[aarch64-port-dev ] RFR(S): 8237524: AArch64: String.compareTo() may return incorrect result

[Nick Gasson]

On 21/01/2020 17:33, Andrew Haley wrote:
> On 1/21/20 8:40 AM, Pengfei Li wrote:
>> Root cause is in the AArch64 String.compareTo intrinsics. In the code of
>> MacroAssembler::string_compare(), we have a fast path that compares the
>> addresses of initial bytes of the two arrays. If the result is equal, we
>> skip the inflation of the Latin one and the byte-wise comparison part.
>> But we shouldn't do in this way if the encodings of the two strings are
>> different (the LU/UL cases). This patch removes the incorrect fast path
>> check.
> 
> Is this really a bug? The test case is violating the protections
> provided by the Java runtime, and the programmer deserves everything
> that happens.
> 

Even if it's not strictly a bug, the pointer equality checks in the 
LU/UL branches are unnecessary: the only time they succeed is when the 
Strings were constructed in this backdoor way, and in that case they 
give the wrong result. So it seems better to just remove them.


Nick