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147 lines
4.2 KiB
Groff
147 lines
4.2 KiB
Groff
.\" Copyright (c) 2012 Konstantin Belousov <kib@FreeBSD.org>
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
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.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
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.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
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.\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
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.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
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.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
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.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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.\"
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.\" $FreeBSD$
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.\"
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.Dd August 14, 2012
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.Dt AOUT 4
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.Os
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.Sh NAME
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.Nm aout
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.Nd kernel support for executing binary files in legacy a.out format
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.Sh SYNOPSIS
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.Bd -literal -offset indent
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kldload a.out
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.Ed
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.Sh DESCRIPTION
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The
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.Xr a.out 5
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executable format was used before the release of
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.Fx 3.0 .
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Since i386 was the only supported architecture at that time,
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.Xr a.out 5
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executables can only be activated on platforms that support
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execution of i386 code, such as i386 and amd64.
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.Pp
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To add kernel support for old syscalls and old syscall invocation methods,
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place the following options in the kernel configuration file:
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.Bd -ragged -offset indent
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.Cd "options COMPAT_43"
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.br
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.Cd "options COMPAT_FREEBSD32"
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.Ed
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.Pp
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The
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.Va COMPAT_FREEBSD32
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option is only required on 64-bit CPU architectures.
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.Pp
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The
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.Va aout.ko
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module needs to be loaded with the
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.Xr kldload 8
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utility in order to support the
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.Xr a.out 5
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image activator:
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.Bd -ragged -offset indent
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.Ic kldload aout
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.Ed
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.Pp
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Alternatively, to load the module at boot time, place the following line in
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.Xr loader.conf 5 :
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.Bd -literal -offset indent
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aout_load="YES"
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.Ed
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.Pp
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The
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.Xr a.out 5
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format was mainstream quite a long time ago.
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Reasonable default settings and security requirements of
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modern operating systems today contradict the default environment of that time
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and require adjustments of the system to mimic natural environment for
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old binaries.
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.Pp
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The following
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.Xr sysctl 8
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tunables are useful for this:
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.Bl -tag -offset indent -width "XXXXXXXXXXXXXXXXXXXXXXXXX"
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.It Xo Va security.bsd.map_at_zero
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.Xc
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Set to 1 to allow mapping of process pages at address 0.
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Some very old
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.Va ZMAGIC
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executable images require text mapping at address 0.
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.It Xo Va kern.pid_max
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.Xc
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Old versions of
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.Fx
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used signed 16-bit type for
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.Vt pid_t .
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Current kernels use 32-bit type for
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.Vt pid_t ,
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and allow process id's up to 99999.
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Such values cannot be represented by old
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.Vt pid_t ,
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mostly causing issues for processes using
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.Xr wait 2
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syscalls, for example shells.
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Set the sysctl to 30000 to work around the problem.
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.It Xo Va kern.elf32.read_exec
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.Xc
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Set to 1 to force any accessible memory mapping performed by 32-bit
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process to allow execution, see
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.Xr mmap 2 .
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Old i386 CPUs did not have a bit in PTE which disallowed execution
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from the page, so many old programs did not specify
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.Va PROT_EXEC
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even for mapping of executable code.
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The sysctl forces
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.Va PROT_EXEC
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if mapping has any access allowed at all.
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The setting is only needed if the host architecture allows
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non-executable mappings.
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.El
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.Sh SEE ALSO
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.Xr execve 2 ,
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.Xr a.out 5 ,
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.Xr elf 5 ,
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.Xr sysctl 8
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.Sh HISTORY
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The
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.Xr a.out 5
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executable format was used on ancient
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.At
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and served as the main executable format for
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.Fx
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from the beginning up to
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.Fx 2.2.9 .
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In
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.Fx 3.0
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it was superseded by
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.Xr elf 5 .
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.Sh AUTHORS
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The
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.Nm
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manual page was written by
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.An Konstantin Belousov Aq Mt kib@FreeBSD.org .
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.Sh BUGS
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On 64bit architectures, not all wrappers for older syscalls are implemented.
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