Re: [PATCH 3/6] linux: Implement mremap in C

[Stafford Horne via Libc-alpha <libc-alpha@sourceware.org>]

On Mon, Nov 22, 2021 at 03:54:34PM -0300, Adhemerval Zanella wrote:
> Variadic function calls in syscalls.list does not work for all ABIs
> (for instance where the argument are passed on the stack instead of
> registers) and might have underlying issues depending of the variadic
> type (for instance if a 64-bit argument is used).
> 
> Checked on x86_64-linux-gnu.
> ---
>  sysdeps/unix/sysv/linux/Makefile      |  1 +
>  sysdeps/unix/sysv/linux/mremap.c      | 41 +++++++++++++++++++++++++++
>  sysdeps/unix/sysv/linux/syscalls.list |  1 -
>  3 files changed, 42 insertions(+), 1 deletion(-)
>  create mode 100644 sysdeps/unix/sysv/linux/mremap.c
> 
> diff --git a/sysdeps/unix/sysv/linux/Makefile b/sysdeps/unix/sysv/linux/Makefile
> index aa10754b98..1dd6ec9ef9 100644
> --- a/sysdeps/unix/sysv/linux/Makefile
> +++ b/sysdeps/unix/sysv/linux/Makefile
> @@ -68,6 +68,7 @@ sysdep_routines += adjtimex clone umount umount2 readahead sysctl \
>  		   closefrom_fallback \
>  		   clone3 clone-internal \
>  		   fanotify_mark \
> +		   mremap \
>  
>  CFLAGS-gethostid.c = -fexceptions
>  CFLAGS-tee.c = -fexceptions -fasynchronous-unwind-tables
> diff --git a/sysdeps/unix/sysv/linux/mremap.c b/sysdeps/unix/sysv/linux/mremap.c
> new file mode 100644
> index 0000000000..83b4e95338
> --- /dev/null
> +++ b/sysdeps/unix/sysv/linux/mremap.c
> @@ -0,0 +1,41 @@
> +/* Remap a virtual memory address.  Linux specific syscall.
> +   Copyright (C) 2020 Free Software Foundation, Inc.
> +   This file is part of the GNU C Library.

2021

> +
> +   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 <sys/mman.h>
> +#include <sysdep.h>
> +#include <stdarg.h>
> +#include <stddef.h>
> +
> +void *
> +__mremap (void *addr, size_t old_len, size_t new_len, int flags, ...)
> +{
> +  va_list va;
> +  void *new_addr = NULL;
> +
> +  if (flags & MREMAP_FIXED)
> +    {
> +      va_start (va, flags);
> +      new_addr = va_arg (va, void *);
> +      va_end (va);
> +    }
> +
> +  return (void *) INLINE_SYSCALL_CALL (mremap, addr, old_len, new_len, flags,
> +				       new_addr);
> +}
> +libc_hidden_def (__mremap)
> +weak_alias (__mremap, mremap)
> diff --git a/sysdeps/unix/sysv/linux/syscalls.list b/sysdeps/unix/sysv/linux/syscalls.list
> index 29899eb264..2acd7551d3 100644
> --- a/sysdeps/unix/sysv/linux/syscalls.list
> +++ b/sysdeps/unix/sysv/linux/syscalls.list
> @@ -35,7 +35,6 @@ mincore		-	mincore		i:aUV	mincore
>  mlock		-	mlock		i:bU	mlock
>  mlockall	-	mlockall	i:i	mlockall
>  mount		EXTRA	mount		i:sssUp	__mount	mount
> -mremap		EXTRA	mremap		b:aUUip	__mremap	mremap
>  munlock		-	munlock		i:aU	munlock
>  munlockall	-	munlockall	i:	munlockall
>  nfsservctl	EXTRA	nfsservctl	i:ipp	__compat_nfsservctl	nfsservctl@GLIBC_2.0:GLIBC_2.28
> -- 
> 2.32.0
>

This looks OK to me.

Note, I guess this syscall would be broken in or1k at the moment as it passes
variadic args on the stack.  However,  I didn't see any test failures due to
this.

-Stafford