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runtime: enable framepointer on all arm64

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Frame pointers were already enabled on linux, darwin, ios,
but not freebsd, android, openbsd, netbsd.

But the space was reserved on all platforms, leading to
two different arm64 framepointer conditions in different
parts of the code, one of which had no name
(framepointer_enabled || GOARCH == "arm64",
which might have been "framepointer_space_reserved").

So on the disabled systems, the stack layouts were still
set up for frame pointers and the only difference was not
actually maintaining the FP register in the generated code.

Reduce complexity by just enabling the frame pointer
completely on all the arm64 systems.

This commit passes on freebsd, android, netbsd.
I have not been able to try it on openbsd.

This CL is part of a stack adding windows/arm64
support (#36439), intended to land in the Go 1.17 cycle.
This CL is, however, not windows/arm64-specific.
It is cleanup meant to make the port (and future ports) easier.

Change-Id: I83bd23369d24b76db4c6a648fa74f6917819a093
Reviewed-on: https://go-review.googlesource.com/c/go/+/288814
Trust: Russ Cox <rsc@golang.org>
Reviewed-by: Cherry Zhang <cherryyz@google.com>
This commit is contained in:
Russ Cox 2021-01-27 11:34:42 -05:00
parent b19e7b518e
commit 09e059afb1
7 changed files with 164 additions and 136 deletions
Download patch file Download diff file Expand all files Collapse all files

3
src/cmd/compile/internal/dwarfgen/dwarf.go
View file

@ -271,8 +271,7 @@ func createSimpleVar(fnsym *obj.LSym, n *ir.Name) *dwarf.Var {
if base.Ctxt.FixedFrameSize() == 0 {
offs -= int64(types.PtrSize)
}
if objabi.Framepointer_enabled || objabi.GOARCH == "arm64" {
// There is a word space for FP on ARM64 even if the frame pointer is disabled
if objabi.Framepointer_enabled {
offs -= int64(types.PtrSize)
}

3
src/cmd/compile/internal/ssagen/pgen.go
View file

@ -213,8 +213,7 @@ func StackOffset(slot ssa.LocalSlot) int32 {
if base.Ctxt.FixedFrameSize() == 0 {
off -= int64(types.PtrSize)
}
if objabi.Framepointer_enabled || objabi.GOARCH == "arm64" {
// There is a word space for FP on ARM64 even if the frame pointer is disabled
if objabi.Framepointer_enabled {
off -= int64(types.PtrSize)
}
case ir.PPARAM, ir.PPARAMOUT:

2
src/cmd/internal/obj/arm64/a.out.go
View file

@ -239,7 +239,7 @@ const (
REGCTXT = REG_R26 // environment for closures
REGTMP = REG_R27 // reserved for liblink
REGG = REG_R28 // G
REGFP = REG_R29 // frame pointer, unused in the Go toolchain
REGFP = REG_R29 // frame pointer
REGLINK = REG_R30
// ARM64 uses R31 as both stack pointer and zero register,

39
src/cmd/internal/obj/arm64/obj7.go
View file

@ -622,7 +622,7 @@ func preprocess(ctxt *obj.Link, cursym *obj.LSym, newprog obj.ProgAlloc) {
prologueEnd.Pos = prologueEnd.Pos.WithXlogue(src.PosPrologueEnd)
if objabi.Framepointer_enabled {
// Frame pointer.
q1 = obj.Appendp(q1, c.newprog)
q1.Pos = p.Pos
q1.As = AMOVD
@ -640,7 +640,6 @@ func preprocess(ctxt *obj.Link, cursym *obj.LSym, newprog obj.ProgAlloc) {
q1.Reg = REGSP
q1.To.Type = obj.TYPE_REG
q1.To.Reg = REGFP
}
if c.cursym.Func().Text.From.Sym.Wrapper() {
// if(g->panic != nil && g->panic->argp == FP) g->panic->argp = bottom-of-frame
@ -765,7 +764,7 @@ func preprocess(ctxt *obj.Link, cursym *obj.LSym, newprog obj.ProgAlloc) {
p.To.Reg = REGSP
p.Spadj = -c.autosize
if objabi.Framepointer_enabled {
// Frame pointer.
p = obj.Appendp(p, c.newprog)
p.As = ASUB
p.From.Type = obj.TYPE_CONST
@ -774,11 +773,10 @@ func preprocess(ctxt *obj.Link, cursym *obj.LSym, newprog obj.ProgAlloc) {
p.To.Type = obj.TYPE_REG
p.To.Reg = REGFP
}
}
} else {
/* want write-back pre-indexed SP+autosize -> SP, loading REGLINK*/
if objabi.Framepointer_enabled {
// Frame pointer.
p.As = AMOVD
p.From.Type = obj.TYPE_MEM
p.From.Reg = REGSP
@ -786,7 +784,6 @@ func preprocess(ctxt *obj.Link, cursym *obj.LSym, newprog obj.ProgAlloc) {
p.To.Type = obj.TYPE_REG
p.To.Reg = REGFP
p = obj.Appendp(p, c.newprog)
}
aoffset := c.autosize
@ -821,6 +818,28 @@ func preprocess(ctxt *obj.Link, cursym *obj.LSym, newprog obj.ProgAlloc) {
}
}
// If enabled, this code emits 'MOV PC, R27' before every 'MOV LR, PC',
// so that if you are debugging a low-level crash where PC and LR are zero,
// you can look at R27 to see what jumped to the zero.
// This is useful when bringing up Go on a new system.
// (There is similar code in ../ppc64/obj9.go:/if.false.)
const debugRETZERO = false
if debugRETZERO {
if p.As != obj.ARET {
q = newprog()
q.Pos = p.Pos
q.Link = p.Link
p.Link = q
p = q
}
p.As = AADR
p.From.Type = obj.TYPE_BRANCH
p.From.Offset = 0
p.To.Type = obj.TYPE_REG
p.To.Reg = REGTMP
}
if p.As != obj.ARET {
q = newprog()
q.Pos = p.Pos
@ -866,7 +885,6 @@ func preprocess(ctxt *obj.Link, cursym *obj.LSym, newprog obj.ProgAlloc) {
}
case obj.ADUFFCOPY:
if objabi.Framepointer_enabled {
// ADR ret_addr, R27
// STP (FP, R27), -24(SP)
// SUB 24, SP, FP
@ -896,7 +914,7 @@ func preprocess(ctxt *obj.Link, cursym *obj.LSym, newprog obj.ProgAlloc) {
q2.To.Reg = REGSP
q2.To.Offset = -24
// maintaine FP for DUFFCOPY
// maintain FP for DUFFCOPY
q3 := obj.Appendp(q2, c.newprog)
q3.Pos = p.Pos
q3.As = ASUB
@ -916,10 +934,8 @@ func preprocess(ctxt *obj.Link, cursym *obj.LSym, newprog obj.ProgAlloc) {
q5.To.Reg = REGFP
q1.From.SetTarget(q5)
p = q5
}
case obj.ADUFFZERO:
if objabi.Framepointer_enabled {
// ADR ret_addr, R27
// STP (FP, R27), -24(SP)
// SUB 24, SP, FP
@ -949,7 +965,7 @@ func preprocess(ctxt *obj.Link, cursym *obj.LSym, newprog obj.ProgAlloc) {
q2.To.Reg = REGSP
q2.To.Offset = -24
// maintaine FP for DUFFZERO
// maintain FP for DUFFZERO
q3 := obj.Appendp(q2, c.newprog)
q3.Pos = p.Pos
q3.As = ASUB
@ -970,7 +986,6 @@ func preprocess(ctxt *obj.Link, cursym *obj.LSym, newprog obj.ProgAlloc) {
q1.From.SetTarget(q5)
p = q5
}
}
if p.To.Type == obj.TYPE_REG && p.To.Reg == REGSP && p.Spadj == 0 {
f := c.cursym.Func()

2
src/cmd/internal/objabi/util.go
View file

@ -137,7 +137,7 @@ func init() {
}
// Note: must agree with runtime.framepointer_enabled.
var Framepointer_enabled = GOARCH == "amd64" || GOARCH == "arm64" && (GOOS == "linux" || GOOS == "darwin" || GOOS == "ios")
var Framepointer_enabled = GOARCH == "amd64" || GOARCH == "arm64"
func addexp(s string) {
// Could do general integer parsing here, but the runtime copy doesn't yet.

2
src/runtime/runtime2.go
View file

@ -1106,4 +1106,4 @@ var (
)
// Must agree with cmd/internal/objabi.Framepointer_enabled.
const framepointer_enabled = GOARCH == "amd64" || GOARCH == "arm64" && (GOOS == "linux" || GOOS == "darwin" || GOOS == "ios")
const framepointer_enabled = GOARCH == "amd64" || GOARCH == "arm64"

17
src/runtime/traceback.go
View file

@ -275,7 +275,22 @@ func gentraceback(pc0, sp0, lr0 uintptr, gp *g, skip int, pcbuf *uintptr, max in
// For architectures with frame pointers, if there's
// a frame, then there's a saved frame pointer here.
if frame.varp > frame.sp && (GOARCH == "amd64" || GOARCH == "arm64") {
//
// NOTE: This code is not as general as it looks.
// On x86, the ABI is to save the frame pointer word at the
// top of the stack frame, so we have to back down over it.
// On arm64, the frame pointer should be at the bottom of
// the stack (with R29 (aka FP) = RSP), in which case we would
// not want to do the subtraction here. But we started out without
// any frame pointer, and when we wanted to add it, we didn't
// want to break all the assembly doing direct writes to 8(RSP)
// to set the first parameter to a called function.
// So we decided to write the FP link *below* the stack pointer
// (with R29 = RSP - 8 in Go functions).
// This is technically ABI-compatible but not standard.
// And it happens to end up mimicking the x86 layout.
// Other architectures may make different decisions.
if frame.varp > frame.sp && framepointer_enabled {
frame.varp -= sys.PtrSize
}