[lld-macho] Require -arch and -platform_version to always be specified

[int3]

Summary

We previously defaulted to x86_64 and an unknown platform, which was fine when
we only supported one arch and did no platform checks, but that will no longer
be true going ahead. Therefore, we should require those flags to be specified
whenever the linker is invoked.

Note that LLD-ELF and ld64 both infer the arch from their input object files,
but the usefulness of that is questionable since clang will always specify these
flags, and most of the time lld will be invoked via clang.

[int3]

note in lit.local.config that -syslibroot does not only use last value

lld/MachO/Driver.cpp

for (StringRef dir : config->frameworkSearchPaths) {
 
     if (Optional<std::string> path = resolveDylibPath(symlink))
       return path;
   }
   return {};
 }
 
 static TargetInfo *createTargetInfo(opt::InputArgList &args) {
-  // TODO: should unspecified arch be an error rather than defaulting?
-  // Jez: ld64 seems to make unspecified arch an error when LTO is
-  // being used. I'm not sure why though. Feels like we should be able
-  // to infer the arch from our input files regardless
-  StringRef archName = args.getLastArgValue(OPT_arch, "x86_64");
+  StringRef archName = args.getLastArgValue(OPT_arch);
+  if (archName.empty())
+    fatal("must specify -arch");
   config->arch = MachO::getArchitectureFromName(archName);
   switch (MachO::getCPUTypeFromArchitecture(config->arch).first) {
   case MachO::CPU_TYPE_X86_64:
     return createX86_64TargetInfo();
   case MachO::CPU_TYPE_ARM64:
     return createARM64TargetInfo();
   default:
     fatal("missing or unsupported -arch " + archName);

 static std::string lowerDash(StringRef s) {
   return std::string(map_iterator(s.begin(), toLowerDash),
                      map_iterator(s.end(), toLowerDash));
 }
 
 static PlatformInfo getPlatformVersion(const opt::ArgList &args) {
   const opt::Arg *arg = args.getLastArg(OPT_platform_version);
   PlatformInfo platform;
-  if (!arg)
+  if (!arg) {
+    error("must specify -platform_version");
     return platform;
+  }
 
   StringRef platformStr = arg->getValue(0);
   StringRef minVersionStr = arg->getValue(1);
   StringRef sdkVersionStr = arg->getValue(2);
 
   // TODO(compnerd) see if we can generate this case list via XMACROS
   platform.kind =
       StringSwitch<PlatformKind>(lowerDash(platformStr))

lld/MachO/InputFiles.cpp

ObjFile::ObjFile(MemoryBufferRef mb, uint32_t modTime, StringRef archiveName)
   MachO::Architecture arch =
       MachO::getArchitectureFromCpuType(hdr->cputype, hdr->cpusubtype);
   if (arch != config->arch) {
     error(toString(this) + " has architecture " + getArchitectureName(arch) +
           " which is incompatible with target architecture " +
           getArchitectureName(config->arch));
     return;
   }
+  // TODO: check platform too
 
   if (const load_command *cmd = findCommand(hdr, LC_LINKER_OPTION)) {
     auto *c = reinterpret_cast<const linker_option_command *>(cmd);
     StringRef data{reinterpret_cast<const char *>(c + 1),
                    c->cmdsize - sizeof(linker_option_command)};
     parseLCLinkerOption(this, c->count, data);
   }
 

lld/test/MachO/lit.local.cfg

 # -*- Python -*-
 
 import os
 
-lld = ('ld64.lld -syslibroot ' +
+# We specify the most commonly-used arch and platform version in our tests here
+# Tests which need different settings can just append to this, as only the last
+# value will be used.
+#
+# Note however that this does not apply to `-syslibroot`: each instance of that
+# flag will append to the set of library roots.
+lld = ('ld64.lld -arch x86_64 -platform_version macos 10.0 11.0 -syslibroot ' +
     os.path.join(config.test_source_root, "MachO", "Inputs", "MacOSX.sdk"))
 config.substitutions.append(('%lld', lld + ' -fatal_warnings'))
 config.substitutions.append(('%no_fatal_warnings_lld', lld))

lld/test/MachO/syslibroot.test

 # Ensure that a nonexistent path is ignored with a syslibroot
 
-RUN: ld64.lld -v -dylib -o /dev/null -syslibroot /var/empty | FileCheck %s -check-prefix CHECK-NONEXISTENT-SYSLIBROOT
+RUN: ld64.lld -arch x86_64 -platform_version macos 10 11 -v -dylib -o /dev/null \
+RUN:   -syslibroot /var/empty | FileCheck %s -check-prefix CHECK-NONEXISTENT-SYSLIBROOT
 
 CHECK-NONEXISTENT-SYSLIBROOT: Library search paths:
 CHECK-NONEXISTENT-SYSLIBROOT-NEXT: Framework search paths:
 
 RUN: mkdir -p %t/usr/lib
-RUN: ld64.lld -v -dylib -o /dev/null -syslibroot %t 2>&1 | FileCheck %s -check-prefix CHECK-SYSLIBROOT -DROOT=%t
+RUN: ld64.lld -arch x86_64 -platform_version macos 10 11 -v -dylib -o /dev/null \
+RUN:   -syslibroot %t 2>&1 | FileCheck %s -check-prefix CHECK-SYSLIBROOT -DROOT=%t
 
 CHECK-SYSLIBROOT-NOT: directory not found{{.*}}usr/local/lib
 CHECK-SYSLIBROOT: Library search paths:
 CHECK-SYSLIBROOT-NEXT: [[ROOT]]/usr/lib
 
 RUN: mkdir -p %t/Library/libxml2-development
-RUN: ld64.lld -v -dylib -o /dev/null -syslibroot %t -L /Library/libxml2-development | FileCheck %s -check-prefix CHECK-ABSOLUTE-PATH-REROOTED -DROOT=%t
+RUN: ld64.lld -arch x86_64 -platform_version macos 10 11 -v -dylib -o /dev/null \
+RUN:   -syslibroot %t -L /Library/libxml2-development | FileCheck %s -check-prefix CHECK-ABSOLUTE-PATH-REROOTED -DROOT=%t
 
 CHECK-ABSOLUTE-PATH-REROOTED: Library search paths:
 CHECK-ABSOLUTE-PATH-REROOTED: [[ROOT]]/Library/libxml2-development
 CHECK-ABSOLUTE-PATH-REROOTED: [[ROOT]]/usr/lib
 
-RUN: ld64.lld -v -dylib -o /dev/null -syslibroot %t -L %t/Library/libxml2-development | FileCheck %s -check-prefix CHECK-PATH-WITHOUT-REROOT -DPATH=%t/Library/libxml2-development
+RUN: ld64.lld -arch x86_64 -platform_version macos 10 11 -v -dylib -o /dev/null \
+RUN:   -syslibroot %t -L %t/Library/libxml2-development | FileCheck %s -check-prefix CHECK-PATH-WITHOUT-REROOT -DPATH=%t/Library/libxml2-development
 CHECK-PATH-WITHOUT-REROOT:      Library search paths:
 CHECK-PATH-WITHOUT-REROOT-NEXT: [[PATH]]
 
 RUN: mkdir -p %t.2/usr/lib
-RUN: ld64.lld -v -dylib -o /dev/null -syslibroot %t -syslibroot %t.2 | FileCheck %s -check-prefix CHECK-SYSLIBROOT-MATRIX -DROOT=%t
+RUN: ld64.lld -arch x86_64 -platform_version macos 10 11 -v -dylib -o /dev/null \
+RUN:   -syslibroot %t -syslibroot %t.2 | FileCheck %s -check-prefix CHECK-SYSLIBROOT-MATRIX -DROOT=%t
 
 CHECK-SYSLIBROOT-MATRIX: Library search paths:
 CHECK-SYSLIBROOT-MATRIX: [[ROOT]]/usr/lib
 CHECK-SYSLIBROOT-MATRIX: [[ROOT]].2/usr/lib
 
-RUN: ld64.lld -v -dylib -o /dev/null -syslibroot %t -syslibroot %t.2 -syslibroot / | FileCheck %s -check-prefix CHECK-SYSLIBROOT-IGNORED -DROOT=%t
+RUN: ld64.lld -arch x86_64 -platform_version macos 10 11 -v -dylib -o /dev/null \
+RUN:   -syslibroot %t -syslibroot %t.2 -syslibroot / | \
+RUN:   FileCheck %s -check-prefix CHECK-SYSLIBROOT-IGNORED -DROOT=%t
 
 CHECK-SYSLIBROOT-IGNORED: Library search paths:
 CHECK-SYSLIBROOT-IGNORED-NOT: [[ROOT]]/usr/lib
 CHECK-SYSLIBROOT-IGNORED-NOT: [[ROOT]].2/usr/lib
 
 RUN: mkdir -p %t/System/Library/Frameworks
-RUN: ld64.lld -v -dylib -o /dev/null -syslibroot %t | FileCheck %s -check-prefix CHECK-SYSLIBROOT-FRAMEWORK -DROOT=%t
+RUN: ld64.lld -arch x86_64 -platform_version macos 10 11 -v -dylib -o /dev/null \
+RUN:   -syslibroot %t | FileCheck %s -check-prefix CHECK-SYSLIBROOT-FRAMEWORK -DROOT=%t
 
 CHECK-SYSLIBROOT-FRAMEWORK: Framework search paths:
 CHECK-SYSLIBROOT-FRAMEWORK: [[ROOT]]/System/Library/Frameworks
 
 RUN: mkdir -p %t/Library/Frameworks
 RUN: mkdir -p %t.2/Library/Frameworks
-RUN: ld64.lld -v -dylib -o /dev/null -syslibroot %t -syslibroot %t.2 -F /Library/Frameworks | FileCheck %s -check-prefix CHECK-SYSLIBROOT-FRAMEWORK-MATRIX -DROOT=%t
+RUN: ld64.lld -arch x86_64 -platform_version macos 10 11 -v -dylib -o /dev/null \
+RUN:   -syslibroot %t -syslibroot %t.2 -F /Library/Frameworks | \
+RUN:   FileCheck %s -check-prefix CHECK-SYSLIBROOT-FRAMEWORK-MATRIX -DROOT=%t
 
 CHECK-SYSLIBROOT-FRAMEWORK-MATRIX: Framework search paths:
 CHECK-SYSLIBROOT-FRAMEWORK-MATRIX: [[ROOT]]/Library/Frameworks
 CHECK-SYSLIBROOT-FRAMEWORK-MATRIX: [[ROOT]].2/Library/Frameworks
 
-RUN: ld64.lld -v -dylib -o /dev/null -syslibroot %t -syslibroot %t.2 -syslibroot / -F /Library/Frameworks | FileCheck %s -check-prefix CHECK-SYSLIBROOT-FRAMEWORK-IGNORED -DROOT=%t
+RUN: ld64.lld -arch x86_64 -platform_version macos 10 11 -v -dylib -o /dev/null \
+RUN:   -syslibroot %t -syslibroot %t.2 -syslibroot / -F /Library/Frameworks | \
+RUN:   FileCheck %s -check-prefix CHECK-SYSLIBROOT-FRAMEWORK-IGNORED -DROOT=%t
 
 CHECK-SYSLIBROOT-FRAMEWORK-IGNORED: Framework search paths:
 CHECK-SYSLIBROOT-FRAMEWORK-IGNORED-NOT: [[ROOT]]/Library/Frameworks
 CHECK-SYSLIBROOT-FRAMEWORK-IGNORED-NOT: [[ROOT]].2/Library/Frameworks