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runtime/internal/atomic: panic nicely on unaligned 64-bit atomics

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On 386 and arm, unaligned 64-bit atomics aren't safe, so we check for
this and panic. Currently, we panic by dereferencing nil, which may be
expedient but is pretty user-hostile since it gives no hint of what
the actual problem was.

This CL replaces this with an actual panic. The only subtlety here is
now the atomic assembly implementations are calling back into Go, so
they have to play nicely with stack maps and stack scanning. On 386,
this just requires declaring NO_LOCAL_POINTERS. On arm, this is
somewhat more complicated: first, we have to move the alignment check
into the functions that have Go signatures. Then we have to support
both the tail call from these functions to the underlying
implementation (which requires that they have no frame) and the call
into Go to panic (which requires that they have a frame). We resolve
this by forcing them to have no frame and setting up the frame
manually just before the panic call.

Change-Id: I19f1e860045df64088013db37a18acea47342c69
Reviewed-on: https://go-review.googlesource.com/c/go/+/262778
Trust: Austin Clements <austin@google.com>
Run-TryBot: Austin Clements <austin@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Cherry Zhang <cherryyz@google.com>
Reviewed-by: Michael Knyszek <mknyszek@google.com>
This commit is contained in:
Austin Clements 2020-10-15 15:52:58 -04:00
parent afba990169
commit 83317d9e3c
6 changed files with 96 additions and 39 deletions
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17
src/runtime/internal/atomic/asm_386.s
View File

@ -3,6 +3,7 @@
// license that can be found in the LICENSE file.
#include "textflag.h"
#include "funcdata.h"
// bool Cas(int32 *val, int32 old, int32 new)
// Atomically:
@ -44,7 +45,6 @@ TEXT ·Loadint64(SB), NOSPLIT, $0-12
TEXT ·Xaddint64(SB), NOSPLIT, $0-20
JMP ·Xadd64(SB)
// bool ·Cas64(uint64 *val, uint64 old, uint64 new)
// Atomically:
// if(*val == *old){
@ -54,10 +54,11 @@ TEXT ·Xaddint64(SB), NOSPLIT, $0-20
// return 0;
// }
TEXT ·Cas64(SB), NOSPLIT, $0-21
NO_LOCAL_POINTERS
MOVL ptr+0(FP), BP
TESTL $7, BP
JZ 2(PC)
MOVL 0, BP // crash with nil ptr deref
CALL ·panicUnaligned(SB)
MOVL old_lo+4(FP), AX
MOVL old_hi+8(FP), DX
MOVL new_lo+12(FP), BX
@ -98,11 +99,12 @@ TEXT ·Xadd(SB), NOSPLIT, $0-12
RET
TEXT ·Xadd64(SB), NOSPLIT, $0-20
NO_LOCAL_POINTERS
// no XADDQ so use CMPXCHG8B loop
MOVL ptr+0(FP), BP
TESTL $7, BP
JZ 2(PC)
MOVL 0, AX // crash when unaligned
CALL ·panicUnaligned(SB)
// DI:SI = delta
MOVL delta_lo+4(FP), SI
MOVL delta_hi+8(FP), DI
@ -144,11 +146,12 @@ TEXT ·Xchguintptr(SB), NOSPLIT, $0-12
JMP ·Xchg(SB)
TEXT ·Xchg64(SB),NOSPLIT,$0-20
NO_LOCAL_POINTERS
// no XCHGQ so use CMPXCHG8B loop
MOVL ptr+0(FP), BP
TESTL $7, BP
JZ 2(PC)
MOVL 0, AX // crash when unaligned
CALL ·panicUnaligned(SB)
// CX:BX = new
MOVL new_lo+4(FP), BX
MOVL new_hi+8(FP), CX
@ -188,10 +191,11 @@ TEXT ·StoreRel(SB), NOSPLIT, $0-8
// uint64 atomicload64(uint64 volatile* addr);
TEXT ·Load64(SB), NOSPLIT, $0-12
NO_LOCAL_POINTERS
MOVL ptr+0(FP), AX
TESTL $7, AX
JZ 2(PC)
MOVL 0, AX // crash with nil ptr deref
CALL ·panicUnaligned(SB)
MOVQ (AX), M0
MOVQ M0, ret+4(FP)
EMMS
@ -199,10 +203,11 @@ TEXT ·Load64(SB), NOSPLIT, $0-12
// void ·Store64(uint64 volatile* addr, uint64 v);
TEXT ·Store64(SB), NOSPLIT, $0-12
NO_LOCAL_POINTERS
MOVL ptr+0(FP), AX
TESTL $7, AX
JZ 2(PC)
MOVL 0, AX // crash with nil ptr deref
CALL ·panicUnaligned(SB)
// MOVQ and EMMS were introduced on the Pentium MMX.
MOVQ val+4(FP), M0
MOVQ M0, (AX)

89
src/runtime/internal/atomic/asm_arm.s
View File

@ -3,6 +3,7 @@
// license that can be found in the LICENSE file.
#include "textflag.h"
#include "funcdata.h"
// bool armcas(int32 *val, int32 old, int32 new)
// Atomically:
@ -96,11 +97,7 @@ TEXT ·Xaddint64(SB),NOSPLIT,$0-20
// atomics with locks.
TEXT armCas64<>(SB),NOSPLIT,$0-21
MOVW addr+0(FP), R1
// make unaligned atomic access panic
AND.S $7, R1, R2
BEQ 2(PC)
MOVW R2, (R2) // crash. AND.S above left only low 3 bits in R2.
// addr is already in R1
MOVW old_lo+4(FP), R2
MOVW old_hi+8(FP), R3
MOVW new_lo+12(FP), R4
@ -129,11 +126,7 @@ cas64fail:
RET
TEXT armXadd64<>(SB),NOSPLIT,$0-20
MOVW addr+0(FP), R1
// make unaligned atomic access panic
AND.S $7, R1, R2
BEQ 2(PC)
MOVW R2, (R2) // crash. AND.S above left only low 3 bits in R2.
// addr is already in R1
MOVW delta_lo+4(FP), R2
MOVW delta_hi+8(FP), R3
@ -155,11 +148,7 @@ add64loop:
RET
TEXT armXchg64<>(SB),NOSPLIT,$0-20
MOVW addr+0(FP), R1
// make unaligned atomic access panic
AND.S $7, R1, R2
BEQ 2(PC)
MOVW R2, (R2) // crash. AND.S above left only low 3 bits in R2.
// addr is already in R1
MOVW new_lo+4(FP), R2
MOVW new_hi+8(FP), R3
@ -179,11 +168,7 @@ swap64loop:
RET
TEXT armLoad64<>(SB),NOSPLIT,$0-12
MOVW addr+0(FP), R1
// make unaligned atomic access panic
AND.S $7, R1, R2
BEQ 2(PC)
MOVW R2, (R2) // crash. AND.S above left only low 3 bits in R2.
// addr is already in R1
LDREXD (R1), R2 // loads R2 and R3
DMB MB_ISH
@ -193,11 +178,7 @@ TEXT armLoad64<>(SB),NOSPLIT,$0-12
RET
TEXT armStore64<>(SB),NOSPLIT,$0-12
MOVW addr+0(FP), R1
// make unaligned atomic access panic
AND.S $7, R1, R2
BEQ 2(PC)
MOVW R2, (R2) // crash. AND.S above left only low 3 bits in R2.
// addr is already in R1
MOVW val_lo+4(FP), R2
MOVW val_hi+8(FP), R3
@ -213,35 +194,83 @@ store64loop:
DMB MB_ISH
RET
TEXT ·Cas64(SB),NOSPLIT,$0-21
// The following functions all panic if their address argument isn't
// 8-byte aligned. Since we're calling back into Go code to do this,
// we have to cooperate with stack unwinding. In the normal case, the
// functions tail-call into the appropriate implementation, which
// means they must not open a frame. Hence, when they go down the
// panic path, at that point they push the LR to create a real frame
// (they don't need to pop it because panic won't return).
TEXT ·Cas64(SB),NOSPLIT,$-4-21
NO_LOCAL_POINTERS
MOVW addr+0(FP), R1
// make unaligned atomic access panic
AND.S $7, R1, R2
BEQ 3(PC)
MOVW.W R14, -4(R13) // prepare a real frame
BL ·panicUnaligned(SB)
MOVB runtime·goarm(SB), R11
CMP $7, R11
BLT 2(PC)
JMP armCas64<>(SB)
JMP ·goCas64(SB)
TEXT ·Xadd64(SB),NOSPLIT,$0-20
TEXT ·Xadd64(SB),NOSPLIT,$-4-20
NO_LOCAL_POINTERS
MOVW addr+0(FP), R1
// make unaligned atomic access panic
AND.S $7, R1, R2
BEQ 3(PC)
MOVW.W R14, -4(R13) // prepare a real frame
BL ·panicUnaligned(SB)
MOVB runtime·goarm(SB), R11
CMP $7, R11
BLT 2(PC)
JMP armXadd64<>(SB)
JMP ·goXadd64(SB)
TEXT ·Xchg64(SB),NOSPLIT,$0-20
TEXT ·Xchg64(SB),NOSPLIT,$-4-20
NO_LOCAL_POINTERS
MOVW addr+0(FP), R1
// make unaligned atomic access panic
AND.S $7, R1, R2
BEQ 3(PC)
MOVW.W R14, -4(R13) // prepare a real frame
BL ·panicUnaligned(SB)
MOVB runtime·goarm(SB), R11
CMP $7, R11
BLT 2(PC)
JMP armXchg64<>(SB)
JMP ·goXchg64(SB)
TEXT ·Load64(SB),NOSPLIT,$0-12
TEXT ·Load64(SB),NOSPLIT,$-4-12
NO_LOCAL_POINTERS
MOVW addr+0(FP), R1
// make unaligned atomic access panic
AND.S $7, R1, R2
BEQ 3(PC)
MOVW.W R14, -4(R13) // prepare a real frame
BL ·panicUnaligned(SB)
MOVB runtime·goarm(SB), R11
CMP $7, R11
BLT 2(PC)
JMP armLoad64<>(SB)
JMP ·goLoad64(SB)
TEXT ·Store64(SB),NOSPLIT,$0-12
TEXT ·Store64(SB),NOSPLIT,$-4-12
NO_LOCAL_POINTERS
MOVW addr+0(FP), R1
// make unaligned atomic access panic
AND.S $7, R1, R2
BEQ 3(PC)
MOVW.W R14, -4(R13) // prepare a real frame
BL ·panicUnaligned(SB)
MOVB runtime·goarm(SB), R11
CMP $7, R11
BLT 2(PC)

2
src/runtime/internal/atomic/atomic_mipsx.go
View File

@ -34,7 +34,7 @@ func spinUnlock(state *uint32)
func lockAndCheck(addr *uint64) {
// ensure 8-byte alignment
if uintptr(unsafe.Pointer(addr))&7 != 0 {
addr = nil
panicUnaligned()
}
// force dereference before taking lock
_ = *addr

9
src/runtime/internal/atomic/atomic_test.go
View File

@ -73,8 +73,15 @@ func TestXadduintptrOnUint64(t *testing.T) {
func shouldPanic(t *testing.T, name string, f func()) {
defer func() {
if recover() == nil {
// Check that all GC maps are sane.
runtime.GC()
err := recover()
want := "unaligned 64-bit atomic operation"
if err == nil {
t.Errorf("%s did not panic", name)
} else if s, _ := err.(string); s != want {
t.Errorf("%s: wanted panic %q, got %q", name, want, err)
}
}()
f()

9
src/runtime/internal/atomic/unaligned.go Normal file
View File

@ -0,0 +1,9 @@
// Copyright 2020 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package atomic
func panicUnaligned() {
panic("unaligned 64-bit atomic operation")
}

9
src/sync/atomic/atomic_test.go
View File

@ -1397,8 +1397,15 @@ func TestStoreLoadRelAcq64(t *testing.T) {
func shouldPanic(t *testing.T, name string, f func()) {
defer func() {
if recover() == nil {
// Check that all GC maps are sane.
runtime.GC()
err := recover()
want := "unaligned 64-bit atomic operation"
if err == nil {
t.Errorf("%s did not panic", name)
} else if s, _ := err.(string); s != want {
t.Errorf("%s: wanted panic %q, got %q", name, want, err)
}
}()
f()