Message-ID: <3770EBC8.84BDD15@uiuc.edu>
Date: Wed, 23 Jun 1999 09:14:32 -0500
From: Jon <jcmcknny AT uiuc DOT edu>
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To: pgcc AT delorie DOT com
Subject: Re: pgcc does better, reboot, then does terrible!(SOLVED)
References: <199906230757 DOT JAA16919 AT mail2 DOT it DOT kth DOT se>
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Reply-To: pgcc AT delorie DOT com

Janne Johansson wrote:
> 
> > As to -mpentium.  I'm not sure how -m, -mcpu, -march are different.
> >
> > For example, the kernel compiles with -m486 -DCPU=686 (or something like
> > that), with your CPU set to 686.  Why not use -mpentium at least??
> 
> The -m<something> tells the compiler to act differently or use instructions
> and optimizations for the architecture that you specified, while the
> -Dsomething_else is a #define that affects the source, and makes the source
> act in different ways.
> 
> Just because the -D happens to define a constant that has the name "686"
> doesn't mean anything, it could as easily be -Dmight_have_large_L2_cache,
> -Dhas_variable_mmu_table_size, -Dimpress_users or whatever.
> 
> See the difference?

I never said -D did anything special in particular.

My question was what's the difference between -m, -mcpu, and -march, not
-m and -D.

Someone already answered why they don't use -mpentium, for compatibility
with 2.7.x gcc.

Thanks,
Jon