used without --onto
+ * --trailer
 
 In addition, the following pairs of options are incompatible:
 
diff --git a/builtin/am.c b/builtin/am.c
index e0c767e223dbce..9d0b51c651924a 100644
--- a/builtin/am.c
+++ b/builtin/am.c
@@ -1937,7 +1937,7 @@ static void am_run(struct am_state *state, int resume)
 	 */
 	if (!state->rebasing) {
 		am_destroy(state);
-		run_auto_maintenance(state->quiet);
+		run_auto_maintenance(the_repository, state->quiet);
 	}
 }
 
diff --git a/builtin/commit.c b/builtin/commit.c
index 844bdcc72803b9..02a04f68be0209 100644
--- a/builtin/commit.c
+++ b/builtin/commit.c
@@ -1720,7 +1720,8 @@ int cmd_commit(int argc,
 		OPT_STRING(0, "fixup", &fixup_message, N_("[(amend|reword):]commit"), N_("use autosquash formatted message to fixup or amend/reword specified commit")),
 		OPT_STRING(0, "squash", &squash_message, N_("commit"), N_("use autosquash formatted message to squash specified commit")),
 		OPT_BOOL(0, "reset-author", &renew_authorship, N_("the commit is authored by me now (used with -C/-c/--amend)")),
-		OPT_PASSTHRU_ARGV(0, "trailer", &trailer_args, N_("trailer"), N_("add custom trailer(s)"), PARSE_OPT_NONEG),
+		OPT_STRVEC(0, "trailer", &trailer_args, N_("trailer"),
+			   N_("add custom trailer(s)")),
 		OPT_BOOL('s', "signoff", &signoff, N_("add a Signed-off-by trailer")),
 		OPT_FILENAME('t', "template", &template_file, N_("use specified template file")),
 		OPT_BOOL('e', "edit", &edit_flag, N_("force edit of commit")),
@@ -1820,6 +1821,9 @@ int cmd_commit(int argc,
 	argc = parse_and_validate_options(argc, argv, builtin_commit_options,
 					  builtin_commit_usage,
 					  prefix, current_head, &s);
+	if (trailer_args.nr)
+		trailer_config_init();
+
 	if (verbose == -1)
 		verbose = (config_commit_verbose < 0) ? 0 : config_commit_verbose;
 
@@ -1958,7 +1962,7 @@ int cmd_commit(int argc,
 	git_test_write_commit_graph_or_die(the_repository->objects->sources);
 
 	repo_rerere(the_repository, 0);
-	run_auto_maintenance(quiet);
+	run_auto_maintenance(the_repository, quiet);
 	run_commit_hook(use_editor, repo_get_index_file(the_repository),
 			NULL, "post-commit", NULL);
 	if (amend && !no_post_rewrite) {
diff --git a/builtin/fetch.c b/builtin/fetch.c
index 8a36cf67b5f140..4795b2a13c30e3 100644
--- a/builtin/fetch.c
+++ b/builtin/fetch.c
@@ -2873,7 +2873,7 @@ int cmd_fetch(int argc,
 			if (opt_val != 0)
 				git_config_push_parameter("maintenance.incremental-repack.auto=-1");
 		}
-		run_auto_maintenance(verbosity < 0);
+		run_auto_maintenance(the_repository, verbosity < 0);
 	}
 
  cleanup:
diff --git a/builtin/gc.c b/builtin/gc.c
index fb329c2cffab80..5d8d358f7a511d 100644
--- a/builtin/gc.c
+++ b/builtin/gc.c
@@ -1030,7 +1030,7 @@ int cmd_gc(int argc,
 		struct child_process repack_cmd = CHILD_PROCESS_INIT;
 
 		repack_cmd.git_cmd = 1;
-		repack_cmd.close_object_store = 1;
+		repack_cmd.odb_to_close = the_repository->objects;
 		strvec_pushv(&repack_cmd.args, repack_args.v);
 		if (run_command(&repack_cmd))
 			die(FAILED_RUN, repack_args.v[0]);
@@ -1199,7 +1199,8 @@ static int run_write_commit_graph(struct maintenance_run_opts *opts)
 {
 	struct child_process child = CHILD_PROCESS_INIT;
 
-	child.git_cmd = child.close_object_store = 1;
+	child.git_cmd = 1;
+	child.odb_to_close = the_repository->objects;
 	strvec_pushl(&child.args, "commit-graph", "write",
 		     "--split", "--reachable", NULL);
 
@@ -1268,7 +1269,8 @@ static int maintenance_task_gc_background(struct maintenance_run_opts *opts,
 {
 	struct child_process child = CHILD_PROCESS_INIT;
 
-	child.git_cmd = child.close_object_store = 1;
+	child.git_cmd = 1;
+	child.odb_to_close = the_repository->objects;
 	strvec_push(&child.args, "gc");
 
 	if (opts->auto_flag)
@@ -1484,7 +1486,8 @@ static int multi_pack_index_expire(struct maintenance_run_opts *opts)
 {
 	struct child_process child = CHILD_PROCESS_INIT;
 
-	child.git_cmd = child.close_object_store = 1;
+	child.git_cmd = 1;
+	child.odb_to_close = the_repository->objects;
 	strvec_pushl(&child.args, "multi-pack-index", "expire", NULL);
 
 	if (opts->quiet)
@@ -1542,7 +1545,8 @@ static int multi_pack_index_repack(struct maintenance_run_opts *opts)
 {
 	struct child_process child = CHILD_PROCESS_INIT;
 
-	child.git_cmd = child.close_object_store = 1;
+	child.git_cmd = 1;
+	child.odb_to_close = the_repository->objects;
 	strvec_pushl(&child.args, "multi-pack-index", "repack", NULL);
 
 	if (opts->quiet)
diff --git a/builtin/interpret-trailers.c b/builtin/interpret-trailers.c
index 41b0750e5af324..acaf42b2d9333b 100644
--- a/builtin/interpret-trailers.c
+++ b/builtin/interpret-trailers.c
@@ -93,37 +93,6 @@ static int parse_opt_parse(const struct option *opt, const char *arg,
 	return 0;
 }
 
-static struct tempfile *trailers_tempfile;
-
-static FILE *create_in_place_tempfile(const char *file)
-{
-	struct stat st;
-	struct strbuf filename_template = STRBUF_INIT;
-	const char *tail;
-	FILE *outfile;
-
-	if (stat(file, &st))
-		die_errno(_("could not stat %s"), file);
-	if (!S_ISREG(st.st_mode))
-		die(_("file %s is not a regular file"), file);
-	if (!(st.st_mode & S_IWUSR))
-		die(_("file %s is not writable by user"), file);
-
-	/* Create temporary file in the same directory as the original */
-	tail = strrchr(file, '/');
-	if (tail)
-		strbuf_add(&filename_template, file, tail - file + 1);
-	strbuf_addstr(&filename_template, "git-interpret-trailers-XXXXXX");
-
-	trailers_tempfile = xmks_tempfile_m(filename_template.buf, st.st_mode);
-	strbuf_release(&filename_template);
-	outfile = fdopen_tempfile(trailers_tempfile, "w");
-	if (!outfile)
-		die_errno(_("could not open temporary file"));
-
-	return outfile;
-}
-
 static void read_input_file(struct strbuf *sb, const char *file)
 {
 	if (file) {
@@ -140,55 +109,31 @@ static void interpret_trailers(const struct process_trailer_options *opts,
 			       struct list_head *new_trailer_head,
 			       const char *file)
 {
-	LIST_HEAD(head);
-	struct strbuf sb = STRBUF_INIT;
-	struct strbuf trailer_block_sb = STRBUF_INIT;
-	struct trailer_block *trailer_block;
-	FILE *outfile = stdout;
+	struct strbuf input = STRBUF_INIT;
+	struct strbuf out = STRBUF_INIT;
+	struct tempfile *tempfile = NULL;
+	int fd = 1;
 
 	trailer_config_init();
 
-	read_input_file(&sb, file);
-
-	if (opts->in_place)
-		outfile = create_in_place_tempfile(file);
-
-	trailer_block = parse_trailers(opts, sb.buf, &head);
-
-	/* Print the lines before the trailer block */
-	if (!opts->only_trailers)
-		fwrite(sb.buf, 1, trailer_block_start(trailer_block), outfile);
-
-	if (!opts->only_trailers && !blank_line_before_trailer_block(trailer_block))
-		fprintf(outfile, "\n");
+	read_input_file(&input, file);
 
-
-	if (!opts->only_input) {
-		LIST_HEAD(config_head);
-		LIST_HEAD(arg_head);
-		parse_trailers_from_config(&config_head);
-		parse_trailers_from_command_line_args(&arg_head, new_trailer_head);
-		list_splice(&config_head, &arg_head);
-		process_trailers_lists(&head, &arg_head);
+	if (opts->in_place) {
+		tempfile = trailer_create_in_place_tempfile(file);
+		if (!tempfile)
+			die(NULL);
+		fd = tempfile->fd;
 	}
+	process_trailers(opts, new_trailer_head, &input, &out);
 
-	/* Print trailer block. */
-	format_trailers(opts, &head, &trailer_block_sb);
-	free_trailers(&head);
-	fwrite(trailer_block_sb.buf, 1, trailer_block_sb.len, outfile);
-	strbuf_release(&trailer_block_sb);
-
-	/* Print the lines after the trailer block as is. */
-	if (!opts->only_trailers)
-		fwrite(sb.buf + trailer_block_end(trailer_block), 1,
-		       sb.len - trailer_block_end(trailer_block), outfile);
-	trailer_block_release(trailer_block);
-
+	if (write_in_full(fd, out.buf, out.len) < 0)
+		die_errno(_("could not write to temporary file '%s'"), file);
 	if (opts->in_place)
-		if (rename_tempfile(&trailers_tempfile, file))
+		if (rename_tempfile(&tempfile, file))
 			die_errno(_("could not rename temporary file to %s"), file);
 
-	strbuf_release(&sb);
+	strbuf_release(&input);
+	strbuf_release(&out);
 }
 
 int cmd_interpret_trailers(int argc,
diff --git a/builtin/merge.c b/builtin/merge.c
index 4e456a381c192d..2cbce56f8da9f7 100644
--- a/builtin/merge.c
+++ b/builtin/merge.c
@@ -506,7 +506,7 @@ static void finish(struct commit *head_commit,
 			 * We ignore errors in 'gc --auto', since the
 			 * user should see them.
 			 */
-			run_auto_maintenance(verbosity < 0);
+			run_auto_maintenance(the_repository, verbosity < 0);
 		}
 	}
 	if (new_head && show_diffstat) {
diff --git a/builtin/pull.c b/builtin/pull.c
index 6ad420ce6f9b41..7e67fdce97fd1d 100644
--- a/builtin/pull.c
+++ b/builtin/pull.c
@@ -454,7 +454,7 @@ static int run_fetch(const char *repo, const char **refspecs)
 	} else if (*refspecs)
 		BUG("refspecs without repo?");
 	cmd.git_cmd = 1;
-	cmd.close_object_store = 1;
+	cmd.odb_to_close = the_repository->objects;
 	return run_command(&cmd);
 }
 
diff --git a/builtin/rebase.c b/builtin/rebase.c
index c487e1090779c2..a1c7d78196750e 100644
--- a/builtin/rebase.c
+++ b/builtin/rebase.c
@@ -36,6 +36,7 @@
 #include "reset.h"
 #include "trace2.h"
 #include "hook.h"
+#include "trailer.h"
 
 static char const * const builtin_rebase_usage[] = {
 	N_("git rebase [-i] [options] [--exec <cmd>] "
@@ -113,6 +114,7 @@ struct rebase_options {
 	enum action action;
 	char *reflog_action;
 	int signoff;
+	struct strvec trailer_args;
 	int allow_rerere_autoupdate;
 	int keep_empty;
 	int autosquash;
@@ -143,6 +145,7 @@ struct rebase_options {
 		.flags = REBASE_NO_QUIET, 		\
 		.git_am_opts = STRVEC_INIT,		\
 		.exec = STRING_LIST_INIT_NODUP,		\
+		.trailer_args = STRVEC_INIT,		\
 		.git_format_patch_opt = STRBUF_INIT,	\
 		.fork_point = -1,			\
 		.reapply_cherry_picks = -1,             \
@@ -166,6 +169,7 @@ static void rebase_options_release(struct rebase_options *opts)
 	free(opts->strategy);
 	string_list_clear(&opts->strategy_opts, 0);
 	strbuf_release(&opts->git_format_patch_opt);
+	strvec_clear(&opts->trailer_args);
 }
 
 static struct replay_opts get_replay_opts(const struct rebase_options *opts)
@@ -177,6 +181,10 @@ static struct replay_opts get_replay_opts(const struct rebase_options *opts)
 	sequencer_init_config(&replay);
 
 	replay.signoff = opts->signoff;
+
+	for (size_t i = 0; i < opts->trailer_args.nr; i++)
+		strvec_push(&replay.trailer_args, opts->trailer_args.v[i]);
+
 	replay.allow_ff = !(opts->flags & REBASE_FORCE);
 	if (opts->allow_rerere_autoupdate)
 		replay.allow_rerere_auto = opts->allow_rerere_autoupdate;
@@ -562,7 +570,9 @@ static int finish_rebase(struct rebase_options *opts)
 	 * We ignore errors in 'git maintenance run --auto', since the
 	 * user should see them.
 	 */
-	run_auto_maintenance(!(opts->flags & (REBASE_NO_QUIET|REBASE_VERBOSE)));
+	run_auto_maintenance(the_repository,
+			!(opts->flags & (REBASE_NO_QUIET|REBASE_VERBOSE)));
+
 	if (opts->type == REBASE_MERGE) {
 		struct replay_opts replay = REPLAY_OPTS_INIT;
 
@@ -1132,6 +1142,8 @@ int cmd_rebase(int argc,
 			.flags = PARSE_OPT_NOARG,
 			.defval = REBASE_DIFFSTAT,
 		},
+		OPT_STRVEC(0, "trailer", &options.trailer_args, N_("trailer"),
+			   N_("add custom trailer(s)")),
 		OPT_BOOL(0, "signoff", &options.signoff,
 			 N_("add a Signed-off-by trailer to each commit")),
 		OPT_BOOL(0, "committer-date-is-author-date",
@@ -1285,6 +1297,12 @@ int cmd_rebase(int argc,
 			     builtin_rebase_options,
 			     builtin_rebase_usage, 0);
 
+	if (options.trailer_args.nr) {
+		if (validate_trailer_args(&options.trailer_args))
+			die(NULL);
+		options.flags |= REBASE_FORCE;
+	}
+
 	if (preserve_merges_selected)
 		die(_("--preserve-merges was replaced by --rebase-merges\n"
 			"Note: Your `pull.rebase` configuration may also be set to 'preserve',\n"
@@ -1542,6 +1560,9 @@ int cmd_rebase(int argc,
 	if (options.root && !options.onto_name)
 		imply_merge(&options, "--root without --onto");
 
+	if (options.trailer_args.nr)
+		imply_merge(&options, "--trailer");
+
 	if (isatty(2) && options.flags & REBASE_NO_QUIET)
 		strbuf_addstr(&options.git_format_patch_opt, " --progress");
 
diff --git a/builtin/receive-pack.c b/builtin/receive-pack.c
index d6225df890d888..e34edff406959a 100644
--- a/builtin/receive-pack.c
+++ b/builtin/receive-pack.c
@@ -2727,7 +2727,7 @@ int cmd_receive_pack(int argc,
 		if (auto_gc) {
 			struct child_process proc = CHILD_PROCESS_INIT;
 
-			if (prepare_auto_maintenance(1, &proc)) {
+			if (prepare_auto_maintenance(the_repository, 1, &proc)) {
 				proc.no_stdin = 1;
 				proc.stdout_to_stderr = 1;
 				proc.err = use_sideband ? -1 : 0;
diff --git a/builtin/submodule--helper.c b/builtin/submodule--helper.c
index 143f7cb3cca7d0..f3e132888fabd4 100644
--- a/builtin/submodule--helper.c
+++ b/builtin/submodule--helper.c
@@ -1160,7 +1160,7 @@ static void submodule_summary_callback(struct diff_queue_struct *q,
 
 		if (!S_ISGITLINK(p->one->mode) && !S_ISGITLINK(p->two->mode))
 			continue;
-		temp = (struct module_cb*)malloc(sizeof(struct module_cb));
+		temp = xmalloc(sizeof(*temp));
 		temp->mod_src = p->one->mode;
 		temp->mod_dst = p->two->mode;
 		temp->oid_src = p->one->oid;
diff --git a/builtin/tag.c b/builtin/tag.c
index aeb04c487fe95a..e0f05f94fdbe3e 100644
--- a/builtin/tag.c
+++ b/builtin/tag.c
@@ -499,8 +499,8 @@ int cmd_tag(int argc,
 		OPT_CALLBACK_F('m', "message", &msg, N_("message"),
 			       N_("tag message"), PARSE_OPT_NONEG, parse_msg_arg),
 		OPT_FILENAME('F', "file", &msgfile, N_("read message from file")),
-		OPT_PASSTHRU_ARGV(0, "trailer", &trailer_args, N_("trailer"),
-				  N_("add custom trailer(s)"), PARSE_OPT_NONEG),
+		OPT_STRVEC(0, "trailer", &trailer_args, N_("trailer"),
+			   N_("add custom trailer(s)")),
 		OPT_BOOL('e', "edit", &edit_flag, N_("force edit of tag message")),
 		OPT_BOOL('s', "sign", &opt.sign, N_("annotated and GPG-signed tag")),
 		OPT_CLEANUP(&cleanup_arg),
@@ -568,6 +568,9 @@ int cmd_tag(int argc,
 	if (cmdmode == 'l')
 		setup_auto_pager("tag", 1);
 
+	if (trailer_args.nr)
+		trailer_config_init();
+
 	if (opt.sign == -1)
 		opt.sign = cmdmode ? 0 : config_sign_tag > 0;
 
diff --git a/builtin/worktree.c b/builtin/worktree.c
index bc2d0d645ba945..4035b1cb06cba7 100644
--- a/builtin/worktree.c
+++ b/builtin/worktree.c
@@ -539,7 +539,7 @@ static int add_worktree(const char *path, const char *refname,
 
 	strbuf_reset(&sb);
 	strbuf_addf(&sb, "%s/gitdir", sb_repo.buf);
-	write_worktree_linking_files(sb_git, sb, opts->relative_paths);
+	write_worktree_linking_files(sb_git.buf, sb.buf, opts->relative_paths);
 	strbuf_reset(&sb);
 	strbuf_addf(&sb, "%s/commondir", sb_repo.buf);
 	write_file(sb.buf, "../..");
diff --git a/list-objects-filter-options.c b/list-objects-filter-options.c
index 7f3e7b8f505ebc..cef67e591954a9 100644
--- a/list-objects-filter-options.c
+++ b/list-objects-filter-options.c
@@ -125,9 +125,9 @@ int gently_parse_list_objects_filter(
 static const char *RESERVED_NON_WS = "~`!@#$^&*()[]{}\\;'\",<>?";
 
 static int has_reserved_character(
-	struct strbuf *sub_spec, struct strbuf *errbuf)
+	const char *sub_spec, struct strbuf *errbuf)
 {
-	const char *c = sub_spec->buf;
+	const char *c = sub_spec;
 	while (*c) {
 		if (*c <= ' ' || strchr(RESERVED_NON_WS, *c)) {
 			strbuf_addf(
@@ -144,7 +144,7 @@ static int has_reserved_character(
 
 static int parse_combine_subfilter(
 	struct list_objects_filter_options *filter_options,
-	struct strbuf *subspec,
+	const char *subspec,
 	struct strbuf *errbuf)
 {
 	size_t new_index = filter_options->sub_nr;
@@ -155,7 +155,7 @@ static int parse_combine_subfilter(
 		      filter_options->sub_alloc);
 	list_objects_filter_init(&filter_options->sub[new_index]);
 
-	decoded = url_percent_decode(subspec->buf);
+	decoded = url_percent_decode(subspec);
 
 	result = has_reserved_character(subspec, errbuf);
 	if (result)
@@ -182,34 +182,34 @@ static int parse_combine_filter(
 	const char *arg,
 	struct strbuf *errbuf)
 {
-	struct strbuf **subspecs = strbuf_split_str(arg, '+', 0);
-	size_t sub;
+	const char *p = arg;
+	struct strbuf sub = STRBUF_INIT;
 	int result = 0;
 
-	if (!subspecs[0]) {
+	if (!*p) {
 		strbuf_addstr(errbuf, _("expected something after combine:"));
 		result = 1;
 		goto cleanup;
 	}
 
-	for (sub = 0; subspecs[sub] && !result; sub++) {
-		if (subspecs[sub + 1]) {
-			/*
-			 * This is not the last subspec. Remove trailing "+" so
-			 * we can parse it.
-			 */
-			size_t last = subspecs[sub]->len - 1;
-			assert(subspecs[sub]->buf[last] == '+');
-			strbuf_remove(subspecs[sub], last, 1);
-		}
-		result = parse_combine_subfilter(
-			filter_options, subspecs[sub], errbuf);
+	while (*p && !result) {
+		const char *end = strchrnul(p, '+');
+
+		strbuf_reset(&sub);
+		strbuf_add(&sub, p, end - p);
+
+		if (sub.len)
+			result = parse_combine_subfilter(filter_options, sub.buf, errbuf);
+
+		if (!*end)
+			break;
+		p = end + 1;
 	}
+	strbuf_release(&sub);
 
 	filter_options->choice = LOFC_COMBINE;
 
 cleanup:
-	strbuf_list_free(subspecs);
 	if (result)
 		list_objects_filter_release(filter_options);
 	return result;
diff --git a/run-command.c b/run-command.c
index a8a8974638d7ef..32c290ee6a221f 100644
--- a/run-command.c
+++ b/run-command.c
@@ -1,4 +1,3 @@
-#define USE_THE_REPOSITORY_VARIABLE
 #define DISABLE_SIGN_COMPARE_WARNINGS
 
 #include "git-compat-util.h"
@@ -742,8 +741,8 @@ int start_command(struct child_process *cmd)
 
 	fflush(NULL);
 
-	if (cmd->close_object_store)
-		odb_close(the_repository->objects);
+	if (cmd->odb_to_close)
+		odb_close(cmd->odb_to_close);
 
 #ifndef GIT_WINDOWS_NATIVE
 {
@@ -1937,11 +1936,12 @@ void run_processes_parallel(const struct run_process_parallel_opts *opts)
 		trace2_region_leave(tr2_category, tr2_label, NULL);
 }
 
-int prepare_auto_maintenance(int quiet, struct child_process *maint)
+int prepare_auto_maintenance(struct repository *r, int quiet,
+			     struct child_process *maint)
 {
 	int enabled, auto_detach;
 
-	if (!repo_config_get_bool(the_repository, "maintenance.auto", &enabled) &&
+	if (!repo_config_get_bool(r, "maintenance.auto", &enabled) &&
 	    !enabled)
 		return 0;
 
@@ -1950,12 +1950,12 @@ int prepare_auto_maintenance(int quiet, struct child_process *maint)
 	 * honoring `gc.autoDetach`. This is somewhat weird, but required to
 	 * retain behaviour from when we used to run git-gc(1) here.
 	 */
-	if (repo_config_get_bool(the_repository, "maintenance.autodetach", &auto_detach) &&
-	    repo_config_get_bool(the_repository, "gc.autodetach", &auto_detach))
+	if (repo_config_get_bool(r, "maintenance.autodetach", &auto_detach) &&
+	    repo_config_get_bool(r, "gc.autodetach", &auto_detach))
 		auto_detach = git_env_bool("GIT_TEST_MAINT_AUTO_DETACH", true);
 
 	maint->git_cmd = 1;
-	maint->close_object_store = 1;
+	maint->odb_to_close = r->objects;
 	strvec_pushl(&maint->args, "maintenance", "run", "--auto", NULL);
 	strvec_push(&maint->args, quiet ? "--quiet" : "--no-quiet");
 	strvec_push(&maint->args, auto_detach ? "--detach" : "--no-detach");
@@ -1963,10 +1963,10 @@ int prepare_auto_maintenance(int quiet, struct child_process *maint)
 	return 1;
 }
 
-int run_auto_maintenance(int quiet)
+int run_auto_maintenance(struct repository *r, int quiet)
 {
 	struct child_process maint = CHILD_PROCESS_INIT;
-	if (!prepare_auto_maintenance(quiet, &maint))
+	if (!prepare_auto_maintenance(r, quiet, &maint))
 		return 0;
 	return run_command(&maint);
 }
diff --git a/run-command.h b/run-command.h
index 428d76ebd620ff..8ca496d7bdebfd 100644
--- a/run-command.h
+++ b/run-command.h
@@ -5,6 +5,8 @@
 
 #include "strvec.h"
 
+struct repository;
+
 /**
  * The run-command API offers a versatile tool to run sub-processes with
  * redirected input and output as well as with a modified environment
@@ -136,7 +138,7 @@ struct child_process {
 	 * want to repack because that would delete `.pack` files (and on
 	 * Windows, you cannot delete files that are still in use).
 	 */
-	unsigned close_object_store:1;
+	struct object_database *odb_to_close;
 
 	unsigned stdout_to_stderr:1;
 	unsigned clean_on_exit:1;
@@ -227,12 +229,13 @@ int run_command(struct child_process *);
  * process has been prepared and is ready to run, or 0 in case auto-maintenance
  * should be skipped.
  */
-int prepare_auto_maintenance(int quiet, struct child_process *maint);
+int prepare_auto_maintenance(struct repository *r, int quiet,
+			     struct child_process *maint);
 
 /*
  * Trigger an auto-gc
  */
-int run_auto_maintenance(int quiet);
+int run_auto_maintenance(struct repository *r, int quiet);
 
 /**
  * Execute the given command, sending "in" to its stdin, and capturing its
diff --git a/sequencer.c b/sequencer.c
index aafd0bc959664a..e5af49cecd0859 100644
--- a/sequencer.c
+++ b/sequencer.c
@@ -209,6 +209,7 @@ static GIT_PATH_FUNC(rebase_path_reschedule_failed_exec, "rebase-merge/reschedul
 static GIT_PATH_FUNC(rebase_path_no_reschedule_failed_exec, "rebase-merge/no-reschedule-failed-exec")
 static GIT_PATH_FUNC(rebase_path_drop_redundant_commits, "rebase-merge/drop_redundant_commits")
 static GIT_PATH_FUNC(rebase_path_keep_redundant_commits, "rebase-merge/keep_redundant_commits")
+static GIT_PATH_FUNC(rebase_path_trailer, "rebase-merge/trailer")
 
 /*
  * A 'struct replay_ctx' represents the private state of the sequencer.
@@ -420,6 +421,7 @@ void replay_opts_release(struct replay_opts *opts)
 	if (opts->revs)
 		release_revisions(opts->revs);
 	free(opts->revs);
+	strvec_clear(&opts->trailer_args);
 	replay_ctx_release(ctx);
 	free(opts->ctx);
 }
@@ -2027,12 +2029,15 @@ static int append_squash_message(struct strbuf *buf, const char *body,
 	if (is_fixup_flag(command, flag) && !seen_squash(ctx)) {
 		/*
 		 * We're replacing the commit message so we need to
-		 * append the Signed-off-by: trailer if the user
-		 * requested '--signoff'.
+		 * append any trailers if the user requested
+		 * '--signoff' or '--trailer'.
 		 */
 		if (opts->signoff)
 			append_signoff(buf, 0, 0);
 
+		if (opts->trailer_args.nr)
+			amend_strbuf_with_trailers(buf, &opts->trailer_args);
+
 		if ((command == TODO_FIXUP) &&
 		    (flag & TODO_REPLACE_FIXUP_MSG) &&
 		    (file_exists(rebase_path_fixup_msg()) ||
@@ -2451,6 +2456,9 @@ static int do_pick_commit(struct repository *r,
 	if (opts->signoff && !is_fixup(command))
 		append_signoff(&ctx->message, 0, 0);
 
+	if (opts->trailer_args.nr && !is_fixup(command))
+		amend_strbuf_with_trailers(&ctx->message, &opts->trailer_args);
+
 	if (is_rebase_i(opts) && write_author_script(msg.message) < 0)
 		res = -1;
 	else if (!opts->strategy ||
@@ -3180,6 +3188,33 @@ static void read_strategy_opts(struct replay_opts *opts, struct strbuf *buf)
 	parse_strategy_opts(opts, buf->buf);
 }
 
+static int read_trailers(struct replay_opts *opts, struct strbuf *buf)
+{
+	ssize_t len;
+
+	strbuf_reset(buf);
+	len = strbuf_read_file(buf, rebase_path_trailer(), 0);
+	if (len > 0) {
+		char *p = buf->buf, *nl;
+
+		trailer_config_init();
+
+		while ((nl = strchr(p, '\n'))) {
+			*nl = '\0';
+			if (!*p)
+				return error(_("trailers file contains empty line"));
+			strvec_push(&opts->trailer_args, p);
+			p = nl + 1;
+		}
+	} else if (!len) {
+		return error(_("trailers file is empty"));
+	} else if (errno != ENOENT) {
+		return error(_("cannot read trailers files"));
+	}
+
+	return 0;
+}
+
 static int read_populate_opts(struct replay_opts *opts)
 {
 	struct replay_ctx *ctx = opts->ctx;
@@ -3241,6 +3276,11 @@ static int read_populate_opts(struct replay_opts *opts)
 			opts->keep_redundant_commits = 1;
 
 		read_strategy_opts(opts, &buf);
+
+		if (read_trailers(opts, &buf)) {
+			ret = -1;
+			goto done_rebase_i;
+		}
 		strbuf_reset(&buf);
 
 		if (read_oneliner(&ctx->current_fixups,
@@ -3336,6 +3376,14 @@ int write_basic_state(struct replay_opts *opts, const char *head_name,
 		write_file(rebase_path_reschedule_failed_exec(), "%s", "");
 	else
 		write_file(rebase_path_no_reschedule_failed_exec(), "%s", "");
+	if (opts->trailer_args.nr) {
+		struct strbuf buf = STRBUF_INIT;
+
+		for (size_t i = 0; i < opts->trailer_args.nr; i++)
+			strbuf_addf(&buf, "%s\n", opts->trailer_args.v[i]);
+		write_file(rebase_path_trailer(), "%s", buf.buf);
+		strbuf_release(&buf);
+	}
 
 	return 0;
 }
diff --git a/sequencer.h b/sequencer.h
index 719684c8a9fb2e..bea20da085f0a2 100644
--- a/sequencer.h
+++ b/sequencer.h
@@ -57,6 +57,8 @@ struct replay_opts {
 	int ignore_date;
 	int commit_use_reference;
 
+	struct strvec trailer_args;
+
 	int mainline;
 
 	char *gpg_sign;
@@ -84,6 +86,7 @@ struct replay_opts {
 #define REPLAY_OPTS_INIT {			\
 	.edit = -1,				\
 	.action = -1,				\
+	.trailer_args = STRVEC_INIT,		\
 	.xopts = STRVEC_INIT,			\
 	.ctx = replay_ctx_new(),		\
 }
diff --git a/t/helper/test-example-tap.c b/t/helper/test-example-tap.c
index 229d495ecfa668..998a1f0b428bed 100644
--- a/t/helper/test-example-tap.c
+++ b/t/helper/test-example-tap.c
@@ -63,6 +63,8 @@ static void t_messages(void)
 	check_str("NULL", NULL);
 	check_char('a', ==, '\n');
 	check_char('\\', ==, '\'');
+	check_char('\a', ==, '\v');
+	check_char('\x00', ==, '\x01');
 }
 
 static void t_empty(void)
@@ -123,6 +125,8 @@ int cmd__example_tap(int argc UNUSED, const char **argv UNUSED)
 		check_str("NULL", NULL);
 		check_char('a', ==, '\n');
 		check_char('\\', ==, '\'');
+		check_char('\a', ==, '\v');
+		check_char('\x00', ==, '\x01');
 	}
 	if_test ("if_test test with no checks")
 		; /* nothing */
diff --git a/t/meson.build b/t/meson.build
index 9b2fa4dee807d6..e539117ca4fedd 100644
--- a/t/meson.build
+++ b/t/meson.build
@@ -393,6 +393,7 @@ integration_tests = [
   't3436-rebase-more-options.sh',
   't3437-rebase-fixup-options.sh',
   't3438-rebase-broken-files.sh',
+  't3440-rebase-trailer.sh',
   't3450-history.sh',
   't3451-history-reword.sh',
   't3500-cherry.sh',
diff --git a/t/t0080-unit-test-output.sh b/t/t0080-unit-test-output.sh
index 3db10f095c2edc..66838a00b220cc 100755
--- a/t/t0080-unit-test-output.sh
+++ b/t/t0080-unit-test-output.sh
@@ -6,10 +6,10 @@ test_description='Test the output of the unit test framework'
 
 test_expect_success 'TAP output from unit tests' - <<\EOT
 	cat >expect <<-EOF &&
-	# BUG: check outside of test at t/helper/test-example-tap.c:75
+	# BUG: check outside of test at t/helper/test-example-tap.c:77
 	ok 1 - passing test
 	ok 2 - passing test and assertion return 1
-	# check "1 == 2" failed at t/helper/test-example-tap.c:79
+	# check "1 == 2" failed at t/helper/test-example-tap.c:81
 	#    left: 1
 	#   right: 2
 	not ok 3 - failing test
@@ -34,53 +34,65 @@ test_expect_success 'TAP output from unit tests' - <<\EOT
 	not ok 15 - failing check after TEST_TODO()
 	ok 16 - failing check after TEST_TODO() returns 0
 	# check "!strcmp("\thello\\\\", "there\"\n")" failed at t/helper/test-example-tap.c:62
-	#    left: "\011hello\\\\"
-	#   right: "there\"\012"
+	#    left: "\thello\\\\"
+	#   right: "there\"\n"
 	# check "!strcmp("NULL", NULL)" failed at t/helper/test-example-tap.c:63
 	#    left: "NULL"
 	#   right: NULL
 	# check "'a' == '\n'" failed at t/helper/test-example-tap.c:64
 	#    left: 'a'
-	#   right: '\012'
+	#   right: '\n'
 	# check "'\\\\' == '\\''" failed at t/helper/test-example-tap.c:65
 	#    left: '\\\\'
 	#   right: '\\''
+	# check "'\a' == '\v'" failed at t/helper/test-example-tap.c:66
+	#    left: '\a'
+	#   right: '\v'
+	# check "'\x00' == '\x01'" failed at t/helper/test-example-tap.c:67
+	#    left: '\000'
+	#   right: '\001'
 	not ok 17 - messages from failing string and char comparison
-	# BUG: test has no checks at t/helper/test-example-tap.c:94
+	# BUG: test has no checks at t/helper/test-example-tap.c:96
 	not ok 18 - test with no checks
 	ok 19 - test with no checks returns 0
 	ok 20 - if_test passing test
-	# check "1 == 2" failed at t/helper/test-example-tap.c:100
+	# check "1 == 2" failed at t/helper/test-example-tap.c:102
 	#    left: 1
 	#   right: 2
 	not ok 21 - if_test failing test
 	not ok 22 - if_test passing TEST_TODO() # TODO
-	# todo check 'check(1)' succeeded at t/helper/test-example-tap.c:104
+	# todo check 'check(1)' succeeded at t/helper/test-example-tap.c:106
 	not ok 23 - if_test failing TEST_TODO()
-	# check "0" failed at t/helper/test-example-tap.c:106
+	# check "0" failed at t/helper/test-example-tap.c:108
 	# skipping test - missing prerequisite
-	# skipping check '1' at t/helper/test-example-tap.c:108
+	# skipping check '1' at t/helper/test-example-tap.c:110
 	ok 24 - if_test test_skip() # SKIP
 	# skipping test - missing prerequisite
 	ok 25 - if_test test_skip() inside TEST_TODO() # SKIP
-	# check "0" failed at t/helper/test-example-tap.c:113
+	# check "0" failed at t/helper/test-example-tap.c:115
 	not ok 26 - if_test TEST_TODO() after failing check
-	# check "0" failed at t/helper/test-example-tap.c:119
+	# check "0" failed at t/helper/test-example-tap.c:121
 	not ok 27 - if_test failing check after TEST_TODO()
-	# check "!strcmp("\thello\\\\", "there\"\n")" failed at t/helper/test-example-tap.c:122
-	#    left: "\011hello\\\\"
-	#   right: "there\"\012"
-	# check "!strcmp("NULL", NULL)" failed at t/helper/test-example-tap.c:123
+	# check "!strcmp("\thello\\\\", "there\"\n")" failed at t/helper/test-example-tap.c:124
+	#    left: "\thello\\\\"
+	#   right: "there\"\n"
+	# check "!strcmp("NULL", NULL)" failed at t/helper/test-example-tap.c:125
 	#    left: "NULL"
 	#   right: NULL
-	# check "'a' == '\n'" failed at t/helper/test-example-tap.c:124
+	# check "'a' == '\n'" failed at t/helper/test-example-tap.c:126
 	#    left: 'a'
-	#   right: '\012'
-	# check "'\\\\' == '\\''" failed at t/helper/test-example-tap.c:125
+	#   right: '\n'
+	# check "'\\\\' == '\\''" failed at t/helper/test-example-tap.c:127
 	#    left: '\\\\'
 	#   right: '\\''
+	# check "'\a' == '\v'" failed at t/helper/test-example-tap.c:128
+	#    left: '\a'
+	#   right: '\v'
+	# check "'\x00' == '\x01'" failed at t/helper/test-example-tap.c:129
+	#    left: '\000'
+	#   right: '\001'
 	not ok 28 - if_test messages from failing string and char comparison
-	# BUG: test has no checks at t/helper/test-example-tap.c:127
+	# BUG: test has no checks at t/helper/test-example-tap.c:131
 	not ok 29 - if_test test with no checks
 	1..29
 	EOF
diff --git a/t/t3200-branch.sh b/t/t3200-branch.sh
index c58e505c43f9b9..e7829c2c4bfdc3 100755
--- a/t/t3200-branch.sh
+++ b/t/t3200-branch.sh
@@ -1494,7 +1494,8 @@ test_expect_success 'refuse --edit-description on unborn branch for now' '
 '
 
 test_expect_success '--merged catches invalid object names' '
-	test_must_fail git branch --merged 0000000000000000000000000000000000000000
+	test_must_fail git branch --merged $ZERO_OID 2>err &&
+	test_grep "must point to a commit" err
 '
 
 test_expect_success '--list during rebase' '
diff --git a/t/t3440-rebase-trailer.sh b/t/t3440-rebase-trailer.sh
new file mode 100755
index 00000000000000..8b4757956603db
--- /dev/null
+++ b/t/t3440-rebase-trailer.sh
@@ -0,0 +1,147 @@
+#!/bin/sh
+#
+
+test_description='git rebase --trailer integration tests
+We verify that --trailer works with the merge backend,
+and that it is rejected early when the apply backend is requested.'
+
+GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME=main
+export GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME
+
+. ./test-lib.sh
+. "$TEST_DIRECTORY"/lib-rebase.sh # test_commit_message, helpers
+
+REVIEWED_BY_TRAILER="Reviewed-by: Dev <dev@example.com>"
+SP=" "
+
+test_expect_success 'setup repo with a small history' '
+	git commit --allow-empty -m "Initial empty commit" &&
+	test_commit first file a &&
+	test_commit second file &&
+	git checkout -b conflict-branch first &&
+	test_commit file-2 file-2 &&
+	test_commit conflict file &&
+	test_commit third file &&
+	git checkout main
+'
+
+test_expect_success 'apply backend is rejected with --trailer' '
+	git checkout -B apply-backend third &&
+	test_expect_code 128 \
+		git rebase --apply --trailer "$REVIEWED_BY_TRAILER" HEAD^ 2>err &&
+	test_grep "fatal: --trailer requires the merge backend" err
+'
+
+test_expect_success 'reject empty --trailer argument' '
+	git checkout -B empty-trailer third &&
+	test_expect_code 128 git rebase --trailer "" HEAD^ 2>err &&
+	test_grep "empty --trailer" err
+'
+
+test_expect_success 'reject trailer with missing key before separator' '
+	git checkout -B missing-key third &&
+	test_expect_code 128 git rebase --trailer ": no-key" HEAD^ 2>err &&
+	test_grep "missing key before separator" err
+'
+
+test_expect_success 'allow trailer with missing value after separator' '
+	git checkout -B missing-value third &&
+	git rebase --trailer "Acked-by:" HEAD^ &&
+	test_commit_message HEAD <<-EOF
+	third
+
+	Acked-by:${SP}
+	EOF
+'
+
+test_expect_success 'CLI trailer duplicates allowed; replace policy keeps last' '
+	git checkout -B replace-policy third &&
+	git -c trailer.Bug.ifexists=replace -c trailer.Bug.ifmissing=add \
+		rebase --trailer "Bug: 123" --trailer "Bug: 456" HEAD^ &&
+	test_commit_message HEAD <<-EOF
+	third
+
+	Bug: 456
+	EOF
+'
+
+test_expect_success 'multiple Signed-off-by trailers all preserved' '
+	git checkout -B multiple-signoff third &&
+	git rebase --trailer "Signed-off-by: Dev A <a@example.com>" \
+		--trailer "Signed-off-by: Dev B <b@example.com>" HEAD^ &&
+	test_commit_message HEAD <<-EOF
+	third
+
+	Signed-off-by: Dev A <a@example.com>
+	Signed-off-by: Dev B <b@example.com>
+	EOF
+'
+
+test_expect_success 'rebase --trailer adds trailer after conflicts' '
+	git checkout -B trailer-conflict third &&
+	test_commit fourth file &&
+	test_must_fail git rebase --trailer "$REVIEWED_BY_TRAILER" second &&
+	git checkout --theirs file &&
+	git add file &&
+	git rebase --continue &&
+	test_commit_message HEAD <<-EOF &&
+	fourth
+
+	$REVIEWED_BY_TRAILER
+	EOF
+	test_commit_message HEAD^ <<-EOF
+	third
+
+	$REVIEWED_BY_TRAILER
+	EOF
+'
+
+test_expect_success '--trailer handles fixup commands in todo list' '
+	git checkout -B fixup-trailer third &&
+	test_commit fixup-base base &&
+	test_commit fixup-second second &&
+	cat >todo <<-\EOF &&
+	pick fixup-base fixup-base
+	fixup fixup-second fixup-second
+	EOF
+	(
+		set_replace_editor todo &&
+		git rebase -i --trailer "$REVIEWED_BY_TRAILER" HEAD~2
+	) &&
+	test_commit_message HEAD <<-EOF &&
+	fixup-base
+
+	$REVIEWED_BY_TRAILER
+	EOF
+	git reset --hard fixup-second &&
+	cat >todo <<-\EOF &&
+	pick fixup-base fixup-base
+	fixup -C fixup-second fixup-second
+	EOF
+	(
+		set_replace_editor todo &&
+		git rebase -i --trailer "$REVIEWED_BY_TRAILER" HEAD~2
+	) &&
+	test_commit_message HEAD <<-EOF
+	fixup-second
+
+	$REVIEWED_BY_TRAILER
+	EOF
+'
+
+test_expect_success 'rebase --root honors trailer.<name>.key' '
+	git checkout -B root-trailer first &&
+	git -c trailer.review.key=Reviewed-by rebase --root \
+		--trailer=review="Dev <dev@example.com>" &&
+	test_commit_message HEAD <<-EOF &&
+	first
+
+	Reviewed-by: Dev <dev@example.com>
+	EOF
+	test_commit_message HEAD^ <<-EOF
+	Initial empty commit
+
+	Reviewed-by: Dev <dev@example.com>
+	EOF
+'
+test_done
diff --git a/t/t6112-rev-list-filters-objects.sh b/t/t6112-rev-list-filters-objects.sh
index 0387f35a326d74..39211ef989cc58 100755
--- a/t/t6112-rev-list-filters-objects.sh
+++ b/t/t6112-rev-list-filters-objects.sh
@@ -483,10 +483,6 @@ test_expect_success 'combine:... with non-encoded reserved chars' '
 		"must escape char in sub-filter-spec: .\~."
 '
 
-test_expect_success 'validate err msg for "combine:<valid-filter>+"' '
-	expect_invalid_filter_spec combine:tree:2+ "expected .tree:<depth>."
-'
-
 test_expect_success 'combine:... with edge-case hex digits: Ff Aa 0 9' '
 	git -C r3 rev-list --objects --filter="combine:tree:2+bl%6Fb:n%6fne" \
 		HEAD >actual &&
diff --git a/t/t9200-git-cvsexportcommit.sh b/t/t9200-git-cvsexportcommit.sh
index a44eabf0d80fa8..14cbe9652779bc 100755
--- a/t/t9200-git-cvsexportcommit.sh
+++ b/t/t9200-git-cvsexportcommit.sh
@@ -30,13 +30,17 @@ export CVSROOT CVSWORK GIT_DIR
 
 rm -rf "$CVSROOT" "$CVSWORK"
 
-cvs init &&
-test -d "$CVSROOT" &&
-cvs -Q co -d "$CVSWORK" . &&
-echo >empty &&
-git add empty &&
-git commit -q -a -m "Initial" 2>/dev/null ||
-exit 1
+if ! cvs init || ! test -d "$CVSROOT" || ! cvs -Q co -d "$CVSWORK" .
+then
+	skip_all="cvs repository set-up fails"
+	test_done
+fi
+
+test_expect_success 'git setup' '
+	echo >empty &&
+	git add empty &&
+	git commit -q -a -m Initial
+'
 
 check_entries () {
 	# $1 == directory, $2 == expected
@@ -303,7 +307,7 @@ test_expect_success 're-commit a removed filename which remains in CVS attic' '
 	git commit -m "Added attic_gremlin" &&
 	git cvsexportcommit -w "$CVSWORK" -c HEAD &&
 	(cd "$CVSWORK" && cvs -Q update -d) &&
-	test -f "$CVSWORK/attic_gremlin"
+	test_path_is_file "$CVSWORK/attic_gremlin"
 '
 
 # the state of the CVS sandbox may be indeterminate for ' space'
diff --git a/t/unit-tests/test-lib.c b/t/unit-tests/test-lib.c
index 87e1f5c201f253..72ee20a06f3951 100644
--- a/t/unit-tests/test-lib.c
+++ b/t/unit-tests/test-lib.c
@@ -396,8 +396,23 @@ int check_uint_loc(const char *loc, const char *check, int ok,
 static void print_one_char(char ch, char quote)
 {
 	if ((unsigned char)ch < 0x20u || ch == 0x7f) {
-		/* TODO: improve handling of \a, \b, \f ... */
-		printf("\\%03o", (unsigned char)ch);
+		char esc;
+		switch (ch) {
+		case '\a': esc = 'a'; break;
+		case '\b': esc = 'b'; break;
+		case '\t': esc = 't'; break;
+		case '\n': esc = 'n'; break;
+		case '\v': esc = 'v'; break;
+		case '\f': esc = 'f'; break;
+		case '\r': esc = 'r'; break;
+		default: esc = 0; break;
+		}
+		if (esc) {
+			putc('\\', stdout);
+			putc(esc, stdout);
+		} else {
+			printf("\\%03o", (unsigned char)ch);
+		}
 	} else {
 		if (ch == '\\' || ch == quote)
 			putc('\\', stdout);
diff --git a/trailer.c b/trailer.c
index 911a81ed993ec6..ca8abd18826bf2 100644
--- a/trailer.c
+++ b/trailer.c
@@ -7,8 +7,11 @@
 #include "string-list.h"
 #include "run-command.h"
 #include "commit.h"
+#include "strvec.h"
 #include "trailer.h"
 #include "list.h"
+#include "tempfile.h"
+
 /*
  * Copyright (c) 2013, 2014 Christian Couder <chriscool@tuxfamily.org>
  */
@@ -772,6 +775,35 @@ void parse_trailers_from_command_line_args(struct list_head *arg_head,
 	free(cl_separators);
 }
 
+int validate_trailer_args(const struct strvec *cli_args)
+{
+	char *cl_separators;
+	int ret = 0;
+
+	trailer_config_init();
+
+	cl_separators = xstrfmt("=%s", separators);
+
+	for (size_t i = 0; i < cli_args->nr; i++) {
+		const char *txt = cli_args->v[i];
+		ssize_t separator_pos;
+
+		if (!*txt) {
+			ret = error(_("empty --trailer argument"));
+			goto out;
+		}
+		separator_pos = find_separator(txt, cl_separators);
+		if (separator_pos == 0) {
+			ret = error(_("invalid trailer '%s': missing key before separator"),
+				    txt);
+			goto out;
+		}
+	}
+out:
+	free(cl_separators);
+	return ret;
+}
+
 static const char *next_line(const char *str)
 {
 	const char *nl = strchrnul(str, '\n');
@@ -1224,14 +1256,146 @@ void trailer_iterator_release(struct trailer_iterator *iter)
 	strbuf_release(&iter->key);
 }
 
-int amend_file_with_trailers(const char *path, const struct strvec *trailer_args)
+struct tempfile *trailer_create_in_place_tempfile(const char *file)
+{
+	struct tempfile *tempfile = NULL;
+	struct stat st;
+	struct strbuf filename_template = STRBUF_INIT;
+	const char *tail;
+
+	if (stat(file, &st)) {
+		error_errno(_("could not stat %s"), file);
+		return NULL;
+	}
+	if (!S_ISREG(st.st_mode)) {
+		error(_("file %s is not a regular file"), file);
+		return NULL;
+	}
+	if (!(st.st_mode & S_IWUSR)) {
+		error(_("file %s is not writable by user"), file);
+		return NULL;
+	}
+	/* Create temporary file in the same directory as the original */
+	tail = find_last_dir_sep(file);
+	if (tail)
+		strbuf_add(&filename_template, file, tail - file + 1);
+	strbuf_addstr(&filename_template, "git-interpret-trailers-XXXXXX");
+
+	tempfile = mks_tempfile_m(filename_template.buf, st.st_mode);
+
+	strbuf_release(&filename_template);
+
+	return tempfile;
+}
+
+int amend_strbuf_with_trailers(struct strbuf *buf,
+				const struct strvec *trailer_args)
 {
-	struct child_process run_trailer = CHILD_PROCESS_INIT;
-
-	run_trailer.git_cmd = 1;
-	strvec_pushl(&run_trailer.args, "interpret-trailers",
-		     "--in-place", "--no-divider",
-		     path, NULL);
-	strvec_pushv(&run_trailer.args, trailer_args->v);
-	return run_command(&run_trailer);
+	struct process_trailer_options opts = PROCESS_TRAILER_OPTIONS_INIT;
+	LIST_HEAD(new_trailer_head);
+	struct strbuf out = STRBUF_INIT;
+	size_t i;
+	int ret = 0;
+
+	opts.no_divider = 1;
+
+	for (i = 0; i < trailer_args->nr; i++) {
+		const char *text = trailer_args->v[i];
+		struct new_trailer_item *item;
+
+		if (!*text) {
+			ret = error(_("empty --trailer argument"));
+			goto out;
+		}
+		item = xcalloc(1, sizeof(*item));
+		item->text = xstrdup(text);
+		list_add_tail(&item->list, &new_trailer_head);
+	}
+
+	process_trailers(&opts, &new_trailer_head, buf, &out);
+
+	strbuf_swap(buf, &out);
+out:
+	strbuf_release(&out);
+	free_trailers(&new_trailer_head);
+
+	return ret;
+}
+
+static int write_file_in_place(const char *path, const struct strbuf *buf)
+{
+	struct tempfile *tempfile = trailer_create_in_place_tempfile(path);
+	if (!tempfile)
+		return -1;
+
+	if (write_in_full(tempfile->fd, buf->buf, buf->len) < 0)
+		return error_errno(_("could not write to temporary file"));
+
+	if (rename_tempfile(&tempfile, path))
+		return error_errno(_("could not rename temporary file to %s"), path);
+
+	return 0;
+}
+
+int amend_file_with_trailers(const char *path,
+			     const struct strvec *trailer_args)
+{
+	struct strbuf buf = STRBUF_INIT;
+	int ret = 0;
+
+	if (!trailer_args)
+		BUG("amend_file_with_trailers called with NULL trailer_args");
+	if (!trailer_args->nr)
+		return 0;
+
+	if (validate_trailer_args(trailer_args)) {
+		ret = -1;
+		goto out;
+	}
+	if (strbuf_read_file(&buf, path, 0) < 0)
+		ret = error_errno(_("could not read '%s'"), path);
+	else
+		amend_strbuf_with_trailers(&buf, trailer_args);
+
+	if (!ret)
+		ret = write_file_in_place(path, &buf);
+out:
+	strbuf_release(&buf);
+	return ret;
+}
+
+void process_trailers(const struct process_trailer_options *opts,
+		      struct list_head *new_trailer_head,
+		      struct strbuf *input, struct strbuf *out)
+{
+	LIST_HEAD(head);
+	struct trailer_block *trailer_block;
+
+	trailer_block = parse_trailers(opts, input->buf, &head);
+
+	/* Print the lines before the trailer block */
+	if (!opts->only_trailers)
+		strbuf_add(out, input->buf, trailer_block_start(trailer_block));
+
+	if (!opts->only_trailers && !blank_line_before_trailer_block(trailer_block))
+		strbuf_addch(out, '\n');
+
+	if (!opts->only_input) {
+		LIST_HEAD(config_head);
+		LIST_HEAD(arg_head);
+		parse_trailers_from_config(&config_head);
+		parse_trailers_from_command_line_args(&arg_head, new_trailer_head);
+		list_splice(&config_head, &arg_head);
+		process_trailers_lists(&head, &arg_head);
+	}
+
+	/* Print trailer block. */
+	format_trailers(opts, &head, out);
+	free_trailers(&head);
+
+	/* Print the lines after the trailer block as is. */
+	if (!opts->only_trailers)
+		strbuf_add(out, input->buf + trailer_block_end(trailer_block),
+			   input->len - trailer_block_end(trailer_block));
+	trailer_block_release(trailer_block);
 }
diff --git a/trailer.h b/trailer.h
index 4740549586a8e5..b49338858c482a 100644
--- a/trailer.h
+++ b/trailer.h
@@ -68,6 +68,8 @@ void parse_trailers_from_config(struct list_head *config_head);
 void parse_trailers_from_command_line_args(struct list_head *arg_head,
 					   struct list_head *new_trailer_head);
 
+int validate_trailer_args(const struct strvec *cli_args);
+
 void process_trailers_lists(struct list_head *head,
 			    struct list_head *arg_head);
 
@@ -196,10 +198,38 @@ int trailer_iterator_advance(struct trailer_iterator *iter);
 void trailer_iterator_release(struct trailer_iterator *iter);
 
 /*
- * Augment a file to add trailers to it by running git-interpret-trailers.
- * This calls run_command() and its return value is the same (i.e. 0 for
- * success, various non-zero for other errors). See run-command.h.
+ * Append trailers specified in trailer_args to buf in-place.
+ *
+ * Each element of trailer_args should be in the same format as the value
+ * accepted by --trailer=<trailer> (i.e., without the --trailer= prefix).
+ */
+int amend_strbuf_with_trailers(struct strbuf *buf,
+				const struct strvec *trailer_args);
+
+/*
+ * Augment a file by appending trailers specified in trailer_args.
+ *
+ * Each element of trailer_args should be in the same format as the value
+ * accepted by --trailer=<trailer> (i.e., without the --trailer= prefix).
+ *
+ * Returns 0 on success or a non-zero error code on failure.
  */
 int amend_file_with_trailers(const char *path, const struct strvec *trailer_args);
 
+/*
+ * Create a tempfile ""git-interpret-trailers-XXXXXX" in the same
+ * directory as file.
+ */
+struct tempfile *trailer_create_in_place_tempfile(const char *file);
+
+/*
+ * Rewrite the contents of input by processing its trailer block according to
+ * opts and (optionally) appending trailers from new_trailer_head.
+ *
+ * The rewritten message is appended to out (callers should strbuf_reset()
+ * first if needed).
+ */
+void process_trailers(const struct process_trailer_options *opts,
+		      struct list_head *new_trailer_head,
+		      struct strbuf *input, struct strbuf *out);
 #endif /* TRAILER_H */
diff --git a/worktree.c b/worktree.c
index 6552e300536cc6..56732f8f3312bf 100644
--- a/worktree.c
+++ b/worktree.c
@@ -445,7 +445,7 @@ void update_worktree_location(struct worktree *wt, const char *path_,
 	strbuf_realpath(&path, path_, 1);
 	strbuf_addf(&dotgit, "%s/.git", path.buf);
 	if (fspathcmp(wt->path, path.buf)) {
-		write_worktree_linking_files(dotgit, gitdir, use_relative_paths);
+		write_worktree_linking_files(dotgit.buf, gitdir.buf, use_relative_paths);
 
 		free(wt->path);
 		wt->path = strbuf_detach(&path, NULL);
@@ -685,7 +685,7 @@ static void repair_gitfile(struct worktree *wt,
 
 	if (repair) {
 		fn(0, wt->path, repair, cb_data);
-		write_worktree_linking_files(dotgit, gitdir, use_relative_paths);
+		write_worktree_linking_files(dotgit.buf, gitdir.buf, use_relative_paths);
 	}
 
 done:
@@ -743,7 +743,7 @@ void repair_worktree_after_gitdir_move(struct worktree *wt, const char *old_path
 	if (!file_exists(dotgit.buf))
 		goto done;
 
-	write_worktree_linking_files(dotgit, gitdir, is_relative_path);
+	write_worktree_linking_files(dotgit.buf, gitdir.buf, is_relative_path);
 done:
 	strbuf_release(&gitdir);
 	strbuf_release(&dotgit);
@@ -915,7 +915,7 @@ void repair_worktree_at_path(const char *path,
 
 	if (repair) {
 		fn(0, gitdir.buf, repair, cb_data);
-		write_worktree_linking_files(dotgit, gitdir, use_relative_paths);
+		write_worktree_linking_files(dotgit.buf, gitdir.buf, use_relative_paths);
 	}
 done:
 	free(dotgit_contents);
@@ -1089,17 +1089,17 @@ int init_worktree_config(struct repository *r)
 	return res;
 }
 
-void write_worktree_linking_files(struct strbuf dotgit, struct strbuf gitdir,
+void write_worktree_linking_files(const char *dotgit, const char *gitdir,
 				  int use_relative_paths)
 {
 	struct strbuf path = STRBUF_INIT;
 	struct strbuf repo = STRBUF_INIT;
 	struct strbuf tmp = STRBUF_INIT;
 
-	strbuf_addbuf(&path, &dotgit);
+	strbuf_addstr(&path, dotgit);
 	strbuf_strip_suffix(&path, "/.git");
 	strbuf_realpath(&path, path.buf, 1);
-	strbuf_addbuf(&repo, &gitdir);
+	strbuf_addstr(&repo, gitdir);
 	strbuf_strip_suffix(&repo, "/gitdir");
 	strbuf_realpath(&repo, repo.buf, 1);
 
@@ -1112,11 +1112,11 @@ void write_worktree_linking_files(struct strbuf dotgit, struct strbuf gitdir,
 	}
 
 	if (use_relative_paths) {
-		write_file(gitdir.buf, "%s/.git", relative_path(path.buf, repo.buf, &tmp));
-		write_file(dotgit.buf, "gitdir: %s", relative_path(repo.buf, path.buf, &tmp));
+		write_file(gitdir, "%s/.git", relative_path(path.buf, repo.buf, &tmp));
+		write_file(dotgit, "gitdir: %s", relative_path(repo.buf, path.buf, &tmp));
 	} else {
-		write_file(gitdir.buf, "%s/.git", path.buf);
-		write_file(dotgit.buf, "gitdir: %s", repo.buf);
+		write_file(gitdir, "%s/.git", path.buf);
+		write_file(dotgit, "gitdir: %s", repo.buf);
 	}
 
 	strbuf_release(&path);
diff --git a/worktree.h b/worktree.h
index e450d1a3317e23..026ef303e81f5a 100644
--- a/worktree.h
+++ b/worktree.h
@@ -240,7 +240,7 @@ int init_worktree_config(struct repository *r);
  *  dotgit: "/path/to/foo/.git"
  *  gitdir: "/path/to/repo/worktrees/foo/gitdir"
  */
-void write_worktree_linking_files(struct strbuf dotgit, struct strbuf gitdir,
+void write_worktree_linking_files(const char *dotgit, const char *gitdir,
 				  int use_relative_paths);
 
 #endif