.\"	@(#) thud.1 
.\"
.TH thud 1 "03 Nov 1904"
.AT 3
.SH NAME
thud \- run a program and catch null-pointer dereferences.
.SH SYNOPSIS
.B thud
.B [-a|
program [args] ...
.sp 0
.SH DESCRIPTION
.I thud
runs programs which regularly dereference null pointers, catching
the errors and logging information about them. It then "fixes" the
program and lets it run normally thereafter.
.PP
It's purpose to to allow programs written for VAXes or other
non-unix machines to continue to work, while reporting the
location of the bug.
.PP
The bug is trypically a test of the form
.nf
.nj
    while (*p->q != 0) {
        ...
        p++;
    }
.fi
.ju
which attempts to dereference a pointer without testing first to
see if it is null.
This is known as the "all the world's a VAX" bug.
.PP
  It's default
mode of operation is to catch the first dereference, report, and
then map in a page of zeros at address 0 to allow the program
to continue normally.
.PP
.TP
.B \-a
All signals will be caught, not just sigsegv 
.PP

.SH FILES
.sp 0

.SH "SEE ALSO"
compress(1), fiz(1)

.SH BUGS

.SH DIAGNOSTICS

.SH COMPATIBILITY

.SH CHANGES

.SH ACKNOWLEDGEMENTS

.SH AUTHOR