Yes. That would be fine. I know that your code compiled just
fine when I got rid of the ifdef that checked for 386, so I know
the assembler will not choke on the instruction, even though the
compiler is being called with -m386.
Richard's solution sounds OK too. As you are probably aware,
there have been similiar discussions about this type of approach
to MMX and other x86 instruction additions. I guess it's a function
of how much overhead you see as associated with the run time check
for the 386 CPU.
If the run time check for a 386 is a small overhead, but
something you would still like to avoid when possible, and if
do not want to implement Richard's proposed emulation for whatever
reason, then you might want to consider arranging things so that
you only compile in the checks if CONFIG_M386 is set, since not
setting CONFIG_M386 will already generate a kernel that cannot run
on a 386 (because it will compile in bswap instructions which do not exist
on a 386). So, if CONFIG_M386 is not set, you know this kernel already
can only run on a processor that supports cmpxchg, so you can skip the
run time tests. The best style for doing this would be to define a
symbol like CONFIG_X86_CMPXCHG in arch/i386/config.in, and test
for that symbol.
Adam J. Richter __ ______________ 4880 Stevens Creek Blvd, Suite 104
adam@yggdrasil.com \ / San Jose, California 95129-1034
+1 408 261-6630 | g g d r a s i l United States of America
fax +1 408 261-6631 "Free Software For The Rest Of Us."
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