[Bug gold/23969] New: PowerPC64 ELFv1 --defsym func1=func2 call to func1 errors

[amodra at gmail dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=23969

            Bug ID: 23969
           Summary: PowerPC64 ELFv1 --defsym func1=func2 call to func1
                    errors
           Product: binutils
           Version: 2.32 (HEAD)
            Status: NEW
          Severity: normal
          Priority: P2
         Component: gold
          Assignee: ccoutant at gmail dot com
          Reporter: amodra at gmail dot com
                CC: ian at airs dot com
  Target Milestone: ---

Running the gold testsuite plugin_test_defsym results in a segfault, due to the
call to "bar" branching to the opd entry for "foo".  This isn't something
specific to the plugin, just compiling the testcase with
powerpc64-linux-gcc -Bgcctestdir/ -g -O2 -o test_defsym -Wl,--defsym,bar=foo
~/src/binutils-gdb/gold/testsuite/plugin_test_defsym.c
results in a test_defsym binary with the error.

The problem is caused by gold defining --defsym symbols as constants. 
Target_powerpc::symval_for_branch fails to detect such function symbols as
being defined in a .opd section (only FROM_OBJECT symbols are supported), and
therefore does not look up the code entry point in the function descriptor
during relocation.  Even worse, --defsym symbols have value zero at the time
Target::relax is called, so calls to symval_for_branch at that point cannot
look up descriptors even if some other mechanism was devised for detecting
symbols within .opd sections.  (Target::relax is where powerpc64 adds stubs for
long branches and plt calls.)

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