Bug 1577161 - Limit length of filename saved for profiler. r=jandem

When profiling scripts with large numbers of dynamic Functions and
complex URLs the profiler overhead can severely skew results. This puts
a cap on the filename length we send to profiler to reduce the impact of
this when using data urls.

Move the definition of strnlen from CTypes into util/Text.h and rename
it to js_strnlen.

Differential Revision: https://phabricator.services.mozilla.com/D43836

--HG--
extra : moz-landing-system : lando

js/src/ctypes/CTypes.cpp

@@ -47,6 +47,7 @@
 #include "js/UniquePtr.h"
 #include "js/Utility.h"
 #include "js/Vector.h"
+#include "util/Text.h"
 #include "util/Unicode.h"
 #include "util/Windows.h"
 #include "vm/JSContext.h"
@@ -2999,17 +3000,6 @@ void IntegerToString(IntegerType i, int radix,
   }
 }
 
-template <class CharType>
-static size_t strnlen(const CharType* begin, size_t max) {
-  for (size_t i = 0; i < max; i++) {
-    if (begin[i] == '\0') {
-      return i;
-    }
-  }
-
-  return max;
-}
-
 // Convert C binary value 'data' of CType 'typeObj' to a JS primitive, where
 // possible; otherwise, construct and return a CData object. The following
 // semantics apply when constructing a CData object for return:
@@ -7761,7 +7751,7 @@ static bool ReadStringCommon(JSContext* cx, InflateUTF8Method inflateUTF8,
     case TYPE_signed_char:
     case TYPE_unsigned_char: {
       char* bytes = static_cast<char*>(data);
-      size_t length = strnlen(bytes, maxLength);
+      size_t length = js_strnlen(bytes, maxLength);
 
       // Determine the length.
       UniqueTwoByteChars dst(
@@ -7784,7 +7774,7 @@ static bool ReadStringCommon(JSContext* cx, InflateUTF8Method inflateUTF8,
     case TYPE_unsigned_short:
     case TYPE_char16_t: {
       char16_t* chars = static_cast<char16_t*>(data);
-      size_t length = strnlen(chars, maxLength);
+      size_t length = js_strnlen(chars, maxLength);
       result = JS_NewUCStringCopyN(cx, chars, length);
       break;
     }

js/src/util/Text.h

@@ -37,6 +37,16 @@ template <typename CharT>
 extern const CharT* js_strchr_limit(const CharT* s, char16_t c,
                                     const CharT* limit);
 
+template <typename CharT>
+static MOZ_ALWAYS_INLINE size_t js_strnlen(const CharT* s, size_t maxlen) {
+  for (size_t i = 0; i < maxlen; ++i) {
+    if (s[i] == '\0') {
+      return i;
+    }
+  }
+  return maxlen;
+}
+
 extern int32_t js_fputs(const char16_t* s, FILE* f);
 
 namespace js {

js/src/vm/GeckoProfiler.cpp

@@ -290,9 +290,11 @@ UniqueChars GeckoProfilerRuntime::allocProfileString(JSContext* cx,
     hasName = true;
   }
 
-  // Calculate filename length.
+  // Calculate filename length. We cap this to a reasonable limit to avoid
+  // performance impact of strlen/alloc/memcpy.
+  constexpr size_t MaxFilenameLength = 200;
   const char* filenameStr = script->filename() ? script->filename() : "(null)";
-  size_t filenameLength = strlen(filenameStr);
+  size_t filenameLength = js_strnlen(filenameStr, MaxFilenameLength);
 
   // Calculate line + column length.
   bool hasLineAndColumn = false;