Use zone memory for StackTrace::ToCString.

runtime/vm/zone_text_buffer.cc

+// Copyright (c) 2017, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+#include "vm/zone_text_buffer.h"
+
+#include "platform/assert.h"
+#include "platform/globals.h"
+#include "platform/utils.h"
+#include "vm/os.h"
+#include "vm/zone.h"
+
+namespace dart {
+
+ZoneTextBuffer::ZoneTextBuffer(Zone* zone, intptr_t initial_capacity)
+    : zone_(zone), buffer_(NULL), length_(0), capacity_(0) {
+  ASSERT(initial_capacity > 0);
+  buffer_ = reinterpret_cast<char*>(zone->Alloc<char>(initial_capacity));
+  capacity_ = initial_capacity;
+}
+
+
+intptr_t ZoneTextBuffer::Printf(const char* format, ...) {
+  va_list args;
+  va_start(args, format);
+  intptr_t remaining = capacity_ - length_;
+  ASSERT(remaining >= 0);
+  intptr_t len = OS::VSNPrint(buffer_ + length_, remaining, format, args);
+  va_end(args);
+  if (len >= remaining) {
+    EnsureCapacity(len);
+    remaining = capacity_ - length_;
+    ASSERT(remaining > len);
+    va_list args2;
+    va_start(args2, format);
+    intptr_t len2 = OS::VSNPrint(buffer_ + length_, remaining, format, args2);
+    va_end(args2);
+    ASSERT(len == len2);
+  }
+  length_ += len;
+  buffer_[length_] = '\0';
+  return len;
+}
+
+
+void ZoneTextBuffer::AddString(const char* s) {
+  Printf("%s", s);
+}
+
+
+void ZoneTextBuffer::EnsureCapacity(intptr_t len) {
+  intptr_t remaining = capacity_ - length_;
+  if (remaining <= len) {
+    const int kBufferSpareCapacity = 64;  // Somewhat arbitrary.
+    // TODO(turnidge): do we need to guard against overflow or other
+    // security issues here? Text buffers are used by the debugger
+    // to send user-controlled data (e.g. values of string variables) to
+    // the debugger front-end.
+    intptr_t new_capacity = capacity_ + len + kBufferSpareCapacity;
+    buffer_ = zone_->Realloc<char>(buffer_, capacity_, new_capacity);
+    capacity_ = new_capacity;
+  }
+}
+
+}  // namespace dart