[lldb-dev] Adding D language demangling support

Thu Sep 22 09:56:54 PDT 2016

On Wed, Sep 21, 2016 at 4:13 PM, Greg Clayton via lldb-dev <
lldb-dev at lists.llvm.org> wrote:

> You could have a setting that allows you to specify prefix as the key with
> a dylib path as a value. Would you expect a function with certain name or
> would you need to specify the function name (probably mangled) as well? Let
> me know what you are thinking?
>
>
whatever works it doesn't really matter so long there's something to get
started, I was going for something simple to start with but if you want
this level of flexibility how about using a json config file:

export LLDB_DEMANGLE_CONFIG_FILE="~/.lldbl.demangle.conf"

cat ~/.lldbl.demangle.conf

{"demangle":
  ["D": {"prefix" : "_D", "shared_libary_file" :
"/path/libdemangled.dylib", "mangled_name", "_demangle_custom_D"}],
  ["nim":  /* same for nim language */ ],
}

Greg
>
> > On Sep 21, 2016, at 3:50 PM, Timothee Cour <timothee.cour2 at gmail.com>
> wrote:
> >
> >
> >
> > On Wed, Sep 21, 2016 at 3:35 PM, Greg Clayton via lldb-dev <
> lldb-dev at lists.llvm.org> wrote:
> > Sounds like you could then make a setting that is a dictionary where you
> say what the prefix is (like maybe "_D") and the value is the path to the
> tool to use? This would be easy to implement. Demangling does tend to be
> one of the most expensive parts of symbol file and debug info parsing, so
> if you do this, you will want to make sure the shell tool can be spawned
> and kept running maybe?
> >
> > Greg
> >
> >
> > where in the lldb code would be such entry point?
> >
> > instead of a binary it can just be a library dynamically loaded via
> dlopen (as i wrote, though I should've called it LLDB_DEMANGLER_LIB instead
> of LLDB_DEMANGLER_EXE), and the dynamically loaded symbol be cached to make
> sure it's dlopen'd at most once per process.
> >
> > Then it's easy enough for us to write a demangleCustom that is fast on
> the D side of things. It can also work with a binary instead of a dllib but
> would be a bit slower (could have a client server model, but that's more
> complex than the simple dllib solution i was proposing).
> >
> > yes, we could use a prefix for that as well.
> >
> >
> > > On Sep 21, 2016, at 3:30 PM, Timothee Cour <timothee.cour2 at gmail.com>
> wrote:
> > >
> > >
> > >
> > > On Wed, Sep 21, 2016 at 3:10 PM, Greg Clayton <gclayton at apple.com>
> wrote:
> > > There is no external demangling plug-in infrastructure at the moment,
> but you could add functionality that would allow it. No one is going to
> have D installed by default. Where do you expect your demangler dylib to
> live?
> > > Would you just add code that tries to locate the dylib in N places on
> the current system and try to dlopen it? Avoiding duplication and just not
> having the functionality at all unless something else is might not make it
> that useful. Is D stable? Is the mangling changing at all? Will you require
> a demangler to be vended with each new version of the tool? Are all
> previous demanglings still valid in newer versions? Can you figure out the
> version of the D from a compiled executable so that you might be able to
> locate one of 5 different installs of D and select the right one? Let me
> know what you use case is.
> > >
> > > Greg
> > >
> > >
> > > one simple flexible backward compatible option would be to have a
> generic environment variable:
> > >
> > > ```
> > > export LLDB_DEMANGLER_EXE="/usr/bin/ddemangle"
> > > lldb myprog
> > > ```
> > >
> > > inside lldb (D-like pseudo code):
> > >
> > > ```
> > > bool demangle(string symbol, string* output){
> > >   auto path=env["LLDB_DEMANGLER_EXE"];
> > >   if(!path.empty) {
> > >      auto demangleCustom=cast(proper_type) dlopen(path);
> > >      if(demangleCustom(symbol, output)) return true;
> > >      // fallsback to default code if custom code didn't handle symbol
> > >   }
> > >   return run_default_lldb_demangle(symbol, output);
> > > }
> > > ```
> > >
> > > user defined demangler (eg D's demangler)
> > > ```
> > > // return true if can demangle symbol (ie it's a D symbol in our case)
> > > bool demangleCustom(string symbol, string* output);
> > >
> > > ```
> > >
> > > >> Is the mangling changing at all?
> > >
> > > yes, there's some ongoing work on making the mangling scheme produce
> much shorter symbols. The logic is complex, and it'd be a lot of work to
> reproduce this.
> > >
> > > Bottomline: this scheme is very flexible, and it'd be no less useful
> than current situation, where lldb just returns the symbol unchanged if it
> can't demangle.
> > >
> > >
> > >
> > >
> > > > On Sep 21, 2016, at 3:00 PM, Timothee Cour <thelastmammoth at gmail.com>
> wrote:
> > > >
> > > > Is there a way to provide a hook (eg, via an extern(C) function, or
> using a dynamically loaded shared library) to do this, so as to simply
> reuse D's https://dlang.org/phobos/std_demangle.html and make sure it's
> always in sync with D's demangling instead of duplicating code
> > > >
> > > > On Wed, Sep 21, 2016 at 10:24 AM, Greg Clayton via lldb-dev <
> lldb-dev at lists.llvm.org> wrote:
> > > > It might be nice to add demangling support to llvm and then use it
> by modifying "Mangled::GetDemangledName()" in Mangled.cpp. This is where
> all demangling happens. Hopefully you have a great prefix that won't
> conflict with other languages "_Z" for C++, "_T" for swift. But the code in
> Mangled::GetDemangledName() will look at the prefix and attempt to demangle
> the name based on what prefix it starts with.
> > > >
> > > >
> > > > > On Sep 21, 2016, at 5:52 AM, Johan Engelen via lldb-dev <
> lldb-dev at lists.llvm.org> wrote:
> > > > >
> > > > > Hi all,
> > > > >   I recently looked into adding demangling support for D in LLDB,
> but got lost in the code.
> > > > > (right now, basic D support is there with:
> https://reviews.llvm.org/D24794)
> > > > >
> > > > > I'd like some pointers to where demangling is done for the other
> languages, and to where I should add D support for it.
> > > > >
> > > > > Thanks a lot,
> > > > >   Johan
> > > > >
> > > > > _______________________________________________
> > > > > lldb-dev mailing list
> > > > > lldb-dev at lists.llvm.org
> > > > > http://lists.llvm.org/cgi-bin/mailman/listinfo/lldb-dev
> > > >
> > > > _______________________________________________
> > > > lldb-dev mailing list
> > > > lldb-dev at lists.llvm.org
> > > > http://lists.llvm.org/cgi-bin/mailman/listinfo/lldb-dev
> > > >
> > >
> > >
> >
> > _______________________________________________
> > lldb-dev mailing list
> > lldb-dev at lists.llvm.org
> > http://lists.llvm.org/cgi-bin/mailman/listinfo/lldb-dev
> >
>
> _______________________________________________
> lldb-dev mailing list
> lldb-dev at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/lldb-dev
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/lldb-dev/attachments/20160922/0650c792/attachment-0001.html>