[lldb-dev] Increasing support for other gdbservers

Wed Apr 1 10:55:35 PDT 2015

May be this is a stupid question, are there reasons that lldb needs to 
use xml format ? Can it switch to using YAML ?

If not, may be having a XML parser like a YAML parser would be useful 
inside of LLVM ??

Shankar Easwaran

On 4/1/2015 11:37 AM, Zachary Turner wrote:
> I think forcing python would be significantly worse actually.  libxml2 is
> already used in some places in the code, and is used by clang.  So it's
> already the accepted way to parse xml in LLVM projects, and even in LLDB
> since it's already used in a couple places like what Jason mentioned
> earlier.  Plus, how would you do it in python?  It seems like you'd have to
> write hundreds of lines of ugly C code to set up callables and invoke them
> with the right arguments, since we would be calling Python from C.  And
> then what happens when you don't want to link against python?  You lose the
> ability to use these seemingly unrelated features.
>
> On Wed, Apr 1, 2015 at 9:26 AM Ted Woodward <ted.woodward at codeaurora.org>
> wrote:
>
>> But which is a worse dependency when we want to parse gdbserver’s xml
>> files – add a dependency to libxml2, or force python?
>>
>>
>>
>> *From:* Zachary Turner [mailto:zturner at google.com]
>> *Sent:* Wednesday, April 01, 2015 10:37 AM
>> *To:* Ted Woodward; Vince Harron
>>
>>
>> *Cc:* lldb-dev at cs.uiuc.edu
>> *Subject:* Re: [lldb-dev] Increasing support for other gdbservers
>>
>>
>>
>> You mean write python code to do xml parsing? I've done some work lately
>> to separate python from the rest of the codebase so that in theory it can
>> be replaced with an interpreter for a different language. Plus there's
>> already LLDB_DISABLE_PYTHON, and since the functionality that the xml
>> parser is needed for is not logically tied to the python interpreter, it
>> would be a shame to make them physically tied.
>>
>> Plus clang already uses libxml2 so it makes some sense to remain
>> consistent
>>
>> On Wed, Apr 1, 2015 at 8:29 AM Ted Woodward <ted.woodward at codeaurora.org>
>> wrote:
>>
>> Since you mentioned Python…a thought came to mind. Python includes several
>> XML parsers. I use minidom to parse the TLB and Pagetable XML files that
>> the Hexagon Simulator produces and Hexagon GDB consumes. If we’re going to
>> require a dependency, why not one that we already use, and use a Python XML
>> parser?
>>
>>
>>
>> *From:* lldb-dev-bounces at cs.uiuc.edu [mailto:lldb-dev-bounces at cs.uiuc.edu]
>> *On Behalf Of *Vince Harron
>> *Sent:* Wednesday, April 01, 2015 2:46 AM
>> *To:* Zachary Turner
>>
>>
>> *Cc:* lldb-dev at cs.uiuc.edu
>> *Subject:* Re: [lldb-dev] Increasing support for other gdbservers
>>
>>
>>
>> I think I get it.  Objection withdrawn.
>>
>>
>>
>> On Wed, Apr 1, 2015 at 12:44 AM, Vince Harron <vince at nethacker.com> wrote:
>>
>> This is a pretty cool feature for people who want to use lldb on windows
>> against gdbserver
>>
>>
>>
>>
>>
>> On Tue, Mar 31, 2015 at 5:57 PM, Zachary Turner <zturner at google.com>
>> wrote:
>>
>> I think uses of it would only need to be guarded if we plan to use it in
>> generic code. So yea, if all the code that uses it goes into a file that
>> isn't compiled on windows anyway, then the problem becomes very simple
>>
>> On Tue, Mar 31, 2015 at 5:41 PM Jason Molenda <jmolenda at apple.com> wrote:
>>
>> fwiw on Mac OS X we use libxml2 over in
>> Plugins/SymbolVendor/MacOSX/SymbolVendorMacOSX.cpp.  That plugin's
>> initialization is #ifdef __APPLE__ over in SystemInitializerFull.cpp; we
>> don't have ifdef guard around the use of libxml2 in SymbolVendorMacOSX
>> itself.
>>
>>
>>> On Mar 31, 2015, at 4:18 PM, Vince Harron <vince at nethacker.com> wrote:
>>>
>>> I really don't want LLDB to embed a copy of libxml2.  I think we should
>> build it externally and reference it from LLDB.  Systems with package
>> managers can get this trivially.  Windows can download and build all
>> dependencies with one script.
>>> On Mar 31, 2015 2:10 PM, "Colin Riley" <colin at codeplay.com> wrote:
>>> I noticed that use in cmake also. FWIW, my primary LLDB platform is
>> Windows, which is why we were using TinyXML2 for ease of prototyping. If
>> libxml2 works on all the targets we will use it - I do worry about the
>> usual issues you get with windows prebuilts. So source may still be
>> required. We'll look into it.
>>> Colin
>>>
>>> On 31/03/2015 20:45, Zachary Turner wrote:
>>>> There's already some stuff in the CMake to try to find libxml, but it's
>> behind a Darwin specific branch in the CMake.  So I think what would need
>> to happen is that we move this into a platform agnostic codepath, and then
>> set a define like LLDB_HAVE_LIBXML2 in the code to a value that indicates
>> whether it is present (search clang for CLANG_HAVE_LIBXML in *.* to see how
>> this is done).  Then, in the code, we would need to put xml code behind a
>> check for this define.
>>>> On Tue, Mar 31, 2015 at 10:02 AM Zachary Turner <zturner at google.com>
>> wrote:
>>>> A good rule of thumb for anything is that "Windows doesn't have it" and
>> that holds true for libxml2 as well.  It appears that libxml2 does support
>> Windows though (http://xmlsoft.org/downloads.html), it just isn't
>> something that's there by default.  It would be nice if everyone were using
>> the same thing, could we clone this repo in our own repo and then just
>> build it ourselves as part of the build process.  The license looks very
>> permissive, but IANAL.
>>>> On Tue, Mar 31, 2015 at 9:47 AM Greg Clayton <gclayton at apple.com>
>> wrote:
>>>>> On Mar 31, 2015, at 3:35 AM, Aidan Dodds <aidan at codeplay.com> wrote:
>>>>>
>>>>> On 30/03/2015 18:38, Greg Clayton wrote:
>>>>>> I know about the register numbering stuff and I would love to see
>> support for the "$qXfer:features:" added to LLDB. The one thing this data
>> doesn't contain is the register numbers for the ABI (DWARF register numbers
>> (for debug info), compiler register numbers (for like .eh_frame)), but that
>> info could be inferred from an ABI plugin that we could infer from the
>> "osabi" of "GNU/Linux" in the target.xml:
>>>>>> So please do submit patches that implement this and we will be
>> happy to approve them.
>>>>> I am currently prototyping $qXfer:features support in LLDB with an
>> aim to upstream it. It will require an XML parser, so I wanted to have a
>> discussion about adding one to LLDB.
>>>> Most unix variants have libxml2 that is available. I am not sure on
>> windows though. I have CC'ed Zachary to get some input on windows XML (in
>> case LLVM doesn't already have some support for this).
>>>>> I have been using TinyXML2 in my prototype, which is open sourced
>> under the ZLib license. Is there any policy in LLDB for handling external
>> library dependencies?
>>>>> Would there be objections to TinyXML2 making its way into the LLDB
>> code base as an external? Writing a new XML parser from scratch in LLDB
>> isn't ideal.
>>>> It would be great to stick with stuff that everyone has installed and
>> hopefully that is libxml2. Windows is the biggest question. I am also not
>> sure if llvm or clang has any XML support, but we should first look to see
>> if llvm has XML support and if not, then look for alternatives. We
>> definitely do not want to write our own.
>>>>> I would still like to have a discussion about adding a plugin
>> architecture to gdb-remote making it easier to handle packets outwith the
>> LLDB based servers. The code in gdb-remote that sends and handles packets
>> is scattered over one or two huge classes, it would be beneficial to start
>> looking at breaking this up and modularizing it. At least for the packets
>> which are not supported by lldb's own RSP producers.
>>>> I say just build all and any support it into
>> GDBRemoteCommunicationClient and GDBRemoteCommunicationServer. I don't see
>> the need to break it up.
>>>> Greg Clayton
>>>>
>>>>
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