RFR: 8256387: Unexpected result if patching an entire instruction on AArch64 [v2]

[Aleksey Shipilev]

On Tue, 24 Nov 2020 11:16:13 GMT, Eric Liu <github.com+10482586+erik1iu at openjdk.org> wrote:

>> This patch fixed some potential risks in assembler_aarch64.hpp.
>> 
>> According to the C standard, shift operation is undefined if the shift
>> count greater than or equals to the length in bits of the promoted left
>> operand.
>> 
>> In assembler_aarch64.hpp, there are some utility functions for easily
>> operating the encoded instructions. E.g.
>> 
>>         Instruction_aarch64::patch(address, int, int, uint64_t)
>> 
>> All those functions use `(1U << nbits) - 1` to calculate mask which may
>> have some potential risks if `nbits` equals 32. That would be an
>> unexpected result if someone intends to deal with an entire instruction.
>> 
>> To fix this issue, this patch simply uses `1ULL` to replace `1U`.
>
> Eric Liu has updated the pull request incrementally with one additional commit since the last revision:
> 
>   uses pre-defined macro `right_n_bits` to get the right-most bits set.
>   
>   Change-Id: I456bcc883434b04527db912adaccc6a5f2dd96a0

Marked as reviewed by shade (Reviewer).

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PR: https://git.openjdk.java.net/jdk/pull/1248