Thank you Daniel. Comment's fixed. Cheers, Thomas
On Sun, Jun 18, 2023 at 2:25 AM Daniel Jarabek <jarabe...@gmail.com> wrote: > Hi Thomas, > > Thank you for this quick fix! > > I have tested (after much difficultly getting cross compilation to work - > a good learning experience) and this fix works for me. Using QEMU_STRACE, I > verified that argv[0] is now the program name and argv[1] contains the fd > data. > > While you are correct, that changes to jspawnhelper aren't needed (since > it uses argv[argc-1]), you may want to update this comment here: > https://github.com/openjdk/jdk/blob/959a61fdd483c9523764b9ba0972f59ca06db0ee/src/java.base/unix/native/jspawnhelper/jspawnhelper.c#L139 > > -DJ > > On 6/17/2023 16:43, Thomas Stüfe wrote: > > 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 >>> >>
