Date: Sat, 22 Aug 1998 13:50:31 +0200 From: Alexander Sanda <entropy@compufit.at> To: wwoods@cybcon.com Cc: freebsd-current@FreeBSD.ORG Subject: Re: gcc 2.8 Message-ID: <19980822135031.A358@compufit.at> In-Reply-To: <XFMail.980821171017.wwoods@cybcon.com>; from William Woods on Fri, Aug 21, 1998 at 05:10:17PM -0700 References: <XFMail.980821171017.wwoods@cybcon.com>
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On Fri, Aug 21, 1998 at 05:10:17PM -0700, William Woods wrote: > Anybody here useing gcc 2.8 to compile world and/or kernel? gcc-2.8.1 has some problems with current kernel source (as of last weekend). However, I have installed gcc-2.8.1 from the packages collection, and I have the vague feeling, that this compiler has some problems. I compiled one of my kde apps, using -O2 and -mpentiumpro and the app started to segfault occasionally. Since I recompiled with gcc-2.7.2.1, it never segfaulted again... Moving to gcc-2.8.x or egcs/pgcc makes sense for bigger C++ projects (like KDE for example). The C land doesn't gain much from it. The processor-specific optimizations (-mpentiumpro e.g.) won't give you a faster kernel. At least, this is true in the Linux world - the kernel itself contains handmade processor-specific optimizations, which - of course - work better than any compiler generated optimizations. Once a while ago, I did some experiments with compiling the Linux kernel using different compilers (stock gcc-2.7, egcs, pgcc) and benchmarking them with lmbench or byte. The results: They all ranged within measurement tolerance, imho. Even if you run lmbench twice on the same system, the results will slightly differ. For kernel code, any compiler-induced problem can be lethal and will probably result in an unstable system. Bad enough, those bugs would be extremely hard to track. As far as we all know, gcc-2.7.2.1 produces ok code. Known problems (if any, I'am not an expert here) can be workarounded by the really skilled kernel hackers. Moving to another compiler will perhaps introduce new problems - as long as the performance gain is practically non-existant, this is not very desireable. -- # /AS/ http://privat.schlund.de/entropy/ # # # # XX has detected, that your mouse cursor has changed position. Please # # restart XX, so it can be updated. -- From The Gimp manual # To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-current" in the body of the message
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