Q45195: Run-Time Library FP Signal Handler Assumes SS=DS

Article: Q45195
Product(s): See article
Version(s): 5.10
Operating System(s): MS-DOS
Keyword(s): ENDUSER | softlib CFPLIBS.ARC S12318.EXE | mspl13_c
Last Modified: 25-JUL-1989

Note that the Microsoft Run-Time Library Exception handler will call
another routine that calls the task's SIGFPE signal handler, if one
exists.

However, this intervening routine assumes that the stack segment is
that of the program that caused the 8087 exception. It is known that
certain 8087 instructions can take a (relatively) long time to
execute. It is also known that other interrupt routines, such as the
timer or the disk interrupt or one belonging to a TSR, may in fact be
running when the 8087 interrupt occurs.

As the NMI, it will nest, and the run-time library routine's
assumption about the stack segment may not be valid.

This problem is very rare; however, it is a valid concern. Instead of
sacrificing speed, the decision was made to take the small chance that
SS=DS. Checking for SS=DS would slow the floating-point libraries
considerably.

There is a file in the OnLine Software/Data Library that contains two
floating-point libraries. These libraries should protect you from the
unlikely event of SS!=DS. These libraries are approximately 10%
slower than the retail floating-point libraries.

This file can be found in the Software/Data Library by searching on
the keyword CFPLIBS, the Q number of this article, or S12318. CFPLIBS
was archived using the PKware file-compression utility.

These libraries eliminate the possibility of SS!=DS within a
floating-point signal handler. However, these libraries are about 10%
slower than the original floating-point libraries. To include these
files in your combined libraries, first make backup copies of the
original floating-point libraries, rename these new libraries to
EM.LIB and 87.LIB, and then run SETUP with the /L option to rebuild
libraries. This will rebuild the combined libraries with these new
floating-point components.

The libraries provided with this archived file are fully tested.
However, they are not regularly released with Microsoft C 5.10.
Consequently, they will not be maintained, and any problem reported
with them will not result in a patch or any other immediate fix.
Please report all problems experienced with these libraries.

The archived file contains the following files:

   README.DOC
   PIEM.LIB
   PI87.LIB

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