[PATCH v3 1/7] Add --enable-newlib-reent-binary-compat

Add the --enable-newlib-reent-binary-compat configure option.  This option is
disabled by default.  If enabled, then unused members in struct _reent are
preserved to maintain the structure layout.
---
 newlib/README                    |  6 ++++++
 newlib/configure                 | 21 +++++++++++++++++++++
 newlib/configure.ac              | 15 +++++++++++++++
 newlib/libc/include/sys/config.h |  6 ++++++
 newlib/newlib.hin                |  3 +++
 5 files changed, 51 insertions(+)

diff --git a/newlib/README b/newlib/README
index 97890b9d2..c99ab47c6 100644
--- a/newlib/README
+++ b/newlib/README
@@ -362,6 +362,12 @@ One feature can be enabled by specifying `--enable-FEATURE=yes' or
      less conversion accuracy.
      Enabled by default.
 
+`--enable-newlib-reent-binary-compat'
+     Enable backward binary compatibility for struct _reent.  If enabled, then
+     unused members in struct _reent are preserved to maintain the structure
+     layout.
+     Disabled by default.
+
 `--enable-multilib'
      Build many library versions.
      Enabled by default.
diff --git a/newlib/configure b/newlib/configure
index c83511da6..4ff02360b 100755
--- a/newlib/configure
+++ b/newlib/configure
@@ -972,6 +972,7 @@ enable_newlib_iconv_external_ccs
 enable_newlib_atexit_dynamic_alloc
 enable_newlib_global_atexit
 enable_newlib_reent_small
+enable_newlib_reent_binary_compat
 enable_newlib_global_stdio_streams
 enable_newlib_fvwrite_in_streamio
 enable_newlib_fseek_optimization
@@ -1639,6 +1640,7 @@ Optional Features:
   --disable-newlib-atexit-dynamic-alloc    disable dynamic allocation of atexit entries
   --enable-newlib-global-atexit	enable atexit data structure as global
   --enable-newlib-reent-small   enable small reentrant struct support
+  --enable-newlib-reent-binary-compat   enable backward binary compatibility for struct _reent
   --enable-newlib-global-stdio-streams   enable global stdio streams
   --disable-newlib-fvwrite-in-streamio    disable iov in streamio
   --disable-newlib-fseek-optimization    disable fseek optimization
@@ -2390,6 +2392,19 @@ else
   newlib_reent_small=
 fi
 
+# Check whether --enable-newlib-reent-binary-compat was given.
+if test "${enable_newlib_reent_binary_compat+set}" = set; then :
+  enableval=$enable_newlib_reent_binary_compat; if test "${newlib_enable_reent_binary_compat+set}" != set; then
+  case "${enableval}" in
+    yes) newlib_enable_reent_binary_compat=yes ;;
+    no)  newlib_enable_reent_binary_compat=no  ;;
+    *)   as_fn_error $? "bad value ${enableval} for newlib-enable-reent-binary-compat option" "$LINENO" 5 ;;
+  esac
+ fi
+else
+  newlib_enable_reent_binary_compat=no
+fi
+
 # Check whether --enable-newlib-global-stdio-streams was given.
 if test "${enable_newlib_global_stdio_streams+set}" = set; then :
   enableval=$enable_newlib_global_stdio_streams; case "${enableval}" in
@@ -6418,6 +6433,12 @@ $as_echo "#define _WANT_REENT_SMALL 1" >>confdefs.h
 
 fi
 
+if test "${newlib_enable_reent_binary_compat}" = "yes"; then
+
+$as_echo "#define _WANT_REENT_BACKWARD_BINARY_COMPAT 1" >>confdefs.h
+
+fi
+
 if test "${newlib_global_stdio_streams}" = "yes"; then
 
 $as_echo "#define _WANT_REENT_GLOBAL_STDIO_STREAMS 1" >>confdefs.h
diff --git a/newlib/configure.ac b/newlib/configure.ac
index 195d336f2..7c7297564 100644
--- a/newlib/configure.ac
+++ b/newlib/configure.ac
@@ -162,6 +162,17 @@ AC_ARG_ENABLE(newlib-reent-small,
   *)   AC_MSG_ERROR(bad value ${enableval} for newlib-reent-small option) ;;
  esac], [newlib_reent_small=])dnl
 
+dnl Support --enable-newlib-reent-binary-compat
+AC_ARG_ENABLE(newlib-reent-binary-compat,
+[  --enable-newlib-reent-binary-compat   enable backward binary compatibility for struct _reent],
+[if test "${newlib_enable_reent_binary_compat+set}" != set; then
+  case "${enableval}" in
+    yes) newlib_enable_reent_binary_compat=yes ;;
+    no)  newlib_enable_reent_binary_compat=no  ;;
+    *)   AC_MSG_ERROR(bad value ${enableval} for newlib-enable-reent-binary-compat option) ;;
+  esac
+ fi], [newlib_enable_reent_binary_compat=no])dnl
+
 dnl Support --enable-newlib-global-stdio-streams
 AC_ARG_ENABLE(newlib-global-stdio-streams,
 [  --enable-newlib-global-stdio-streams   enable global stdio streams],
@@ -420,6 +431,10 @@ if test "${newlib_reent_small}" = "yes"; then
   AC_DEFINE(_WANT_REENT_SMALL, 1, [Optional reentrant struct support.  Used mostly on platforms with very restricted storage.])
 fi
 
+if test "${newlib_enable_reent_binary_compat}" = "yes"; then
+  AC_DEFINE(_WANT_REENT_BACKWARD_BINARY_COMPAT, 1, [Define to enable backward binary compatibility for struct _reent.])
+fi
+
 if test "${newlib_global_stdio_streams}" = "yes"; then
   AC_DEFINE(_WANT_REENT_GLOBAL_STDIO_STREAMS, 1,
 	    [Define to move the stdio stream FILE objects out of struct _reent and make them global.
diff --git a/newlib/libc/include/sys/config.h b/newlib/libc/include/sys/config.h
index 61a6f95d8..b4d755957 100644
--- a/newlib/libc/include/sys/config.h
+++ b/newlib/libc/include/sys/config.h
@@ -299,6 +299,12 @@
 #endif
 #endif
 
+#ifdef _WANT_REENT_BACKWARD_BINARY_COMPAT
+#ifndef _REENT_BACKWARD_BINARY_COMPAT
+#define _REENT_BACKWARD_BINARY_COMPAT
+#endif
+#endif
+
 /* If _MB_EXTENDED_CHARSETS_ALL is set, we want all of the extended
    charsets.  The extended charsets add a few functions and a couple
    of tables of a few K each. */
diff --git a/newlib/newlib.hin b/newlib/newlib.hin
index b52bc7460..4a9614970 100644
--- a/newlib/newlib.hin
+++ b/newlib/newlib.hin
@@ -402,6 +402,9 @@
 /* Positional argument support in printf functions enabled. */
 #undef _WANT_IO_POS_ARGS
 
+/* Define to enable backward binary compatibility for struct _reent. */
+#undef _WANT_REENT_BACKWARD_BINARY_COMPAT
+
 /* Define to move the stdio stream FILE objects out of struct _reent and make
    them global. The stdio stream pointers of struct _reent are initialized to
    point to the global stdio FILE stream objects. */
-- 
2.35.3