[SystemZ][z/OS] Add the functions needed for handling EBCDIC I/O

This patch adds the basic functions needed for controlling auto conversion on z/OS.
Auto conversion is enabled on untagged input file to ASCII by making the assumption that all untagged files are EBCDIC encoded. Output files are auto converted to EBCDIC IBM-1047.
This change also enables conversion for stdin/stdout/stderr.

For more information on how fcntl controls codepage https://www.ibm.com/docs/en/zos/2.4.0?topic=descriptions-fcntl-bpx1fct-bpx4fct-control-open-file-descriptors

Reviewed By: anirudhp

Differential Revision: https://reviews.llvm.org/D100483

1 files changed, 7 insertions, 0 deletions

diff --git a/llvm/lib/Support/MemoryBuffer.cpp b/llvm/lib/Support/MemoryBuffer.cpp
index 49524f3..bcf13d8 100644
--- a/llvm/lib/Support/MemoryBuffer.cpp
+++ b/llvm/lib/Support/MemoryBuffer.cpp
@@ -13,6 +13,7 @@
 #include "llvm/Support/MemoryBuffer.h"
 #include "llvm/ADT/SmallString.h"
 #include "llvm/Config/config.h"
+#include "llvm/Support/AutoConvert.h"
 #include "llvm/Support/Errc.h"
 #include "llvm/Support/Errno.h"
 #include "llvm/Support/FileSystem.h"
@@ -467,6 +468,12 @@ getOpenFileImpl(sys::fs::file_t FD, const Twine &Filename, uint64_t FileSize,
       return std::move(Result);
   }
 
+#ifdef __MVS__
+  // Set codepage auto-conversion for z/OS.
+  if (auto EC = llvm::enableAutoConversion(FD))
+    return EC;
+#endif
+
   auto Buf = WritableMemoryBuffer::getNewUninitMemBuffer(MapSize, Filename);
   if (!Buf) {
     // Failed to create a buffer. The only way it can fail is if