Created attachment 19614 [details]
Testcase

It produces error: undefined reference to 'i'

Works when linking in comm.o main.o order.  I guess the linker
resolution handling is bogus.

I see

2
main.o 2
78 PREVAILING_DEF main
81 RESOLVED_IR i
comm.o 1
78 RESOLVED_IR i

which is obviously bogus for comm.o.

*** Bug 43355 has been marked as a duplicate of this bug. ***

Ian?  What's gold up to here?

It works with the llvm plugin for gold. I also find the gold output funny. What the llvm plugin does is

 if (I->syms[i].resolution == LDPR_PREVAILING_DEF ||
            (I->syms[i].def == LDPK_COMMON &&
             I->syms[i].resolution == LDPR_RESOLVED_IR)) {

....

So it has a special case for common + resolved_ir.  Let me try to find when this was added.

The llvm change is

http://llvm.org/viewvc/llvm-project?view=rev&revision=64616

so I still don't know why gold is not returning LDPR_PREVAILING_DEF for the common symbol definition.

Cary, can you give advice and/or fix gold and/or the linker plugin?

(In reply to comment #2)
> Works when linking in comm.o main.o order.

FWIW one can construct test cases where neither order works, e.g.,

cat >main.c <<\EOF
extern int i;
int j;

int main(void)
{
    i = 0;
    return i;
}
EOF

cat >comm.c <<\EOF
extern int j;
int i;
int f() { return j; }
EOF

(libtool likes to produce such code with preload symfiles)

Created attachment 20267 [details]
Gold patch to fix common symbol handling

This gold patch ought to fix the problem. Please verify and I'll send it upstream to binutils.

        * plugin.cc (Pluginobj::get_symbol_resolution_info): Check for
        prevailing definitions of common symbols.
        * testsuite/plugin_test_6.sh: New testcase.
        * testsuite/plugin_common_test_1.c: New testcase.
        * testsuite/plugin_common_test_2.c: New testcase.

Created attachment 20269 [details]
Updated gold patch to fix common symbol handling

Sorry, I forgot to include the updated testsuite/Makefile.* in the patch...

        * plugin.cc (Pluginobj::get_symbol_resolution_info): Check for
        prevailing definitions of common symbols.
        * testsuite/plugin_test_6.sh: New test case.
        * testsuite/plugin_common_test_1.c: New test case.
        * testsuite/plugin_common_test_2.c: New test case.
        * testsuite/Makefile.am (plugin_test_6): New test case.
        * testsuite/Makefile.in: Regenerate.

(In reply to comment #11)

This patch works for me.  Thanks for looking into this!

gold patch committed