[PATCH] D67479: [ELF] Support -z undefs

[Fangrui Song via Phabricator via llvm-commits]

MaskRay added a comment.

Some findings related to the topic. There are two kinds of unresolved references: 1) from object files 2) from shared objects. `--unresolved-symbols=` toggles both bits while `-z (un)defs` and `--(no-)allow-shlib-undefined` toggles one bit, respectively. I personally favor the fine-grained options over `--unresolved-symbols=`

It seems we can actually model `--unresolved-symbols=ignore-in-object-files` in terms of `--allow-shlib-undefined` but I think that is probably unnecessary. I can't find any use of "ignore-in-object-files" outside lld and binutils.

  // ld/emultempl/elf32.em
      case 'z':
        if (strcmp (optarg, "defs") == 0)
  	link_info.unresolved_syms_in_objects = RM_GENERATE_ERROR;
        else if (strcmp (optarg, "undefs") == 0)
  	link_info.unresolved_syms_in_objects = RM_IGNORE;
  
  // ld/lexsup.c
  	case OPTION_NO_UNDEFINED:
  	  link_info.unresolved_syms_in_objects
  	    = how_to_report_unresolved_symbols;
  	  break;
  	case OPTION_ALLOW_SHLIB_UNDEFINED:
  	  link_info.unresolved_syms_in_shared_libs = RM_IGNORE;
  	  break;
  	case OPTION_NO_ALLOW_SHLIB_UNDEFINED:
  	  link_info.unresolved_syms_in_shared_libs
  	    = how_to_report_unresolved_symbols;
  	  break;
  	case OPTION_UNRESOLVED_SYMBOLS:
  	  if (strcmp (optarg, "ignore-all") == 0)
  	    {
  	      link_info.unresolved_syms_in_objects = RM_IGNORE;
  	      link_info.unresolved_syms_in_shared_libs = RM_IGNORE;
  	    }
  	  else if (strcmp (optarg, "report-all") == 0)
  	    {
  	      link_info.unresolved_syms_in_objects
  		= how_to_report_unresolved_symbols;
  	      link_info.unresolved_syms_in_shared_libs
  		= how_to_report_unresolved_symbols;
  	    }
  	  else if (strcmp (optarg, "ignore-in-object-files") == 0)
  	    {
  	      link_info.unresolved_syms_in_objects = RM_IGNORE;
  	      link_info.unresolved_syms_in_shared_libs
  		= how_to_report_unresolved_symbols;
  	    }
  	  else if (strcmp (optarg, "ignore-in-shared-libs") == 0)
  	    {
  	      link_info.unresolved_syms_in_objects
  		= how_to_report_unresolved_symbols;
  	      link_info.unresolved_syms_in_shared_libs = RM_IGNORE;
  	    }


Repository:
  rLLD LLVM Linker

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  https://reviews.llvm.org/D67479/new/

https://reviews.llvm.org/D67479