Re: [PATCH v2 11/17] gdbstub: Try unlinking the unix socket before binding

["Alex Bennée" <alex.bennee@linaro.org>]

Ilya Leoshkevich <iii@linux.ibm.com> writes:

> On 2025-05-20 15:50, Michael Tokarev wrote:
>> 07.02.2025 18:31, Alex Bennée wrote:
>>> From: Ilya Leoshkevich <iii@linux.ibm.com>
>>> In case an emulated process execve()s another emulated process,
>>> bind()
>>> will fail, because the socket already exists. So try deleting it. Use
>>> the existing unix_listen() function which does this. Link qemu-user
>>> with qemu-sockets.c and add the monitor_get_fd() stub.
>>> Note that it is not possible to handle this in do_execv(): deleting
>>> gdbserver_user_state.socket_path before safe_execve() is not correct,
>>> because the latter may fail, and afterwards we may lose control.
>> Please note: this is linux-user stuff, which is usually linked
>> statically.
>> By linking it with qemu-sockets, we basically broke static linking,
>> because
>> qemu-sockets uses getaddrinfo() &Co.  The previous code, I think,
>> was there
>> for a reason, - to avoid this linkage.
>> How do you think about reverting this one and addressing the
>> original
>> problem without using qemu-sockets?
>> Alternatively, it might be possible to split qemu-sockets.c into
>> unix-related
>> stuff and generic stuff.
>> Thanks,
>> /mjt
>
> I can split it.
>
> However, wasn't it already broken in this regard?
> With fccb744f41c69fec6fd92225fe907c6e69de5d44^ I get:
>
> [2/2] Linking target qemu-s390x
> /usr/bin/ld: /usr/lib64/libglib-2.0.a(gutils.c.o): in function
> `g_get_user_database_entry':
> (.text+0xeb): warning: Using 'getpwnam_r' in statically linked
> applications requires at runtime the shared libraries from the glibc
> version used for linking
> /usr/bin/ld: (.text+0x2be): warning: Using 'getpwuid' in statically
> linked applications requires at runtime the shared libraries from the
> glibc version used for linking
> /usr/bin/ld: (.text+0x134): warning: Using 'getpwuid_r' in statically
> linked applications requires at runtime the shared libraries from the
> glibc version used for linking
>
> This comes from glib, but the ultimate result is still the same.
>
> Also, what are the symptoms of the breakage? IIUC as long as execution
> does not reach getaddrinfo(), which it in this case should not, because
> it is used only on inet paths, there should not be any issues, right?
>
> In any case, the new warning is annoying and I better fix it for this
> reason alone.

I sent:

  Message-Id: <20250520165706.3976971-1-alex.bennee@linaro.org>
  Date: Tue, 20 May 2025 17:57:06 +0100
  Subject: [RFC PATCH] util: split unix socket functions out of qemu-sockets
  From: =?UTF-8?q?Alex=20Benn=C3=A9e?= <alex.bennee@linaro.org>

Although I'm still seeing some warnings on my build:

  # QEMU configure log Tue 20 May 18:14:18 BST 2025
  # Configured with: '../../configure' '--disable-docs' '--disable-tools' '--disable-system' '--disable-vhost-kernel' '--disable-vhost-user' '--disable-vhost-net' '--static'

Gives:

  [142/142] Linking target qemu-xtensaeb
  /usr/bin/ld: /usr/lib/x86_64-linux-gnu/libglib-2.0.a(gutils.c.o): in function `g_get_user_database_entry':
  (.text+0x287): warning: Using 'getpwuid' in statically linked applications requires at runtime the shared libraries from the glibc version used for linking
  /usr/bin/ld: (.text+0xe0): warning: Using 'getpwnam_r' in statically linked applications requires at runtime the shared libraries from the glibc version used for linking
  /usr/bin/ld: (.text+0x11e): warning: Using 'getpwuid_r' in statically linked applications requires at runtime the shared libraries from the glibc version used for linking

-- 
Alex Bennée
Virtualisation Tech Lead @ Linaro