From 87ead54b585e8f4913c05d135fc8790ec72b0c97 Mon Sep 17 00:00:00 2001
From: Jun Aruga <jaruga@redhat.com>
Date: Fri, 29 Sep 2023 10:20:18 +0200
Subject: [PATCH] Document running specs on s390x CPU architecture [ci skip]

Fixes #1083
---
 README.md | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/README.md b/README.md
index 536388e7c..115392835 100644
--- a/README.md
+++ b/README.md
@@ -128,6 +128,12 @@ MSpec can automatically add new top-level constants in this file with:
 
     $ CHECK_LEAKS=save mspec ../mspec/bin/mspec file
 
+### Running Specs on S390x CPU Architecture
+
+Run the specs with `DFLTCC=0` if you see failing specs related to the zlib library on s390x CPU architecture. The failures can happen with the zlib library applying the patch madler/zlib#410 to enable the deflate algorithm producing a different compressed byte stream.
+
+    $ DFLTCC=0 ../mspec/bin/mspec
+
 ### Contributing and Writing Specs
 
 See [CONTRIBUTING.md](https://github.com/ruby/spec/blob/master/CONTRIBUTING.md) for documentation about contributing and writing specs (guards, matchers, etc).