Re: [Qemu-devel] [PATCH 0/3] scripts/qemu-gdb: Add event tracing support

[Markus Armbruster]

Jan Kiszka <address@hidden> writes:

> On 2015-05-15 15:21, Markus Armbruster wrote:
>> Jan Kiszka <address@hidden> writes:
>> 
>>> On 2015-05-15 14:18, Markus Armbruster wrote:
>>>> Peter Maydell <address@hidden> writes:
>>>>
>>>>> On 15 May 2015 at 08:58, Markus Armbruster <address@hidden> wrote:
>>>>>> Since you're touching qemu-gdb.py anyway, could you stick in a brief
>>>>>> comment explaining how to put it to use?
>>>>>
>>>>> Good idea. It turns out the answer is just "source it from gdb",
>>>>> but it took me a little while to find that out, so worth commenting.
>>>>> I also have a patch which makes it do the 'ignore SIGUSR1' bit
>>>>> by doing 'handle SIGUSR1 pass noprint nostop' for you.
>>>>
>>>> Here's how to load scripts/qemu-gdb.py automatically:
>>>>
>>>> * Apply the appended patch to turn it into a gdb init file
>>>>
>>>>   That's what it is, after all.  It's not a standalone Python program.
>>>>
>>>> * Tell gdb to trust it
>>>>
>>>>   Add a line like
>>>>
>>>>       add-auto-load-safe-path ~/work/qemu/scripts/qemu-gdb.py
>>>>
>>>>   to your ~/.gdbinit
>>>>
>>>> * Link it into the directory where you run gdb --args qemu...

Left out the important part: name the link .gdbinit !

>>>> * Verify it works:
>>>>
>>>>       $ gdb
>>>>       [...]
>>>>       (gdb) help qemu
>>>>       Prefix for QEMU debug support commands
>>>>
>>>>       List of qemu subcommands:
>>>>
>>>>       qemu coroutine -- Display coroutine backtrace
>>>>       qemu mtree -- Display the memory tree hierarchy
>>>>
>>>>       Type "help qemu" followed by qemu subcommand name for full 
>>>> documentation.
>>>>       Type "apropos word" to search for commands related to "word".
>>>>       Command name abbreviations are allowed if unambiguous.
>>>>       (gdb) 
>>>>
>>>> If you know a better way to do this, please post it.
>>>>
>>>
>>> Yep, that's the basic idea behind gdb python scripts: myapp-gdb.py gets
>>> auto-pulled on "gdb myapp". Since some gdb 7.x, we have that security
>>> feature above which prevents pulling from arbitrary sources.
>>>
>>>>
>>>> diff --git a/scripts/qemu-gdb.py b/scripts/qemu-gdb.py
>>>> index 6c7f4fb..ac3087c 100644
>>>> --- a/scripts/qemu-gdb.py
>>>> +++ b/scripts/qemu-gdb.py
>>>> @@ -1,5 +1,3 @@
>>>> -#!/usr/bin/python
>>>> -
>>>>  # GDB debugging support
>>>>  #
>>>>  # Copyright 2012 Red Hat, Inc. and/or its affiliates
>>>> @@ -13,7 +11,7 @@
>>>>  # Contributions after 2012-01-13 are licensed under the terms of the
>>>>  # GNU GPL, version 2 or (at your option) any later version.
>>>>  
>>>> -
>>>> +python
>>>
>>> What is this line doing?
>> 
>> Found here:
>> https://stackoverflow.com/questions/16553283/python-code-in-gdb-init-file-gdbinit
>
> The author there puts his code into .gdbinit, which is a gdb script, not
> a python one.

That's exactly what I did in my experiments.

>> 
>> It doesn't work for me without it.
>
> When sourcing? Works fine here (gdb 7.7.something).

Nope, when auto-loading as .gdbinit from the current directory.

> In any case, when you pull in the script via auto-load, that extra
> non-python statement will break. Try "python python". ;)

I know nothing about this kind of auto-load.

I just read gdb-kernel-debugging.txt, and still know nothing :)

Digging around in "info gdb"... aha, there's a section on "Python
Auto-loading".  Hmm... "set debug auto-load on"...  Try linking it into
the build tree, like this:

    $ cd bld/x86_64-softmmu/
    $ ln -s ../../scripts/qemu-gdb.py qemu-system-x86_64-gdb.py

Works.

Could you post a patch so that make creates such links automatically?