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<p>Hi Thomas,<br>
</p>
<p>Thank you for this quick fix!</p>
<p>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.</p>
<p>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:
<a class="moz-txt-link-freetext" href="https://github.com/openjdk/jdk/blob/959a61fdd483c9523764b9ba0972f59ca06db0ee/src/java.base/unix/native/jspawnhelper/jspawnhelper.c#L139">https://github.com/openjdk/jdk/blob/959a61fdd483c9523764b9ba0972f59ca06db0ee/src/java.base/unix/native/jspawnhelper/jspawnhelper.c#L139</a></p>
<p>-DJ</p>
<p></p>
<div class="moz-cite-prefix">On 6/17/2023 16:43, Thomas Stüfe wrote:<br>
</div>
<blockquote type="cite"
cite="mid:CAA-vtUwkxqpAE1Ff-Uhno_HAGMBgD9tdR+zC0etD=LR0DvNfcw@mail.gmail.com">
<meta http-equiv="content-type" content="text/html; charset=UTF-8">
<div dir="ltr">Mind testing <a
href="https://github.com/openjdk/jdk/pull/14531"
moz-do-not-send="true" class="moz-txt-link-freetext">https://github.com/openjdk/jdk/pull/14531</a>
?</div>
<br>
<div class="gmail_quote">
<div dir="ltr" class="gmail_attr">On Sat, Jun 17, 2023 at
8:20 PM Thomas Stüfe <<a
href="mailto:thomas.stuefe@gmail.com" moz-do-not-send="true"
class="moz-txt-link-freetext">thomas.stuefe@gmail.com</a>>
wrote:<br>
</div>
<blockquote class="gmail_quote"
style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-style:solid;border-left-color:rgb(204,204,204);padding-left:1ex">
<div dir="ltr">Hi Daniel,
<div><br>
</div>
<div>thank you for that thorough analysis. I opened <a
href="https://bugs.openjdk.org/browse/JDK-8310265"
target="_blank" moz-do-not-send="true"
class="moz-txt-link-freetext">https://bugs.openjdk.org/browse/JDK-8310265</a>
to track this issue.</div>
<div><br>
</div>
<div>Looking at the code, this should be easy to fix, we
would not even have to fix jspawnhelper itself, just its
spawn point.</div>
<div><br>
</div>
<div>I did a small patch which seemed to work. But this code
is notorious for being tricky and I may overlooking
something. Lets see.</div>
<div><br>
</div>
<div>Cheers, Thomas</div>
<div><br>
</div>
<div><br>
</div>
<div><br>
</div>
<div><br>
</div>
</div>
<br>
<div class="gmail_quote">
<div dir="ltr" class="gmail_attr">On Sat, Jun 17, 2023 at
6:33 AM Daniel Jarabek <<a
href="mailto:jarabekit@gmail.com" target="_blank"
moz-do-not-send="true" class="moz-txt-link-freetext">jarabekit@gmail.com</a>>
wrote:<br>
</div>
<blockquote class="gmail_quote"
style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-style:solid;border-left-color:rgb(204,204,204);padding-left:1ex">Hi,<br>
<br>
While trying to run jshell in qemu-user-static using
binfmt_misc <br>
(specifically, using this docker based tool [1]), I ran
into an issue. <br>
Jshell would fail to start and print `This command is not
for general <br>
use and should only be run as the result of a call to <br>
ProcessBuilder.start() or Runtime.exec() in a java
application` along <br>
with a stack trace including `Failed to exec spawn
helper`. After <br>
searching this error, I found JDK-8296001 [2]. This issue
presented a <br>
very similar scenario (using a userspace architecture
emulator). I <br>
looked into this issue and I believe I have identified the
root cause.<br>
<br>
My specific investigation was done around jdk17, but this
issue also <br>
occurs on jdk20 and older jdk versions (though it seems
like the "spawn" <br>
strategy is not used by default on linux with jdk 8 and
11).<br>
<br>
Note: I use argv0 to refer to "argv[0]" to prevent
confusion with footnotes.<br>
<br>
Traditionally, argv0 contains the name of the program
being executed. <br>
While this is more a convention than anything [3], it is
very widely <br>
used. jspawnhelper [4] is an executable used to assist in
launching <br>
processes via ProcessBuilder and Runtime.exec. Unlike the
convention, <br>
jspawnhelper uses argv0 for passing data [5]. When
binfmts_misc [6] <br>
executes an interpreter, it overwrites argv0, unless a
flag is set. This <br>
causes jspawnhelper to fail to parse argv0 (since it's the
application <br>
path, and not the data sent by the JDK), so it prints the
warning about <br>
not being for general use. By setting the binfmt_misc `P`
<br>
(preserve-argv0) flag, it preserves argv0 which fixes this
problem.<br>
<br>
Since qemu-user correctly supports this flag, all I had to
do to fix the <br>
issue in my case was run qemu-binfmt-conf.sh with
`--preserve-argv0 yes` <br>
to set that flag. It's likely that in the case of the
above issue, the <br>
same problem is occurring and it may have a similar
resolution. This <br>
could be fixed in OpenJDK by using argv1 instead, but at
least in my <br>
case of binfmts_misc, this is an external configuration
issue that can <br>
be easily fixed. However, I would appreciate it if someone
with <br>
permission could comment on the above issue with a link to
this email <br>
for anyone who runs into this in the future.<br>
<br>
-DJ<br>
<br>
[1] <a
href="https://github.com/multiarch/qemu-user-static"
rel="noreferrer" target="_blank" moz-do-not-send="true"
class="moz-txt-link-freetext">https://github.com/multiarch/qemu-user-static</a><br>
[2] <a href="https://bugs.openjdk.org/browse/JDK-8296001"
rel="noreferrer" target="_blank" moz-do-not-send="true"
class="moz-txt-link-freetext">https://bugs.openjdk.org/browse/JDK-8296001</a><br>
[3] <a href="https://stackoverflow.com/a/2051031"
rel="noreferrer" target="_blank" moz-do-not-send="true"
class="moz-txt-link-freetext">https://stackoverflow.com/a/2051031</a><br>
[4] <br>
<a
href="https://github.com/openjdk/jdk/blob/master/src/java.base/unix/native/jspawnhelper/jspawnhelper.c"
rel="noreferrer" target="_blank" moz-do-not-send="true"
class="moz-txt-link-freetext">https://github.com/openjdk/jdk/blob/master/src/java.base/unix/native/jspawnhelper/jspawnhelper.c</a><br>
[5] <br>
<a
href="https://github.com/openjdk/jdk/blob/bcc4d36857b0907e865d0afc4447f9b0780f8101/src/java.base/unix/native/libjava/ProcessImpl_md.c#L498-L500"
rel="noreferrer" target="_blank" moz-do-not-send="true"
class="moz-txt-link-freetext">https://github.com/openjdk/jdk/blob/bcc4d36857b0907e865d0afc4447f9b0780f8101/src/java.base/unix/native/libjava/ProcessImpl_md.c#L498-L500</a><br>
[6] <a
href="https://docs.kernel.org/admin-guide/binfmt-misc.html"
rel="noreferrer" target="_blank" moz-do-not-send="true"
class="moz-txt-link-freetext">https://docs.kernel.org/admin-guide/binfmt-misc.html</a><br>
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