Index: llvm/utils/lit/lit/main.py
===================================================================
--- llvm/utils/lit/lit/main.py
+++ llvm/utils/lit/lit/main.py
@@ -245,7 +245,9 @@
     tmp_dir = None
     if 'LIT_PRESERVES_TMP' not in os.environ:
         import tempfile
-        tmp_dir = tempfile.mkdtemp(prefix='lit_tmp_')
+        # z/OS linker limitation: When TMPDIR is exported and contains '_', it
+        # will cause lit test cases fail at linker step, use '-' to replace '_'.
+        tmp_dir = tempfile.mkdtemp(prefix='lit-tmp-')
         tmp_dir_envs = {k: tmp_dir for k in ['TMP', 'TMPDIR', 'TEMP', 'TEMPDIR']}
         os.environ.update(tmp_dir_envs)
         for cfg in {t.config for t in run.tests}: