Bug#609690: Debian x86 32-bits built for i586 !?
On Sun, 15 May 2011, Ben Hutchings wrote:
> 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.
Assuming we can't just do away with i486 support for now, did anyone track
down exactly what was causing breakages that forced the change from
march=486 to march=586?
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