Method createUnsafeSliceStringCheck

compiler/asserts.go:95–122

createUnsafeSliceStringCheck inserts a runtime check used for unsafe.Slice and unsafe.String. This function must panic if the ptr/len parameters are invalid.

(name string, ptr, len llvm.Value, elementType llvm.Type, lenType *types.Basic)

// and unsafe.String. This function must panic if the ptr/len parameters are
// invalid.
func (b *builder) createUnsafeSliceStringCheck(name string, ptr, len llvm.Value, elementType llvm.Type, lenType *types.Basic) {
	// From the documentation of unsafe.Slice and unsafe.String:
	//   > At run time, if len is negative, or if ptr is nil and len is not
	//   > zero, a run-time panic occurs.
	// However, in practice, it is also necessary to check that the length is
	// not too big that a GEP wouldn't be possible without wrapping the pointer.
	// These two checks (non-negative and not too big) can be merged into one
	// using an unsigned greater than.

	// Make sure the len value is at least as big as a uintptr.
	len = b.extendInteger(len, lenType, b.uintptrType)

	// Determine the maximum slice size, and therefore the maximum value of the
	// len parameter.
	maxSize := b.maxSliceSize(elementType)
	maxSizeValue := llvm.ConstInt(len.Type(), maxSize, false)

	// Do the check. By using unsigned greater than for the length check, signed
	// negative values are also checked (which are very large numbers when
	// interpreted as signed values).
	zero := llvm.ConstInt(len.Type(), 0, false)
	lenOutOfBounds := b.CreateICmp(llvm.IntUGT, len, maxSizeValue, "")
	ptrIsNil := b.CreateICmp(llvm.IntEQ, ptr, llvm.ConstNull(ptr.Type()), "")
	lenIsNotZero := b.CreateICmp(llvm.IntNE, len, zero, "")
	assert := b.CreateAnd(ptrIsNil, lenIsNotZero, "")
	assert = b.CreateOr(assert, lenOutOfBounds, "")
	b.createRuntimeAssert(assert, name, "unsafeSlicePanic")
}

// createChanBoundsCheck creates a bounds check before creating a new channel to
// check that the value is not too big for runtime.chanMake.