Re: [PATCH 03/28] elf: Implement _dl_write

[Adhemerval Zanella <adhemerval.zanella@linaro.org>]

On 01/10/2020 13:31, Florian Weimer via Libc-alpha wrote:
> 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.

I think we can in fact replace the _dl_writev usage by _dl_write
with a bonus of a possible code size reduction (since it will be
replace by a function call).

LGTM, thanks.

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

> ---
>  elf/Makefile                       |  2 +-
>  elf/dl-write.c                     | 56 ++++++++++++++++++++++++++++++
>  sysdeps/generic/ldsodefs.h         |  6 ++++
>  sysdeps/unix/sysv/linux/dl-write.c | 30 ++++++++++++++++
>  4 files changed, 93 insertions(+), 1 deletion(-)
>  create mode 100644 elf/dl-write.c
>  create mode 100644 sysdeps/unix/sysv/linux/dl-write.c
> 
> diff --git a/elf/Makefile b/elf/Makefile
> index e0a8bf2998..ab792d45c2 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

Ok.

> diff --git a/elf/dl-write.c b/elf/dl-write.c
> new file mode 100644
> index 0000000000..7350aff003
> --- /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;
> +}

Ok.

> diff --git a/sysdeps/generic/ldsodefs.h b/sysdeps/generic/ldsodefs.h
> index ba114ab4b1..7cb1fccc80 100644
> --- a/sysdeps/generic/ldsodefs.h
> +++ b/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, ...)

Ok.

> diff --git a/sysdeps/unix/sysv/linux/dl-write.c b/sysdeps/unix/sysv/linux/dl-write.c
> new file mode 100644
> index 0000000000..1c6298fb41
> --- /dev/null
> +++ b/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;
> +}
> 

Ok.