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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>
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@rsc
rsc committed Feb 19, 2021
1 parent b19e7b5 commit 09e059a
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Showing 7 changed files with 175 additions and 147 deletions.
3 changes: 1 addition & 2 deletions src/cmd/compile/internal/dwarfgen/dwarf.go
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Original file line number Diff line number Diff line change
Expand Up @@ -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)
}

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3 changes: 1 addition & 2 deletions src/cmd/compile/internal/ssagen/pgen.go
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Original file line number Diff line number Diff line change
Expand Up @@ -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:
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2 changes: 1 addition & 1 deletion src/cmd/internal/obj/arm64/a.out.go
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Original file line number Diff line number Diff line change
Expand Up @@ -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,
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293 changes: 154 additions & 139 deletions src/cmd/internal/obj/arm64/obj7.go
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Original file line number Diff line number Diff line change
Expand Up @@ -622,25 +622,24 @@ func preprocess(ctxt *obj.Link, cursym *obj.LSym, newprog obj.ProgAlloc) {

prologueEnd.Pos = prologueEnd.Pos.WithXlogue(src.PosPrologueEnd)

if objabi.Framepointer_enabled {
q1 = obj.Appendp(q1, c.newprog)
q1.Pos = p.Pos
q1.As = AMOVD
q1.From.Type = obj.TYPE_REG
q1.From.Reg = REGFP
q1.To.Type = obj.TYPE_MEM
q1.To.Reg = REGSP
q1.To.Offset = -8

q1 = obj.Appendp(q1, c.newprog)
q1.Pos = p.Pos
q1.As = ASUB
q1.From.Type = obj.TYPE_CONST
q1.From.Offset = 8
q1.Reg = REGSP
q1.To.Type = obj.TYPE_REG
q1.To.Reg = REGFP
}
// Frame pointer.
q1 = obj.Appendp(q1, c.newprog)
q1.Pos = p.Pos
q1.As = AMOVD
q1.From.Type = obj.TYPE_REG
q1.From.Reg = REGFP
q1.To.Type = obj.TYPE_MEM
q1.To.Reg = REGSP
q1.To.Offset = -8

q1 = obj.Appendp(q1, c.newprog)
q1.Pos = p.Pos
q1.As = ASUB
q1.From.Type = obj.TYPE_CONST
q1.From.Offset = 8
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
Expand Down Expand Up @@ -765,28 +764,26 @@ func preprocess(ctxt *obj.Link, cursym *obj.LSym, newprog obj.ProgAlloc) {
p.To.Reg = REGSP
p.Spadj = -c.autosize

if objabi.Framepointer_enabled {
p = obj.Appendp(p, c.newprog)
p.As = ASUB
p.From.Type = obj.TYPE_CONST
p.From.Offset = 8
p.Reg = REGSP
p.To.Type = obj.TYPE_REG
p.To.Reg = REGFP
}
// Frame pointer.
p = obj.Appendp(p, c.newprog)
p.As = ASUB
p.From.Type = obj.TYPE_CONST
p.From.Offset = 8
p.Reg = REGSP
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 {
p.As = AMOVD
p.From.Type = obj.TYPE_MEM
p.From.Reg = REGSP
p.From.Offset = -8
p.To.Type = obj.TYPE_REG
p.To.Reg = REGFP
p = obj.Appendp(p, c.newprog)
}
// Frame pointer.
p.As = AMOVD
p.From.Type = obj.TYPE_MEM
p.From.Reg = REGSP
p.From.Offset = -8
p.To.Type = obj.TYPE_REG
p.To.Reg = REGFP
p = obj.Appendp(p, c.newprog)

aoffset := c.autosize

Expand Down Expand Up @@ -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
Expand Down Expand Up @@ -866,110 +885,106 @@ 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
// DUFFCOPY
// ret_addr:
// SUB 8, SP, FP

q1 := p
// copy DUFFCOPY from q1 to q4
q4 := obj.Appendp(p, c.newprog)
q4.Pos = p.Pos
q4.As = obj.ADUFFCOPY
q4.To = p.To

q1.As = AADR
q1.From.Type = obj.TYPE_BRANCH
q1.To.Type = obj.TYPE_REG
q1.To.Reg = REG_R27

q2 := obj.Appendp(q1, c.newprog)
q2.Pos = p.Pos
q2.As = ASTP
q2.From.Type = obj.TYPE_REGREG
q2.From.Reg = REGFP
q2.From.Offset = int64(REG_R27)
q2.To.Type = obj.TYPE_MEM
q2.To.Reg = REGSP
q2.To.Offset = -24

// maintaine FP for DUFFCOPY
q3 := obj.Appendp(q2, c.newprog)
q3.Pos = p.Pos
q3.As = ASUB
q3.From.Type = obj.TYPE_CONST
q3.From.Offset = 24
q3.Reg = REGSP
q3.To.Type = obj.TYPE_REG
q3.To.Reg = REGFP

q5 := obj.Appendp(q4, c.newprog)
q5.Pos = p.Pos
q5.As = ASUB
q5.From.Type = obj.TYPE_CONST
q5.From.Offset = 8
q5.Reg = REGSP
q5.To.Type = obj.TYPE_REG
q5.To.Reg = REGFP
q1.From.SetTarget(q5)
p = q5
}
// ADR ret_addr, R27
// STP (FP, R27), -24(SP)
// SUB 24, SP, FP
// DUFFCOPY
// ret_addr:
// SUB 8, SP, FP

q1 := p
// copy DUFFCOPY from q1 to q4
q4 := obj.Appendp(p, c.newprog)
q4.Pos = p.Pos
q4.As = obj.ADUFFCOPY
q4.To = p.To

q1.As = AADR
q1.From.Type = obj.TYPE_BRANCH
q1.To.Type = obj.TYPE_REG
q1.To.Reg = REG_R27

q2 := obj.Appendp(q1, c.newprog)
q2.Pos = p.Pos
q2.As = ASTP
q2.From.Type = obj.TYPE_REGREG
q2.From.Reg = REGFP
q2.From.Offset = int64(REG_R27)
q2.To.Type = obj.TYPE_MEM
q2.To.Reg = REGSP
q2.To.Offset = -24

// maintain FP for DUFFCOPY
q3 := obj.Appendp(q2, c.newprog)
q3.Pos = p.Pos
q3.As = ASUB
q3.From.Type = obj.TYPE_CONST
q3.From.Offset = 24
q3.Reg = REGSP
q3.To.Type = obj.TYPE_REG
q3.To.Reg = REGFP

q5 := obj.Appendp(q4, c.newprog)
q5.Pos = p.Pos
q5.As = ASUB
q5.From.Type = obj.TYPE_CONST
q5.From.Offset = 8
q5.Reg = REGSP
q5.To.Type = obj.TYPE_REG
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
// DUFFZERO
// ret_addr:
// SUB 8, SP, FP

q1 := p
// copy DUFFZERO from q1 to q4
q4 := obj.Appendp(p, c.newprog)
q4.Pos = p.Pos
q4.As = obj.ADUFFZERO
q4.To = p.To

q1.As = AADR
q1.From.Type = obj.TYPE_BRANCH
q1.To.Type = obj.TYPE_REG
q1.To.Reg = REG_R27

q2 := obj.Appendp(q1, c.newprog)
q2.Pos = p.Pos
q2.As = ASTP
q2.From.Type = obj.TYPE_REGREG
q2.From.Reg = REGFP
q2.From.Offset = int64(REG_R27)
q2.To.Type = obj.TYPE_MEM
q2.To.Reg = REGSP
q2.To.Offset = -24

// maintaine FP for DUFFZERO
q3 := obj.Appendp(q2, c.newprog)
q3.Pos = p.Pos
q3.As = ASUB
q3.From.Type = obj.TYPE_CONST
q3.From.Offset = 24
q3.Reg = REGSP
q3.To.Type = obj.TYPE_REG
q3.To.Reg = REGFP

q5 := obj.Appendp(q4, c.newprog)
q5.Pos = p.Pos
q5.As = ASUB
q5.From.Type = obj.TYPE_CONST
q5.From.Offset = 8
q5.Reg = REGSP
q5.To.Type = obj.TYPE_REG
q5.To.Reg = REGFP
q1.From.SetTarget(q5)
p = q5
}
// ADR ret_addr, R27
// STP (FP, R27), -24(SP)
// SUB 24, SP, FP
// DUFFZERO
// ret_addr:
// SUB 8, SP, FP

q1 := p
// copy DUFFZERO from q1 to q4
q4 := obj.Appendp(p, c.newprog)
q4.Pos = p.Pos
q4.As = obj.ADUFFZERO
q4.To = p.To

q1.As = AADR
q1.From.Type = obj.TYPE_BRANCH
q1.To.Type = obj.TYPE_REG
q1.To.Reg = REG_R27

q2 := obj.Appendp(q1, c.newprog)
q2.Pos = p.Pos
q2.As = ASTP
q2.From.Type = obj.TYPE_REGREG
q2.From.Reg = REGFP
q2.From.Offset = int64(REG_R27)
q2.To.Type = obj.TYPE_MEM
q2.To.Reg = REGSP
q2.To.Offset = -24

// maintain FP for DUFFZERO
q3 := obj.Appendp(q2, c.newprog)
q3.Pos = p.Pos
q3.As = ASUB
q3.From.Type = obj.TYPE_CONST
q3.From.Offset = 24
q3.Reg = REGSP
q3.To.Type = obj.TYPE_REG
q3.To.Reg = REGFP

q5 := obj.Appendp(q4, c.newprog)
q5.Pos = p.Pos
q5.As = ASUB
q5.From.Type = obj.TYPE_CONST
q5.From.Offset = 8
q5.Reg = REGSP
q5.To.Type = obj.TYPE_REG
q5.To.Reg = REGFP
q1.From.SetTarget(q5)
p = q5
}

if p.To.Type == obj.TYPE_REG && p.To.Reg == REGSP && p.Spadj == 0 {
Expand Down
2 changes: 1 addition & 1 deletion src/cmd/internal/objabi/util.go
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Original file line number Diff line number Diff line change
Expand Up @@ -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.
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2 changes: 1 addition & 1 deletion src/runtime/runtime2.go
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Original file line number Diff line number Diff line change
Expand Up @@ -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 changes: 16 additions & 1 deletion src/runtime/traceback.go
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Original file line number Diff line number Diff line change
Expand Up @@ -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
}

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