[lld-macho] handle option -headerpad_max_install_names

[int3]

lld/MachO/Writer.cpp

371

nit: make 1024 a named constant

nit 2: I assume we are checking for MH_DYLIB here because the LC_DYLIB_ID command also contains an install name. Would be good to have a comment.

Also -- don't we need to allocate space for the LC_REEXPORT_DYLIB commands as well?

372–373

would be nice to have a test where the -headerpad argument is higher than the max install names size

lld/test/MachO/headerpad.s

56

ultra nit: delete one space for alignment

[gkm]

lld/MachO/Writer.cpp

371

Yes to all.

[gkm]

• Count instances of LCDylib inside constructor rather than at construction sites
• Elide uninteresting columns from llvm-objdump --all-headers output to reduce length and noise of the lines
• Add tests for all types of LCDylib: self, load, reexport
• Add tests for null-effect of -headerpad_max_install_names when no LCDylibs are present
• Add test for -headerpad N exceeding size of -headerpad_max_install_names

[gkm]

• revert unnecessary parens in MachHeaderSection::getSize()

[int3]

it would be nice to have some comments in the test indicating what behaviors are being tested... PADOVR and PADx aren't the most descriptive :)

[gkm]

• Add overview comments to tests

lld/MachO/Config.h

 };
 
 struct Configuration {
   Symbol *entry;
   bool hasReexports = false;
   bool allLoad = false;
   bool forceLoadObjC = false;
   bool staticLink = false;
+  bool headerPadMaxInstallNames = false;
   uint32_t headerPad;
   llvm::StringRef installName;
   llvm::StringRef outputFile;
   llvm::MachO::Architecture arch;
   PlatformInfo platform;
   llvm::MachO::HeaderFileType outputType;
   std::vector<llvm::StringRef> systemLibraryRoots;
   std::vector<llvm::StringRef> librarySearchPaths;

lld/MachO/Driver.cpp

bool macho::link(llvm::ArrayRef<const char *> argsArr, bool canExitEarly,
   symtab = make<SymbolTable>();
   target = createTargetInfo(args);
 
   config->entry = symtab->addUndefined(args.getLastArgValue(OPT_e, "_main"));
   config->outputFile = args.getLastArgValue(OPT_o, "a.out");
   config->installName =
       args.getLastArgValue(OPT_install_name, config->outputFile);
   config->headerPad = args::getHex(args, OPT_headerpad, /*Default=*/32);
+  config->headerPadMaxInstallNames =
+      args.hasArg(OPT_headerpad_max_install_names);
   config->outputType = args.hasArg(OPT_dylib) ? MH_DYLIB : MH_EXECUTE;
   config->runtimePaths = args::getStrings(args, OPT_rpath);
   config->allLoad = args.hasArg(OPT_all_load);
   if (auto *arg = args.getLastArg(OPT_static, OPT_dynamic))
     config->staticLink = (arg->getOption().getID() == OPT_static);
 
   std::vector<StringRef> &roots = config->systemLibraryRoots;
   for (const Arg *arg : args.filtered(OPT_syslibroot))
for (const auto &arg : args) {
     case OPT_all_load:
     case OPT_o:
     case OPT_dylib:
     case OPT_e:
     case OPT_F:
     case OPT_L:
     case OPT_ObjC:
     case OPT_headerpad:
+    case OPT_headerpad_max_install_names:
     case OPT_install_name:
     case OPT_rpath:
     case OPT_sub_library:
     case OPT_Z:
     case OPT_arch:
     case OPT_syslibroot:
     case OPT_sectcreate:
     case OPT_dynamic:

lld/MachO/Options.td

def client_name : Separate<["-"], "client_name">,
      Group<grp_rare>;
 def umbrella : Separate<["-"], "umbrella">,
      MetaVarName<"<<name>>">,
      HelpText<"Re-export this dylib through the umbrella framework <name>a">,
      Flags<[HelpHidden]>,
      Group<grp_rare>;
 def headerpad : Separate<["-"], "headerpad">,
      MetaVarName<"<size>">,
-     HelpText<"Allocate hex <size> extra space for future expansion of the load commands via install_name_tool">,
+     HelpText<"Allocate hex <size> extra space for future expansion of the load commands via install_name_tool (default is 0x20)">,
      Group<grp_rare>;
 def headerpad_max_install_names : Flag<["-"], "headerpad_max_install_names">,
      HelpText<"Allocate extra space so all load-command paths can expand to MAXPATHLEN via install_name_tool">,
-     Flags<[HelpHidden]>,
      Group<grp_rare>;
 def bind_at_load : Flag<["-"], "bind_at_load">,
      HelpText<"Tell dyld to bind all symbols at load time, rather than lazily">,
      Flags<[HelpHidden]>,
      Group<grp_rare>;
 def force_flat_namespace : Flag<["-"], "force_flat_namespace">,
      HelpText<"Tell dyld to use a flat namespace on this executable and all its dependent dylibs & bundles">,
      Flags<[HelpHidden]>,

lld/MachO/Writer.cpp

void Writer::createLoadCommands() {
   in.header->addLoadCommand(make<LCBuildVersion>(config->platform));
 
   uint8_t segIndex = 0;
   for (OutputSegment *seg : outputSegments) {
     in.header->addLoadCommand(make<LCSegment>(seg->name, seg));
     seg->index = segIndex++;
   }
 
-  uint64_t dylibOrdinal = 1;
+  uint64_t dylibCount = 0;
   for (InputFile *file : inputFiles) {
     if (auto *dylibFile = dyn_cast<DylibFile>(file)) {
       in.header->addLoadCommand(
           make<LCDylib>(LC_LOAD_DYLIB, dylibFile->dylibName));
-      dylibFile->ordinal = dylibOrdinal++;
+      dylibFile->ordinal = ++dylibCount;
 
       if (dylibFile->reexport)
         in.header->addLoadCommand(
             make<LCDylib>(LC_REEXPORT_DYLIB, dylibFile->dylibName));
     }
   }
+  if (config->headerPadMaxInstallNames) {
+    size_t installNamesPadSize =
+        (dylibCount + ((config->outputType == MH_DYLIB) ? 1 : 0)) * 1024;
+    if (config->headerPad < installNamesPadSize)
+      config->headerPad = installNamesPadSize;
+  }
 }
 
 static size_t getSymbolPriority(const SymbolPriorityEntry &entry,
                                 const InputFile &file) {
   return std::max(entry.objectFiles.lookup(sys::path::filename(file.getName())),
                   entry.anyObjectFile);
 }
 

lld/test/MachO/headerpad.s

 # REQUIRES: x86
 
 ## NOTE: Here we check that the first non-header section -- __text -- appears
 ## *exactly* `-headerpad` bytes from the end of the header. ld64 actually
 ## starts laying out the non-header sections in the __TEXT segment from the end
 ## of the (page-aligned) segment rather than the front, so its binaries
 ## typically have more than `-headerpad` bytes of actual padding. `-headerpad`
 ## just enforces a lower bound. We should consider implementing the same
 ## alignment behavior.
 
 # RUN: llvm-mc -filetype=obj -triple=x86_64-apple-darwin %s -o %t.o
+# RUN: lld -flavor darwinnew -o %t %t.o
+# RUN: llvm-objdump --macho --all-headers %t | FileCheck %s --check-prefix=PADN
+# PADN:      magic        cputype  cpusubtype  caps    filetype ncmds sizeofcmds               flags
+# PADN-NEXT: MH_MAGIC_64  X86_64   ALL         LIB64   EXECUTE  9     [[#%u, CMDSIZE:]] {{.*}}
+# PADN:      sectname __text
+# PADN-NEXT: segname __TEXT
+# PADN-NEXT: addr
+# PADN-NEXT: size
+# PADN-NEXT: offset [[#%u, CMDSIZE + 0x20 + 0x20]]
+
+# RUN: llvm-mc -filetype=obj -triple=x86_64-apple-darwin %s -o %t.o
 # RUN: lld -flavor darwinnew -o %t %t.o -headerpad 0
 # RUN: llvm-objdump --macho --all-headers %t | FileCheck %s --check-prefix=PAD0
 # PAD0:      magic        cputype  cpusubtype  caps    filetype ncmds sizeofcmds               flags
 # PAD0-NEXT: MH_MAGIC_64  X86_64   ALL         LIB64   EXECUTE  9     [[#%u, CMDSIZE:]] {{.*}}
 # PAD0:      sectname __text
 # PAD0-NEXT: segname __TEXT
 # PAD0-NEXT: addr
 # PAD0-NEXT: size
-# PAD0-NEXT: offset [[#%u, CMDSIZE + 32]]
+# PAD0-NEXT: offset [[#%u, CMDSIZE + 0x20 + 0]]
 
 # RUN: lld -flavor darwinnew -o %t %t.o -headerpad 11
 # RUN: llvm-objdump --macho --all-headers %t | FileCheck %s --check-prefix=PAD11
 # PAD11:      magic        cputype  cpusubtype  caps    filetype ncmds sizeofcmds               flags
 # PAD11-NEXT: MH_MAGIC_64  X86_64   ALL         LIB64   EXECUTE  9     [[#%u, CMDSIZE:]] {{.*}}
 # PAD11:      sectname __text
 # PAD11-NEXT: segname __TEXT
 # PAD11-NEXT: addr
 # PAD11-NEXT: size
-# PAD11-NEXT: offset [[#%u, CMDSIZE + 32 + 0x11]]
+# PAD11-NEXT: offset [[#%u, CMDSIZE + 0x20 + 0x11]]
+
+# RUN: lld -flavor darwinnew -o %t %t.o -headerpad_max_install_names
+# RUN: llvm-objdump --macho --all-headers %t | FileCheck %s --check-prefix=PADMAX0
+# PADMAX0:      magic        cputype  cpusubtype  caps    filetype ncmds sizeofcmds               flags
+# PADMAX0-NEXT: MH_MAGIC_64  X86_64   ALL         LIB64   EXECUTE  9     [[#%u, CMDSIZE:]] {{.*}}
+# PADMAX0:      sectname __text
+# PADMAX0-NEXT: segname __TEXT
+# PADMAX0-NEXT: addr
+# PADMAX0-NEXT: size
+# PADMAX0-NEXT: offset [[#%u, CMDSIZE + 0x20 + 0x20]]
+
+# RUN: lld -flavor darwinnew -o %t %t.o -headerpad_max_install_names -L%S/Inputs/MacOSX.sdk/usr/lib -lSystem
+# RUN: llvm-objdump --macho --all-headers %t | FileCheck %s --check-prefix=PADMAX1
+# PADMAX1:      magic        cputype  cpusubtype  caps    filetype ncmds sizeofcmds               flags
+# PADMAX1-NEXT: MH_MAGIC_64  X86_64   ALL         LIB64   EXECUTE  10     [[#%u, CMDSIZE:]] {{.*}}
+# PADMAX1:      sectname __text
+# PADMAX1-NEXT: segname __TEXT
+# PADMAX1-NEXT: addr
+# PADMAX1-NEXT: size
+# PADMAX1-NEXT: offset [[#%u, CMDSIZE + 0x20 + 0x400]]
 
 .globl _main
 _main:
   ret