[Linaro-dev] Discussion on new ARM hard-float port on debian-arm@

[Richard Earnshaw]

On Mon, 2010-07-12 at 10:28 +0100, Dave Martin wrote:
> 2. Use ABI tagging (high effort, involving modifications to affected
> projects - permits hardvfp ABI for explicitly selected functions)

While this might sound attractive at first, I'm not sure it will fly.

Consider tagging all the functions in libm() to use hard float.

Firstly, many people 'know' that sinf()'s prototype is

float sinf (float);

and will declare it directly rather than including math.h.  That's going
to quietly break.  Autoconf-like tools are notorious for making
assumptions like this.

Secondly, if I understand what you're suggesting, I think this just
makes the world more fragmented rather than less.  A library that
exports

float __attribute__((pcs("aapcs-vfp"))) sinf(float)

can't be replaced by a library that exports 

float __attribute__((pcs("aapcs"))) sinf(float)

because the caller must know which PCS convention is used at compile
time.

R.