V8/usr/man/man2/syscall.2

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.TH SYSCALL 2 
.SH NAME
syscall \- indirect system call
.SH SYNOPSIS
.nf
.BR "syscall(number, arg, ... )" \  \  (VAX)
.PP
.BR "syscall(number, r0, r1, arg ... )" \  \  (PDP11)
.fi
.SH DESCRIPTION
.I Syscall
performs the system call whose assembly language
interface has the specified
.I number
and arguments.
.PP
On a PDP11 the first two arguments correspond to
registers r0 and r1,
regardless of whether the entry point really
uses them.
.PP
The r0 value of the system call is returned.
.SH DIAGNOSTICS
When the C-bit is set,
.I syscall
returns \-1 and sets the
external variable 
.I errno
(see
.IR intro (2)).
.SH BUGS
There is no way to simulate system calls
such as
.IR pipe (2),
which return values in register r1.