demangling (Ubuntu 64bit 12.04, dmd 64bit 2.060)

[Sean Kelly]

On Aug 20, 2012, at 1:45 PM, Carl Sturtivant <sturtivant at gmail.com> wrote:

> I've been looking at the objects etcetera produced by dmd, and using D's function demangle in std.demangle to decrypt some of the symbols found in such objects by nm.
> 
> http://sourceware.org/binutils/docs-2.22/binutils/nm.html
> 
> While demangle does produce a demangled version of some symbols, it does not in other cases where they nevertheless look as if they may be mangled names of some kind. I considered that perhaps they are C++ mangled names, but have been unable to get nm to unmangle them, even though it nominally knows about C++ name mangling.
> 
> Is there a better analog of demangle I can use to translate back some of these more intractable mangled names? I tried the one in core.demangle but it did no better. Or is there somewhere I could determine the demangling rules and implement them for myself? Any suggestions will be gratefully received.

std.demangle calls core.demangle, so it's no surprise that you got the same result.


> Here are some examples that are not demangled by std.demangle.demangle :
> 
> _D13libd_demangle12__ModuleInfoZ
> _D15TypeInfo_Struct6__vtblZ
> _D3std5stdio12__ModuleInfoZ
> _D3std6traits15__T8DemangleTkZ8Demangle6__initZ
> _D47TypeInfo_S3std6traits15__T8DemangleTkZ8Demangle6__initZ

demangle is currently designed to demangle functions names, while the strings above are types.  During parsing, demangle sees the string as a qualified name and then expects a type, and when it doesn't find one it figures the symbol isn't valid.  It sounds like we either need a separate function for demangling types or if the demangle function encounters a 'Z' when it expects a type name it should realize it's demangling a type name, back up, and try again according to that logic.  I suggest submitting a ticket.

To learn how the demangler works, the easiest thing is to copy core.demangle into your workspace and compile a small app with it directly, turning on the debug info.  For example:

module abc;
import demangle_;
import std.stdio;

void main() {
	writeln(decodeDmdString("_D47TypeInfo_S3std6traits15__T8DemangleTkZ8Demangle6__initZ"));
}

$ dmd abc -debug=trace -debug=info demangle