[dev.typeparams] Revert "[dev.typeparams] runtime,cmd/compile,cmd/link: replace jmpdefer with a loop"

This reverts CL 227652.

I'm reverting CL 337651 and this builds on top of it.

Change-Id: I03ce363be44c2a3defff2e43e7b1aad83386820d
Reviewed-on: https://go-review.googlesource.com/c/go/+/338709
Trust: Austin Clements <austin@google.com>
Run-TryBot: Austin Clements <austin@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Cherry Mui <cherryyz@google.com>

src/cmd/compile/internal/amd64/galign.go

@@ -18,6 +18,7 @@ func Init(arch *ssagen.ArchInfo) {
 
 	arch.ZeroRange = zerorange
 	arch.Ginsnop = ginsnop
+	arch.Ginsnopdefer = ginsnop
 
 	arch.SSAMarkMoves = ssaMarkMoves
 	arch.SSAGenValue = ssaGenValue

src/cmd/compile/internal/arm/galign.go

@@ -18,6 +18,7 @@ func Init(arch *ssagen.ArchInfo) {
 	arch.SoftFloat = buildcfg.GOARM == 5
 	arch.ZeroRange = zerorange
 	arch.Ginsnop = ginsnop
+	arch.Ginsnopdefer = ginsnop
 
 	arch.SSAMarkMoves = func(s *ssagen.State, b *ssa.Block) {}
 	arch.SSAGenValue = ssaGenValue

src/cmd/compile/internal/arm64/galign.go

@@ -18,6 +18,7 @@ func Init(arch *ssagen.ArchInfo) {
 	arch.PadFrame = padframe
 	arch.ZeroRange = zerorange
 	arch.Ginsnop = ginsnop
+	arch.Ginsnopdefer = ginsnop
 
 	arch.SSAMarkMoves = func(s *ssagen.State, b *ssa.Block) {}
 	arch.SSAGenValue = ssaGenValue

src/cmd/compile/internal/mips/galign.go

@@ -21,6 +21,7 @@ func Init(arch *ssagen.ArchInfo) {
 	arch.SoftFloat = (buildcfg.GOMIPS == "softfloat")
 	arch.ZeroRange = zerorange
 	arch.Ginsnop = ginsnop
+	arch.Ginsnopdefer = ginsnop
 	arch.SSAMarkMoves = func(s *ssagen.State, b *ssa.Block) {}
 	arch.SSAGenValue = ssaGenValue
 	arch.SSAGenBlock = ssaGenBlock

src/cmd/compile/internal/mips64/galign.go

@@ -21,6 +21,7 @@ func Init(arch *ssagen.ArchInfo) {
 	arch.SoftFloat = buildcfg.GOMIPS64 == "softfloat"
 	arch.ZeroRange = zerorange
 	arch.Ginsnop = ginsnop
+	arch.Ginsnopdefer = ginsnop
 
 	arch.SSAMarkMoves = func(s *ssagen.State, b *ssa.Block) {}
 	arch.SSAGenValue = ssaGenValue

src/cmd/compile/internal/ppc64/galign.go

@@ -20,6 +20,7 @@ func Init(arch *ssagen.ArchInfo) {
 
 	arch.ZeroRange = zerorange
 	arch.Ginsnop = ginsnop
+	arch.Ginsnopdefer = ginsnopdefer
 
 	arch.SSAMarkMoves = ssaMarkMoves
 	arch.SSAGenValue = ssaGenValue

src/cmd/compile/internal/ppc64/ggen.go

@@ -53,3 +53,30 @@ func ginsnop(pp *objw.Progs) *obj.Prog {
 	p.To.Reg = ppc64.REG_R0
 	return p
 }
+
+func ginsnopdefer(pp *objw.Progs) *obj.Prog {
+	// On PPC64 two nops are required in the defer case.
+	//
+	// (see gc/cgen.go, gc/plive.go -- copy of comment below)
+	//
+	// On ppc64, when compiling Go into position
+	// independent code on ppc64le we insert an
+	// instruction to reload the TOC pointer from the
+	// stack as well. See the long comment near
+	// jmpdefer in runtime/asm_ppc64.s for why.
+	// If the MOVD is not needed, insert a hardware NOP
+	// so that the same number of instructions are used
+	// on ppc64 in both shared and non-shared modes.
+
+	ginsnop(pp)
+	if base.Ctxt.Flag_shared {
+		p := pp.Prog(ppc64.AMOVD)
+		p.From.Type = obj.TYPE_MEM
+		p.From.Offset = 24
+		p.From.Reg = ppc64.REGSP
+		p.To.Type = obj.TYPE_REG
+		p.To.Reg = ppc64.REG_R2
+		return p
+	}
+	return ginsnop(pp)
+}

src/cmd/compile/internal/riscv64/galign.go

@@ -16,6 +16,7 @@ func Init(arch *ssagen.ArchInfo) {
 	arch.MAXWIDTH = 1 << 50
 
 	arch.Ginsnop = ginsnop
+	arch.Ginsnopdefer = ginsnop
 	arch.ZeroRange = zeroRange
 
 	arch.SSAMarkMoves = ssaMarkMoves

src/cmd/compile/internal/s390x/galign.go

@@ -16,6 +16,7 @@ func Init(arch *ssagen.ArchInfo) {
 
 	arch.ZeroRange = zerorange
 	arch.Ginsnop = ginsnop
+	arch.Ginsnopdefer = ginsnop
 
 	arch.SSAMarkMoves = ssaMarkMoves
 	arch.SSAGenValue = ssaGenValue

src/cmd/compile/internal/ssagen/arch.go

@@ -29,7 +29,8 @@ type ArchInfo struct {
 	// at function entry, and it is ok to clobber registers.
 	ZeroRange func(*objw.Progs, *obj.Prog, int64, int64, *uint32) *obj.Prog
 
-	Ginsnop func(*objw.Progs) *obj.Prog
+	Ginsnop      func(*objw.Progs) *obj.Prog
+	Ginsnopdefer func(*objw.Progs) *obj.Prog // special ginsnop for deferreturn
 
 	// SSAMarkMoves marks any MOVXconst ops that need to avoid clobbering flags.
 	SSAMarkMoves func(*State, *ssa.Block)

src/cmd/compile/internal/ssagen/ssa.go

@@ -7335,6 +7335,18 @@ func (s *State) PrepareCall(v *ssa.Value) {
 
 	call, ok := v.Aux.(*ssa.AuxCall)
 
+	if ok && call.Fn == ir.Syms.Deferreturn {
+		// Deferred calls will appear to be returning to
+		// the CALL deferreturn(SB) that we are about to emit.
+		// However, the stack trace code will show the line
+		// of the instruction byte before the return PC.
+		// To avoid that being an unrelated instruction,
+		// insert an actual hardware NOP that will have the right line number.
+		// This is different from obj.ANOP, which is a virtual no-op
+		// that doesn't make it into the instruction stream.
+		Arch.Ginsnopdefer(s.pp)
+	}
+
 	if ok {
 		// Record call graph information for nowritebarrierrec
 		// analysis.

src/cmd/compile/internal/wasm/ssa.go

@@ -24,6 +24,7 @@ func Init(arch *ssagen.ArchInfo) {
 
 	arch.ZeroRange = zeroRange
 	arch.Ginsnop = ginsnop
+	arch.Ginsnopdefer = ginsnop
 
 	arch.SSAMarkMoves = ssaMarkMoves
 	arch.SSAGenValue = ssaGenValue
@@ -125,11 +126,7 @@ func ssaGenValue(s *ssagen.State, v *ssa.Value) {
 	case ssa.OpWasmLoweredStaticCall, ssa.OpWasmLoweredClosureCall, ssa.OpWasmLoweredInterCall:
 		s.PrepareCall(v)
 		if call, ok := v.Aux.(*ssa.AuxCall); ok && call.Fn == ir.Syms.Deferreturn {
-			// The runtime needs to inject jumps to
-			// deferreturn calls using the address in
-			// _func.deferreturn. Hence, the call to
-			// deferreturn must itself be a resumption
-			// point so it gets a target PC.
+			// add a resume point before call to deferreturn so it can be called again via jmpdefer
 			s.Prog(wasm.ARESUMEPOINT)
 		}
 		if v.Op == ssa.OpWasmLoweredClosureCall {

src/cmd/compile/internal/x86/galign.go

@@ -34,6 +34,7 @@ func Init(arch *ssagen.ArchInfo) {
 
 	arch.ZeroRange = zerorange
 	arch.Ginsnop = ginsnop
+	arch.Ginsnopdefer = ginsnop
 
 	arch.SSAMarkMoves = ssaMarkMoves
 }

src/cmd/internal/obj/arm/asm5.go

@@ -355,10 +355,11 @@ var oprange [ALAST & obj.AMask][]Optab
 var xcmp [C_GOK + 1][C_GOK + 1]bool
 
 var (
-	symdiv  *obj.LSym
-	symdivu *obj.LSym
-	symmod  *obj.LSym
-	symmodu *obj.LSym
+	deferreturn *obj.LSym
+	symdiv      *obj.LSym
+	symdivu     *obj.LSym
+	symmod      *obj.LSym
+	symmodu     *obj.LSym
 )
 
 // Note about encoding: Prog.scond holds the condition encoding,
@@ -1218,6 +1219,8 @@ func buildop(ctxt *obj.Link) {
 		return
 	}
 
+	deferreturn = ctxt.LookupABI("runtime.deferreturn", obj.ABIInternal)
+
 	symdiv = ctxt.Lookup("runtime._div")
 	symdivu = ctxt.Lookup("runtime._divu")
 	symmod = ctxt.Lookup("runtime._mod")

src/cmd/internal/obj/wasm/wasmobj.go

@@ -129,6 +129,8 @@ var (
 	morestackNoCtxt *obj.LSym
 	gcWriteBarrier  *obj.LSym
 	sigpanic        *obj.LSym
+	deferreturn     *obj.LSym
+	jmpdefer        *obj.LSym
 )
 
 const (
@@ -141,6 +143,10 @@ func instinit(ctxt *obj.Link) {
 	morestackNoCtxt = ctxt.Lookup("runtime.morestack_noctxt")
 	gcWriteBarrier = ctxt.LookupABI("runtime.gcWriteBarrier", obj.ABIInternal)
 	sigpanic = ctxt.LookupABI("runtime.sigpanic", obj.ABIInternal)
+	deferreturn = ctxt.LookupABI("runtime.deferreturn", obj.ABIInternal)
+	// jmpdefer is defined in assembly as ABI0. The compiler will
+	// generate a direct ABI0 call from Go, so look for that.
+	jmpdefer = ctxt.LookupABI(`"".jmpdefer`, obj.ABI0)
 }
 
 func preprocess(ctxt *obj.Link, s *obj.LSym, newprog obj.ProgAlloc) {
@@ -417,6 +423,12 @@ func preprocess(ctxt *obj.Link, s *obj.LSym, newprog obj.ProgAlloc) {
 				pcAfterCall-- // sigpanic expects to be called without advancing the pc
 			}
 
+			// jmpdefer manipulates the return address on the stack so deferreturn gets called repeatedly.
+			// Model this in WebAssembly with a loop.
+			if call.To.Sym == deferreturn {
+				p = appendp(p, ALoop)
+			}
+
 			// SP -= 8
 			p = appendp(p, AGet, regAddr(REG_SP))
 			p = appendp(p, AI32Const, constAddr(8))
@@ -467,6 +479,15 @@ func preprocess(ctxt *obj.Link, s *obj.LSym, newprog obj.ProgAlloc) {
 				break
 			}
 
+			// jmpdefer removes the frame of deferreturn from the Go stack.
+			// However, its WebAssembly function still returns normally,
+			// so we need to return from deferreturn without removing its
+			// stack frame (no RET), because the frame is already gone.
+			if call.To.Sym == jmpdefer {
+				p = appendp(p, AReturn)
+				break
+			}
+
 			// return value of call is on the top of the stack, indicating whether to unwind the WebAssembly stack
 			if call.As == ACALLNORESUME && call.To.Sym != sigpanic { // sigpanic unwinds the stack, but it never resumes
 				// trying to unwind WebAssembly stack but call has no resume point, terminate with error
@@ -479,6 +500,21 @@ func preprocess(ctxt *obj.Link, s *obj.LSym, newprog obj.ProgAlloc) {
 				unwindExitBranches = append(unwindExitBranches, p)
 			}
 
+			// jump to before the call if jmpdefer has reset the return address to the call's PC
+			if call.To.Sym == deferreturn {
+				// get PC_B from -8(SP)
+				p = appendp(p, AGet, regAddr(REG_SP))
+				p = appendp(p, AI32Const, constAddr(8))
+				p = appendp(p, AI32Sub)
+				p = appendp(p, AI32Load16U, constAddr(0))
+				p = appendp(p, ATee, regAddr(REG_PC_B))
+
+				p = appendp(p, AI32Const, constAddr(call.Pc))
+				p = appendp(p, AI32Eq)
+				p = appendp(p, ABrIf, constAddr(0))
+				p = appendp(p, AEnd) // end of Loop
+			}
+
 		case obj.ARET, ARETUNWIND:
 			ret := *p
 			p.As = obj.ANOP

src/cmd/internal/obj/x86/asm6.go

@@ -43,6 +43,7 @@ import (
 
 var (
 	plan9privates *obj.LSym
+	deferreturn   *obj.LSym
 )
 
 // Instruction layout.

src/cmd/internal/objabi/funcid.go

@@ -34,6 +34,7 @@ const (
 	FuncID_gogo
 	FuncID_gopanic
 	FuncID_handleAsyncEvent
+	FuncID_jmpdefer
 	FuncID_mcall
 	FuncID_morestack
 	FuncID_mstart
@@ -59,6 +60,7 @@ var funcIDs = map[string]FuncID{
 	"gogo":             FuncID_gogo,
 	"gopanic":          FuncID_gopanic,
 	"handleAsyncEvent": FuncID_handleAsyncEvent,
+	"jmpdefer":         FuncID_jmpdefer,
 	"main":             FuncID_runtime_main,
 	"mcall":            FuncID_mcall,
 	"morestack":        FuncID_morestack,

src/cmd/link/internal/ld/pcln.go

@@ -129,10 +129,11 @@ func computeDeferReturn(ctxt *Link, deferReturnSym, s loader.Sym) uint32 {
 	for ri := 0; ri < relocs.Count(); ri++ {
 		r := relocs.At(ri)
 		if target.IsWasm() && r.Type() == objabi.R_ADDR {
-			// wasm/ssa.go generates an ARESUMEPOINT just
-			// before the deferreturn call. The "PC" of
-			// the deferreturn call is stored in the
-			// R_ADDR relocation on the ARESUMEPOINT.
+			// Wasm does not have a live variable set at the deferreturn
+			// call itself. Instead it has one identified by the
+			// resumption point immediately preceding the deferreturn.
+			// The wasm code has a R_ADDR relocation which is used to
+			// set the resumption point to PC_B.
 			lastWasmAddr = uint32(r.Add())
 		}
 		if r.Type().IsDirectCall() && (r.Sym() == deferReturnSym || ldr.IsDeferReturnTramp(r.Sym())) {

src/runtime/asm_386.s

@@ -582,6 +582,26 @@ TEXT ·publicationBarrier(SB),NOSPLIT,$0-0
 	// compile barrier.
 	RET
 
+// void jmpdefer(fn, sp);
+// called from deferreturn.
+// 1. pop the caller
+// 2. sub 5 bytes (the length of CALL & a 32 bit displacement) from the callers
+//    return (when building for shared libraries, subtract 16 bytes -- 5 bytes
+//    for CALL & displacement to call __x86.get_pc_thunk.cx, 6 bytes for the
+//    LEAL to load the offset into BX, and finally 5 for the call & displacement)
+// 3. jmp to the argument
+TEXT runtime·jmpdefer(SB), NOSPLIT, $0-8
+	MOVL	fv+0(FP), DX	// fn
+	MOVL	argp+4(FP), BX	// caller sp
+	LEAL	-4(BX), SP	// caller sp after CALL
+#ifdef GOBUILDMODE_shared
+	SUBL	$16, (SP)	// return to CALL again
+#else
+	SUBL	$5, (SP)	// return to CALL again
+#endif
+	MOVL	0(DX), BX
+	JMP	BX	// but first run the deferred function
+
 // Save state of caller into g->sched,
 // but using fake PC from systemstack_switch.
 // Must only be called from functions with no locals ($0)

src/runtime/asm_amd64.s

@@ -662,6 +662,21 @@ TEXT ·publicationBarrier(SB),NOSPLIT,$0-0
 	// compile barrier.
 	RET
 
+// func jmpdefer(fv func(), argp uintptr)
+// argp is a caller SP.
+// called from deferreturn.
+// 1. pop the caller
+// 2. sub 5 bytes from the callers return
+// 3. jmp to the argument
+TEXT runtime·jmpdefer(SB), NOSPLIT, $0-16
+	MOVQ	fv+0(FP), DX	// fn
+	MOVQ	argp+8(FP), BX	// caller sp
+	LEAQ	-8(BX), SP	// caller sp after CALL
+	MOVQ	-8(SP), BP	// restore BP as if deferreturn returned (harmless if framepointers not in use)
+	SUBQ	$5, (SP)	// return to CALL again
+	MOVQ	0(DX), BX
+	JMP	BX	// but first run the deferred function
+
 // Save state of caller into g->sched,
 // but using fake PC from systemstack_switch.
 // Must only be called from functions with no locals ($0)

src/runtime/asm_arm.s

@@ -506,6 +506,20 @@ CALLFN(·call268435456, 268435456)
 CALLFN(·call536870912, 536870912)
 CALLFN(·call1073741824, 1073741824)
 
+// void jmpdefer(fn, sp);
+// called from deferreturn.
+// 1. grab stored LR for caller
+// 2. sub 4 bytes to get back to BL deferreturn
+// 3. B to fn
+TEXT runtime·jmpdefer(SB),NOSPLIT,$0-8
+	MOVW	0(R13), LR
+	MOVW	$-4(LR), LR	// BL deferreturn
+	MOVW	fv+0(FP), R7
+	MOVW	argp+4(FP), R13
+	MOVW	$-4(R13), R13	// SP is 4 below argp, due to saved LR
+	MOVW	0(R7), R1
+	B	(R1)
+
 // Save state of caller into g->sched,
 // but using fake PC from systemstack_switch.
 // Must only be called from functions with no locals ($0)

src/runtime/asm_arm64.s

@@ -982,6 +982,23 @@ again:
 	CBNZ	R0, again
 	RET
 
+// void jmpdefer(fv, sp);
+// called from deferreturn.
+// 1. grab stored LR for caller
+// 2. sub 4 bytes to get back to BL deferreturn
+// 3. BR to fn
+TEXT runtime·jmpdefer(SB), NOSPLIT|NOFRAME, $0-16
+	MOVD	0(RSP), R0
+	SUB	$4, R0
+	MOVD	R0, LR
+
+	MOVD	fv+0(FP), R26
+	MOVD	argp+8(FP), R0
+	MOVD	R0, RSP
+	SUB	$8, RSP
+	MOVD	0(R26), R3
+	B	(R3)
+
 // Save state of caller into g->sched,
 // but using fake PC from systemstack_switch.
 // Must only be called from functions with no locals ($0)

src/runtime/asm_mips64x.s

@@ -384,6 +384,22 @@ CALLFN(·call1073741824, 1073741824)
 TEXT runtime·procyield(SB),NOSPLIT,$0-0
 	RET
 
+// void jmpdefer(fv, sp);
+// called from deferreturn.
+// 1. grab stored LR for caller
+// 2. sub 8 bytes to get back to JAL deferreturn
+// 3. JMP to fn
+TEXT runtime·jmpdefer(SB), NOSPLIT|NOFRAME, $0-16
+	MOVV	0(R29), R31
+	ADDV	$-8, R31
+
+	MOVV	fv+0(FP), REGCTXT
+	MOVV	argp+8(FP), R29
+	ADDV	$-8, R29
+	NOR	R0, R0	// prevent scheduling
+	MOVV	0(REGCTXT), R4
+	JMP	(R4)
+
 // Save state of caller into g->sched,
 // but using fake PC from systemstack_switch.
 // Must only be called from functions with no locals ($0)

src/runtime/asm_mipsx.s

@@ -382,6 +382,22 @@ CALLFN(·call1073741824, 1073741824)
 TEXT runtime·procyield(SB),NOSPLIT,$0-4
 	RET
 
+// void jmpdefer(fv, sp);
+// called from deferreturn.
+// 1. grab stored LR for caller
+// 2. sub 8 bytes to get back to JAL deferreturn
+// 3. JMP to fn
+TEXT runtime·jmpdefer(SB),NOSPLIT,$0-8
+	MOVW	0(R29), R31
+	ADDU	$-8, R31
+
+	MOVW	fv+0(FP), REGCTXT
+	MOVW	argp+4(FP), R29
+	ADDU	$-4, R29
+	NOR	R0, R0	// prevent scheduling
+	MOVW	0(REGCTXT), R4
+	JMP	(R4)
+
 // Save state of caller into g->sched,
 // but using fake PC from systemstack_switch.
 // Must only be called from functions with no locals ($0)

src/runtime/asm_ppc64x.s

@@ -503,6 +503,34 @@ again:
 	OR	R6, R6, R6	// Set PPR priority back to medium-low
 	RET
 
+// void jmpdefer(fv, sp);
+// called from deferreturn.
+// 1. grab stored LR for caller
+// 2. sub 8 bytes to get back to either nop or toc reload before deferreturn
+// 3. BR to fn
+// When dynamically linking Go, it is not sufficient to rewind to the BL
+// deferreturn -- we might be jumping between modules and so we need to reset
+// the TOC pointer in r2. To do this, codegen inserts MOVD 24(R1), R2 *before*
+// the BL deferreturn and jmpdefer rewinds to that.
+TEXT runtime·jmpdefer(SB), NOSPLIT|NOFRAME, $0-16
+	MOVD	0(R1), R31
+	SUB     $8, R31
+	MOVD	R31, LR
+
+	MOVD	fv+0(FP), R11
+	MOVD	argp+8(FP), R1
+	SUB	$FIXED_FRAME, R1
+#ifdef GOOS_aix
+	// AIX won't trigger a SIGSEGV if R11 = nil
+	// So it manually triggers it
+	CMP	R0, R11
+	BNE	2(PC)
+	MOVD	R0, 0(R0)
+#endif
+	MOVD	0(R11), R12
+	MOVD	R12, CTR
+	BR	(CTR)
+
 // Save state of caller into g->sched,
 // but using fake PC from systemstack_switch.
 // Must only be called from functions with no locals ($0)

src/runtime/asm_riscv64.s

@@ -248,6 +248,21 @@ TEXT gogo<>(SB), NOSPLIT|NOFRAME, $0
 	MOV	gobuf_pc(T0), T0
 	JALR	ZERO, T0
 
+// func jmpdefer(fv func(), argp uintptr)
+// called from deferreturn
+// 1. grab stored return address from the caller's frame
+// 2. sub 8 bytes to get back to JAL deferreturn
+// 3. JMP to fn
+TEXT runtime·jmpdefer(SB), NOSPLIT|NOFRAME, $0-16
+	MOV	0(X2), RA
+	ADD	$-8, RA
+
+	MOV	fv+0(FP), CTXT
+	MOV	argp+8(FP), X2
+	ADD	$-8, X2
+	MOV	0(CTXT), T0
+	JALR	ZERO, T0
+
 // func procyield(cycles uint32)
 TEXT runtime·procyield(SB),NOSPLIT,$0-0
 	RET

src/runtime/asm_s390x.s

@@ -480,6 +480,21 @@ TEXT callfnMVC<>(SB),NOSPLIT|NOFRAME,$0-0
 TEXT runtime·procyield(SB),NOSPLIT,$0-0
 	RET
 
+// void jmpdefer(fv, sp);
+// called from deferreturn.
+// 1. grab stored LR for caller
+// 2. sub 6 bytes to get back to BL deferreturn (size of BRASL instruction)
+// 3. BR to fn
+TEXT runtime·jmpdefer(SB),NOSPLIT|NOFRAME,$0-16
+	MOVD	0(R15), R1
+	SUB	$6, R1, LR
+
+	MOVD	fv+0(FP), R12
+	MOVD	argp+8(FP), R15
+	SUB	$8, R15
+	MOVD	0(R12), R3
+	BR	(R3)
+
 // Save state of caller into g->sched,
 // but using fake PC from systemstack_switch.
 // Must only be called from functions with no locals ($0)

src/runtime/asm_wasm.s

@@ -193,6 +193,35 @@ TEXT runtime·return0(SB), NOSPLIT, $0-0
 	MOVD $0, RET0
 	RET
 
+TEXT runtime·jmpdefer(SB), NOSPLIT, $0-16
+	MOVD fv+0(FP), CTXT
+
+	Get CTXT
+	I64Eqz
+	If
+		CALLNORESUME runtime·sigpanic<ABIInternal>(SB)
+	End
+
+	// caller sp after CALL
+	I64Load argp+8(FP)
+	I64Const $8
+	I64Sub
+	I32WrapI64
+	Set SP
+
+	// decrease PC_B by 1 to CALL again
+	Get SP
+	I32Load16U (SP)
+	I32Const $1
+	I32Sub
+	I32Store16 $0
+
+	// but first run the deferred function
+	Get CTXT
+	I32WrapI64
+	I64Load $0
+	JMP
+
 TEXT runtime·asminit(SB), NOSPLIT, $0-0
 	// No per-thread init.
 	RET

src/runtime/panic.go

@@ -396,39 +396,47 @@ func freedeferfn() {
 	throw("freedefer with d.fn != nil")
 }
 
-// deferreturn runs deferred functions for the caller's frame.
+// Run a deferred function if there is one.
 // The compiler inserts a call to this at the end of any
 // function which calls defer.
+// If there is a deferred function, this will call runtime·jmpdefer,
+// which will jump to the deferred function such that it appears
+// to have been called by the caller of deferreturn at the point
+// just before deferreturn was called. The effect is that deferreturn
+// is called again and again until there are no more deferred functions.
 func deferreturn() {
 	gp := getg()
-	for {
-		d := gp._defer
-		if d == nil {
-			return
+	d := gp._defer
+	if d == nil {
+		return
+	}
+	sp := getcallersp()
+	if d.sp != sp {
+		return
+	}
+	if d.openDefer {
+		done := runOpenDeferFrame(gp, d)
+		if !done {
+			throw("unfinished open-coded defers in deferreturn")
 		}
-		sp := getcallersp()
-		if d.sp != sp {
-			return
-		}
-		if d.openDefer {
-			done := runOpenDeferFrame(gp, d)
-			if !done {
-				throw("unfinished open-coded defers in deferreturn")
-			}
-			gp._defer = d.link
-			freedefer(d)
-			// If this frame uses open defers, then this
-			// must be the only defer record for the
-			// frame, so we can just return.
-			return
-		}
-
-		fn := d.fn
-		d.fn = nil
 		gp._defer = d.link
 		freedefer(d)
-		fn()
+		return
 	}
+
+	fn := d.fn
+	d.fn = nil
+	gp._defer = d.link
+	freedefer(d)
+	// If the defer function pointer is nil, force the seg fault to happen
+	// here rather than in jmpdefer. gentraceback() throws an error if it is
+	// called with a callback on an LR architecture and jmpdefer is on the
+	// stack, because jmpdefer manipulates SP (see issue #8153).
+	_ = **(**funcval)(unsafe.Pointer(&fn))
+	// We must not split the stack between computing argp and
+	// calling jmpdefer because argp is a uintptr stack pointer.
+	argp := getcallersp() + sys.MinFrameSize
+	jmpdefer(fn, argp)
 }
 
 // Goexit terminates the goroutine that calls it. No other goroutine is affected.

src/runtime/stubs.go

@@ -176,6 +176,8 @@ func cgocallback(fn, frame, ctxt uintptr)
 
 func gogo(buf *gobuf)
 
+//go:noescape
+func jmpdefer(fv func(), argp uintptr)
 func asminit()
 func setg(gg *g)
 func breakpoint()

src/runtime/symtab.go

@@ -331,6 +331,7 @@ const (
 	funcID_gogo
 	funcID_gopanic
 	funcID_handleAsyncEvent
+	funcID_jmpdefer
 	funcID_mcall
 	funcID_morestack
 	funcID_mstart