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Re: [PATCH] Linux kernel thread runtime support
- From: Philipp Rudo <prudo at linux dot vnet dot ibm dot com>
- To: Peter Griffin <peter dot griffin at linaro dot org>
- Cc: gdb-patches at sourceware dot org, palves at redhat dot com, brobecker at adacore dot com, kevinb at redhat dot com, cagney at gnu dot org, dje at google dot com, drow at false dot org, kettenis at gnu dot org, yao dot qi at arm dot com, stanshebs at google dot com, Ulrich dot Weigand at de dot ibm dot com, elena dot zannoni at oracle dot com, eliz at gnu dot org, arnez at linux dot vnet dot ibm dot com
- Date: Wed, 15 Feb 2017 17:45:12 +0100
- Subject: Re: [PATCH] Linux kernel thread runtime support
- Authentication-results: sourceware.org; auth=none
- References: <1482427864-4317-1-git-send-email-peter.griffin@linaro.org>
Hi Peter,
while looking into your patch in more detail, I found some problems
with your code. In particular I dislike your general approach using
private_thread_info, since the remote-target already uses this field
inside thread_info. Thus "forcibly" adding your own version of
private_thread_info, like you do, can lead to undefined behavior. For
example remote_stopped_by_sw_breakpoint requires information from
private_tread_info and won't work reliably. Even worse, remote_resume
you call by passing target_resume to the target beneath writes (via
resume_clear_thread_private_info) to the private_thread_info thus
causing a memory corruption.
With your and the remote-target being that interlaced, I don't think
it's possible to separate them cleanly. That's why I see no other way
than allowing each target to manage its own thread list.
Philipp
On Thu, 22 Dec 2016 17:31:03 +0000
Peter Griffin <peter.griffin@linaro.org> wrote:
> Hi GDB maintainers,
>
> The following patch implements a Linux kernel thread runtime stratum
> which can be used when using GDB to debug a Linux kernel. For example
> when connecting to a QEMU GDB stub, or OpenOCD which then communicates
> with the target via JTAG or SWD.
>
> This patch is a refactored version based on the 'Linux kernel
> debugger' GDB plugin written at STMicroelectronics which used to
> be packaged with their JTAG debuggers. There has been some discussion
> previously on the list by myself [1], Kieran [2] and one of the
> original authors at ST Marc Titinger [3].
>
> This patchset I'm hoping is a lot closer to something which can
> be upstreamed to GDB project after some discussion about structure
> with Yao Qi at Linaro Connect, the code has been refactored to be
> structured much more like the existing upstream thread runtimes (such
> as ravenscar-thread.c and sparc-ravenscar-thread etc).
>
> Since the original email [1] various helper commands have also been
> migrated into python and merged into the Linux kernel source tree.
> The GDB python extensions, combined with the linux-kthread GDB
> thread runtime implemented in this patchset provide a powerful
> Linux kernel debug solution, and is a working implementation
> of what Andreas talked about on slide 17 and 18 of his talk at GNU
> Cauldron [4].
>
> I have currently been testing this patchset using mainline GDB
> debugging arm-linux kernels in Qemu and via OpenoCD to real hardware.
> It is straight forward with the current strructure to add new
> architecture support, and I'm looking at adding PowerPC so I can
> easily validate big endian targets.
>
> What I'm really hoping for now is some patch review on the GDB
> mailing list from the GDB maintainers and community with a view to
> getting this functionality which has been talked about for quite a
> few years finally merged to the upstream GDB project.
>
> All patch review feedback greatfully received :)
>
> kind regards,
>
> Peter.
>
> [1] https://cygwin.com/ml/gdb/2015-09/msg00032.html
> [2] https://www.sourceware.org/ml/gdb/2016-01/msg00028.html
> [3]
> https://lists.linaro.org/pipermail/linaro-toolchain/2011-November/001754.html
> [4]
> https://gcc.gnu.org/wiki/cauldron2015?action=AttachFile&do=view&target=Andreas+Arnez_+Debugging+Linux+kernel+dumps+with+GDB.pdf
>
>
>
> Peter Griffin (1):
> Add Linux kernel thread runtime support.
>
> gdb/ChangeLog | 12 +
> gdb/Makefile.in | 8 +-
> gdb/arm-linux-kthread.c | 178 +++++
> gdb/arm-linux-kthread.h | 27 +
> gdb/arm-tdep.c | 4 +
> gdb/configure.tgt | 6 +-
> gdb/gdbarch.c | 23 +
> gdb/gdbarch.h | 5 +
> gdb/gdbarch.sh | 3 +
> gdb/linux-kthread.c | 1828
> +++++++++++++++++++++++++++++++++++++++++++++++
> gdb/linux-kthread.h | 223 ++++++ 11 files changed, 2311
> insertions(+), 6 deletions(-) create mode 100644
> gdb/arm-linux-kthread.c create mode 100644 gdb/arm-linux-kthread.h
> create mode 100644 gdb/linux-kthread.c
> create mode 100644 gdb/linux-kthread.h
>