After upgrading to a new version of GNU ld for PowerPC e500, I started
seeing build errors on e500 systems again. It turns out that the
PowerPC "string instructions" are unimplemented on PPC440 and most other
embedded cores, and also cause unexpectedly high instruction latencies
and pipeline stalls even on POWER processors.
This historically worked in the past because the unknown string opcodes
are trapped on PPC440 and similar systems and emulated in the kernel,
though that is obviously very inefficient and undesirable.
Since the struct-copy code doesn't really need to be implemented in
assembly, this patch ensures that there is always enough space to store
both r3 and r4 and then uses C to extract the 1-8 byte "small struct"
into the user-provided memory.
Even with all the big new comments, it's still removes 11 lines of code,
and the ASM is much simpler and easier to understand now.
Please consider applying.