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[PATCH] Y2038: provide kernel support indication


* New function __y2038_get_kernel_support() returns:
  * 0 if the underlying kernel does not support Y2038 at all
  * > 0 if the underlying kernel has some support for Y2038
  * < 0 if the underlying kernel support for Y2038 is broken
* New function __y2038_set_kernel_support() allows indicating
  a kernel's Y2038 support (or support failure)
* Default implementation (covering non-Linux kernels) always
  returns 0 (no support).
---

This patch is part of the Y2038 patch series, which is available at
<https://sourceware.org/git/?p=glibc.git;a=shortlog;h=refs/heads/aaribaud/y2038>.
Warning: this branch may be rebased on current master and/or updated based on
feedback from the list at any time.

 misc/Makefile                           |  2 +-
 misc/Versions                           |  4 +++
 misc/y2038-support.c                    | 32 ++++++++++++++++++++
 misc/y2038-support.h                    | 36 ++++++++++++++++++++++
 sysdeps/unix/sysv/linux/y2038-support.c | 40 +++++++++++++++++++++++++
 sysdeps/unix/sysv/linux/y2038-support.h | 30 +++++++++++++++++++
 6 files changed, 143 insertions(+), 1 deletion(-)
 create mode 100644 misc/y2038-support.c
 create mode 100644 misc/y2038-support.h
 create mode 100644 sysdeps/unix/sysv/linux/y2038-support.c
 create mode 100644 sysdeps/unix/sysv/linux/y2038-support.h

diff --git a/misc/Makefile b/misc/Makefile
index 9a87e81ae5..dd64bf256f 100644
--- a/misc/Makefile
+++ b/misc/Makefile
@@ -71,7 +71,7 @@ routines := brk sbrk sstk ioctl \
 	    fgetxattr flistxattr fremovexattr fsetxattr getxattr \
 	    listxattr lgetxattr llistxattr lremovexattr lsetxattr \
 	    removexattr setxattr getauxval ifunc-impl-list makedev \
-	    allocate_once
+	    allocate_once y2038-support
 
 generated += tst-error1.mtrace tst-error1-mem.out \
   tst-allocate_once.mtrace tst-allocate_once-mem.out
diff --git a/misc/Versions b/misc/Versions
index 900e4ffb79..e242bf7218 100644
--- a/misc/Versions
+++ b/misc/Versions
@@ -158,6 +158,10 @@ libc {
   GLIBC_2.26 {
     preadv2; preadv64v2; pwritev2; pwritev64v2;
   }
+  GLIBC_2.29 {
+    __y2038_get_kernel_support;
+    __y2038_set_kernel_support;
+  }
   GLIBC_PRIVATE {
     __madvise;
     __mktemp;
diff --git a/misc/y2038-support.c b/misc/y2038-support.c
new file mode 100644
index 0000000000..e401cb1112
--- /dev/null
+++ b/misc/y2038-support.c
@@ -0,0 +1,32 @@
+/* y2038 general kernel support indication.
+   Copyright (C) 2018 Free Software Foundation, Inc.
+
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <http://www.gnu.org/licenses/>.  */
+
+/* By default glibc assumes the underlying kernel does not support Y2038 */ 
+int __default_y2038_get_kernel_support (void)
+{
+  return 0;
+}
+weak_alias (__default_y2038_get_kernel_support, __y2038_get_kernel_support)
+
+/* By default glibc just ignores Y2038 support indication setting */ 
+int __default_y2038_set_kernel_support (int new with __attribute__ ((unused)))
+{
+  return 0;
+}
+weak_alias (__default_y2038_set_kernel_support, __y2038_set_kernel_support)
diff --git a/misc/y2038-support.h b/misc/y2038-support.h
new file mode 100644
index 0000000000..ec7891b63b
--- /dev/null
+++ b/misc/y2038-support.h
@@ -0,0 +1,36 @@
+/* y2038 general kernel support indication.
+   Copyright (C) 2018 Free Software Foundation, Inc.
+
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <http://www.gnu.org/licenses/>.  */
+
+/* Get Y2038 kernel support.
+ * 0 means no suppport
+ * > 0 means (some) support
+ * < 0 means support is broken
+ */
+extern int __y2038_get_kernel_support (void);
+
+/* Set Y2038 support.
+ * 0 means no suppport
+ * > 0 means (some) support
+ * < 0 means support is broken
+ * Architectures should call this with new > 0 as soon as they know that
+ * their underlying kernel has Y2038 support.
+ * Implementations should call this with new < 0 as soon as they detect
+ * that a Y2038 kernel support failure occurred.
+ * As a courtesy, the previous support indication is returned. */
+extern int __y2038_set_kernel_support (int new);
diff --git a/sysdeps/unix/sysv/linux/y2038-support.c b/sysdeps/unix/sysv/linux/y2038-support.c
new file mode 100644
index 0000000000..f325efc7d8
--- /dev/null
+++ b/sysdeps/unix/sysv/linux/y2038-support.c
@@ -0,0 +1,40 @@
+/* y2038 Linux kernel support indication.
+   Copyright (C) 2018 Free Software Foundation, Inc.
+
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <http://www.gnu.org/licenses/>.  */
+
+/* By default the underlying Linux kernel is assumed not to support Y2038.
+ * Any Linux architecture may claim Y2038 kernel support by setting
+ * __y2038_linux_support.
+ */
+int __y2038_linux_support = 0;
+
+/* For Linux, Y2038 kernel support is determined by __y2038_linux_support  */
+
+int __linux_y2038_get_kernel_support (void)
+{
+  return __y2038_linux_support;
+}
+strong_alias (__linux_y2038_get_kernel_support, __y2038_get_kernel_support)
+
+int __linux_y2038_set_kernel_support (int new)
+{
+  int previous = __y2038_linux_support;
+  __y2038_linux_support = new;
+  return previous;
+}
+strong_alias (__linux_y2038_set_kernel_support, __y2038_set_kernel_support)
diff --git a/sysdeps/unix/sysv/linux/y2038-support.h b/sysdeps/unix/sysv/linux/y2038-support.h
new file mode 100644
index 0000000000..7dcbe0b313
--- /dev/null
+++ b/sysdeps/unix/sysv/linux/y2038-support.h
@@ -0,0 +1,30 @@
+/* y2038 Linux kernel support indication.
+   Copyright (C) 2018 Free Software Foundation, Inc.
+
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <http://www.gnu.org/licenses/>.  */
+
+/* Indicates Y2038 support.
+ * 0 means no suppport
+ * > 0 means (some) support
+ * < 0 means support is broken
+ * Can be read directly from within libc linux-related files.
+ * Can be written non-zero to indicate support or lack thereof.
+ */
+extern int __y2038_linux_support;
+
+/* As a fallback, provide generic Y2038 support indication */
+#include <misc/y2038-support.h>
-- 
2.17.1


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