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[RFC] time: Create a endian_t.h headerfile

From: Alistair Francis <alistair dot francis at wdc dot com>
To: libc-alpha at sourceware dot org
Cc: joseph at codesourcery dot com, Alistair Francis <alistair dot francis at wdc dot com>
Date: Thu, 19 Sep 2019 15:18:28 -0700
Subject: [RFC] time: Create a endian_t.h headerfile
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Wdcironportexception: Internal

To allow struct __timespec64 and struct timespec to be the same on a
32-bit architecture with a 64-bit time_t we need to add padding to the
struct timespec. This padding requires knowledge of the machines
endianess, which requires us exporting the endianness in
time/bits/types/struct_timespec.h.

To reduce the number of macros that we are exporting let's split out an
endian_t.h header file that can be used.

2019-09-19  Alistair Francis  <alistair.francis@wdc.com>

	* bits/endian.h: Create a endian_t.h headerfile.
	* string/endian.h: Create a endian_t.h headerfile.
	* sysdeps/aarch64/bits/endian.h: Allow including from
	endian_t.h.
	* sysdeps/alpha/bits/endian.h: Likewise.
	* sysdeps/arm/bits/endian.h: Likewise.
	* sysdeps/csky/bits/endian.h: Likewise.
	* sysdeps/hppa/bits/endian.h: Likewise.
	* sysdeps/m68k/bits/endian.h: Likewise.
	* sysdeps/microblaze/bits/endian.h: Likewise.
	* sysdeps/mips/bits/endian.h: Likewise.
	* sysdeps/nios2/bits/endian.h: Likewise.
	* sysdeps/powerpc/bits/endian.h: Likewise.
	* sysdeps/riscv/bits/endian.h: Likewise.
	* sysdeps/s390/bits/endian.h: Likewise.
	* sysdeps/sh/bits/endian.h: Likewise.
	* sysdeps/sparc/bits/endian.h: Likewise.
	* sysdeps/unix/sysv/linux/ia64/bits/endian.h: Likewise.
	* sysdeps/x86/bits/endian.h: Likewise.
	* time/bits/types/endian_t.h: New file.
---
This is based on the feedback from:
 https://sourceware.org/ml/libc-alpha/2019-09/msg00272.html

 bits/endian.h                              |  2 +-
 string/endian.h                            | 16 +---------
 sysdeps/aarch64/bits/endian.h              |  2 +-
 sysdeps/alpha/bits/endian.h                |  2 +-
 sysdeps/arm/bits/endian.h                  |  2 +-
 sysdeps/csky/bits/endian.h                 |  2 +-
 sysdeps/hppa/bits/endian.h                 |  2 +-
 sysdeps/m68k/bits/endian.h                 |  2 +-
 sysdeps/microblaze/bits/endian.h           |  2 +-
 sysdeps/mips/bits/endian.h                 |  2 +-
 sysdeps/nios2/bits/endian.h                |  2 +-
 sysdeps/powerpc/bits/endian.h              |  2 +-
 sysdeps/riscv/bits/endian.h                |  2 +-
 sysdeps/s390/bits/endian.h                 |  2 +-
 sysdeps/sh/bits/endian.h                   |  2 +-
 sysdeps/sparc/bits/endian.h                |  2 +-
 sysdeps/unix/sysv/linux/ia64/bits/endian.h |  2 +-
 sysdeps/x86/bits/endian.h                  |  2 +-
 time/bits/types/endian_t.h                 | 36 ++++++++++++++++++++++
 19 files changed, 54 insertions(+), 32 deletions(-)
 create mode 100644 time/bits/types/endian_t.h

diff --git a/bits/endian.h b/bits/endian.h
index 45afd4ae477..29838739049 100644
--- a/bits/endian.h
+++ b/bits/endian.h
@@ -6,7 +6,7 @@
    So if cross-compiling to a machine with a different byte order,
    the bits/endian.h file for that machine must exist.  */
 
-#ifndef _ENDIAN_H
+#ifndef _ENDIAN_T_H
 # error "Never use <bits/endian.h> directly; include <endian.h> instead."
 #endif
 
diff --git a/string/endian.h b/string/endian.h
index 17e4e893fb5..e23484c1f0f 100644
--- a/string/endian.h
+++ b/string/endian.h
@@ -19,21 +19,7 @@
 #define	_ENDIAN_H	1
 
 #include <features.h>
-
-/* Definitions for byte order, according to significance of bytes,
-   from low addresses to high addresses.  The value is what you get by
-   putting '4' in the most significant byte, '3' in the second most
-   significant byte, '2' in the second least significant byte, and '1'
-   in the least significant byte, and then writing down one digit for
-   each byte, starting with the byte at the lowest address at the left,
-   and proceeding to the byte with the highest address at the right.  */
-
-#define	__LITTLE_ENDIAN	1234
-#define	__BIG_ENDIAN	4321
-#define	__PDP_ENDIAN	3412
-
-/* This file defines `__BYTE_ORDER' for the particular machine.  */
-#include <bits/endian.h>
+#include <time/bits/types/endian_t.h>
 
 /* Some machines may need to use a different endianness for floating point
    values.  */
diff --git a/sysdeps/aarch64/bits/endian.h b/sysdeps/aarch64/bits/endian.h
index 03801d312a7..26ab0f556e4 100644
--- a/sysdeps/aarch64/bits/endian.h
+++ b/sysdeps/aarch64/bits/endian.h
@@ -16,7 +16,7 @@
    License along with the GNU C Library.  If not, see
    <https://www.gnu.org/licenses/>.  */
 
-#ifndef _ENDIAN_H
+#ifndef _ENDIAN_T_H
 # error "Never use <bits/endian.h> directly; include <endian.h> instead."
 #endif
 
diff --git a/sysdeps/alpha/bits/endian.h b/sysdeps/alpha/bits/endian.h
index 8a16e14e24e..df2e6380726 100644
--- a/sysdeps/alpha/bits/endian.h
+++ b/sysdeps/alpha/bits/endian.h
@@ -1,6 +1,6 @@
 /* Alpha is little-endian.  */
 
-#ifndef _ENDIAN_H
+#ifndef _ENDIAN_T_H
 # error "Never use <bits/endian.h> directly; include <endian.h> instead."
 #endif
 
diff --git a/sysdeps/arm/bits/endian.h b/sysdeps/arm/bits/endian.h
index f49f6ab1c9b..f3d17a449a3 100644
--- a/sysdeps/arm/bits/endian.h
+++ b/sysdeps/arm/bits/endian.h
@@ -1,4 +1,4 @@
-#ifndef _ENDIAN_H
+#ifndef _ENDIAN_T_H
 # error "Never use <bits/endian.h> directly; include <endian.h> instead."
 #endif
 
diff --git a/sysdeps/csky/bits/endian.h b/sysdeps/csky/bits/endian.h
index 51df38d8f91..bfd4eaedcd0 100644
--- a/sysdeps/csky/bits/endian.h
+++ b/sysdeps/csky/bits/endian.h
@@ -1,4 +1,4 @@
-#ifndef _ENDIAN_H
+#ifndef _ENDIAN_T_H
 # error "Never use <bits/endian.h> directly; include <endian.h> instead."
 #endif
 
diff --git a/sysdeps/hppa/bits/endian.h b/sysdeps/hppa/bits/endian.h
index 585db0c0faa..c1c6b23aff4 100644
--- a/sysdeps/hppa/bits/endian.h
+++ b/sysdeps/hppa/bits/endian.h
@@ -1,6 +1,6 @@
 /* hppa1.1 big-endian.  */
 
-#ifndef _ENDIAN_H
+#ifndef _ENDIAN_T_H
 # error "Never use <bits/endian.h> directly; include <endian.h> instead."
 #endif
 
diff --git a/sysdeps/m68k/bits/endian.h b/sysdeps/m68k/bits/endian.h
index bf4ecb60a4c..f3edd102a28 100644
--- a/sysdeps/m68k/bits/endian.h
+++ b/sysdeps/m68k/bits/endian.h
@@ -1,6 +1,6 @@
 /* m68k is big-endian.  */
 
-#ifndef _ENDIAN_H
+#ifndef _ENDIAN_T_H
 # error "Never use <bits/endian.h> directly; include <endian.h> instead."
 #endif
 
diff --git a/sysdeps/microblaze/bits/endian.h b/sysdeps/microblaze/bits/endian.h
index 6e961a55474..6e19d2c5dff 100644
--- a/sysdeps/microblaze/bits/endian.h
+++ b/sysdeps/microblaze/bits/endian.h
@@ -16,7 +16,7 @@
    License along with the GNU C Library.  If not, see
    <https://www.gnu.org/licenses/>.  */
 
-#ifndef _ENDIAN_H
+#ifndef _ENDIAN_T_H
 # error "Never use <bits/endian.h> directly; include <endian.h> instead."
 #endif
 
diff --git a/sysdeps/mips/bits/endian.h b/sysdeps/mips/bits/endian.h
index 126059799d7..12b14bc5aae 100644
--- a/sysdeps/mips/bits/endian.h
+++ b/sysdeps/mips/bits/endian.h
@@ -3,7 +3,7 @@
    want to be able to share the installed header files between
    both, so we define __BYTE_ORDER based on GCC's predefines.  */
 
-#ifndef _ENDIAN_H
+#ifndef _ENDIAN_T_H
 # error "Never use <bits/endian.h> directly; include <endian.h> instead."
 #endif
 
diff --git a/sysdeps/nios2/bits/endian.h b/sysdeps/nios2/bits/endian.h
index 164f9e4d785..f83a74d0d8a 100644
--- a/sysdeps/nios2/bits/endian.h
+++ b/sysdeps/nios2/bits/endian.h
@@ -1,6 +1,6 @@
 /* The Nios II architecture has selectable endianness.  */
 
-#ifndef _ENDIAN_H
+#ifndef _ENDIAN_T_H
 # error "Never use <bits/endian.h> directly; include <endian.h> instead."
 #endif
 
diff --git a/sysdeps/powerpc/bits/endian.h b/sysdeps/powerpc/bits/endian.h
index c82f7ad4de6..8463d17fd66 100644
--- a/sysdeps/powerpc/bits/endian.h
+++ b/sysdeps/powerpc/bits/endian.h
@@ -17,7 +17,7 @@
 
 /* PowerPC can be little or big endian.  Hopefully gcc will know...  */
 
-#ifndef _ENDIAN_H
+#ifndef _ENDIAN_T_H
 # error "Never use <bits/endian.h> directly; include <endian.h> instead."
 #endif
 
diff --git a/sysdeps/riscv/bits/endian.h b/sysdeps/riscv/bits/endian.h
index 4aaf559d4f4..c07ea5f748f 100644
--- a/sysdeps/riscv/bits/endian.h
+++ b/sysdeps/riscv/bits/endian.h
@@ -1,4 +1,4 @@
-#ifndef _ENDIAN_H
+#ifndef _ENDIAN_T_H
 # error "Never use <bits/endian.h> directly; include <endian.h> instead."
 #endif
 
diff --git a/sysdeps/s390/bits/endian.h b/sysdeps/s390/bits/endian.h
index ac27f0119a8..a2b93390d5a 100644
--- a/sysdeps/s390/bits/endian.h
+++ b/sysdeps/s390/bits/endian.h
@@ -1,6 +1,6 @@
 /* s390 is big-endian */
 
-#ifndef _ENDIAN_H
+#ifndef _ENDIAN_T_H
 # error "Never use <bits/endian.h> directly; include <endian.h> instead."
 #endif
 
diff --git a/sysdeps/sh/bits/endian.h b/sysdeps/sh/bits/endian.h
index 1fef1ff938f..46f8fd3d3ec 100644
--- a/sysdeps/sh/bits/endian.h
+++ b/sysdeps/sh/bits/endian.h
@@ -1,6 +1,6 @@
 /* SH is bi-endian but with a big-endian FPU.  */
 
-#ifndef _ENDIAN_H
+#ifndef _ENDIAN_T_H
 # error "Never use <bits/endian.h> directly; include <endian.h> instead."
 #endif
 
diff --git a/sysdeps/sparc/bits/endian.h b/sysdeps/sparc/bits/endian.h
index 8acfdf5df6f..60394ea43aa 100644
--- a/sysdeps/sparc/bits/endian.h
+++ b/sysdeps/sparc/bits/endian.h
@@ -1,7 +1,7 @@
 /* Sparc is big-endian, but v9 supports endian conversion on loads/stores
    and GCC supports such a mode.  Be prepared.  */
 
-#ifndef _ENDIAN_H
+#ifndef _ENDIAN_T_H
 # error "Never use <bits/endian.h> directly; include <endian.h> instead."
 #endif
 
diff --git a/sysdeps/unix/sysv/linux/ia64/bits/endian.h b/sysdeps/unix/sysv/linux/ia64/bits/endian.h
index 98a5e239916..8bb227ecd53 100644
--- a/sysdeps/unix/sysv/linux/ia64/bits/endian.h
+++ b/sysdeps/unix/sysv/linux/ia64/bits/endian.h
@@ -1,6 +1,6 @@
 /* Linux/ia64 is little-endian.  */
 
-#ifndef _ENDIAN_H
+#ifndef _ENDIAN_T_H
 # error "Never use <bits/endian.h> directly; include <endian.h> instead."
 #endif
 
diff --git a/sysdeps/x86/bits/endian.h b/sysdeps/x86/bits/endian.h
index 5a56c726f71..c159872ae64 100644
--- a/sysdeps/x86/bits/endian.h
+++ b/sysdeps/x86/bits/endian.h
@@ -1,6 +1,6 @@
 /* i386/x86_64 are little-endian.  */
 
-#ifndef _ENDIAN_H
+#ifndef _ENDIAN_T_H
 # error "Never use <bits/endian.h> directly; include <endian.h> instead."
 #endif
 
diff --git a/time/bits/types/endian_t.h b/time/bits/types/endian_t.h
new file mode 100644
index 00000000000..d68f5ba2f8b
--- /dev/null
+++ b/time/bits/types/endian_t.h
@@ -0,0 +1,36 @@
+/* Copyright (C) 1992-2019 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
+   <https://www.gnu.org/licenses/>.  */
+
+#ifndef	_ENDIAN_T_H
+#define	_ENDIAN_T_H	1
+
+/* Definitions for byte order, according to significance of bytes,
+   from low addresses to high addresses.  The value is what you get by
+   putting '4' in the most significant byte, '3' in the second most
+   significant byte, '2' in the second least significant byte, and '1'
+   in the least significant byte, and then writing down one digit for
+   each byte, starting with the byte at the lowest address at the left,
+   and proceeding to the byte with the highest address at the right.  */
+
+#define	__LITTLE_ENDIAN	1234
+#define	__BIG_ENDIAN	4321
+#define	__PDP_ENDIAN	3412
+
+/* This file defines `__BYTE_ORDER' for the particular machine.  */
+#include <bits/endian.h>
+
+#endif
-- 
2.23.0

Follow-Ups:
- Re: [RFC] time: Create a endian_t.h headerfile
  - From: Joseph Myers

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