[gccsdk] New VFP/NEON capable GCC release?

Lee Noar leenoar at sky.com
Wed Aug 5 12:48:37 PDT 2015

On 05/08/15 18:58, Theo Markettos wrote:
> It appears[1] that there's some demand for a build of GCC that supports VFP
> and NEON.  Currently our existing release build 4.7.4-Rel1-1 doesn't support
> it.  Would it make sense to cut a new release build?  This would also
> involve releasing SharedUnixLibrary 0.13 which is a necessary prerequisite.
> Are there any gotchas to be aware of, or loose ends that need tidying up
> first?

I would be in favour of a new release. As you say, VFP is generating
some interest and there have also been fixes to module code generation,
Unixlib and the dynamic linker. A new release would also include the
changes required for a Qt5 web browser to be run.

As far as VFP is concerned, I'm in the middle of developing a version of
Qt for the RPi which uses VFP and OpenGL. I'm compiling it using the

-mfloat-abi=softfp -mfpu=vfp -mtune=arm1176jzf-s -march=armv6zk

So far I've got a very basic version of one of the opengl examples
running that displays a spinning triangle.
While it's difficult to say whether the code paths are touching many VFP
instructions, looking at the binary shows that the triangle render
function does contain VFP instructions so I think it's safe to say that
VFP code is being exercised.
Not exactly an exhaustive test, but there don't seem to be any issues.

I can't really say anything about NEON.

Obviously, it will be necessary to package the VFP versions of the
runtime libraries. The shared libraries should be stored in
!SharedLibs.lib.abi-2/0.vfp. Binaries needs to be linked with
-mfpu=vfp so that the dynamic linker knows to look for VFP libraries.
I can't remember if I documented that; I'll have to check.


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