Patch: Improve demangling w.r.t. possible underscore prefix

[Andrew Haley <aph at redhat dot com>]

Ranjit Mathew writes:
 > Hi,
 > 
 >     This patch proposes to add GCC's USER_LABEL_PREFIX to the
 > symbols returned by addr2line so that they are at par with those
 > returned by addr2name.awk or dladdr( ), i.e. on systems where an
 > underscore is used as a prefix for names exported from C/C++/Java
 > programs, this allows c++filt to correctly demangle names generated
 > by addr2line, which uses symbolic debugging information instead of
 > the actual exported labels that are used by dladdr and 
 > addr2name.awk (via "nm").
 > 
 > The train of reasoning leading to this patch can be found in the
 > thread starting from this message:
 > 
 >     http://gcc.gnu.org/ml/java/2003-02/msg00145.html
 > 
 > __USER_LABEL_PREFIX__ is a predefined macro in the GCC preprocessor
 > that stands for the string (*not* string constant) that is prefixed
 > to a method name when it is exported as a label.
 > 
 > The XGLUE/GLUE idiom you see in the patch is borrowed from the
 > GCC sources and has been the only way I could make this
 > macro work as needed. I do not completely understand why the double
 > macro indirection is the only way it works. :-( (Search for 
 > "__USER_LABEL_PREFIX__" within the subfolders of the "gcc/config"
 > folder in the GCC sources for instances of its usage within GCC.)
 > 
 > I have checked this patch with the current 3.3 snapshot on
 > Win32 (MinGW). I would greatly appreciate if someone could also
 > test this out on some other platform, say Linux, especially one
 > that does not have such a prefix, before committing it.
 > 
 > With this patch in place, stacktraces on Win32 finally show up
 > as one would expect them to, complete with class names
 > and method signatures!

It seems like it will break if ever __USER_LABEL_PREFIX__is not '_'.

Why can't you just cat __USER_LABEL_PREFIX__ to the start of the name?
Surround the whole thing by #ifdef __USER_LABEL_PREFIX__.

Andrew.