Re: dwarf_output overview

[Mark Wielaard <mjw at redhat dot com>]

On Tue, 2010-08-10 at 12:22 -0700, Roland McGrath wrote:
> > The testwriter -T variants of this test fail with:
> > terminate called after throwing an instance of 'std::logic_error'
> >   what():  basic_string::_S_construct NULL not valid
> > 
> > Because of the throw in entry_copier::populate
> 
> That is a re-throw, so the actual exception came from deeper in the soup.
> In gdb, "catch throw" or "break __cxa_throw" are highly recommended.

The actual exception came from the dwarf_data::directory_table
constructor that takes a dwarf::directory_table. Because it tries to
convert the const char* directory strings from dwarf_getsrcdirs to
std::strings. But the first entry is the CU directory path which can be
NULL. If so the copy constructor throws because it cannot convert from
NULL to std::string.

Writing an explicit constructor that takes a NULL const char* into
account works around this:

       template<typename table>
       directory_table (const table &other)
-       : _base (other.begin (), other.end ()) {}
+      {
+       typename table::const_iterator it;
+       for (it = other.begin (); it != other.end (); it++)
+         _base::push_back (*it != NULL ? std::string(*it) : "");
+      }

But then I get in similar trouble inside the subr::equal_to template
code. Specifically the elfutils::subr::equal_to<std::basic_string<char,
std::char_traits<char>, std::allocator<char> >, char const*>::operator()
instance, which will crash and burn trying to compare the empty string
and the NULL. Still looking into that. Hints and tips for how to
generically deal with char*/std::string in C++ code appreciated.

Cheers,

mark