cmd/compile: mark DUFFZERO/DUFFCOPY as async unsafe

These operations are async unsafe on architectures that use
frame pointers.

The reason is they rely on data being safe when stored below the stack
pointer. They do:

  45da69:       48 89 6c 24 f0          mov    %rbp,-0x10(%rsp)
  45da6e:       48 8d 6c 24 f0          lea    -0x10(%rsp),%rbp
  45da73:       e8 7d d0 ff ff          callq  45aaf5 <runtime.duffzero+0x115>
  45da78:       48 8b 6d 00             mov    0x0(%rbp),%rbp

This dance ensures that inside duffzero, it looks like there is a
proper frame pointer set up, so that stack walkbacks work correctly if
the kernel samples during duffzero.

However, this instruction sequence depends on data not being clobbered
even though it is below the stack pointer.

If there is an async interrupt at any of those last 3 instructions,
and the interrupt decides to insert a call to asyncPreempt, then the
saved frame pointer on the stack gets clobbered. The last instruction
above then restores junk to the frame pointer.

To prevent this, mark these instructions as async unsafe.

(The body of duffzero is already async unsafe, as it is in package runtime.)

Change-Id: I5562e82f9f5bd2fb543dcf2b6b9133d87ff83032
Reviewed-on: https://go-review.googlesource.com/c/go/+/248261
Run-TryBot: Keith Randall <khr@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Martin Möhrmann <moehrmann@google.com>
Reviewed-by: Cherry Zhang <cherryyz@google.com>

diff --git a/src/cmd/compile/internal/ssa/gen/AMD64Ops.go b/src/cmd/compile/internal/ssa/gen/AMD64Ops.go
index a3b29049df667277d3b4b8cf1ce5a3d9cf187839..e6d66957ddd5f761e38397870aec49ec0545cccf 100644 (file)
--- a/src/cmd/compile/internal/ssa/gen/AMD64Ops.go
+++ b/src/cmd/compile/internal/ssa/gen/AMD64Ops.go
@@ -748,6 +748,7 @@ func init() {
                                clobbers: buildReg("DI"),
                        },
                        faultOnNilArg0: true,
+                       unsafePoint:    true, // FP maintenance around DUFFCOPY can be clobbered by interrupts
                },
                {name: "MOVOconst", reg: regInfo{nil, 0, []regMask{fp}}, typ: "Int128", aux: "Int128", rematerializeable: true},
 
@@ -786,6 +787,7 @@ func init() {
                        clobberFlags:   true,
                        faultOnNilArg0: true,
                        faultOnNilArg1: true,
+                       unsafePoint:    true, // FP maintenance around DUFFCOPY can be clobbered by interrupts
                },
 
                // arg0 = destination pointer

diff --git a/src/cmd/compile/internal/ssa/gen/ARM64Ops.go b/src/cmd/compile/internal/ssa/gen/ARM64Ops.go
index b402e35ea6f86ac05ba112ccfbbb7e7a751c8208..2424e67e201dabefedf1bdc1bac63fe4b2dcc94f 100644 (file)
--- a/src/cmd/compile/internal/ssa/gen/ARM64Ops.go
+++ b/src/cmd/compile/internal/ssa/gen/ARM64Ops.go
@@ -507,6 +507,7 @@ func init() {
                                clobbers: buildReg("R20 R30"),
                        },
                        faultOnNilArg0: true,
+                       unsafePoint:    true, // FP maintenance around DUFFZERO can be clobbered by interrupts
                },
 
                // large zeroing
@@ -547,6 +548,7 @@ func init() {
                        },
                        faultOnNilArg0: true,
                        faultOnNilArg1: true,
+                       unsafePoint:    true, // FP maintenance around DUFFCOPY can be clobbered by interrupts
                },
 
                // large move

diff --git a/src/cmd/compile/internal/ssa/opGen.go b/src/cmd/compile/internal/ssa/opGen.go
index 9efa1bfcc4bdc4bc8dd922433f80d44421763aac..408c855dbdd5f1aa4e39f509e07d0fea060c9887 100644 (file)
--- a/src/cmd/compile/internal/ssa/opGen.go
+++ b/src/cmd/compile/internal/ssa/opGen.go
@@ -13119,6 +13119,7 @@ var opcodeTable = [...]opInfo{
                auxType:        auxInt64,
                argLen:         3,
                faultOnNilArg0: true,
+               unsafePoint:    true,
                reg: regInfo{
                        inputs: []inputInfo{
                                {0, 128},   // DI
@@ -13196,6 +13197,7 @@ var opcodeTable = [...]opInfo{
                clobberFlags:   true,
                faultOnNilArg0: true,
                faultOnNilArg1: true,
+               unsafePoint:    true,
                reg: regInfo{
                        inputs: []inputInfo{
                                {0, 128}, // DI
@@ -20734,6 +20736,7 @@ var opcodeTable = [...]opInfo{
                auxType:        auxInt64,
                argLen:         2,
                faultOnNilArg0: true,
+               unsafePoint:    true,
                reg: regInfo{
                        inputs: []inputInfo{
                                {0, 1048576}, // R20
@@ -20760,6 +20763,7 @@ var opcodeTable = [...]opInfo{
                argLen:         3,
                faultOnNilArg0: true,
                faultOnNilArg1: true,
+               unsafePoint:    true,
                reg: regInfo{
                        inputs: []inputInfo{
                                {0, 2097152}, // R21