Swap byte-order in binary serializer to support big-endian arch (#5813)

* fixed some endian issues

* Use dmlc::ByteSwap() to simplify code

* Fix lint check

* [CI] Add test for s390x

* Download latest CMake on s390x

* Fix a bug in my code

* Save magic number in dmatrix with byteswap on big-endian machine

* Save version in binary with byteswap on big-endian machine

* Load scalar with byteswap in MetaInfo

* Add a debugging message

* Handle arrays correctly when byteswapping

* EOF can also be 255

* Handle magic number in MetaInfo carefully

* Skip Tree.Load test for big-endian, since the test manually builds little-endian binary model

* Handle missing packages in Python tests

* Don't use boto3 in model compatibility tests

* Add s390 Docker file for local testing

* Add model compatibility tests

* Add R compatibility test

* Revert "Add R compatibility test"

This reverts commit c2d2bdcb7dbae133cbb927fcd20f7e83ee2b18a8.

Co-authored-by: Qi Zhang <q.zhang@ibm.com>
Co-authored-by: Hyunsu Cho <chohyu01@cs.washington.edu>

tests/cpp/common/test_json.cc

@@ -453,7 +453,8 @@ TEST(Json, Invalid) {
       Json load{Json::Load(StringView(str.c_str(), str.size()))};
     } catch (dmlc::Error const &e) {
       std::string msg = e.what();
-      ASSERT_NE(msg.find("EOF"), std::string::npos);
+      ASSERT_TRUE(msg.find("EOF") != std::string::npos
+                  || msg.find("255") != std::string::npos);  // EOF is printed as 255 on s390x
       has_thrown = true;
     };
     ASSERT_TRUE(has_thrown);

tests/cpp/tree/test_tree_model.cc

@@ -6,6 +6,7 @@
 #include "xgboost/json_io.h"
 
 namespace xgboost {
+#if DMLC_IO_NO_ENDIAN_SWAP  // skip on big-endian machines
 // Manually construct tree in binary format
 // Do not use structs in case they change
 // We want to preserve backwards compatibility
@@ -85,6 +86,7 @@ TEST(Tree, Load) {
   EXPECT_EQ(tree[1].LeafValue(), 0.1f);
   EXPECT_TRUE(tree[1].IsLeaf());
 }
+#endif  // DMLC_IO_NO_ENDIAN_SWAP
 
 TEST(Tree, AllocateNode) {
   RegTree tree;