RFR: 8273108: RunThese24H crashes with SEGV in markWord::displaced_mark_helper() after JDK-8268276

[Scott Gibbons]

On Thu, 9 Dec 2021 23:10:00 GMT, Sandhya Viswanathan <sviswanathan at openjdk.org> wrote:

>> The base64 decoder overwrites memory past the end of its output buffer in certain cases.  It will not overwrite if the encoded string length is < 64 bytes.  It also will not overwrite if the encoded string length mod 64 is >= 16.  So the case where it *will* overwrite is when the input string length (the encoded byte length) mod 64 is less than 16.
>> 
>> I also added a test case to detect this overrun.
>
> src/hotspot/cpu/x86/stubGenerator_x86_64.cpp line 6264:
> 
>> 6262:       __ jcc(Assembler::lessEqual, L_finalBit);
>> 6263: 
>> 6264:       __ mov64(rax, 0x0000ffffffffffff);
> 
> The constant should have an l suffix.

I do not believe this is necessary.  There are multiple occurrences of mov64()s without the `l` suffix.  For example, lines 687-688:

    __ mov64(c_rarg3, 0x8000000000000000);
    __ mov64(rax, 0x7fffffffffffffff);

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PR: https://git.openjdk.java.net/jdk/pull/6786