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[Strings] Avoid mishandling unicode in interpreter (#6405)
Our interpreter implementations of `stringview_wtf16.length`, `stringview_wtf16.get_codeunit`, and `string.encode_wtf16_array` are not unicode-aware, so they were previously incorrect in the face of multi-byte code units. As a fix, bail out of the interpretation if there is a non-ascii code point that would make our naive implementation incorrect.
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‎src/wasm-interpreter.h‎

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Original file line numberDiff line numberDiff line change
@@ -1902,6 +1902,16 @@ class ExpressionRunner : public OverriddenVisitor<SubType, Flow> {
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Flow visitStringConst(StringConst* curr) {
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return Literal(curr->string.toString());
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}
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bool hasNonAsciiUpTo(const Literals& values, Index end) {
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for (Index i = 0; i < end; ++i) {
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if (uint32_t(values[i].geti32()) > 127) {
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return true;
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}
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}
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return false;
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}
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Flow visitStringMeasure(StringMeasure* curr) {
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// For now we only support JS-style strings.
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if (curr->op != StringMeasureWTF16View) {
@@ -1917,6 +1927,13 @@ class ExpressionRunner : public OverriddenVisitor<SubType, Flow> {
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if (!data) {
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trap("null ref");
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}
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// This is only correct if all the bytes stored in `values` correspond to
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// single unicode code points. See `visitStringWTF16Get` for details.
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if (hasNonAsciiUpTo(data->values, data->values.size())) {
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return Flow(NONCONSTANT_FLOW);
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}
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return Literal(int32_t(data->values.size()));
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}
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Flow visitStringConcat(StringConcat* curr) {
@@ -1980,6 +1997,11 @@ class ExpressionRunner : public OverriddenVisitor<SubType, Flow> {
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trap("oob");
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}
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// We don't handle non-ascii code points correctly yet.
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if (hasNonAsciiUpTo(refValues, refValues.size())) {
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return Flow(NONCONSTANT_FLOW);
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}
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for (Index i = 0; i < refValues.size(); i++) {
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ptrValues[startVal + i] = refValues[i];
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}
@@ -2095,6 +2117,18 @@ class ExpressionRunner : public OverriddenVisitor<SubType, Flow> {
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if (i >= values.size()) {
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trap("string oob");
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}
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// This naive indexing approach is only correct if the first `i` bytes
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// stored in `values` each corresponds to a single unicode code point. To
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// implement this correctly in general, we would have to reinterpret the
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// bytes as WTF-8, then count up to the `i`th code point, accounting
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// properly for code points that would be represented by surrogate pairs in
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// WTF-16. Alternatively, we could represent string contents as WTF-16 to
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// begin with.
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if (hasNonAsciiUpTo(values, i + 1)) {
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return Flow(NONCONSTANT_FLOW);
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}
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return Literal(values[i].geti32());
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}
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Flow visitStringIterNext(StringIterNext* curr) {

‎test/lit/passes/precompute-strings.wast‎

Lines changed: 101 additions & 5 deletions
Original file line numberDiff line numberDiff line change
@@ -1,12 +1,15 @@
11
;; NOTE: Assertions have been generated by update_lit_checks.py and should not be edited.
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3-
;; RUN: wasm-opt %s --precompute --fuzz-exec -all -S -o - | filecheck %s
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;; RUN: wasm-opt %s --precompute -all -S -o - | filecheck %s
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(module
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;; CHECK: (type $array16 (array (mut i16)))
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(type $array16 (array (mut i16)))
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;; CHECK: (func $eq-no (type $0) (result i32)
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;; CHECK-NEXT: (i32.const 0)
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;; CHECK-NEXT: )
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(func $eq-no (export "eq-no") (result i32)
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(func $eq-no (result i32)
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(string.eq
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(string.const "ab")
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(string.const "cdefg")
@@ -16,7 +19,7 @@
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;; CHECK: (func $eq-yes (type $0) (result i32)
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;; CHECK-NEXT: (i32.const 1)
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;; CHECK-NEXT: )
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(func $eq-yes (export "eq-yes") (result i32)
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(func $eq-yes (result i32)
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(string.eq
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(string.const "ab")
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(string.const "ab")
@@ -26,11 +29,104 @@
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;; CHECK: (func $concat (type $0) (result i32)
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;; CHECK-NEXT: (i32.const 1)
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;; CHECK-NEXT: )
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(func $concat (export "concat") (result i32)
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(func $concat (result i32)
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(string.eq
3134
(string.concat (string.const "a") (string.const "b"))
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(string.const "ab")
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)
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)
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)
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;; CHECK: (func $length (type $0) (result i32)
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;; CHECK-NEXT: (i32.const 7)
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;; CHECK-NEXT: )
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(func $length (result i32)
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(stringview_wtf16.length
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(string.as_wtf16
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(string.const "1234567")
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)
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)
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)
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;; CHECK: (func $length-bad (type $0) (result i32)
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;; CHECK-NEXT: (stringview_wtf16.length
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;; CHECK-NEXT: (string.as_wtf16
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;; CHECK-NEXT: (string.const "$_\c2\a3_\e2\82\ac_\f0\90\8d\88")
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;; CHECK-NEXT: )
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;; CHECK-NEXT: )
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;; CHECK-NEXT: )
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(func $length-bad (result i32)
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;; Not precomputable because we don't handle unicode yet.
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(stringview_wtf16.length
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(string.as_wtf16
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;; $_£_€_𐍈
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(string.const "$_\C2\A3_\E2\82\AC_\F0\90\8D\88")
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)
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)
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)
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;; CHECK: (func $get_codepoint (type $0) (result i32)
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;; CHECK-NEXT: (i32.const 95)
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;; CHECK-NEXT: )
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(func $get_codepoint (result i32)
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;; This is computable because everything up to the requested index is ascii. Returns 95 ('_').
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(stringview_wtf16.get_codeunit
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(string.as_wtf16
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;; $_£_€_𐍈
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(string.const "$_\C2\A3_\E2\82\AC_\F0\90\8D\88")
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)
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(i32.const 1)
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)
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)
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;; CHECK: (func $get_codepoint-bad (type $0) (result i32)
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;; CHECK-NEXT: (stringview_wtf16.get_codeunit
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;; CHECK-NEXT: (string.as_wtf16
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;; CHECK-NEXT: (string.const "$_\c2\a3_\e2\82\ac_\f0\90\8d\88")
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;; CHECK-NEXT: )
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;; CHECK-NEXT: (i32.const 2)
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;; CHECK-NEXT: )
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;; CHECK-NEXT: )
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(func $get_codepoint-bad (export "get_codepoint-bad") (result i32)
90+
;; This is not computable because the requested code unit is not ascii.
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(stringview_wtf16.get_codeunit
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(string.as_wtf16
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;; $_£_€_𐍈
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(string.const "$_\C2\A3_\E2\82\AC_\F0\90\8D\88")
95+
)
96+
(i32.const 2)
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)
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)
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;; CHECK: (func $encode (type $0) (result i32)
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;; CHECK-NEXT: (i32.const 2)
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;; CHECK-NEXT: )
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(func $encode (result i32)
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(string.encode_wtf16_array
105+
(string.const "$_")
106+
(array.new_default $array16
107+
(i32.const 20)
108+
)
109+
(i32.const 0)
110+
)
111+
)
112+
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;; CHECK: (func $encode-bad (type $0) (result i32)
114+
;; CHECK-NEXT: (string.encode_wtf16_array
115+
;; CHECK-NEXT: (string.const "$_\c2\a3_\e2\82\ac_\f0\90\8d\88")
116+
;; CHECK-NEXT: (array.new_default $array16
117+
;; CHECK-NEXT: (i32.const 20)
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;; CHECK-NEXT: )
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;; CHECK-NEXT: (i32.const 0)
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;; CHECK-NEXT: )
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;; CHECK-NEXT: )
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(func $encode-bad (result i32)
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(string.encode_wtf16_array
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;; $_£_€_𐍈
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(string.const "$_\C2\A3_\E2\82\AC_\F0\90\8D\88")
126+
(array.new_default $array16
127+
(i32.const 20)
128+
)
129+
(i32.const 0)
130+
)
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)
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)

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