.\"	$OpenBSD: msyscall.2,v 1.2 2019/11/27 20:53:05 schwarze Exp $
.\"
.\" Copyright (c) 2019 Theo de Raadt <deraadt@openbsd.org>
.\"
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.\" copyright notice and this permission notice appear in all copies.
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.Dd $Mdocdate: November 27 2019 $
.Dt MSYSCALL 2
.Os
.Sh NAME
.Nm msyscall
.Nd permit syscalls from a region of pages
.Sh SYNOPSIS
.In sys/mman.h
.Ft int
.Fn msyscall "void *addr" "size_t len"
.Sh DESCRIPTION
The
.Fn msyscall
system call permits system call entry from the pages that contain
the address range
.Fa addr
through
.Fa addr
\&+
.Fa len
\- 1
(inclusive).
If
.Fa len
is 0, no action is taken on the page that contains
.Fa addr .
.Pp
.Nm
is currently intended for use by
.Xr ld.so 1
only, and may be called only once to indicate the location of
the loaded
.Pa libc.so
library.
.Sh RETURN VALUES
.Rv -std
.Sh ERRORS
.Fn msyscall
will fail if:
.Bl -tag -width Er
.It Bq Er EINVAL
The specified address range would wrap around.
.It Bq Er EPERM
Attempt to call
.Fn msyscall
after
.Xr ld.so 1
has called it.
.El
.Sh SEE ALSO
.Xr mmap 2
.Sh HISTORY
The
.Fn msyscall
function first appeared in
.Ox 6.7 .