Date: Fri, 8 Sep 1995 00:38:46 -0700 (PDT) From: Jake Hamby <jehamby@lightside.com> To: hackers@freebsd.org Subject: -m486 option to GCC Message-ID: <Pine.BSF.3.91.950908003145.166A-100000@localhost>
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I remember in my Linux days that the '-m486' option was often passed to
GCC to provide optimizations for 486-class PC's. Apparently it didn't
generate 486-specific code but simply padded functions out in such a way
that performance was improved on 486's without sacrificing compatibility
with 386's. If you build GCC on a "i486-*-*" machine it will include the
"-m486" option by default but on a "i386-*-*" machine, it won't.
My question is: In Linux, 'uname -m' will tell you 'i486' if you have a
486 or 'i386' otherwise (I'm not sure about Pentiums), whereas under
FreeBSD, it always returns 'i386'. Therefore GCC by default is built NOT
to include the '-m486' option by default. I would recommend that either:
a) The kernel be changed to return the "proper" machine name, and GCC be
recompiled with 486 optimizations on by default (since it doesn't hurt
performance on 386's). Of course purists would argue that 'i386' is the
generic architecture name and shouldn't change depending on which machine
you run 'uname' on.
b) When running "configure" in the build tree for GCC, the canonical name
be manually overridden to "i486-unknown-freebsd2.x.x" instead of
"i386-unknown-freebsd2.x.x" to build in this optimization.
Note that the default Makefiles generated by imake under XFree86 will
always include '-m486' anyway. Comments?
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Jake Hamby | E-Mail: jehamby@lightside.com
Student, Cal Poly University, Pomona | System Administrator, JPL
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