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 a3b2904..e6d6695 100644
--- a/src/cmd/compile/internal/ssa/gen/AMD64Ops.go
+++ b/src/cmd/compile/internal/ssa/gen/AMD64Ops.go
@@ -748,6 +748,7 @@
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 @@
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 b402e35..2424e67 100644
--- a/src/cmd/compile/internal/ssa/gen/ARM64Ops.go
+++ b/src/cmd/compile/internal/ssa/gen/ARM64Ops.go
@@ -507,6 +507,7 @@
clobbers: buildReg("R20 R30"),
},
faultOnNilArg0: true,
+ unsafePoint: true, // FP maintenance around DUFFZERO can be clobbered by interrupts
},
// large zeroing
@@ -547,6 +548,7 @@
},
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 9efa1bf..408c855 100644
--- a/src/cmd/compile/internal/ssa/opGen.go
+++ b/src/cmd/compile/internal/ssa/opGen.go
@@ -13119,6 +13119,7 @@
auxType: auxInt64,
argLen: 3,
faultOnNilArg0: true,
+ unsafePoint: true,
reg: regInfo{
inputs: []inputInfo{
{0, 128}, // DI
@@ -13196,6 +13197,7 @@
clobberFlags: true,
faultOnNilArg0: true,
faultOnNilArg1: true,
+ unsafePoint: true,
reg: regInfo{
inputs: []inputInfo{
{0, 128}, // DI
@@ -20734,6 +20736,7 @@
auxType: auxInt64,
argLen: 2,
faultOnNilArg0: true,
+ unsafePoint: true,
reg: regInfo{
inputs: []inputInfo{
{0, 1048576}, // R20
@@ -20760,6 +20763,7 @@
argLen: 3,
faultOnNilArg0: true,
faultOnNilArg1: true,
+ unsafePoint: true,
reg: regInfo{
inputs: []inputInfo{
{0, 2097152}, // R21
