[FFmpeg-devel] [RFC] insufficient VFP check?

[Måns Rullgård]

Reimar D?ffinger <Reimar.Doeffinger at gmx.de> writes:

> On Sun, Jan 17, 2010 at 02:03:32AM +0200, Siarhei Siamashka wrote:
>> On Sunday 17 January 2010, Reimar D?ffinger wrote:
>> > On Sat, Jan 16, 2010 at 11:40:34PM +0000, M?ns Rullg?rd wrote:
>> > > Reimar D?ffinger <Reimar.Doeffinger at gmx.de> writes:
>> > > > Hello,
>> > > > the configure vfp check looks for
>> > > > fadds s0, s0, s0
>> > > > However, this detects VFP e.g. for
>> > > > -mcpu=cortex-a8 -mfpu=neon -mfloat-abi=softfp
>> > > > while actual compilation fails with e.g.
>> > > > libavcodec/arm/dsputil_vfp.S:160: Error: selected processor does not
>> > > > support `vmov r7,r8,s4,s5' So what is the right solution, replace the
>> > > > check with something like the failing instruction?
>> > >
>> > > What configure line did you use?  It always works for me...
>> >
>> > Something a bit silly:
>> > ./configure --cross-prefix=armv7a-softfloat-linux-gnueabi-
>> > --extra-cflags="-mcpu=cortex-a8 -mfpu=neon -mfloat-abi=softfp" --arch=arm
>> > --cpu=cortex-a8 However doesn't look silly enough to make it break that
>> > way..
>> 
>> At least gentoo has problems compiling mplayer/ffmpeg with 
>> armv7a-softfloat-linux-gnueabi toolchain (because it has an extra softfloat 
>> related patch applied by ebuild), armv7a-unknown-linux-gnueabi is fine.
>
> Uh, can the -unknown- variant compile vfp/neon?
> I came to the conclusion, idiotic as it is (not commenting on the technical
> point, but from a usability one), that softfloat is necessary
> to have neon/vfp support.

Hmm, I didn't read carefully enough first time, and missed the
softfloat part.  You definitely do *not* want to mess with softfloat
on A8.  The softfloat compilers are configured to emulate FP, and the
-mfloat-abi=softfp flag contradicts that.  No idea what that might
lead to.

With a softfloat compiler I get the same error.

-- 
M?ns Rullg?rd
mans at mansr.com