[Dwarf-Discuss] About DW_AT_external

Michael Eager eager at eagercon.com
Wed Jul 28 09:52:56 PDT 2010


P J P wrote:
> --- On Wed, 28/7/10, Robinson, Paul T (NonStop) <paul.t.robinson at hp.com>
>> The standard consistently says "visible outside of its containing
>> compilation unit" when talking about DW_AT_external.
> 
> Irrespective of where the variable/function is defined?
> 
> Ex.: say an application uses standard library functions/C++ classes like
> malloc, strncpy, strcmp, operator>>, operator<< etc.
> 
> The dwarf DIE of such symbols in the application object file will have
> DW_AT_external set, I guess, right?

C is a bit confusing in how it defines keywords.  The "extern" keyword
does not mean that the symbol is externally visible -- it means that
the symbol is defined elsewhere as a global (i.e. externally visible)
symbol.  In C, external symbols are defined at file scope without
either the "extern" or "static" keywords.

The DIE for "malloc" should have DW_AT_external where it is defined,
not in places the symbol is referenced.

> Is there a way to know whether the function is defined in the same
> compilation unit or is there because of linking with the other compilation
> units?

DIEs for non-defining declarations should have the DW_AT_declaration
flag.

-- 
Michael Eager	 eager at eagercon.com
1960 Park Blvd., Palo Alto, CA 94306  650-325-8077



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