s390x Fedora Clang 3.x buildbot:
https://buildbot.python.org/all/#/builders/3/builds/1385

This change may be caused by this buildbot configuration change:
https://github.com/python/buildmaster-config/commit/8fbb7492d4509df074750bc1a8ea69812ff53aae

---
0:05:48 load avg: 7.72 [215/432/1] test_lib2to3 crashed (Exit code -11) -- running: (...)
Fatal Python error: Segmentation fault

Current thread 0x000003ff94176710 (most recent call first):
  File "/home/dje/cpython-buildarea/3.x.edelsohn-fedora-z.clang/build/Lib/lib2to3/pytree.py", line 845 in generate_matches
  File "/home/dje/cpython-buildarea/3.x.edelsohn-fedora-z.clang/build/Lib/lib2to3/pytree.py", line 785 in _recursive_matches
  File "/home/dje/cpython-buildarea/3.x.edelsohn-fedora-z.clang/build/Lib/lib2to3/pytree.py", line 786 in _recursive_matches
  File "/home/dje/cpython-buildarea/3.x.edelsohn-fedora-z.clang/build/Lib/lib2to3/pytree.py", line 786 in _recursive_matches
  (...)
  File "/home/dje/cpython-buildarea/3.x.edelsohn-fedora-z.clang/build/Lib/lib2to3/pytree.py", line 786 in _recursive_matches
  ...

Extension modules: _testcapi (total: 1)
---

and

---
0:06:29 load avg: 7.50 [245/432/2] test_json crashed (Exit code -11) -- running: (...)
Fatal Python error: Segmentation fault

Current thread 0x000003ffbccf6710 (most recent call first):
  File "/home/dje/cpython-buildarea/3.x.edelsohn-fedora-z.clang/build/Lib/json/encoder.py", line 439 in _iterencode
  File "/home/dje/cpython-buildarea/3.x.edelsohn-fedora-z.clang/build/Lib/json/encoder.py", line 325 in _iterencode_list
  (...)
  File "/home/dje/cpython-buildarea/3.x.edelsohn-fedora-z.clang/build/Lib/json/encoder.py", line 439 in _iterencode
  ...

Extension modules: _testcapi (total: 1)
---

test.pythoninfo difference between successful build 1383 and failing build 1385:

* Py_DEBUG: No => Yes
* pymem.allocator: pymalloc => pymalloc_debug
* sysconfig[CFLAGS]: -Wsign-compare -Wunreachable-code -DNDEBUG -g -fwrapv -O3 -Wall
  => sysconfig[CFLAGS]: -Wsign-compare -g -O0 -Wall

These 2 tests seem to check for RecursionError. See my notes:
https://pythondev.readthedocs.io/unstable_tests.html#unlimited-recursion

The issue seems to be affecting also the PPC64LE Fedora Rawhide Clang 3.x and PPC64LE Fedora Stable Clang 3.x

I managed to reproduce the test_json crash on the "Fedora Stable ppc64le" buildbot using clang. Commands:
---
./configure --with-pydebug CC=clang
make -j10
./python -m test -v test_json
---

I wrote GH-30972 to fix it.

New changeset e7a6285f1be18992191599792524d3aa6aedfa55 by Victor Stinner in branch 'main':
bpo-46542: test_json uses support.infinite_recursion() (GH-30972)
https://github.com/python/cpython/commit/e7a6285f1be18992191599792524d3aa6aedfa55

New changeset 20f53136679e260466a765de5befa3b9db396c9e by Miss Islington (bot) in branch '3.10':
bpo-46542: test_json uses support.infinite_recursion() (GH-30972)
https://github.com/python/cpython/commit/20f53136679e260466a765de5befa3b9db396c9e

New changeset 8cd82461f9bb17381bf9d09989daea316c609cd5 by Miss Islington (bot) in branch '3.9':
bpo-46542: test_json uses support.infinite_recursion() (GH-30972)
https://github.com/python/cpython/commit/8cd82461f9bb17381bf9d09989daea316c609cd5

test_lib2to3 crash if Python is built with clang when running test_all_project_files() of lib2to3.tests.test_all_fixers.Test_all. This test crash on processing the file: "Lib/lib2to3/tests/data/infinite_recursion.py".

The GH-30855 change increased the usage of the stack memory when Python is built with clang:
https://github.com/python/cpython/pull/30855#issuecomment-1024884758

* GCC allocates between 544 bytes (-O3) and 608 bytes (-Og) on the stack
* clang allocates between 656 bytes (-O3) and 9200 bytes (Og) on the stack

The regression was introduced by GH-30855: "bpo-46329: Split calls into precall and call instructions" (commit 89fd7c34520aac493a8784a221366ed04452612b).

New changeset ee0ac328d38a86f7907598c94cb88a97635b32f8 by Victor Stinner in branch 'main':
bpo-46542: test_lib2to3 uses support.infinite_recursion() (GH-31035)
https://github.com/python/cpython/commit/ee0ac328d38a86f7907598c94cb88a97635b32f8

New changeset 30463860796790d3be97b76744290e4c364ad765 by Miss Islington (bot) in branch '3.9':
bpo-46542: test_lib2to3 uses support.infinite_recursion() (GH-31035)
https://github.com/python/cpython/commit/30463860796790d3be97b76744290e4c364ad765

New changeset 34794517d1380e206fbbc9735b8aaaf07a5237ce by Miss Islington (bot) in branch '3.10':
bpo-46542: test_lib2to3 uses support.infinite_recursion() (GH-31035)
https://github.com/python/cpython/commit/34794517d1380e206fbbc9735b8aaaf07a5237ce

s390x Fedora Clang 3.x buildbot is back to green, I close the issue.