v1: https://lore.kernel.org/qemu-devel/20241024200031.80327-1-iii@linux.ibm.com/
v1 -> v2: Rebase, fix conflicts with the QEMU_RTSIG_MAP patch.
          Use qemu_get_thread_id() for %d (Helge, Richard, Warner).
          Add R-bs, except for the Richard's one on 4/8, since
          conflict resolution caused a noticeable change.
          Patches that need review:
          - [PATCH 2/8] gdbstub: Try unlinking the unix socket before binding
          - [PATCH 4/8] user: Introduce host_interrupt_signal  # linux part
          - [PATCH 6/8] gdbstub: Allow late attachment
          - [PATCH 7/8] docs/user: Document the %d placeholder and suspend=n QEMU_GDB features
          - [PATCH 8/8] tests/tcg: Add late gdbstub attach test

Hi,

This series adds the ability to attach GDB to a running qemu-user
instance. This is useful for debugging multi-process apps.

Patches 1 and 2 implement a small related feature: the ability to
create individual UNIX sockets for each child process.

Patches 3-5 add the required infrastructure. In particular, we need
to reserve a host signal for waking up threads, as discussed in [1].
By the way, the problem with atomicity of checking for pending signals
and invoking syscalls that I'm describing in that thread seems to
have already been solved by the safe_syscall infrastructure, so the
changes are fairly simple.

If this series is accepted, I will rebase the all-stop series on top
of it.

Patch 6 is the implementation, patch 7 is a documentation update,
patch 8 is a test. I tested this series on Linux and only
compile-tested on the BSDs.

Best regards,
Ilya

[1] https://lore.kernel.org/qemu-devel/94ebebf2-e775-4fd2-8fcf-921610261a7e@linaro.org/

Ilya Leoshkevich (8):
  gdbstub: Allow the %d placeholder in the socket path
  gdbstub: Try unlinking the unix socket before binding
  user: Introduce user/signal.h
  user: Introduce host_interrupt_signal
  osdep: Introduce qemu_kill_thread()
  gdbstub: Allow late attachment
  docs/user: Document the %d placeholder and suspend=n QEMU_GDB features
  tests/tcg: Add late gdbstub attach test

 bsd-user/main.c                            |   1 -
 bsd-user/signal-common.h                   |   1 -
 bsd-user/signal.c                          |  13 ++
 docs/user/main.rst                         |  16 ++-
 gdbstub/user.c                             | 131 +++++++++++++++++++--
 include/qemu/osdep.h                       |   9 ++
 include/user/signal.h                      |  25 ++++
 linux-user/main.c                          |   1 -
 linux-user/signal-common.h                 |   1 -
 linux-user/signal.c                        |  26 +++-
 linux-user/syscall.c                       |   1 +
 tests/guest-debug/run-test.py              |  15 ++-
 tests/tcg/multiarch/Makefile.target        |   9 +-
 tests/tcg/multiarch/gdbstub/late-attach.py |  28 +++++
 tests/tcg/multiarch/late-attach.c          |  41 +++++++
 util/oslib-posix.c                         |  15 +++
 16 files changed, 308 insertions(+), 25 deletions(-)
 create mode 100644 include/user/signal.h
 create mode 100644 tests/tcg/multiarch/gdbstub/late-attach.py
 create mode 100644 tests/tcg/multiarch/late-attach.c

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2.47.0