elf: Implement _dl_write

The generic version is parallel to _dl_writev.  It cannot use
_dl_writev directly because the errno value needs to be obtained
under a lock.

Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>

elf/Makefile

@@ -34,7 +34,7 @@ dl-routines	= $(addprefix dl-,load lookup object reloc deps \
 				  version profile tls origin scope \
 				  execstack open close trampoline \
 				  exception sort-maps lookup-direct \
-				  call-libc-early-init)
+				  call-libc-early-init write)
 ifeq (yes,$(use-ldconfig))
 dl-routines += dl-cache
 endif

elf/dl-write.c

@@ -0,0 +1,56 @@
+/* Implementation of the _dl_write function.  Generic version.
+   Copyright (C) 2020 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/>.  */
+
+#include <errno.h>
+#include <ldsodefs.h>
+#include <libc-lock.h>
+#include <sys/uio.h>
+
+ssize_t
+_dl_write (int fd, const void *buffer, size_t length)
+{
+  struct iovec iov = { .iov_base = (void *) buffer, .iov_len = length };
+  ssize_t ret;
+
+#if RTLD_PRIVATE_ERRNO
+  /* We have to take this lock just to be sure we don't clobber the private
+     errno when it's being used by another thread that cares about it.
+     Yet we must be sure not to try calling the lock functions before
+     the thread library is fully initialized.  */
+  if (__glibc_unlikely (_dl_starting_up))
+    {
+      ret = __writev (fd, &iov, 1);
+      if (ret < 0)
+        ret = -errno;
+    }
+  else
+    {
+      __rtld_lock_lock_recursive (GL(dl_load_lock));
+      __writev (fd, &iov, 1);
+      if (ret < 0)
+        ret = -errno;
+      __rtld_lock_unlock_recursive (GL(dl_load_lock));
+    }
+#else
+  ret = __writev (fd, &iov, 1);
+  if (ret < 0)
+    ret = -errno;
+#endif
+
+  return ret;
+}

sysdeps/generic/ldsodefs.h

@@ -757,6 +757,12 @@ _dl_dprintf (int fd, const char *fmt, ...)
 }
 #endif
 
+/* Write LENGTH bytes at BUFFER to FD, like write.  Returns the number
+   of bytes written on success, or a negative error constant on
+   failure.  */
+ssize_t _dl_write (int fd, const void *buffer, size_t length)
+  attribute_hidden;
+
 /* Write a message on the specified descriptor standard output.  The
    parameters are interpreted as for a `printf' call.  */
 void _dl_printf (const char *fmt, ...)

sysdeps/unix/sysv/linux/dl-write.c

@@ -0,0 +1,30 @@
+/* Implementation of the _dl_write function.  Linux version.
+   Copyright (C) 2020 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/>.  */
+
+#include <sysdep.h>
+#include <unistd.h>
+#include <ldsodefs.h>
+
+ssize_t
+_dl_write (int fd, const void *buffer, size_t length)
+{
+  long int r = INTERNAL_SYSCALL_CALL (write, fd, buffer, length);
+  if (INTERNAL_SYSCALL_ERROR_P (r))
+    r = - INTERNAL_SYSCALL_ERRNO (r);
+  return r;
+}