Saving to 32 bits of GPRs in signal context

[Benjamin Herrenschmidt]

> But unless you take the time to write it up like a full ABI change you are
> never sure that it IS compatible. And any change to the size/shape of
> ucontext_t is an ABI change.
> 
> Also if you want to debug this code (see long long variables correctly from
> GDB or even see the upper 32-bits of GPRs) you will need an ABI change so
> that GDB/DWARF knows what to do.

I personally don't care about gdb seeing those or anything like that,
those would be strictly local asm optimisations, at least that's my
point of view on the matter.

I intend not to extend or change the shape of ucontext neither. I'll add
the highregs after the ucontext32 on the compat signal frame, the only
change/addition is the use of a pad field to point to it and maybe
setting a flag that was previously unused and always 0 to indicate that
it's there.

Do you see any possible compatibility problem there ? Do you know of any
piece of software that makes hard assumptions on the shape and size of a
complete signal frame (not just the ucontext part of it) ?

Ben.