During LTO, if (1) an IR file contains a COMDAT group that is kept,
(2) a later non-claimed file contains the same group, which we discard,
and (3) the plugin fails to provide a definition of the symbols in that
COMDAT group, gold silently resolves any references to those symbols
to 0.
This patch adds a check for a placeholder symbol when deciding
whether to issue an undefined symbol error. It also adds an extra
note after any undefined placeholder symbol error that explains
that a definition was expected from the plugin.
gold/
PR gold/19842
* errors.cc (Errors::undefined_symbol): Add info message when
symbol should have been provided by a plugin.
* target-reloc.h (issue_undefined_symbol_error): Check for
placeholder symbols defined in discarded sections.
* testsuite/Makefile.am (plugin_test_9b): New test case.
* testsuite/Makefile.in: Regenerate.
* testsuite/plugin_test_9b_elf.cc: New test source file.
* testsuite/plugin_test_9b_ir.cc: New test source file.
Cary Coutant