105 lines
1.8 KiB
Text
105 lines
1.8 KiB
Text
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.TH realemu 8
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.SH NAME
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realemu \- software emulation of /dev/realmode
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.SH SYNOPSIS
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.B aux/realemu
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[
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.B -Dpt
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] [
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.B -s
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.I srvname
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] [
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.B -m
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.I mountpoint
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]
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.SH DESCRIPTION
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.PP
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Originally, kernel provided
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.B /dev/realmode
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files with the
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.IR arch (3)
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device to access and call the
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.SM BIOS.
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.PP
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Interrupts had to be disabled and the processor was switched in the
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legacy 16-bit
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.SM realmode
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with memory protection disabled to execute
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.SM BIOS
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code.
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.PP
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This is problematic in case the
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.SM BIOS
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reprograms hardware currently
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used by the operating system or when it reenables interrupts or just
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crashes. This will freeze or reboot the machine with no way to
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recover or diagnose the problem.
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.PP
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To avoid this,
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.I realemu
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is used to emulate the execution of the
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.SM BIOS
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routines by interpreting the machine instructions and intercepting
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dangerous actions that would compromise the systems stability.
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.PP
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Running
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.I realemu
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with no arguments, it mounts itself before
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.B /dev
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and
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replaces the original
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.B /dev/realmode
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file in the current namespace.
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.PP
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Then programs like
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.IR vga (8)
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can use it to make ther
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.SM BIOS
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calls.
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.PP
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The
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.B D
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flag will enable debug messages for 9P. The
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.B p
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and
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.B t
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flags
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control tracing of i/o port access and cpu instructions to
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stderr (fd 2).
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.PP
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When a
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.I srvname
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is given with the
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.B s
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argument, the default
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.I mountpoint
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is ignored and a
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.SM 9P
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channel is created in
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.B /srv
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that can be used to mount
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the filesystem from another namespace. If a
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.I mountpoint
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is given before
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the
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.I srvname
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argument then it is ignored, otherwise it will be used.
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.SH EXAMPLES
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The
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.I realemu
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process is only needed when accessing
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.B /dev/realmode.
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To invoke a subshell so that
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.I realemu
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exits normally after
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.B aux/vga
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completes:
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.IP
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.EX
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% @{rfork n; aux/realemu; aux/vga -m vesa -l $vgasize}
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.SH SOURCE
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.B /sys/src/cmd/aux/realemu
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.SH "SEE ALSO"
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.IR vga (8),
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.IR arch (3)
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