[Bug c++/47952] [trans-mem] undefined reference to transaction clone

["aldyh at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47952

Aldy Hernandez <aldyh at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jakub at gcc dot gnu.org

--- Comment #3 from Aldy Hernandez <aldyh at gcc dot gnu.org> 2011-03-07 15:37:06 UTC ---
[These notes are from a question via email to Jakub/Richard.  Saving here to
keep everything in one place.  Still awaiting response.]

In this PR we have an undefined reference to symbol
"_ZGTtNSt14_List_iteratorIN4Game12BuildProjectEEC1EPSt15_List_node_base" (see
full .s in attachment). This symbol is only used in the .tm_clone_table:

 .section .tm_clone_table,"aw",@progbits
[...]
 .quad _ZGTtNSt14_List_iteratorIN4Game12BuildProjectEEC1EPSt15_List_node_base
[...]

However, the symbol seems to be an alias to another symbol (which is used):

.globl _ZGTtNSt14_List_iteratorIN4Game12BuildProjectEEC1EPSt15_List_node_base
        .set
_ZGTtNSt14_List_iteratorIN4Game12BuildProjectEEC1EPSt15_List_node_base,
_ZGTtNSt14_List_iteratorIN4Game12BuildProjectEEC2EPSt15_List_node_base

Notice these are constructor variants (C1 versus C2 in the mangling).

The original symbol is defined like this:

        .section
.text._ZGTtNSt14_List_iteratorIN4Game12BuildProjectEEC2EPSt15_List_node_base,"axG",@progbits,_ZNSt14_List_iteratorIN4Game12BuildProjectEEC5EPSt15_List_node_base,comdat
        .align 2
        .weak
_ZGTtNSt14_List_iteratorIN4Game12BuildProjectEEC2EPSt15_List_node_base
        .type
_ZGTtNSt14_List_iteratorIN4Game12BuildProjectEEC2EPSt15_List_node_base,
@function
_ZGTtNSt14_List_iteratorIN4Game12BuildProjectEEC2EPSt15_List_node_base:
[...]
[...]

This is a wild guess, but should we avoid dumping symbols in the
.tm_clone_table if the original function was a weak symbol?  The one-liner
below, fixes the undefined reference at hand, as well as a myriad of other
linking problems in the Glob2 benchmark.

??

Index: varasm.c
===================================================================
--- varasm.c    (revision 170622)
+++ varasm.c    (working copy)
@@ -5867,6 +5867,9 @@ finish_tm_clone_pairs_1 (void **slot, vo
   if (!src_n->needed)
     return 1;

+  if (DECL_WEAK (src_n->decl))
+    return 1;
+
   if (!*switched)
     {
       switch_to_section (get_named_section (NULL, ".tm_clone_table", 3));