On Sun, 2011-05-15 at 09:28 -0300, Henrique de Moraes Holschuh wrote:
On Sun, 15 May 2011, Mike Hommey wrote:
I just found out that gcc is compiled with --with-arch-32=i586, which
effectively means it builds with -march=i586 by default (and that it
still claims an i486-linux-gnu target).
I'm wondering. Is the project at large aware that we're not building for
i486, but for i586 ? That even the maintainer doesn't know why for
No. And unless we got a bug report form an i486 user, our users
probably didn't notice it either.
What are the *exact* differences between code generated for march=i486
to code generated for march=i586? What CPUs would break?
[...]
There are a few new instructions on the Pentium that can be used in ring
3: cmpxchg8 and rdtsc. Linux has separate options for '586' and '586
with TSC', both of which result in -m586, so gcc does not appear to
assume the existence of rdtsc. I would not expect gcc to generate
cmpxchg8 except through an intrinsic, but I could be wrong.