problem with crosstool 0.28-pre28 supplied patch for gcc 3.3.[23] softfloat on ARM

[Dimitry Andric]

On 2004-08-15 at 12:28:13 Lennert Buytenhek wrote:

> Runtime switching between VFP and FPA seems to be about as useful to
> me as being able to switch between ELF and COFF at runtime.  Why can't
> you tell people to just hack gcc's header files and recompile, or
> make it a gcc build-time option (as parameter to configure or so)?

Well, there are some uses for it, and the best example I think is the
ARM Linux kernel itself, which uses -msoft-float everywhere.  Indeed,
as you say later on, this is more about what the defaults are if you
don't specify anything.  And I agree that should probably be hardware
FPA, for various reasons, which have already been discussed.


>> arm-unknown-linux-gcc without options generates hardware FPA.
>> arm-unknown-linux-gcc -msoft-float generates software FPA.
>> arm-unknown-linux-gcc -mhard-float generates hardware FPA, i.e. the
>> same as without options!

> This makes sense to me, though, since you get the same behaviour with
> many other options, like the ones of the form -f{,no-}some-option (for
> example, -f{,no-}strict-aliasing.)

But please, let's not introduce -mno-soft-float etc, because we'll all
go crazy with confusion. ;)


> My reasoning is thus: it makes little sense to me to change the default,
> because since this is rather a niche sector, you'd expect people who care
> about performance and don't care about breaking binary compatibility to
> be able to find the FPA/VFP toggle themselves, no?

Well, if you see the number of questions about this subject, it seems
to be harder than you expect...  But indeed, changing the default
probably isn't fit for general consumption.


> My thought right now is that fpa/vfp should be fixed at gcc compile time.
> Do you have any compelling reasons why this shouldn't be so? :)

Yes, that is quite reasonable.  Once you're on a certain platform,
you'll never switch it anymore anyway.
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