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cmd/compile: fix nilcheck for AIX 

This commit adapts compile tool to create correct nilchecks for AIX.

AIX allows to load a nil pointer. Therefore, the default nilcheck
which issues a load must be replaced by a CMP instruction followed by a
store at 0x0 if the value is nil. The store will trigger a SIGSEGV as on
others OS.

The nilcheck algorithm must be adapted to do not remove nilcheck if it's
only a read. Stores are detected with v.Type.IsMemory().

Tests related to nilptr must be adapted to the previous changements.
nilptr.go cannot be used as it's because the AIX address space starts at
1<<32.

Change-Id: I9f5aaf0b7e185d736a9b119c0ed2fe4e5bd1e7af
Reviewed-on: https://go-review.googlesource.com/c/144538
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>
This commit is contained in:
Clément Chigot 2018-10-16 15:59:43 +02:00 committed by Lynn Boger
parent 041526c6ef
commit 9fe9853ae5
10 changed files with 337 additions and 300 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

3
src/cmd/compile/internal/gc/ssa.go
View File

@ -3651,7 +3651,8 @@ func (s *state) call(n *Node, k callKind) *ssa.Value {
break
}
closure = s.expr(fn)
if thearch.LinkArch.Family == sys.Wasm {
if thearch.LinkArch.Family == sys.Wasm || objabi.GOOS == "aix" && k != callGo {
// On AIX, the closure needs to be verified as fn can be nil, except if it's a call go. This needs to be handled by the runtime to have the "go of nil func value" error.
// TODO(neelance): On other architectures this should be eliminated by the optimization steps
s.nilCheck(closure)
}

46
src/cmd/compile/internal/ppc64/ssa.go
View File

@ -10,6 +10,7 @@ import (
"cmd/compile/internal/types"
"cmd/internal/obj"
"cmd/internal/obj/ppc64"
"cmd/internal/objabi"
"math"
"strings"
)
@ -1183,13 +1184,44 @@ func ssaGenValue(s *gc.SSAGenState, v *ssa.Value) {
p.To.Sym = v.Aux.(*obj.LSym)
case ssa.OpPPC64LoweredNilCheck:
// Issue a load which will fault if arg is nil.
p := s.Prog(ppc64.AMOVBZ)
p.From.Type = obj.TYPE_MEM
p.From.Reg = v.Args[0].Reg()
gc.AddAux(&p.From, v)
p.To.Type = obj.TYPE_REG
p.To.Reg = ppc64.REGTMP
if objabi.GOOS == "aix" {
// CMP Rarg0, R0
// BNE 2(PC)
// STW R0, 0(R0)
// NOP (so the BNE has somewhere to land)
// CMP Rarg0, R0
p := s.Prog(ppc64.ACMP)
p.From.Type = obj.TYPE_REG
p.From.Reg = v.Args[0].Reg()
p.To.Type = obj.TYPE_REG
p.To.Reg = ppc64.REG_R0
// BNE 2(PC)
p2 := s.Prog(ppc64.ABNE)
p2.To.Type = obj.TYPE_BRANCH
// STW R0, 0(R0)
// Write at 0 is forbidden and will trigger a SIGSEGV
p = s.Prog(ppc64.AMOVW)
p.From.Type = obj.TYPE_REG
p.From.Reg = ppc64.REG_R0
p.To.Type = obj.TYPE_MEM
p.To.Reg = ppc64.REG_R0
// NOP (so the BNE has somewhere to land)
nop := s.Prog(obj.ANOP)
gc.Patch(p2, nop)
} else {
// Issue a load which will fault if arg is nil.
p := s.Prog(ppc64.AMOVBZ)
p.From.Type = obj.TYPE_MEM
p.From.Reg = v.Args[0].Reg()
gc.AddAux(&p.From, v)
p.To.Type = obj.TYPE_REG
p.To.Reg = ppc64.REGTMP
}
if gc.Debug_checknil != 0 && v.Pos.Line() > 1 { // v.Pos.Line()==1 in generated wrappers
gc.Warnl(v.Pos, "generated nil check")
}

12
src/cmd/compile/internal/ssa/nilcheck.go
View File

@ -5,6 +5,7 @@
package ssa
import (
"cmd/internal/objabi"
"cmd/internal/src"
)
@ -183,6 +184,9 @@ func nilcheckelim(f *Func) {
// This should agree with minLegalPointer in the runtime.
const minZeroPage = 4096
// faultOnLoad is true if a load to an address below minZeroPage will trigger a SIGSEGV.
var faultOnLoad = objabi.GOOS != "aix"
// nilcheckelim2 eliminates unnecessary nil checks.
// Runs after lowering and scheduling.
func nilcheckelim2(f *Func) {
@ -225,12 +229,16 @@ func nilcheckelim2(f *Func) {
// Find any pointers that this op is guaranteed to fault on if nil.
var ptrstore [2]*Value
ptrs := ptrstore[:0]
if opcodeTable[v.Op].faultOnNilArg0 {
if opcodeTable[v.Op].faultOnNilArg0 && (faultOnLoad || v.Type.IsMemory()) {
// On AIX, only writing will fault.
ptrs = append(ptrs, v.Args[0])
}
if opcodeTable[v.Op].faultOnNilArg1 {
if opcodeTable[v.Op].faultOnNilArg1 && (faultOnLoad || (v.Type.IsMemory() && v.Op != OpPPC64LoweredMove)) {
// On AIX, only writing will fault.
// LoweredMove is a special case because it's considered as a "mem" as it stores on arg0 but arg1 is accessed as a load and should be checked.
ptrs = append(ptrs, v.Args[1])
}
for _, ptr := range ptrs {
// Check to make sure the offset is small.
switch opcodeTable[v.Op].auxType {

3
test/nilptr.go
View File

@ -7,6 +7,9 @@
// Test that the implementation catches nil ptr indirection
// in a large address space.
// +build !aix
// Address space starts at 1<<32 on AIX, so dummy is too far.
package main
import "unsafe"

21
test/nilptr3.go
View File

@ -1,6 +1,7 @@
// errorcheck -0 -d=nil
// +build !wasm
// +build !aix
// Copyright 2013 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
@ -192,21 +193,6 @@ func f4(x *[10]int) {
_ = &x[9] // ERROR "removed[a-z ]* nil check"
}
func f5(p *float32, q *float64, r *float32, s *float64) float64 {
x := float64(*p) // ERROR "removed nil check"
y := *q // ERROR "removed nil check"
*r = 7 // ERROR "removed nil check"
*s = 9 // ERROR "removed nil check"
return x + y
}
type T [29]byte
func f6(p, q *T) {
x := *p // ERROR "removed nil check"
*q = x // ERROR "removed nil check"
}
func m1(m map[int][80]byte) byte {
v := m[3] // ERROR "removed nil check"
return v[5]
@ -257,11 +243,6 @@ func f7() (*Struct, float64) {
return t, *p // ERROR "removed nil check"
}
// make sure to remove nil check for memory move (issue #18003)
func f8(t *[8]int) [8]int {
return *t // ERROR "removed nil check"
}
func f9() []int {
x := new([1]int)
x[0] = 1 // ERROR "removed nil check"

270
test/nilptr3_wasm.go
View File

@ -1,270 +0,0 @@
// errorcheck -0 -d=nil
// +build wasm
// Copyright 2013 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.
// Test that nil checks are removed.
// Optimization is enabled.
package p
type Struct struct {
X int
Y float64
}
type BigStruct struct {
X int
Y float64
A [1 << 20]int
Z string
}
type Empty struct {
}
type Empty1 struct {
Empty
}
var (
intp *int
arrayp *[10]int
array0p *[0]int
bigarrayp *[1 << 26]int
structp *Struct
bigstructp *BigStruct
emptyp *Empty
empty1p *Empty1
)
func f1() {
_ = *intp // ERROR "generated nil check"
// This one should be removed but the block copy needs
// to be turned into its own pseudo-op in order to see
// the indirect.
_ = *arrayp // ERROR "generated nil check"
// 0-byte indirect doesn't suffice.
// we don't registerize globals, so there are no removed.* nil checks.
_ = *array0p // ERROR "generated nil check"
_ = *array0p // ERROR "removed nil check"
_ = *intp // ERROR "removed nil check"
_ = *arrayp // ERROR "removed nil check"
_ = *structp // ERROR "generated nil check"
_ = *emptyp // ERROR "generated nil check"
_ = *arrayp // ERROR "removed nil check"
}
func f2() {
var (
intp *int
arrayp *[10]int
array0p *[0]int
bigarrayp *[1 << 20]int
structp *Struct
bigstructp *BigStruct
emptyp *Empty
empty1p *Empty1
)
_ = *intp // ERROR "generated nil check"
_ = *arrayp // ERROR "generated nil check"
_ = *array0p // ERROR "generated nil check"
_ = *array0p // ERROR "removed.* nil check"
_ = *intp // ERROR "removed.* nil check"
_ = *arrayp // ERROR "removed.* nil check"
_ = *structp // ERROR "generated nil check"
_ = *emptyp // ERROR "generated nil check"
_ = *arrayp // ERROR "removed.* nil check"
_ = *bigarrayp // ERROR "generated nil check" ARM removed nil check before indirect!!
_ = *bigstructp // ERROR "generated nil check"
_ = *empty1p // ERROR "generated nil check"
}
func fx10k() *[10000]int
var b bool
func f3(x *[10000]int) {
// Using a huge type and huge offsets so the compiler
// does not expect the memory hardware to fault.
_ = x[9999] // ERROR "generated nil check"
for {
if x[9999] != 0 { // ERROR "removed nil check"
break
}
}
x = fx10k()
_ = x[9999] // ERROR "generated nil check"
if b {
_ = x[9999] // ERROR "removed.* nil check"
} else {
_ = x[9999] // ERROR "removed.* nil check"
}
_ = x[9999] // ERROR "removed nil check"
x = fx10k()
if b {
_ = x[9999] // ERROR "generated nil check"
} else {
_ = x[9999] // ERROR "generated nil check"
}
_ = x[9999] // ERROR "generated nil check"
fx10k()
// This one is a bit redundant, if we figured out that
// x wasn't going to change across the function call.
// But it's a little complex to do and in practice doesn't
// matter enough.
_ = x[9999] // ERROR "removed nil check"
}
func f3a() {
x := fx10k()
y := fx10k()
z := fx10k()
_ = &x[9] // ERROR "generated nil check"
y = z
_ = &x[9] // ERROR "removed.* nil check"
x = y
_ = &x[9] // ERROR "generated nil check"
}
func f3b() {
x := fx10k()
y := fx10k()
_ = &x[9] // ERROR "generated nil check"
y = x
_ = &x[9] // ERROR "removed.* nil check"
x = y
_ = &x[9] // ERROR "removed.* nil check"
}
func fx10() *[10]int
func f4(x *[10]int) {
// Most of these have no checks because a real memory reference follows,
// and the offset is small enough that if x is nil, the address will still be
// in the first unmapped page of memory.
_ = x[9] // ERROR "generated nil check" // bug: would like to remove this check (but nilcheck and load are in different blocks)
for {
if x[9] != 0 { // ERROR "removed nil check"
break
}
}
x = fx10()
_ = x[9] // ERROR "generated nil check" // bug would like to remove before indirect
if b {
_ = x[9] // ERROR "removed nil check"
} else {
_ = x[9] // ERROR "removed nil check"
}
_ = x[9] // ERROR "removed nil check"
x = fx10()
if b {
_ = x[9] // ERROR "generated nil check" // bug would like to remove before indirect
} else {
_ = &x[9] // ERROR "generated nil check"
}
_ = x[9] // ERROR "generated nil check" // bug would like to remove before indirect
fx10()
_ = x[9] // ERROR "removed nil check"
x = fx10()
y := fx10()
_ = &x[9] // ERROR "generated nil check"
y = x
_ = &x[9] // ERROR "removed[a-z ]* nil check"
x = y
_ = &x[9] // ERROR "removed[a-z ]* nil check"
}
func f5(p *float32, q *float64, r *float32, s *float64) float64 {
x := float64(*p) // ERROR "generated nil check"
y := *q // ERROR "generated nil check"
*r = 7 // ERROR "generated nil check"
*s = 9 // ERROR "generated nil check"
return x + y
}
type T [29]byte
func f6(p, q *T) {
x := *p // ERROR "generated nil check"
*q = x // ERROR "generated nil check"
}
func m1(m map[int][80]byte) byte {
v := m[3] // ERROR "removed nil check"
return v[5]
}
func m2(m map[int][800]byte) byte {
v := m[3] // ERROR "removed nil check"
return v[5]
}
func m3(m map[int][80]byte) (byte, bool) {
v, ok := m[3] // ERROR "removed nil check"
return v[5], ok
}
func m4(m map[int][800]byte) (byte, bool) {
v, ok := m[3] // ERROR "removed nil check"
return v[5], ok
}
func p1() byte {
p := new([100]byte)
return p[5] // ERROR "removed nil check"
}
// make sure not to do nil check for access of PAUTOHEAP
//go:noinline
func (p *Struct) m() {}
func c1() {
var x Struct
func() { x.m() }() // ERROR "removed nil check"
}
type SS struct {
x byte
}
type TT struct {
SS
}
func f(t *TT) *byte {
// See issue 17242.
s := &t.SS // ERROR "generated nil check"
return &s.x // ERROR "removed nil check"
}
// make sure not to do nil check for newobject
func f7() (*Struct, float64) {
t := new(Struct)
p := &t.Y // ERROR "removed nil check"
return t, *p // ERROR "removed nil check"
}
// make sure to remove nil check for memory move (issue #18003)
func f8(t *[8]int) [8]int {
return *t // ERROR "generated nil check"
}
func f9() []int {
x := new([1]int)
x[0] = 1 // ERROR "removed nil check"
y := x[:] // ERROR "removed nil check"
return y
}

33
test/nilptr5.go Normal file
View File

@ -0,0 +1,33 @@
// errorcheck -0 -d=nil
// +build !wasm
// +build !aix
// Copyright 2018 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.
// Test that nil checks are removed.
// Optimization is enabled.
package p
func f5(p *float32, q *float64, r *float32, s *float64) float64 {
x := float64(*p) // ERROR "removed nil check"
y := *q // ERROR "removed nil check"
*r = 7 // ERROR "removed nil check"
*s = 9 // ERROR "removed nil check"
return x + y
}
type T [29]byte
func f6(p, q *T) {
x := *p // ERROR "removed nil check"
*q = x // ERROR "removed nil check"
}
// make sure to remove nil check for memory move (issue #18003)
func f8(t *[8]int) [8]int {
return *t // ERROR "removed nil check"
}

32
test/nilptr5_aix.go Normal file
View File

@ -0,0 +1,32 @@
// errorcheck -0 -d=nil
// +build aix
// Copyright 2018 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.
// Test that nil checks are removed.
// Optimization is enabled.
package p
func f5(p *float32, q *float64, r *float32, s *float64) float64 {
x := float64(*p) // ERROR "generated nil check"
y := *q // ERROR "generated nil check"
*r = 7 // ERROR "removed nil check"
*s = 9 // ERROR "removed nil check"
return x + y
}
type T [29]byte
func f6(p, q *T) {
x := *p // ERROR "generated nil check"
*q = x // ERROR "generated nil check"
}
// make sure to remove nil check for memory move (issue #18003)
func f8(t *[8]int) [8]int {
return *t // ERROR "generated nil check"
}

32
test/nilptr5_wasm.go Normal file
View File

@ -0,0 +1,32 @@
// errorcheck -0 -d=nil
// +build wasm
// Copyright 2018 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.
// Test that nil checks are removed.
// Optimization is enabled.
package p
func f5(p *float32, q *float64, r *float32, s *float64) float64 {
x := float64(*p) // ERROR "generated nil check"
y := *q // ERROR "generated nil check"
*r = 7 // ERROR "generated nil check"
*s = 9 // ERROR "generated nil check"
return x + y
}
type T [29]byte
func f6(p, q *T) {
x := *p // ERROR "generated nil check"
*q = x // ERROR "generated nil check"
}
// make sure to remove nil check for memory move (issue #18003)
func f8(t *[8]int) [8]int {
return *t // ERROR "generated nil check"
}

185
test/nilptr_aix.go Normal file
View File

@ -0,0 +1,185 @@
// run
// Copyright 2018 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.
// Test that the implementation catches nil ptr indirection
// in a large address space.
// +build aix
package main
import "unsafe"
// Having a big address space means that indexing
// at a 1G + 256 MB offset from a nil pointer might not
// cause a memory access fault. This test checks
// that Go is doing the correct explicit checks to catch
// these nil pointer accesses, not just relying on the hardware.
// The reason of the 1G offset is because AIX addresses start after 1G.
var dummy [256 << 20]byte // give us a big address space
func main() {
// the test only tests what we intend to test
// if dummy starts in the first 256 MB of memory.
// otherwise there might not be anything mapped
// at the address that might be accidentally
// dereferenced below.
if uintptr(unsafe.Pointer(&dummy)) < 1<<32 {
panic("dummy not far enough")
}
shouldPanic(p1)
shouldPanic(p2)
shouldPanic(p3)
shouldPanic(p4)
shouldPanic(p5)
shouldPanic(p6)
shouldPanic(p7)
shouldPanic(p8)
shouldPanic(p9)
shouldPanic(p10)
shouldPanic(p11)
shouldPanic(p12)
shouldPanic(p13)
shouldPanic(p14)
shouldPanic(p15)
shouldPanic(p16)
}
func shouldPanic(f func()) {
defer func() {
if recover() == nil {
panic("memory reference did not panic")
}
}()
f()
}
func p1() {
// Array index.
var p *[1 << 33]byte = nil
println(p[1<<32+256<<20]) // very likely to be inside dummy, but should panic
}
var xb byte
func p2() {
var p *[1 << 33]byte = nil
xb = 123
// Array index.
println(p[uintptr(unsafe.Pointer(&xb))]) // should panic
}
func p3() {
// Array to slice.
var p *[1 << 33]byte = nil
var x []byte = p[0:] // should panic
_ = x
}
var q *[1 << 33]byte
func p4() {
// Array to slice.
var x []byte
var y = &x
*y = q[0:] // should crash (uses arraytoslice runtime routine)
}
func fb([]byte) {
panic("unreachable")
}
func p5() {
// Array to slice.
var p *[1 << 33]byte = nil
fb(p[0:]) // should crash
}
func p6() {
// Array to slice.
var p *[1 << 33]byte = nil
var _ []byte = p[10 : len(p)-10] // should crash
}
type T struct {
x [1<<32 + 256<<20]byte
i int
}
func f() *T {
return nil
}
var y *T
var x = &y
func p7() {
// Struct field access with large offset.
println(f().i) // should crash
}
func p8() {
// Struct field access with large offset.
println((*x).i) // should crash
}
func p9() {
// Struct field access with large offset.
var t *T
println(&t.i) // should crash
}
func p10() {
// Struct field access with large offset.
var t *T
println(t.i) // should crash
}
type T1 struct {
T
}
type T2 struct {
*T1
}
func p11() {
t := &T2{}
p := &t.i
println(*p)
}
// ADDR(DOT(IND(p))) needs a check also
func p12() {
var p *T = nil
println(*(&((*p).i)))
}
// Tests suggested in golang.org/issue/6080.
func p13() {
var x *[10]int
y := x[:]
_ = y
}
func p14() {
println((*[1]int)(nil)[:])
}
func p15() {
for i := range (*[1]int)(nil)[:] {
_ = i
}
}
func p16() {
for i, v := range (*[1]int)(nil)[:] {
_ = i + v
}
}