Mind testing https://github.com/openjdk/jdk/pull/14531 ?
On Sat, Jun 17, 2023 at 8:20 PM Thomas Stüfe <thomas.stu...@gmail.com> wrote: > Hi Daniel, > > thank you for that thorough analysis. I opened > https://bugs.openjdk.org/browse/JDK-8310265 to track this issue. > > Looking at the code, this should be easy to fix, we would not even have to > fix jspawnhelper itself, just its spawn point. > > I did a small patch which seemed to work. But this code is notorious for > being tricky and I may overlooking something. Lets see. > > Cheers, Thomas > > > > > > On Sat, Jun 17, 2023 at 6:33 AM Daniel Jarabek <jarabe...@gmail.com> > wrote: > >> Hi, >> >> While trying to run jshell in qemu-user-static using binfmt_misc >> (specifically, using this docker based tool [1]), I ran into an issue. >> Jshell would fail to start and print `This command is not for general >> use and should only be run as the result of a call to >> ProcessBuilder.start() or Runtime.exec() in a java application` along >> with a stack trace including `Failed to exec spawn helper`. After >> searching this error, I found JDK-8296001 [2]. This issue presented a >> very similar scenario (using a userspace architecture emulator). I >> looked into this issue and I believe I have identified the root cause. >> >> My specific investigation was done around jdk17, but this issue also >> occurs on jdk20 and older jdk versions (though it seems like the "spawn" >> strategy is not used by default on linux with jdk 8 and 11). >> >> Note: I use argv0 to refer to "argv[0]" to prevent confusion with >> footnotes. >> >> Traditionally, argv0 contains the name of the program being executed. >> While this is more a convention than anything [3], it is very widely >> used. jspawnhelper [4] is an executable used to assist in launching >> processes via ProcessBuilder and Runtime.exec. Unlike the convention, >> jspawnhelper uses argv0 for passing data [5]. When binfmts_misc [6] >> executes an interpreter, it overwrites argv0, unless a flag is set. This >> causes jspawnhelper to fail to parse argv0 (since it's the application >> path, and not the data sent by the JDK), so it prints the warning about >> not being for general use. By setting the binfmt_misc `P` >> (preserve-argv0) flag, it preserves argv0 which fixes this problem. >> >> Since qemu-user correctly supports this flag, all I had to do to fix the >> issue in my case was run qemu-binfmt-conf.sh with `--preserve-argv0 yes` >> to set that flag. It's likely that in the case of the above issue, the >> same problem is occurring and it may have a similar resolution. This >> could be fixed in OpenJDK by using argv1 instead, but at least in my >> case of binfmts_misc, this is an external configuration issue that can >> be easily fixed. However, I would appreciate it if someone with >> permission could comment on the above issue with a link to this email >> for anyone who runs into this in the future. >> >> -DJ >> >> [1] https://github.com/multiarch/qemu-user-static >> [2] https://bugs.openjdk.org/browse/JDK-8296001 >> [3] https://stackoverflow.com/a/2051031 >> [4] >> >> https://github.com/openjdk/jdk/blob/master/src/java.base/unix/native/jspawnhelper/jspawnhelper.c >> [5] >> >> https://github.com/openjdk/jdk/blob/bcc4d36857b0907e865d0afc4447f9b0780f8101/src/java.base/unix/native/libjava/ProcessImpl_md.c#L498-L500 >> [6] https://docs.kernel.org/admin-guide/binfmt-misc.html >> >
