Date: Sat, 11 Sep 2010 08:26:11 -0400 From: Mehmet Erol Sanliturk <m.e.sanliturk@gmail.com> To: Andrew Brampton <brampton+freebsd@gmail.com> Cc: "O. Hartmann" <ohartman@mail.zedat.fu-berlin.de>, freebsd-questions@freebsd.org Subject: Re: Compiling software with different compiler than cc or clang results in unusable output Message-ID: <AANLkTinmMDSP=Ci5GkogcD744zcy8uyP6gY7uuqLR8-_@mail.gmail.com> In-Reply-To: <AANLkTinymkQeeLhdbWYP=eEHEtViWVRscJ0-dVPJBX6u@mail.gmail.com> References: <4C8B4BC0.1000900@mail.zedat.fu-berlin.de> <AANLkTinymkQeeLhdbWYP=eEHEtViWVRscJ0-dVPJBX6u@mail.gmail.com>
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On Sat, Sep 11, 2010 at 5:43 AM, Andrew Brampton <brampton+freebsd@gmail.com<brampton%2Bfreebsd@gmail.com> > wrote: > On 11 September 2010 10:28, O. Hartmann > <ohartman@mail.zedat.fu-berlin.de> wrote: > > > > Dear Sirs, > > > > you see me a kind of desperate. I wrote my own a small piece of software > in > > C, calculating the orbit and position of astronomical objects, astroids, > in > > a heliocentric coordinate system from Keplerian orbital elements. So far. > > The software calculates the set of points of an ellipse based upon > > ephemeridal datas taken from the Minor Planet Cataloge. Again, so far, > > everything all right. The set of points of an orbit is all right and > > correct. But when it comes to positions at a specific time, then I loose > > hair! > > > > Compiling this piece of software with FreeBSD's gcc (V4.2) and clang > (clang > > devel) on my private and lab's FreeBSD boxes (both most recent FreeBSD > > 8.1/amd64), this program does well, the calculated orbital positions are > > very close to professional applications or observational checks. But when > > compiling the sources with gcc44 or gcc45 (same source, same CFLAG > setting, > > mostly no CFLAGS set), then there is a great discrepancy. Sometimes when > > plotting positions, the results plotted seconds before differs from the > most > > recent. The ellipses are allways correct, but the position of a single > point > > at a specific time isn't correct. > > > > I use the GNU autotools to build the package. > > > > I suspekt miscompilations in memory alloction or in some time- or > > mathematical functions like sin, cos. > > > > before I digg deeper I'd like to ask the community for some hints how to > > hunt down such a problem. > > > > regards, > > Oliver > > Sounds a cool project. I suspect you are miss-using a feature of C or > are using uninitialised memory, and with gcc44/45's more aggressive > optimisations it is getting it wrong. I have three suggestions > > 1) Use valgrind to check if it finds anything wrong when running your > program. Check both the good and the bad builds. > > 2) If your program is made up of multiple C files, then try compiling > all of the C files with gcc42, but just one at a time with gcc44. This > way will help you track down exactly which C file has "the bug". > > 3) Finally do some printf debugging to find the first line of code > that is generating the wrong value. > > I hope these suggestions help. > Andrew > > Another check may be to use Sun Studio C and or Fortran compilers . These can be used in Linux ( Linux version of Sun Studio ) and/or OpenSolaris or Solaris ( Solaris version of SunStudio ( both in x86 , x86_64 , Sparc ) ( all of them are ( Solaris , OpenSolaris , Sun Studio , Linux ) free ) . All of them are freely downloadable from www.sun.com and/or www.opensolaris.com ( these sites or their pages may be redirected to www.oracle.com owned pages ) . Personally I tried GCC compilers , but I found that they are very unreliable . Now I am using Sun Studio compilers in OpenSolaris and Linux , and never GCC compilers . Thank you very much . Mehmet Erol Sanliturk
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