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compiler, runtime: implement recoverable divide-by-zero panic #4758

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7 changes: 7 additions & 0 deletions GNUmakefile
Original file line number Diff line number Diff line change
@@ -362,6 +362,7 @@ TEST_PACKAGES_FAST = \
# debug/plan9obj requires os.ReadAt, which is not yet supported on windows
# image requires recover(), which is not yet supported on wasi
# io/ioutil requires os.ReadDir, which is not yet supported on windows or wasi
# math/bits: needs panic()/recover()
# mime: fail on wasi; neds panic()/recover()
# mime/multipart: needs wasip1 syscall.FDFLAG_NONBLOCK
# mime/quotedprintable requires syscall.Faccessat
@@ -382,8 +383,11 @@ TEST_PACKAGES_LINUX := \
crypto/hmac \
debug/dwarf \
debug/plan9obj \
encoding/binary \
go/constant \
image \
io/ioutil \
math/bits \
mime \
mime/multipart \
mime/quotedprintable \
@@ -403,6 +407,9 @@ TEST_PACKAGES_WINDOWS := \
compress/flate \
crypto/des \
crypto/hmac \
encoding/binary \
go/constant \
math/bits \
strconv \
text/template/parse \
$(nil)
22 changes: 11 additions & 11 deletions compiler/asserts.go
Original file line number Diff line number Diff line change
@@ -31,7 +31,7 @@ func (b *builder) createLookupBoundsCheck(arrayLen, index llvm.Value) {

// Now do the bounds check: index >= arrayLen
outOfBounds := b.CreateICmp(llvm.IntUGE, index, arrayLen, "")
b.createRuntimeAssert(outOfBounds, "lookup", "lookupPanic")
b.createRuntimeAssert(outOfBounds, "lookup", "lookupPanic", true)
}

// createSliceBoundsCheck emits a bounds check before a slicing operation to make
@@ -74,7 +74,7 @@ func (b *builder) createSliceBoundsCheck(capacity, low, high, max llvm.Value, lo
outOfBounds3 := b.CreateICmp(llvm.IntUGT, max, capacity, "slice.maxcap")
outOfBounds := b.CreateOr(outOfBounds1, outOfBounds2, "slice.lowmax")
outOfBounds = b.CreateOr(outOfBounds, outOfBounds3, "slice.lowcap")
b.createRuntimeAssert(outOfBounds, "slice", "slicePanic")
b.createRuntimeAssert(outOfBounds, "slice", "slicePanic", false)
}

// createSliceToArrayPointerCheck adds a check for slice-to-array pointer
@@ -86,7 +86,7 @@ func (b *builder) createSliceToArrayPointerCheck(sliceLen llvm.Value, arrayLen i
// > run-time panic occurs.
arrayLenValue := llvm.ConstInt(b.uintptrType, uint64(arrayLen), false)
isLess := b.CreateICmp(llvm.IntULT, sliceLen, arrayLenValue, "")
b.createRuntimeAssert(isLess, "slicetoarray", "sliceToArrayPointerPanic")
b.createRuntimeAssert(isLess, "slicetoarray", "sliceToArrayPointerPanic", false)
}

// createUnsafeSliceStringCheck inserts a runtime check used for unsafe.Slice
@@ -118,7 +118,7 @@ func (b *builder) createUnsafeSliceStringCheck(name string, ptr, len llvm.Value,
lenIsNotZero := b.CreateICmp(llvm.IntNE, len, zero, "")
assert := b.CreateAnd(ptrIsNil, lenIsNotZero, "")
assert = b.CreateOr(assert, lenOutOfBounds, "")
b.createRuntimeAssert(assert, name, "unsafeSlicePanic")
b.createRuntimeAssert(assert, name, "unsafeSlicePanic", false)
}

// createChanBoundsCheck creates a bounds check before creating a new channel to
@@ -155,7 +155,7 @@ func (b *builder) createChanBoundsCheck(elementSize uint64, bufSize llvm.Value,

// Do the check for a too large (or negative) buffer size.
bufSizeTooBig := b.CreateICmp(llvm.IntUGE, bufSize, maxBufSize, "")
b.createRuntimeAssert(bufSizeTooBig, "chan", "chanMakePanic")
b.createRuntimeAssert(bufSizeTooBig, "chan", "chanMakePanic", false)
}

// createNilCheck checks whether the given pointer is nil, and panics if it is.
@@ -199,7 +199,7 @@ func (b *builder) createNilCheck(inst ssa.Value, ptr llvm.Value, blockPrefix str
isnil := b.CreateICmp(llvm.IntEQ, ptr, nilptr, "")

// Emit the nil check in IR.
b.createRuntimeAssert(isnil, blockPrefix, "nilPanic")
b.createRuntimeAssert(isnil, blockPrefix, "nilPanic", false)
}

// createNegativeShiftCheck creates an assertion that panics if the given shift value is negative.
@@ -212,7 +212,7 @@ func (b *builder) createNegativeShiftCheck(shift llvm.Value) {

// isNegative = shift < 0
isNegative := b.CreateICmp(llvm.IntSLT, shift, llvm.ConstInt(shift.Type(), 0, false), "")
b.createRuntimeAssert(isNegative, "shift", "negativeShiftPanic")
b.createRuntimeAssert(isNegative, "shift", "negativeShiftPanic", false)
}

// createDivideByZeroCheck asserts that y is not zero. If it is, a runtime panic
@@ -225,12 +225,12 @@ func (b *builder) createDivideByZeroCheck(y llvm.Value) {

// isZero = y == 0
isZero := b.CreateICmp(llvm.IntEQ, y, llvm.ConstInt(y.Type(), 0, false), "")
b.createRuntimeAssert(isZero, "divbyzero", "divideByZeroPanic")
b.createRuntimeAssert(isZero, "divbyzero", "divideByZeroPanic", true)
}

// createRuntimeAssert is a common function to create a new branch on an assert
// bool, calling an assert func if the assert value is true (1).
func (b *builder) createRuntimeAssert(assert llvm.Value, blockPrefix, assertFunc string) {
func (b *builder) createRuntimeAssert(assert llvm.Value, blockPrefix, assertFunc string, isInvoke bool) {
// Check whether we can resolve this check at compile time.
if !assert.IsAConstantInt().IsNil() {
val := assert.ZExtValue()
@@ -245,17 +245,17 @@ func (b *builder) createRuntimeAssert(assert llvm.Value, blockPrefix, assertFunc
// current insert position.
faultBlock := b.ctx.AddBasicBlock(b.llvmFn, blockPrefix+".throw")
nextBlock := b.insertBasicBlock(blockPrefix + ".next")
b.blockExits[b.currentBlock] = nextBlock // adjust outgoing block for phi nodes

// Now branch to the out-of-bounds or the regular block.
b.CreateCondBr(assert, faultBlock, nextBlock)

// Fail: the assert triggered so panic.
b.SetInsertPointAtEnd(faultBlock)
b.createRuntimeCall(assertFunc, nil, "")
b.createRuntimeCallCommon(assertFunc, nil, "", isInvoke)
b.CreateUnreachable()

// Ok: assert didn't trigger so continue normally.
b.blockExits[b.currentBlock] = nextBlock // adjust outgoing block for phi nodes
b.SetInsertPointAtEnd(nextBlock)
}

9 changes: 7 additions & 2 deletions compiler/symbol.go
Original file line number Diff line number Diff line change
@@ -688,20 +688,25 @@ func (c *compilerContext) getGlobalInfo(g *ssa.Global) globalInfo {
// Check for //go: pragmas, which may change the link name (among others).
doc := c.astComments[info.linkName]
if doc != nil {
info.parsePragmas(doc)
info.parsePragmas(doc, g)
}
return info
}

// Parse //go: pragma comments from the source. In particular, it parses the
// //go:extern pragma on globals.
func (info *globalInfo) parsePragmas(doc *ast.CommentGroup) {
func (info *globalInfo) parsePragmas(doc *ast.CommentGroup, g *ssa.Global) {
for _, comment := range doc.List {
if !strings.HasPrefix(comment.Text, "//go:") {
continue
}
parts := strings.Fields(comment.Text)
switch parts[0] {
case "//go:linkname":
if len(parts) == 3 && g.Name() == parts[1] {
info.linkName = parts[2]
info.extern = true
}
case "//go:extern":
info.extern = true
if len(parts) == 2 {
6 changes: 6 additions & 0 deletions compiler/testdata/pragma.go
Original file line number Diff line number Diff line change
@@ -2,6 +2,12 @@ package main

import _ "unsafe"

// Use the go:linkname mechanism to link this global to a different package.
// This is used in math/bits.
//
//go:linkname linknamedGlobal runtime.testLinknamedGlobal
var linknamedGlobal int

// Creates an external global with name extern_global.
//
//go:extern extern_global
1 change: 1 addition & 0 deletions compiler/testdata/pragma.ll
Original file line number Diff line number Diff line change
@@ -3,6 +3,7 @@ source_filename = "pragma.go"
target datalayout = "e-m:e-p:32:32-p10:8:8-p20:8:8-i64:64-n32:64-S128-ni:1:10:20"
target triple = "wasm32-unknown-wasi"

@runtime.testLinknamedGlobal = external global i32, align 4
@extern_global = external global [0 x i8], align 1
@main.alignedGlobal = hidden global [4 x i32] zeroinitializer, align 32
@main.alignedGlobal16 = hidden global [4 x i32] zeroinitializer, align 16
18 changes: 18 additions & 0 deletions src/runtime/error.go
Original file line number Diff line number Diff line change
@@ -4,5 +4,23 @@ package runtime
type Error interface {
error

// Method to indicate this is indeed a runtime error.
RuntimeError()
}

type runtimeError struct {
msg string
}

func (r runtimeError) Error() string {
return r.msg
}

// Purely here to satisfy the Error interface.
func (r runtimeError) RuntimeError() {}

var (
divideError error = runtimeError{"runtime error: integer divide by zero"}
lookupError error = runtimeError{"runtime error: index out of range"}
overflowError error = runtimeError{"runtime error: integer overflow"}
)
4 changes: 2 additions & 2 deletions src/runtime/panic.go
Original file line number Diff line number Diff line change
@@ -187,7 +187,7 @@ func nilMapPanic() {

// Panic when trying to access an array or slice out of bounds.
func lookupPanic() {
runtimePanicAt(returnAddress(0), "index out of range")
_panic(lookupError)
}

// Panic when trying to slice a slice out of bounds.
@@ -220,7 +220,7 @@ func negativeShiftPanic() {

// Panic when there is a divide by zero.
func divideByZeroPanic() {
runtimePanicAt(returnAddress(0), "divide by zero")
_panic(divideError)
}

func blockingPanic() {
24 changes: 24 additions & 0 deletions testdata/recover.go
Original file line number Diff line number Diff line change
@@ -30,6 +30,10 @@ func main() {
println("\n# defer panic")
deferPanic()

println("\n# runtime panics")
runtimePanicDivByZero(1, 0)
runtimePanicLookup([]int{1, 2, 3}, 10)

println("\n# runtime.Goexit")
runtimeGoexit()
}
@@ -114,6 +118,26 @@ func deferPanic() {
println("defer panic")
}

func runtimePanicDivByZero(a, b int) int {
defer func() {
if err := recover(); err != nil {
println("recovered:", err)
}
}()

return a / b
}

func runtimePanicLookup(slice []int, index int) int {
defer func() {
if err := recover(); err != nil {
println("recovered:", err)
}
}()

return slice[index]
}

func runtimeGoexit() {
wg.Add(1)
go func() {