compiling glibc distributions: warning

[Allin Cottrell <cottrell@ricardo.ecn.wfu.edu>]

I don't know how widely relevant this is, but I thought I'd
mention a problem I had recently.  

You have to be very careful when compiling a glibc distribution:
I compiled glibc 2.1.1 on an i686 machine then installed the
resulting libraries on an i586 machine, and the results were
disastrous.  Several key programs such as swapon, fsck and mount
failed with "Illegal instruction" messages, rendering the system
unusable.  I failed to take into account that when compiling on
the i686 machine the libraries were by default built with
i686-specific optimizations, producing code that was not usable
on an i586.  

The moral seems to be that a glibc distribution ought to be
built either (a) on a lowest-common-denominator machine, or (b)
using specific compiler flags to ensure that the libraries are
usable on any of the target architectures.

Allin Cottrell.