Split _dl_writev out from _dl_debug_vdprintf.

sysdeps/unix/sysv/linux/dl-writev.h

@@ -0,0 +1,38 @@
+/* Message-writing for the dynamic linker.  Linux version.
+   Copyright (C) 2013 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/>.  */
+
+#include <sys/uio.h>
+#include <sysdep.h>
+
+/* This is used from only one place: dl-misc.c:_dl_debug_vdprintf.
+   Hence it's in a header with the expectation it will be inlined.
+
+   This is writev, but with a constraint added and others loosened:
+
+   1. Under RTLD_PRIVATE_ERRNO, it must not clobber the private errno
+      when another thread holds the dl_load_lock.
+   2. It is not obliged to detect and report errors at all.
+   3. It's not really obliged to deliver a single atomic write
+      (though it may be preferable).  */
+
+static inline void
+_dl_writev (int fd, const struct iovec *iov, size_t niov)
+{
+  INTERNAL_SYSCALL_DECL (err);
+  INTERNAL_SYSCALL (writev, err, 3, fd, iov, niov);
+}