102 lines
3.4 KiB
Groff
102 lines
3.4 KiB
Groff
.\" $Header$
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.TH LIBMON 7ACK
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.ad
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.SH NAME
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libmon \- library of system call routines with EM calling sequence
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.SH DESCRIPTION
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The modules in this library contain the UNIX system calls with EM calling sequence.
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This library is written in EM assembly language and can be used
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for interpreted programs, and \fIa.out\fP programs.
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If these routines are used in Pascal programs, then the calling sequence
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requires some attention.
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Some hints may be useful:
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.IP -
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The c-option {$c+} allows you to declare zero-terminated string
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constants in Pascal like "/etc/passwd".
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Moreover, the identifier \fIstring\fP is then defined as type identifier for
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a pointer to these zero-terminated strings.
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.IP -
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The d-option {$d+} allows you to use double precision integers (longs).
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The lseek system call, for instance, needs a long argument and returns a long result.
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.IP -
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If the system call requires a pointer as argument use a \fIvar\fP parameter.
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For instance declare times as:
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.br
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procedure times(var t:timesbuf); extern;
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.br
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Note that a \fIstring\fP is already a pointer.
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.IP -
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When defining types, use packed records if two bytes must be allocated
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in a single word, as in
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.br
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device = packed record
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.br
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minor,major:0..255;
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.br
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end;
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.IP -
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If a collection of bits is needed, then define an enumerated type and
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a set of this enumerated type. The create mode of a file, for example,
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can be declared as:
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.br
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modebits = (XHIM,WHIM,RHIM,
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.br
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XYOU,WYOU,RYOU,
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.br
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XME, WME, RME,
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.br
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TEXT,SGID,SUID,... );
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.br
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creatmode = set of XHIM..SUID;
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.IP -
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There are special system call routines \fIuread\fP and \fIuwrite\fP
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in libpc(7),
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because the names \fIread\fP and \fIwrite\fP
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are blocked by similar functions in Pascal.
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.PP
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The system call \fIsignal\fP exists, but uses \fIsigtrp\fP.
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This EM system call has the
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following calling sequence:
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.br
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function sigtrp(signo,trapno:integer):integer;
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.br
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The action values of \fIsignal\fP, odd for \fIignore\fP and zero
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for \fIget back to default\fP,
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may interfere with the EM procedure identification in some
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implementations.
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In most interpreters procedures in EM are numbered consecutively from zero up.
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The first argument of \fIsigtrp\fP is the signal number \fIsigno\fP
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as for \fIsignal\fP.
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The second argument is an integer \fItrapno\fP,
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indicating the action to be performed
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when the signal is issued:
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.IP -2 8
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Reset the action for signal \fIsigno\fP to the default.
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.IP -3
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Ignore signal \fIsigno\fP.
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.IP "0-252"
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Perform an EM instruction TRP with error code \fItrapno\fP,
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whenever the signal \fIsigno\fP is issued.
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Note that the error codes 0-127 are reserved for EM machine errors
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and language runtime system errors.
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.PP
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The routine \fIsigtrp\fP returns the old \fItrapno\fP or -1 if an erroneous
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signal number is specified.
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Only the signal numbers 1, 2, 3, 13, 14, 15 and 16 may be used as argument
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for \fIsigtrp\fP.
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.SH FILES
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.IP ~em/lib/*/tail_mon
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.PD
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.SH "SEE ALSO"
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em(1), ack(1), *(2), libpc(7)
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.SH DIAGNOSTICS
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All routines put the UNIX error code in the global variable \fIerrno\fP.
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Errno is not cleared by successful system calls, so it always gives
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the error of the last failed call.
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One exception: ptrace clears errno when successful.
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.SH AUTHOR
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Ed Keizer, Vrije Universiteit
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.SH BUGS
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There should be additional routines giving a fatal error when they fail.
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It would be pleasant to have routines,
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which print a nice message and stop execution for unexpected errors.
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