fsqrt

[Dan Malek]

Hi Ben.

On Jun 7, 2013, at 5:34 PM, Benjamin Herrenschmidt <benh at kernel.crashing.org> wrote:

> The question is whether this is still relevant ?

The only answer I could provide is that it's dependent upon the libraries and how the distributions are built.  It's also dependent upon processors with hardware FP that don't implement all instructions in hardware (who had that bright idea? :))  If distributions are fully all soft-fp in user space or all hardware FP, it removes the one reason that started the whole partial emulation option.

> …  And if the answer is
> yes,

There are multiple options, but I believe they are solved today.  One is the libraries coded with hardware load/store that are used by soft-fp, another is hardware FP that doesn't implement all instructions in hardware (which it seems is the basis of this thread, although I thought was already solved).  The variation here is that in the first case you have to read/write user space soft-fp stack "registers," while in the latter you read/write real FP registers.  There used to be the third variation where the stack was allocated and the emulation had to write both places due to compiler function APIs or optimizations.  Of course, then there is the full-up kernel emulation where hardware is entirely lacking.

> … we still want that "minimum" emulation of load/stores/fmr as an
> option, is there any reason why we can't replace the one in softemu8xx
> with the existing (and unused) equivalent in do_mathemu ?

It appears to me that 8xx custom code can be removed.  I guess I should try to boot it up, if anyone even cares these days. :)

Thanks.

	-- Dan