Instead of storing LR (the return address) at 0(SP) and the FP
(parent's frame pointer) at -8(SP), store them at framesize-8(SP)
and framesize-16(SP), respectively.
We push and pop data onto the stack such that we're never accessing
anything below SP.
The prolog/epilog lengths are unchanged (3 insns for a typical prolog,
2 for a typical epilog).
We use 8 bytes more per frame.
Typical prologue:
STP.W (FP, LR), -16(SP)
MOVD SP, FP
SUB $C, SP
Typical epilogue:
ADD $C, SP
LDP.P 16(SP), (FP, LR)
RET
The previous word where we stored LR, at 0(SP), is now unused.
We could repurpose that slot for storing a local variable.
The new prolog and epilog instructions are recognized by libunwind,
so pc-sampling tools like perf should now be accurate. (TODO: except
maybe after the first RET instruction? Have to look into that.)
Update #73753 (fixes, for arm64)
Update #57302 (Quim thinks this will help on that issue)
Change-Id: I4800036a9a9a08aaaf35d9f99de79a36cf37ebb8
Reviewed-on: https://go-review.googlesource.com/c/go/+/674615 Reviewed-by: David Chase <drchase@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com> Reviewed-by: Keith Randall <khr@google.com>