RFR: 8319589: Attach from root to a user java process not supported in Mac [v8]

[Sergey Chernyshev]

On Fri, 12 Dec 2025 12:44:09 GMT, Serguei Spitsyn <sspitsyn at openjdk.org> wrote:

>> Hi @sspitsyn ,
>> 
>> Thank you for looking at this patch!
>> 
>>> This is a nice fix in general. Thank you for this work! I hope to complete my review tomorrow with one more pass. Question: How was this update tested? Do you have a jtreg test or you've done it manually? Also, did you run mach5 tiers 1-6 to be safe and protected against regressions?
>> 
>> The patch was tested against the current jtreg test groups (tier1-3) on macOS both amd64 and arm64. I also run jcmd and jps tools manually under root, because the change only affects the behavior under root.
>> 
>>> * It seems it was needed to inherit the `PlatformSupport` class which has the method `PlatformSupport.getTemporaryDirectory()`. But it returns the same as the removed function `Java_sun_tools_attach_VirtualMachineImpl_getTempDir()`. So, this implementation can be moved to the `jdk.attach` module.
>> 
>> The removed function `Java_sun_tools_attach_VirtualMachineImpl_getTempDir()` would return always the same string cached inside the libsystem_coreservices.dylib, that would correspond the user specific temporary path as of how the JVM process has started, that would have nothing to do with the target process/pid temporary directory.
>> 
>>> * My understanding is that class `PlatformSupportImpl` and its method `getTemporaryDirectories(int pid)`  is not currently used for `jvmstat` implementation. Is it correct?
>> 
>> I think this is not exactly so. `getTemporaryDirectories(int pid)` is used currently in the LocalVmManager to get the list of active VMs, that is consumed by `jcmd`, `jps` and `jconsole` utilities. When 0 is passed as a parameter, it returns the list of temp directories for all processes, if they were different (for example if there are containerized JVM processes under Linux).
>> 
>>> * Is it right that the `jvmstat` implementation still does not properly support root user on macOS?
>> 
>> Yes and this is what this patch was intended for.
>> 
>>>     * Do we really need 3x implementations of the MacOS `tempdir` finder function?
>> 
>> It was already 2x implementation of HotSpot perfdata files lookup, HotSpot itself uses the `os::get_temp_directory()`, on the java side the LocalVmManager in `sun.jvmstat.perfdata.monitor` relies on `getTemporaryDirectories(int pid)` in the PlatformSupport. The 3rd was the macOS native `Java_sun_tools_attach_VirtualMachineImpl_getTempDir()`, now it's proposed for removal as it returns only the current user temp path, no matter what process is being attached to.
>> 
>>>   ...
>
> @sercher  I have a plan to submit mach5 tiers 1-6 to be completely safe from regressions.
> Will approve this PR if the results are good.

Thank you @sspitsyn and @larry-cable for your reviews.

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PR Comment: https://git.openjdk.org/jdk/pull/25824#issuecomment-3655030577