RFR: 8378110: Add -XX: prefix to settings-file flags in RuntimeMXBean.getInputArguments() [v4]

[Oli Gillespie]

On Fri, 27 Feb 2026 14:36:53 GMT, Oli Gillespie <ogillespie at openjdk.org> wrote:

>> Flags passed via a settings file (`.hotspotrc`, or `-XX:Flags=my-file`) do not have the `-XX:` prefix like they would have if passed as command-line args. `JVM_GetVmArguments` then prints these flags also without the prefix, along with command-line flags that _are_ prefixed.
>> 
>> However, users of `JVM_GetVmArguments` expect the arguments to be in a format that they can pass as command-line args, for example [in CDS static_dump](https://github.com/openjdk/jdk/blob/63f00fff921ed4ac0f595a0a013d399700433a2c/src/java.base/share/classes/jdk/internal/misc/CDS.java#L329-L338) - CDS static_dump currently *does not work* if the main VM uses flags from a settings file.
>> 
>> So, always add the `-XX:` prefix to flags from settings files in `JVM_GetVmArguments`. Updated existing test to cover this behaviour.
>> 
>> I looked for existing users of `JVM_GetVmArguments` and they either seem like they'll benefit from this change (CDS, JMH via `RuntimeMXBean.getInputArguments()`) or they won't care.
>> 
>> **Testing**
>> 
>> * Updated the existing InputArgument test with a case that verifies the new behaviour.
>> * Confirmed that CDS static_dump and JMH now work on a VM with flags from a file.
>
> Oli Gillespie has updated the pull request incrementally with one additional commit since the last revision:
> 
>   D'oh

> OpenJDK 64-Bit Server VM warning: .hotspotrc file is present but has been ignored.  Run with -XX:Flags=.hotspotrc to load the file.

Oh, didn't realise that. Perfect!

-------------

PR Comment: https://git.openjdk.org/jdk/pull/29793#issuecomment-3973455688