[Bug ld/26588] New: enable-reloc-section on .exe with no exported symbols causes segfault if requested to create implib

[sourceware-bugzilla at jdrake dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=26588

            Bug ID: 26588
           Summary: enable-reloc-section on .exe with no exported symbols
                    causes segfault if requested to create implib
           Product: binutils
           Version: 2.36 (HEAD)
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: ld
          Assignee: unassigned at sourceware dot org
          Reporter: sourceware-bugzilla at jdrake dot com
  Target Milestone: ---

Created attachment 12824
  --> https://sourceware.org/bugzilla/attachment.cgi?id=12824&action=edit
proposed patch

PR #17321 added --enable-reloc-section, and PR #19011 made it default. 
However, some (misguided) tools try to create import libraries for executables,
even if they don't export any symbols.  This didn't cause a failure previously,
but now segfaults if --enable-reloc-section is enabled.

0:000> kb
 # RetAddr           : Args to Child                                           
               : Call Site
00 00007ff6`f8aa4907 : 00000000`00000000 00000001`40023760 0000003c`5dbff9ec
00000000`00000044 : msvcrt!strlen+0x31
01 00007ff6`f898f53b : 00000000`00000000 00007ff6`f897618a 0000003c`5dbff9f0
00007ff6`f89680f0 : ld!xstrdup+0x17 [..\..\binutils-2.35\libiberty\xstrdup.c @
33] 
02 00007ff6`f8980a08 : 000001a9`af6758a0 000001a9`ad6d88b0 00007ff6`f8c618c0
00007ff6`f89680f0 : ld!pep_dll_generate_implib+0x53
[..\..\binutils-2.35\ld\pe-dll.c @ 2822] 
03 00007ff6`f8975c27 : 0000003c`5dbffabc 0000000a`af68bd50 00000000`00000025
00000001`00000044 : ld!gld_i386pep_finish+0xb1 [ei386pep.c @ 1823] 
04 00007ff6`f896ab7d : 00000000`00000004 00007ff6`00000001 00000000`00000000
00007ff6`f8976050 : ld!ldemul_finish+0x15 [..\..\binutils-2.35\ld\ldemul.c @
102] 
05 00007ff6`f896f22e : 00007ff6`f8b14608 00007ff6`f8b067c0 000001a9`00000001
00007ffc`50000061 : ld!lang_process+0x6c6 [..\..\binutils-2.35\ld\ldlang.c @
8126] 
06 00007ff6`f89513c1 : 00000000`00000025 000001a9`ad6d1b40 00007ff6`f8c67398
00000000`00000000 : ld!main+0x795 [..\..\binutils-2.35\ld\ldmain.c @ 498] 
07 00007ff6`f89514f6 : 00000000`00000000 00000000`00000000 00000000`00000000
00000000`00000000 : ld!__tmainCRTStartup+0x231
[D:\mingwbuild\mingw-w64-crt-git\src\mingw-w64\mingw-w64-crt\crt\crtexe.c @
337] 
08 00007ffc`a86b6fd4 : 00000000`00000000 00000000`00000000 00000000`00000000
00000000`00000000 : ld!mainCRTStartup+0x16
[D:\mingwbuild\mingw-w64-crt-git\src\mingw-w64\mingw-w64-crt\crt\crtexe.c @
221] 
09 00007ffc`a9b1cec1 : 00000000`00000000 00000000`00000000 00000000`00000000
00000000`00000000 : KERNEL32!BaseThreadInitThunk+0x14
0a 00000000`00000000 : 00000000`00000000 00000000`00000000 00000000`00000000
00000000`00000000 : ntdll!RtlUserThreadStart+0x21


This is

  dll_filename = (def->name) ? def->name : dll_name;
  dll_symname = xstrdup (dll_filename);


the global dll_name is filled in if def->name is not set in generate_edata,
however 

  if (pe_def_file->num_exports == 0 && !bfd_link_pic (info))
    {
      if (pe_dll_enable_reloc_section)
        {
          build_filler_bfd (0);
          pe_output_file_set_long_section_names (filler_bfd);
        }
      return;
    }

  generate_edata (abfd, info);
  build_filler_bfd (1);
  pe_output_file_set_long_section_names (filler_bfd);


I'm not sure whether it would be better to call generate_edata in the no
exports but enable reloc section case, or my proposed patch (attached)

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