Re: crashing bug : found... destroyed

[Alan Hourihane <alanh at xfree86 dot org>]

Sounds reasonable. Looks like miarc.c suffers the same problem.

Can someone plough through the code and submit a patch.

Alan.

On Tue, Jul 31, 2001 at 02:20:50PM -0400, Harold Hunt wrote:
> Alan,
> 
> What do you think?  It sounds logical to me... do you want to commit it if
> it seems straight to you?
> 
> Harold
> 
> > -----Original Message-----
> > From: cygwin-xfree-owner@sources.redhat.com
> > [mailto:cygwin-xfree-owner@sources.redhat.com]On Behalf Of Brian Michael
> > Genisio
> > Sent: Tuesday, July 31, 2001 2:14 PM
> > To: cygwin-xfree@sources.redhat.com
> > Subject: crashing bug : found... destroyed
> >
> >
> > I wanted to report a bug I found in the XWin server. ( It pops up in
> >  the VFB and probably Xnest as well.)  It has to do with the
> > drawing of poly
> > lines. Unfortunately, I do not have a program I can give you to
> > recreate the
> > bug, but take a look, and hopefully add the fix the the XFree source.
> >
> > The problem is in the  mi/miwideline.c file.  It makes use of the
> > math function
> > hypot ( hypotonuse ... sqrt(a*a + b*b) ) from math.h.  Because of
> > the way the
> > defines are set up in the beginning, this file never gets an appropriate
> > prototype for `double hypot(double, double) `.
> >
> > Since it had no proper prototype, I am assuming it was storing
> > the value as a
> > float or int, instead of a double and the value in the line
> >
> > L = hypot ((double) dx, (double) dy);
> >
> > (inside the miWideSegment function) was being stored badly,
> > causing unexpected
> > results... sometimes a crash due to data overwrites (which I was
> > running into).
> >
> > This has probably been run into before, since in the beginning of
> > the file, we
> > see this code :
> >
> > #ifdef _XOPEN_SOURCE
> > #include <math.h>
> > #else
> > #define _XOPEN_SOURCE   /* to get prototype for hypot on some systems */
> > #include <math.h>
> > #undef _XOPEN_SOURCE
> > #endif
> >
> > I looked at the math.h file on my solaris box, and I see that hypot is
> > prototyped if _XOPEN_SOURCE is defined.  Soo.... it looks like it
> > was an issue
> > for solaris.  Unfortunately, math.h in cygwin does not use the define
> > _XOPEN_SOURCE to determine when to use hypot.
> >
> > Instead, it prototypes hypot ONLY when __STRICT_ANSI__ is NOT
> > defined.  Well,
> > in the build of this file, STRICT_ANSI must be getting defined,
> > since I have
> > determined that hypot is not being prototyped.  I determined this
> > by compiling
> > miwideline.c with all of the XFree flags, and included the -E
> > option, which
> > preprocesses the file, but does not compile it.  This output
> > proved that hypot
> > was not being prototyped.
> >
> >
> >
> >
> >
> > THE FIX :
> > I simply undefine __STRICT_ANSI__ before the math.h include, and
> > redefine it
> > after :
> >
> >
> >
> > #if defined(__STRICT_ANSI__) && defined(__CYGWIN__)
> > #undef __STRICT_ANSI__ /* undefine to insure hypot */
> >
> > #ifdef _XOPEN_SOURCE
> > #include <math.h>
> > #else
> > #define _XOPEN_SOURCE   /* to get prototype for hypot on some systems */
> > #include <math.h>
> > #undef _XOPEN_SOURCE
> > #endif
> >
> > #define __STRICT_ANSI__
> > #else /*#if defined(__STRICT_ANSI__) && defined(__CYGWIN__)*/
> >
> > #ifdef _XOPEN_SOURCE
> > #include <math.h>
> > #else
> > #define _XOPEN_SOURCE   /* to get prototype for hypot on some systems */
> > #include <math.h>
> >
> > #undef _XOPEN_SOURCE
> > #endif
> >
> > #endif /*#if defined(__STRICT_ANSI__) && defined(__CYGWIN__)*/
> >
> >
> >
> >
> > By putting this at the beginning of the file, instead of the old
> > version (noted
> > above), the bug is worked around... but we may run into it with
> > other files.
> > Either way, I hope this fix can be incorporated into the XFree code.
> >
> > Thanks,
> > Brian
> >
> >
> >
> >
> > --
> > ---------------------------
> > Brian Genisio
> > genisiob@pilot.msu.edu
> >
> >
> >
> >
> >

-- 
Core Team Member			Email: alanh@XFree86.org
The XFree86 Project, Inc		http://www.xfree86.org/~alanh