Hi Guys,
https://wiki.eclipse.org/TCF#Where_can_I_Read_Documentation.3F
I hope you don't mind me chiming in I've been following this thread. I
am a little familiar with the Eclipse Target Communications Framework (TCF).
------------------------------------------------------------------------
From https://www.eclipse.org/tcf/
TCF is a vendor-neutral lightweight, extensible network protocol for
driving embedded systems (targets).
On top of the protocol, TCF provides a complete modern debugger for
C/C++ and Ada, as well as the "Target Explorer" for system management.
TCF works out of the box for Intel, PPC and ARM Linux targets including
the Raspberry Pi. It supports Proxying and Tunneling for IoT devices,
and is particularly strong for multi-process debugging even with slow
communication links.
------------------------------------------------------------------------
Wind River was one of the original developers. The TCF specification
defines a set of services one of which is a symbols service. The
protocol was designed to support asynchronous communications. It has
been around a while. Eclipse contains a Java client plug in
implementation and there is an example 'TCF Agent' which is a server
implementation in C. For more details you can read up here.
https://wiki.eclipse.org/TCF#Where_can_I_Read_Documentation.3F
I notice on the LLDB project page http://lldb.llvm.org/projects.html
item "3 Make a high speed asynchronous communication channel to replace
the gdb-remote protocol".
The full TCF specification can also replace the MI.
Thanks,
J.R.
On 3/1/2019 13:43, Zachary Turner via lldb-dev wrote:
On Wed, Feb 27, 2019 at 4:35 PM Frédéric Riss <fr...@apple.com
<mailto:fr...@apple.com>> wrote:
On Feb 27, 2019, at 3:14 PM, Zachary Turner <ztur...@google.com
<mailto:ztur...@google.com>> wrote:
On Wed, Feb 27, 2019 at 2:52 PM Frédéric Riss <fr...@apple.com
<mailto:fr...@apple.com>> wrote:
On Feb 27, 2019, at 10:12 AM, Zachary Turner
<ztur...@google.com <mailto:ztur...@google.com>> wrote:
For what it's worth, in an earlier message I mentioned that
I would probably build the server by using mostly code from
LLVM, and making sure that it supported the union of things
currently supported by LLDB and LLVM's DWARF parsers. Doing
that would naturally require merging the two (which has been
talked about for a long time) as a pre-requisite, and I
would expect that for testing purposes we might want
something like llvm-dwarfdump but that dumps a higher level
description of the information (if we change our DWARF
emission code in LLVM for example, to output the exact same
type in slightly different ways in the underlying DWARF, we
wouldn't want our test to break, for example). So for
example imagine you could run something like `lldb-dwarfdump
-lookup-type=foo a.out` and it would dump some description
of the type that is resilient to insignificant changes in
the underlying DWARF.
At which level do you consider the “DWARF parser” to stop and
the debugger policy to start? In my view, the DWARF parser
stop at the DwarfDIE boundary. Replacing it wouldn’t get us
closer to a higher-level abstraction.
At the level where you have an alternative representation that
you no longer have to access to the debug info. In LLDB today,
this "representation" is a combination of LLDB's own internal
symbol hierarchy (e.g. lldb_private::Type,
lldb_private::Function, etc) and the Clang AST. Once you have
constructed those 2 things, the DWARF parser is out of the picture.
A lot of the complexity in processing raw DWARF comes from
handling different versions of the DWARF spec (e.g. supporting
DWARF 4 & DWARF 5), collecting and interpreting the subset of
attributes which happens be present, following references to
other parts of the DWARF, and then at the end of all this (or
perhaps during all of this), dealing with "partial information"
(e.g. something that would have saved me a lot of trouble was
missing, now I have to do extra work to find it).
I'm treading DWARF expressions as an exception though, because it
would be somewhat tedious and not provide much value to convert
those into some text format and then evaluate the text
representation of the expression since it's already in a format
suitable for processing. So for this case, you could just encode
the byte sequence into a hex string and send that.
I hinted at this already, but part of the problem (at least in my
mind) is that our "DWARF parser" is intermingled with the code
that *interprets the parsed DWARF*. We parse a little bit, build
something, parse a little bit more, add on to the thing we're
building, etc. This design is fragile and makes error handling
difficult, so part of what I'm proposing is a separation here,
where "parse as much as possible, and return an intermediate
representation that is as finished as we are able to make it".
This part is independent of whether DWARF parsing is out of
process however. That's still useful even if DWARF parsing is in
process, and we've talked about something like that for a long
time, whereby we have some kind of API that says "give me the
thing, handle all errors internally, and either return me a thing
which I can trust or an error". I'm viewing "thing which I can
trust" as some representation which is separate from the original
DWARF, and which we could test -- for example -- by writing a
tool which dumps this representation
Ok, here we are talking about something different (which you might
have been expressing since the beginning and I misinterpreted). If
you want to decouple dealing with DIEs from creating ASTs as a
preliminary, then I think this would be super valuable and it
addresses my concerns about duplicating the AST creation logic.
I’m sure Greg would have comments about the challenges of lazily
parsing the DWARF in such a design.
Well, I was originally talking about both lumped into one thing.
Because this is a necessary precursor to having it be out of process :)
Since we definitely agree on this portion, the question then becomes:
Suppose we have this firm API boundary across which we either return
errors or things that can be trusted. What are the things which can
be trusted? Are they DIEs? I'm not sure they should be, because we'd
have to synthesize DIEs on the fly in the case where we got something
that was bad but we tried to "fix" it (in order to sanitize the debug
info into something the caller can make basic assumptions about). And
additionally, it doesn't really make the client's job much easier as
far as parsing goes.
So, I think it should build up a little bit higher representation of
the debug info, perhaps by piecing together information from multiple
DIEs and sources, and return that. Definitely laziness will have to
be maintained, but I don't think that's inherently more difficult with
a design where we return something higher level than DIEs.
Thoughts?
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