[LLD] [MinGW] Ignore the --[no-]allow-shlib-undefined option

[mstorsjo]

Summary

GNU ld does accept this option when targeting PE-COFF, even though PE images clearly don't support leaving undefined symbols in a linked image.

Meson has earlier had issues where it tried to unconditionally pass this option when targeting a unix style linker (including the mingw target, which uses unix style options); currently meson tries to detect whether the option is supported and pass it.

For compatibility with GNU ld, just ignore this option, as there may be other projects out there that also blindly pass this option to the linker, even though it makes no sense for a windows target.

[amccarth]

I don't have enough background here, so I'll defer to the decision of other reviewers whether this makes sense. @ruiu ?

[mstorsjo]

In D83721#2148786, @amccarth wrote:

I don't have enough background here, so I'll defer to the decision of other reviewers whether this makes sense. @ruiu ?

Not sure how active @ruiu is these days either (and @rnk is on leave as well)...

GNU ld silently accepts these options when targeting windows (and they have no effect), so therefore we probably should (even though the options themselves are nonsensical for PE-COFF), just to reduce unnecessary differences that one can run into.

[MaskRay]

For compatibility with GNU ld, just ignore this option, as there may be other projects out there that also blindly pass this option to the linker, even though it makes no sense for a windows target.

This is because GNU ld handles most options in one getopt_long/getopt_long_only. Many ELF specific options are handled by non-ELF ports and ignored. Some newer options use -z which is only handled by its ELF ports.

--allow-shlib-undefined is so rare that we should ask the projects to fix their build systems.

[mstorsjo]

This is because GNU ld handles most options in one getopt_long/getopt_long_only. Many ELF specific options are handled by non-ELF ports and ignored. Some newer options use -z which is only handled by its ELF ports.

--allow-shlib-undefined is so rare that we should ask the projects to fix their build systems.

Ok, fair enough. So far, Meson is the only one I've encountered setting this one, and it was fixed once, then regressed, then refixed at a later point. But I guess I should set up continuous testing of the latest version of that to make sure it doesn't regress again.

lld/MinGW/Options.td

 // Alias
 def alias_entry_e: JoinedOrSeparate<["-"], "e">, Alias<entry>;
 def alias_strip_s: Flag<["-"], "s">, Alias<strip_all>;
 def alias_strip_S: Flag<["-"], "S">, Alias<strip_debug>;
 def alias_undefined_u: JoinedOrSeparate<["-"], "u">, Alias<undefined>;
 
 // Ignored options
 def: Joined<["-"], "O">;
+def: F<"allow-shlib-undefined">;
 def: F<"build-id">;
 def: F<"disable-auto-image-base">;
 def: F<"enable-auto-image-base">;
 def: F<"end-group">;
 def: Flag<["--"], "full-shutdown">;
 def: F<"high-entropy-va">;
 def: S<"major-image-version">;
 def: S<"minor-image-version">;
+def: F<"no-allow-shlib-undefined">;
 def: F<"no-seh">;
 def: F<"nxcompat">;
 def: F<"pic-executable">;
 def: S<"plugin">;
 def: J<"plugin=">;
 def: S<"plugin-opt">;
 def: J<"plugin-opt=">;
 def: J<"sysroot">;
 def: F<"start-group">;
 def: F<"tsaware">;