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[PULL 44/44] docs: Document how to use gdb with unix sockets


From: Peter Maydell
Subject: [PULL 44/44] docs: Document how to use gdb with unix sockets
Date: Wed, 25 Aug 2021 11:35:34 +0100

From: Sebastian Meyer <meyer@absint.com>

With gdb 9.0 and better it is possible to connect to a gdbstub
over unix sockets, which is better than a TCP socket connection
in some situations. The QEMU command line to set this up is
non-obvious; document it.

Signed-off-by: Sebastian Meyer <meyer@absint.com>
Message-id: 162867284829.27377.4784930719350564918-0@git.sr.ht
[PMM: Tweaked commit message; adjusted wording in a couple of
places; fixed rST formatting issue; moved section up out of
the 'advanced debugging options' subsection]
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
---
 docs/system/gdb.rst | 26 +++++++++++++++++++++++++-
 1 file changed, 25 insertions(+), 1 deletion(-)

diff --git a/docs/system/gdb.rst b/docs/system/gdb.rst
index 144d083df31..bdb42dae2fe 100644
--- a/docs/system/gdb.rst
+++ b/docs/system/gdb.rst
@@ -15,7 +15,8 @@ The ``-s`` option will make QEMU listen for an incoming 
connection
 from gdb on TCP port 1234, and ``-S`` will make QEMU not start the
 guest until you tell it to from gdb. (If you want to specify which
 TCP port to use or to use something other than TCP for the gdbstub
-connection, use the ``-gdb dev`` option instead of ``-s``.)
+connection, use the ``-gdb dev`` option instead of ``-s``. See
+`Using unix sockets`_ for an example.)
 
 .. parsed-literal::
 
@@ -100,6 +101,29 @@ not just those in the cluster you are currently working 
on::
 
   (gdb) set schedule-multiple on
 
+Using unix sockets
+==================
+
+An alternate method for connecting gdb to the QEMU gdbstub is to use
+a unix socket (if supported by your operating system). This is useful when
+running several tests in parallel, or if you do not have a known free TCP
+port (e.g. when running automated tests).
+
+First create a chardev with the appropriate options, then
+instruct the gdbserver to use that device:
+
+.. parsed-literal::
+
+   |qemu_system| -chardev 
socket,path=/tmp/gdb-socket,server=on,wait=off,id=gdb0 -gdb chardev:gdb0 -S ...
+
+Start gdb as before, but this time connect using the path to
+the socket::
+
+   (gdb) target remote /tmp/gdb-socket
+
+Note that to use a unix socket for the connection you will need
+gdb version 9.0 or newer.
+
 Advanced debugging options
 ==========================
 
-- 
2.20.1




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