Make SubStringStub more robust wrt unsafe arguments.

src/arm/code-stubs-arm.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 5855 matching lines @@
   __ JumpIfSmi(r0, &runtime);
   Condition is_string = masm->IsObjectStringType(r0, r1);
   __ b(NegateCondition(is_string), &runtime);
 
   // Short-cut for the case of trivial substring.
   Label return_r0;
   // r0: original string
   // r2: result string length
   __ ldr(r4, FieldMemOperand(r0, String::kLengthOffset));
   __ cmp(r2, Operand(r4, ASR, 1));
+  // Return original string.
   __ b(eq, &return_r0);
+  // Longer than original string's length or negative: unsafe arguments.
+  __ b(hi, &runtime);
+  // Shorter than original string's length: an actual substring.
 
-  Label result_longer_than_two;
-  // Check for special case of two character ASCII string, in which case
-  // we do a lookup in the symbol table first.
-  __ cmp(r2, Operand(2));
-  __ b(gt, &result_longer_than_two);
-  __ b(lt, &runtime);
-
-  __ JumpIfInstanceTypeIsNotSequentialAscii(r1, r1, &runtime);
-
-  // Get the two characters forming the sub string.
-  __ add(r0, r0, Operand(r3));
-  __ ldrb(r3, FieldMemOperand(r0, SeqAsciiString::kHeaderSize));
-  __ ldrb(r4, FieldMemOperand(r0, SeqAsciiString::kHeaderSize + 1));
-
-  // Try to lookup two character string in symbol table.
-  Label make_two_character_string;
-  StringHelper::GenerateTwoCharacterSymbolTableProbe(
-      masm, r3, r4, r1, r5, r6, r7, r9, &make_two_character_string);
-  __ jmp(&return_r0);
-
-  // r2: result string length.
-  // r3: two characters combined into halfword in little endian byte order.
-  __ bind(&make_two_character_string);
-  __ AllocateAsciiString(r0, r2, r4, r5, r9, &runtime);
-  __ strh(r3, FieldMemOperand(r0, SeqAsciiString::kHeaderSize));
-  __ jmp(&return_r0);
-
-  __ bind(&result_longer_than_two);
   // Deal with different string types: update the index if necessary
   // and put the underlying string into r5.
   // r0: original string
   // r1: instance type
   // r2: length
   // r3: from index (untagged)
   Label underlying_unpacked, sliced_string, seq_or_external_string;
   // If the string is not indirect, it can only be sequential or external.
   STATIC_ASSERT(kIsIndirectStringMask == (kSlicedStringTag & kConsStringTag));
   STATIC_ASSERT(kIsIndirectStringMask != 0);
@@ skipping 1493 matching lines @@
   __ StoreNumberToDoubleElements(r0, r3, r1, r5, r6, r7, r9, r2,
                                  &slow_elements);
   __ Ret();
 }
 
 #undef __
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_ARM