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Re: Deprecate i386 for GCC 4.8?
On 12/19/2012 4:13 PM, Janne Blomqvist wrote:
On Wed, Dec 19, 2012 at 2:32 AM, Joel Sherrill
<joel.sherrill@oarcorp.com> wrote:
My primary concern centers whether any 386 w/o fpu IP cores or space hardened i386dx/sx or 486sx CPUs are impacted. These could be used in new designs.
This also eliminates gcc from use on any older embedded x86 boards w/o fpu.
AFAICT nobody was suggesting dropping 486sx support, so x86 soft-float
support wouldn't be going away.
Wikipedia doesn't list any x86-compatible space hardened CPU's, though
it links to a 1998 press release about Sandia making a rad-hardened
variant of the Pentium for US gov space and defense applications;
presumably not to be available on the open market.
I couldn't find any strong indication such a CPU was available either.
I also couldn't find any strong indication that one could purchase
VHDL or an IP module to build an i386dx class System on Chip.
That leaves only existing HW as impacted. I would best there are no
desktop systems impacted so that leaves embedded systems like
PC-104 stacks.
The RTEMS community can test i386 CPUs at this level but the question
remains of whether there are any users to justify doing this.
So I guess that leaves me back to questioning the original proposal. What
exactly is being proposed to be removed?
+ i386 core.. thus making i486sx the base processor supported
+ soft float and i386.. thus making i486dx the base processor supported
And how much code does this save?
On the positive side, by dropping 386 you could, in some situations,
use the new 486 atomic instructions such as cmpxchg instead of a
critical section with interrupts disabled.
We already build multilib so we do take advantage of i486 features such
as the much faster bit scan instruction when on an i486.
--joel
RTEMS still supports these but depends on gcc as the foundation. We can use qemu to automate testing gcc. We have been periodically posting results but not in the past few months. I did a build sweep in the 4.8 devel cycle but ended up using most of my time to report PRs.
I realize that for mainstream PCs, these are ancient and a good candidate for deprecation.
--joel
"Joseph S. Myers" <joseph@codesourcery.com> wrote:
On Wed, 12 Dec 2012, Steven Bosscher wrote:
Linux support for i386 has been removed. Should we do the same for GCC?
FWIW, glibc hasn't really supported i386 for several years (at least with
the Linux kernel; I don't know about Hurd), since NPTL requires atomic
operations that i386 doesn't have, so fails to link unless you use
-march=i486 or later.
--
Joseph S. Myers
joseph@codesourcery.com
--
Joel Sherrill, Ph.D. Director of Research & Development
joel.sherrill@OARcorp.com On-Line Applications Research
Ask me about RTEMS: a free RTOS Huntsville AL 35805
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