[lld-macho] Add --ignore-auto-link-option

[keith]

Summary

This provides a workaround for a small difference in ld64 behavior where
ld64 ignores invalid LC_LINKER_OPTIONS unless the link fails. Instead of
fully adopting that behavior, this provides an escape hatch by allowing
users to specify --ignore-auto-link-option passing the invalid library
or framework name

Fixes https://github.com/llvm/llvm-project/issues/56939

[keith]

Rename variable, still plural

[int3]

hmm this places the burden on the end user to manually put together the list of frameworks to be ignored. Why not have a flag that turns all LC_LINKER_OPTION load failures into warnings?

I don't feel super strongly about this either way though. @thakis, do you have any opinions?

[keith]

Why not have a flag that turns all LC_LINKER_OPTION load failures into warnings

I think the alternative to this is that we mirror the ld64 behavior somehow, because changing these to warnings would just end up with you having unsolvable warnings instead

[int3]

lgtm (@thakis also gave the OK over discord)

lld/MachO/Config.h

172

can we have a comment explaining the motivation behind this option?

lld/MachO/Options.td

997–1002

this should be under grp_lld (and moved to the top of the file with the rest of the options in that group)

[int3]

I think the alternative to this is that we mirror the ld64 behavior somehow, because changing these to warnings would just end up with you having unsolvable warnings instead

Yeah fair, we shouldn't make it too difficult for people to turn on -fatal_warnings

[keith]

Update option and comments

lld/MachO/Config.h

struct Configuration {
   uint32_t ltoo = 2;
   llvm::CachePruningPolicy thinLTOCachePolicy;
   llvm::StringRef thinLTOCacheDir;
   bool deadStripDylibs = false;
   bool demangle = false;
   bool deadStrip = false;
   bool errorForArchMismatch = false;
   bool ignoreAutolinking = false;
+  llvm::StringSet<> ignoredAutoLinkOptions;
   PlatformInfo platformInfo;
   llvm::Optional<PlatformInfo> secondaryPlatformInfo;
   NamespaceKind namespaceKind = NamespaceKind::twolevel;
   UndefinedSymbolTreatment undefinedSymbolTreatment =
       UndefinedSymbolTreatment::error;
   ICFLevel icfLevel = ICFLevel::none;
   ObjCStubsMode objcStubsMode = ObjCStubsMode::fast;
   llvm::MachO::HeaderFileType outputType;

lld/MachO/Driver.cpp

for (unsigned i = 0; i < argc && offset < data.size(); ++i) {
     offset += strlen(data.data() + offset) + 1;
   }
   if (argv.size() != argc || offset > data.size())
     fatal(toString(f) + ": invalid LC_LINKER_OPTION");
 
   unsigned i = 0;
   StringRef arg = argv[i];
   if (arg.consume_front("-l")) {
+    if (config->ignoredAutoLinkOptions.contains(arg))
+      return;
     addLibrary(arg, /*isNeeded=*/false, /*isWeak=*/false,
                /*isReexport=*/false, /*isHidden=*/false, /*isExplicit=*/false,
                LoadType::LCLinkerOption);
   } else if (arg == "-framework") {
     StringRef name = argv[++i];
+    if (config->ignoredAutoLinkOptions.contains(name))
+      return;
     addFramework(name, /*isNeeded=*/false, /*isWeak=*/false,
                  /*isReexport=*/false, /*isExplicit=*/false,
                  LoadType::LCLinkerOption);
   } else {
     error(arg + " is not allowed in LC_LINKER_OPTION");
   }
 }
 
bool macho::link(ArrayRef<const char *> argsArr, llvm::raw_ostream &stdoutOS,
   config->ignoreOptimizationHints = args.hasArg(OPT_ignore_optimization_hints);
   config->callGraphProfileSort = args.hasFlag(
       OPT_call_graph_profile_sort, OPT_no_call_graph_profile_sort, true);
   config->printSymbolOrder = args.getLastArgValue(OPT_print_symbol_order_eq);
   config->forceExactCpuSubtypeMatch =
       getenv("LD_DYLIB_CPU_SUBTYPES_MUST_MATCH");
   config->objcStubsMode = getObjCStubsMode(args);
   config->ignoreAutolinking = args.hasArg(OPT_ignore_auto_link);
+  for (const Arg *arg : args.filtered(OPT_ignore_auto_link_option))
+    config->ignoredAutoLinkOptions.insert(arg->getValue());
 
   for (const Arg *arg : args.filtered(OPT_alias)) {
     config->aliasedSymbols.push_back(
         std::make_pair(arg->getValue(0), arg->getValue(1)));
   }
 
   // FIXME: Add a commandline flag for this too.
   if (const char *zero = getenv("ZERO_AR_DATE"))

lld/MachO/Options.td

def objc_stubs_small : Flag<["-"], "objc_stubs_small">,
     Group<grp_rare>;
 def dyld_env : Separate<["-"], "dyld_env">,
     MetaVarName<"<dyld_env_var>">,
     HelpText<"Specifies a LC_DYLD_ENVIRONMENT variable value pair.">,
     Group<grp_rare>;
 def ignore_auto_link : Flag<["-"], "ignore_auto_link">,
     HelpText<"Ignore LC_LINKER_OPTIONs">,
     Group<grp_rare>;
+def ignore_auto_link_option : Separate<["--"], "ignore-auto-link-option">,
+    Group<grp_rare>;
+def ignore_auto_link_option_eq : Joined<["--"], "ignore-auto-link-option=">,
+    Alias<!cast<Separate>(ignore_auto_link_option)>,
+    HelpText<"Ignore a single auto-linked library or framework. Useful to ignore invalid requirements that ld64 ignores">,
+    Group<grp_rare>;
 
 def grp_deprecated : OptionGroup<"deprecated">, HelpText<"DEPRECATED">;
 
 def lazy_framework : Separate<["-"], "lazy_framework">,
     MetaVarName<"<name>">,
     HelpText<"This option is deprecated and is now an alias for -framework.">,
     Flags<[HelpHidden]>,
     Group<grp_deprecated>;

lld/test/MachO/lc-linker-option.ll

 ; REQUIRES: x86
 ; RUN: rm -rf %t; split-file %s %t
 
 ; RUN: llvm-as %t/framework.ll -o %t/framework.o
 ; RUN: %lld -lSystem %t/framework.o -o %t/frame
 ; RUN: llvm-otool -l %t/frame | FileCheck --check-prefix=FRAME %s \
 ; RUN:  --implicit-check-not LC_LOAD_DYLIB
 ; FRAME:          cmd LC_LOAD_DYLIB
 ; FRAME-NEXT: cmdsize
 ; FRAME-NEXT:    name /usr/lib/libSystem.dylib
 ; FRAME:          cmd LC_LOAD_DYLIB
 ; FRAME-NEXT: cmdsize
 ; FRAME-NEXT:    name /System/Library/Frameworks/CoreFoundation.framework/CoreFoundation
 
 ; RUN: not %lld %t/framework.o -o %t/frame_no_autolink -ignore_auto_link 2>&1 | FileCheck --check-prefix=NO_AUTOLINK %s
+; RUN: not %lld %t/framework.o -o %t/frame_no_autolink --ignore-auto-link-option CoreFoundation 2>&1 | FileCheck --check-prefix=NO_AUTOLINK %s
+; RUN: not %lld %t/framework.o -o %t/frame_no_autolink --ignore-auto-link-option=CoreFoundation 2>&1 | FileCheck --check-prefix=NO_AUTOLINK %s
 ; NO_AUTOLINK: error: undefined symbol: __CFBigNumGetInt128
 
 ; RUN: llvm-as %t/l.ll -o %t/l.o
 ;; The dynamic call to _CFBigNumGetInt128 uses dyld_stub_binder,
 ;; which needs -lSystem from LC_LINKER_OPTION to get resolved.
 ;; The reference to __cxa_allocate_exception will require -lc++ from
 ;; LC_LINKER_OPTION to get resolved.
 ; RUN: %no-lsystem-lld %t/l.o -o %t/l -framework CoreFoundation