From 719dfcf8a8478d70360bf3c34c0e920be7b32994 Mon Sep 17 00:00:00 2001 From: Keith Randall Date: Sat, 17 May 2025 15:05:56 -0700 Subject: cmd/compile: redo arm64 LR/FP save and restore 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 LUCI-TryBot-Result: Go LUCI Reviewed-by: Keith Randall --- src/runtime/panic.go | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) (limited to 'src/runtime/panic.go') diff --git a/src/runtime/panic.go b/src/runtime/panic.go index 8c91c9435a..04b3afe168 100644 --- a/src/runtime/panic.go +++ b/src/runtime/panic.go @@ -1379,10 +1379,10 @@ func recovery(gp *g) { // the caller gp.sched.bp = fp - 2*goarch.PtrSize case goarch.IsArm64 != 0: - // on arm64, the architectural bp points one word higher - // than the sp. fp is totally useless to us here, because it - // only gets us to the caller's fp. - gp.sched.bp = sp - goarch.PtrSize + // on arm64, the first two words of the frame are caller's PC + // (the saved LR register) and the caller's BP. + // Coincidentally, the same as amd64. + gp.sched.bp = fp - 2*goarch.PtrSize } gogo(&gp.sched) } -- cgit v1.3-5-g9baa