Date: Thu, 16 Mar 2000 14:03:43 -0600 From: "Jeffrey J. Mountin" <jeff-ml@mountin.net> To: Donn Miller <dmmiller@cvzoom.net> Cc: current@FreeBSD.ORG Subject: Re: panic during make depend Message-ID: <4.3.2.20000316134241.00ae2960@207.227.119.2> In-Reply-To: <38D05C92.4F85C798@cvzoom.net> References: <4.3.2.20000315172056.00bf7740@mixcom.com>
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At 11:01 PM 3/15/00 -0500, Donn Miller wrote:
>Sounds like one of those nasty gcc optimization bugs. I generally
>build my kernel and world with -mpentium -O3 -pipe, and I haven't seen
>any bugs at all. I build everything with these flags without
>problems. The only problems I've see, as mentioned previously, was in
>building Qt. I've gotten an "Internal compiler error" with those
>flags, but reverting to what Troll put in qt/configs solved the
>problems. Apparently, there's both compile-time and run-time bugs
>with gcc's opt. code.
It might be, but I'm backing off from -02 to -O for a dozen builds or so
and see. Less if panics keep coming, then the -march will be dropped. All
good then back to -02 and try -mcpu.
>I think there are some bugs with the pentium-specific flags in gcc,
>excluding the generic-pentium flag of -mpentium. I would try using
>-mpentium -O3 -pipe --- I'm pretty confident that will solve your
>problems, and you can still get generic pentium optimization levels.
Why use -O3, which adds -finline-functions. AFAICR, that one isn't very
liked by those more with more knowledge and experience.
>Of course, I don't really know if there's anything to be gained by
>using these flags over the stock -O -pipe -- but I do it anyways for
>the psychological reassurance (placebo effect). I definitely think
>building XFree86 with pentium opt. is a great idea. But with
>buildworld and buildkernel, my advice would be to just use -mpentium,
>as it's probably the "happiest medium" between pentium opt. and
>stability. From what I've heard, compiling mission critical stuff
>with -mpentiumpro is a bad idea. Hmmm... didn't -mpentiumpro come
>from pgcc? I think the best place to use -mpentiumpro is in compiling
>multimedia type stuff, where stability isn't important but speed is.
Don't think your reasoning is all that sound as a "reassurance," but
ensuring that code is optimized for the CPU, and in my case architecture,
is good.
Originally thought that using -march would speed up compiling for one and
another to have more specific code for the system running it. Been a while
since I had a running 486, 8+ years since even seeing a 386, and only have
2 pentiums in operation, so why should the code have instructions for
running on any of these platforms?
As an example I've seen many posts with -mno-486 used. The man page is
clear as mud on what that does. From the wording it should optimize the
code for a 386 then:
-mno-486
Control whether or not code is optimized for a 486
instead of an 386. Code generated for a 486 will
run on a 386 and vice versa.
Perhaps the man pages need updating.
>Basically, gcc is a very good compiler. But, it isn't exactly the
>best compiler to use for optimization. Someone told me that Sun's and
>DEC's compilers, for example, blow away gcc in terms of speed. But,
>they aren't portable.
The DEC compiler might be good for some FBSD users.
Jeff Mountin - jeff@mountin.net
Systems/Network Administrator
FreeBSD - the power to serve
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