[Sugar-devel] Planning for the future (Samuel Greenfeld)

[Daniel Drake]

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[1] which would use sse[2].

-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[3] now that java[4] 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.

I assume you mean javascript there, and bug #4785 does not look like a
sse-related issue to me. That issue shows a SIGSEGV whereas if code is
using sse instructions you would instead expect a SIGILL.

Daniel