curve25519: fix confusing SP adjustments
The curve25519 assembly routines do very non-Go-ABI SP adjustments.
These would thoroughly confuse traceback if it were to fire in one of
these functions (say, because of a signal). Plus, we're about to make
the assembler track SP balance through more operations (which it
should have done all along), and the SP alignment performed by these
functions is going to make the assembler think the SP is out of
balance.
Fix this by eliminating the SP alignment prologue from all four
assembly functions. They don't do any operations that care about SP
alignment, so this is simply unnecessary. square and freeze don't even
use the stack for anything other that saving what were presumably
"callee save" registers in some other ABI, so for these we can
eliminate the stack frame entirely.
Change-Id: If9dbb2fb6800d9cd733daa91f483eb2937e95f0f
Reviewed-on: https://go-review.googlesource.com/31579
Run-TryBot: Austin Clements <austin@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Minux Ma <minux@golang.org>
Reviewed-by: Adam Langley <agl@golang.org>
Austin Clements