Saving fprs only

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For a function that saves and restores m FPRs (m>2), the saving can be done using individual store and load instructions or by calling system-provided routines.

For a function that saves and restores m FPRs (m>2), the saving can be done using individual store and load instructions or by calling system-provided routines as shown in the following example:


#The following example shows the prolog/epilog of a function #which saves m FPRs and no GPRs:
mflr    r0                       #move LR into GPR 0
bla     _savefpr_<32-m>
stwu    r1,<-frame_size>(r1)     #update SP and save caller's SP
...
<save CR if necessary>
...
...                              #body of function
...
<reload save CR if necessary>
...
<reload caller's SP into r1>     #see note below
ba      _restfpr_<32-m>          #restore FPRs and return

Note:

There are no entry points for saving and restoring GPR and FPR numbers higher than 29. It is more efficient to save a small number of registers in the prolog than to call the save and restore functions.
The restoring of the calling function SP can be done by either adding the frame_size value to the current SP whenever frame_size is known, or by reloading it from offset 0 from the current SP. The first approach is more efficient, but not possible for functions that use the alloca subroutine to dynamically allocate stack space.