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

[Aleksey Shipilev]

On Tue, 17 Nov 2020 06:14:37 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`.

So there is a global `right_n_bits` macro that apparently does what we want? @theRealAph might want to look at this issue (probably in disgust).

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