Path: utzoo!utgpu!news-server.csri.toronto.edu!mailrus!wuarchive!uunet!mcsun!unido!mikros!mwtech!mecky!walter
From: walter@mecky.UUCP (Walter Mecky)
Newsgroups: comp.unix.i386
Subject: Re: wait() & negative values
Message-ID: <754@mecky.UUCP>
Date: 25 Aug 90 14:29:00 GMT
References: <70400015@m.cs.uiuc.edu>
Reply-To: walter@mecky.UUCP (Walter Mecky)
Organization: MIKROS Systemware, Buettelborn/W-Germany
Lines: 19

In article <70400015@m.cs.uiuc.edu> carroll@m.cs.uiuc.edu writes:
< 
< I've
< recently tracked at least some of the crashes down to the fact that wait(loc)
< sometimes returns negative values in *loc, e.g. 0xFFFFxxyy  where xx and yy
< are the values you'd normally expect in the bottom 16 bits of the return value.
< TFM specifies the contents of the bottom 16 bits of *loc, but says absolutely
< nothing about the top 16 bits. 

As others noted, only the bottom 16 bits are defined and it's possible,
that the high order bit is propagated. I had to learn hard, that wait(2)
is indeed giving an int some years ago. I thought "He gives me 16
bits, so a short is enough", defined the "loc" variable as short 
and had a hard time to find the mysterious changing of another variable ...

BTW: X/OPEN and Posix defined macros in <sys/wait> to access the parts
     of "loc". SCO-UNIX has them too.
-- 
Walter Mecky	[ walter@mecky.uucp	or  ...uunet!unido!mecky!walter ]