[Sugar-devel] Planning for the future (Samuel Greenfeld)
dsd at laptop.org
Fri Feb 27 07:23:09 EST 2015
On Wed, Feb 25, 2015 at 1:20 PM, Jerry Vonau <me at jvonau.ca> wrote:
> I know this is not a sugar issue directly, more of an OLPC issue but since
> Fedora F12 the entire i686 platform's userland is being compiled with
> -mtune=atom which would use sse.
-mtune is designed not to break any compatibility.
So -mtune=atom means that generated code is optimized for atom but *no
compatibility with other CPUs is broken*.
So -mtune=atom does not imply that gcc will spit out sse instructions
because it feels like it. In fact, it will actively avoid generating
sse instructions in order to maintain compatibility.
(-march is probably what you are thinking of)
> This causes problems for some parts
> of sugar now that java is being used more and the XO-1 lacks sse.
The WebKit issue happened because it generates its own machine code at
runtime (not using gcc). It's definitely a bug that it dropped sse
instructions in there without properly checking if the CPU can do sse,
but not a common case that you will see throughout the distro.
sse-related issue to me. That issue shows a SIGSEGV whereas if code is
using sse instructions you would instead expect a SIGILL.
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