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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?

  "One disk to rule them all, One disk to find them. One disk to bring
  them all and in the darkness grind them. In the Land of Redmond
  where the shadows lie." -- The Silicon Valley Tarot
  Henrique Holschuh

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