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From: br0w+@andrew.cmu.edu (Bruno W. Repetto)
Newsgroups: comp.sys.ibm.pc,comp.lang.fortran,alt.msdos.programmer
Subject: Re: MS Fortran bug
Message-ID: <kZO2zCq00UwBMW1khI@andrew.cmu.edu>
Date: 20 Nov 89 17:09:34 GMT
References: <863@maytag.waterloo.edu>,
	<864@maytag.waterloo.edu>
Organization: Graduate School of Industrial Administration, Carnegie Mellon, Pittsburgh, PA
Lines: 55
In-Reply-To: <864@maytag.waterloo.edu>

Duncan Murdoch's message regarding a MS Fortran bug:

>In article <863@maytag.waterloo.edu> I wrote:
>>
>>The following little program crashes an XT clone with an 8086/8087.  
>
>It turned out to be a bug in the run-time library routine __init80x87.
>It had the sequence
>  FSTCW  [BP-4]
>  FNINIT
>  MOV    CX,01Eh
>  LOOP   in place
>What happens on an 8087 is that the FNINIT aborts the FSTCW instruction, and 
>the control word never got stored.  Later on a garbage control word was loaded
>and the system crashed.  A fix that seems to work is to put the delay loop 
>before the FNINIT.  I'm not sure what the original programmer would have 
>been thinking of writing it this way; the next instruction is an arithmetic
>one that is preceded by a WAIT anyways.
>
>To patch the library LLIBFOR7.LIB, search for the original bytes
>
>  9B D9 7E FC     
>  DB E3
>  B9 1E 00
>  E2 FE
>
>and replace them with
>
>  9B D9 7E FC     ; no change
>  B9 1E 00        ; line 3 above
>  E2 FE           ; line 4 above
>  DB E3           ; line 2 above
>
>In my copy of the library the first 6 bytes of the original gave a
unique search
>string.  I'd guess it's safe to do the same patch on any other library; the 
>original code would never make sense.
>
>Duncan Murdoch


This is all ok, but: what version of MS Fortran are you talking about?

Bruno

Bruno Wiener Repetto
 Department of Operations Research
 Graduate School of Industrial Administration (GSIA)
 Carnegie-Mellon University
 Schenley Park
 Pittsburgh, PA 15213

GSIA Room 8b, x8730 [(412)CMU-8730]

br0w+@andrew.cmu.edu