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>

2 files changed, 57 insertions, 1 deletions

diff --git a/elf/Makefile b/elf/Makefile
index e0a8bf2..ab792d4 100644
--- a/elf/Makefile
+++ b/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
diff --git a/elf/dl-write.c b/elf/dl-write.c
new file mode 100644
index 0000000..7350aff
--- /dev/null
+++ b/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;
+}