RFC: COMDAT group names become anonymouse local symbols

[mitchell at codesourcery dot com (Mark Mitchell)]

When assembling this trivial file:

	.section	A,"axG",%progbits,B,comdat
        # Note that there is no definition of the symbol B.     		

GAS generates a COMDAT group whose "signature" (in the sense of the
ELF spec) is an anonymous local symbol:

Section Headers:
  [Nr] Name              Type            Address          Off    Size   ES Flg Lk Inf Al
  [ 1] B                 GROUP           0000000000000000 000040 000008 04      7   5  4

Symbol table '.symtab' contains 6 entries:
   Num:    Value          Size Type    Bind   Vis      Ndx Name
     5: 0000000000000000     0 SECTION LOCAL  DEFAULT    1 

This seems bad.  The documentation for the .section directive says
that B is the group name, and since the linker's collapsing of COMDAT
groups is done based on the *signature*, not the name referred to by
the section header itself, this seems wrong.

On the other hand, perhaps GCC shouldn't generate code like this.  (It
does, at present, for certain C++ inputs.)  The assembler certainly
shouldn't create a global symbol named "B".  If the assembler were to
create a local symbol with the name "B", would the linker still
combine this COMDAT group with another group in another object file
also named "B", even if both had different local symbols as their
signatures?

Thanks,

--
Mark Mitchell
CodeSourcery
mark@codesourcery.com
(650) 331-3385 x713