t8020-last-modified.sh failure on s390x (Re: [PATCH v4] last-modified: implement faster algorithm)

t8020-last-modified.sh is broken on the s390x platform in v2.52.0. Bisection implicates commit 2a04e8c293766a4976ceceb4c663dd2963e0339e “last-modified: implement faster algorithm” [1].

$ uname -m s390x

$ ./t8020-last-modified.sh ok 1 - setup ok 2 - cannot run last-modified on two trees ok 3 - last-modified non-recursive ok 4 - last-modified recursive ok 5 - last-modified recursive with show-trees ok 6 - last-modified non-recursive with show-trees ok 7 - last-modified subdir ok 8 - last-modified subdir recursive ok 9 - last-modified from non-HEAD commit ok 10 - last-modified from subdir defaults to root ok 11 - last-modified from subdir uses relative pathspecs ok 12 - limit last-modified traversal by count ok 13 - limit last-modified traversal by commit ok 14 - only last-modified files in the current tree ok 15 - subdirectory modified via merge not ok 16 - cross merge boundaries in blaming # # git checkout HEAD^0 && # git rm -rf . && # test_commit m1 && # git checkout HEAD^ && # git rm -rf . && # test_commit m2 && # git merge m1 && # check_last_modified <<-\EOF # m2 m2.t # m1 m1.t # EOF # ok 17 - last-modified merge for resolved conflicts ok 18 - last-modified merge ignores content from branch not ok 19 - last-modified merge undoes changes # # git checkout HEAD^0 && # git rm -rf . && # test_commit b1 file A && # test_commit b2 file B && # test_commit b3 file C && # test_commit b4 file D && # git checkout b2 && # test_commit b5 file2 2 && # git checkout b4 && # git merge --no-commit --no-ff b5 && # git checkout b2 -- file && # git merge --continue && # check_last_modified <<-\EOF # b5 file2 # b2 file # EOF # ok 20 - last-modified complains about unknown arguments # failed 2 among 20 test(s) 1..20

$ ./t8020-last-modified.sh --verbose […]

expecting success of 8020.16 'cross merge boundaries in blaming':
	git checkout HEAD^0 &&
	git rm -rf . &&
	test_commit m1 &&
	git checkout HEAD^ &&
	git rm -rf . &&
	test_commit m2 &&
	git merge m1 &&
	check_last_modified <<-\EOF
	m2 m2.t
	m1 m1.t
	EOF

Note: switching to 'HEAD^0'.

You are in 'detached HEAD' state. You can look around, make experimental changes and commit them, and you can discard any commits you make in this state without impacting any branches by switching back to a branch.

If you want to create a new branch to retain commits you create, you may do so (now or later) by using -c with the switch command. Example:

   git switch -c <new-branch-name>

Or undo this operation with:

   git switch -

Turn off this advice by setting config variable advice.detachedHead to false

HEAD is now at 08525b6 remove a
rm 'file'
[detached HEAD 53e7187] m1
  Author: A U Thor <author@example.com>
  2 files changed, 1 insertion(+), 1 deletion(-)
  delete mode 100644 file
  create mode 100644 m1.t
Previous HEAD position was 53e7187 m1
HEAD is now at 08525b6 remove a
rm 'file'
[detached HEAD 9b81a41] m2
  Author: A U Thor <author@example.com>
  2 files changed, 1 insertion(+), 1 deletion(-)
  delete mode 100644 file
  create mode 100644 m2.t
Merge made by the 'ort' strategy.
  m1.t | 1 +
  1 file changed, 1 insertion(+)
  create mode 100644 m1.t
--- expect	2025-11-19 11:28:57.966106204 +0000
+++ actual	2025-11-19 11:28:58.110112543 +0000