docs: Document how to use gdb with unix socketspull-target-arm-20210825

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>

1 files changed, 25 insertions, 1 deletions

diff --git a/docs/system/gdb.rst b/docs/system/gdb.rst
index 144d083df3..bdb42dae2f 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
 ==========================