[Bug server/26116] New: gdbserver with zsh as the shell hangs at startup when .zshenv forks

[Bug server/26116] New: gdbserver with zsh as the shell hangs at startup when .zshenv forks

[simark at simark dot ca]

https://sourceware.org/bugzilla/show_bug.cgi?id=26116

            Bug ID: 26116
           Summary: gdbserver with zsh as the shell hangs at startup when
                    .zshenv forks
           Product: gdb
           Version: HEAD
            Status: NEW
          Severity: normal
          Priority: P2
         Component: server
          Assignee: unassigned at sourceware dot org
          Reporter: simark at simark dot ca
  Target Milestone: ---

When using zsh as the shell and a command that forks in ~/.zshenv, like
`/bin/echo` here (plain `echo` is the shell builtin, which doesn't fork):

$ cat ~/.zshenv 
echo Before
/bin/echo Hello
echo After

... gdbserver hangs at startup

$ SHELL=zsh ./gdbserver localhost:9000 /bin/ls 
Before
Hello
<hangs here>

Note that when using a similar bash feature, the BASH_ENV environment variable,
it doesn't hang:

$ SHELL=bash BASH_ENV=~/.zshenv ./gdbserver localhost:9000 /bin/ls 
Before
Hello
After
Process /bin/ls created; pid = 745096
Listening on port 9000

It's also possible that the issue is in zsh, but I haven't dug enough to
understand what's happening exactly.

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[Bug server/26116] gdbserver with zsh as the shell hangs at startup when .zshenv forks

[dajiang0055 at gmail dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=26116

dajiang0055 at gmail dot com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |dajiang0055 at gmail dot com

--- Comment #1 from dajiang0055 at gmail dot com ---
I had the same problem with tcsh. 
It seems that gdbserver hangs in sigsuspend() and wait for SIGTRAP.

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[Bug server/26116] gdbserver with zsh as the shell hangs at startup when .zshenv forks

[corydoras at ridiculousfish dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=26116

ridiculous_fish <corydoras at ridiculousfish dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |corydoras at ridiculousfish dot co
                   |                            |m

--- Comment #2 from ridiculous_fish <corydoras at ridiculousfish dot com> ---
fish shell is also seeing this - see
https://github.com/fish-shell/fish-shell/issues/7957

My investigation got as far as follows: gdbserver forks in preparation for
exec'ing the shell. Before exec, it requests ptrace on itself (in
`linux_ptrace_fun`). This causes signals to be delivered to gdbserver before
the inferior shell; however gdbserver does not then arrange for the signal to
be delivered to the shell so it is dropped. fish (and presumably zsh) relies on
SIGCHLD to reap processes, so fish ends up hanging.

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[Bug server/26116] gdbserver with zsh as the shell hangs at startup when .zshenv forks

[k4lizen at proton dot me]

https://sourceware.org/bugzilla/show_bug.cgi?id=26116

k4lizen <k4lizen at proton dot me> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |k4lizen at proton dot me

--- Comment #3 from k4lizen <k4lizen at proton dot me> ---
Encountered this downstream:
https://github.com/Gallopsled/pwntools/issues/2377
    workaround: https://github.com/Gallopsled/pwntools/pull/2378

https://github.com/Gallopsled/pwntools/pull/2321
    which links: https://github.com/Gallopsled/pwntools/issues/2030
                 https://github.com/Gallopsled/pwntools/issues/2060
                
https://github.com/cvanloo/rop/blob/ec10a12e3256344e38e4c745781962f5245f5715/README.md?plain=1#L481

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