On 4 May 2009, at 22:12, Fred Kiefer wrote:
Please keep in mind that my i586 is surely able to execute these
instructions, still I get a link error with your latest patch. I think
we agree that the aim is to get it to work out of the box on as much
environments as possible. The i486 assembler code already restricted
that a bit, but nobody has complained up to now (and the change has
been
in a full year already). The gcc build in change would break it on my
machine and an unknown amount of others as well.
I think it's important to work out why it is failing on your machine.
The reason I suggested this change is that, for me, looking at the
assembly, it generates the same code as our inline asm on x86 but also
works on non-x86 platforms that we currently use a painfully slow code
path for.
I am using GCC 4.2.1, and this compiles correctly with no -march=
anything specified. If I specify -march=i386 it still generates the
LOCK. Looking more deeply at the ISA references, it appears that the
LOCK prefix was part of the original 80386 instruction set, so this is
atomic on any x86 processor (it was the CMPXCHG instruction and
friends that came in with the 80486).
Possibly the GCC version check is incorrect. According to the gcc
docs, these functions appeared in 4.1.0, however it seems that 4.2 is
when they became well-supported. Possibly setting 4.2.0 or 4.2.1 as
the minimum GCC version to adopt them will be better?
David
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