[lld-macho] Implement -force_load

[int3]

Summary

It's similar to lld-ELF's -whole-archive, but applied to individual
archives instead of to a series of them.

[compnerd]

lld/MachO/Driver.cpp

270

Can we do any better in terms of diagnostics here? Perhaps stringify the error?

275

This seems ... duplicative. The fatal is necessary, but Im not sure about printing out a subsequent message.

287

Id just cascade this:

if (Optional<MemoryBufferRef> archive = readFile(path))
  for (MemoryBufferRef member: getArchiveMembers(*archive))
    inputFiles.push_back(make<ObjFile>(member));

[int3]

cascade

lld/MachO/Driver.cpp

270

CHECK does stringify the error

275

this doesn't duplicate the CHECK on line 266 -- it's reporting any errors returned by the children() call

[smeenai]

LGTM

lld/MachO/Driver.cpp

 #include "llvm/Support/Host.h"
 #include "llvm/Support/MemoryBuffer.h"
 #include "llvm/Support/Path.h"
 
 #include <algorithm>
 
 using namespace llvm;
 using namespace llvm::MachO;
-using namespace llvm::sys;
+using namespace llvm::object;
 using namespace llvm::opt;
+using namespace llvm::sys;
 using namespace lld;
 using namespace lld::macho;
 
 Configuration *lld::macho::config;
 
 // Create prefix string literals used in Options.td
 #define PREFIX(NAME, VALUE) const char *NAME[] = VALUE;
 #include "Options.inc"
static void addFileList(StringRef path) {
   Optional<MemoryBufferRef> buffer = readFile(path);
   if (!buffer)
     return;
   MemoryBufferRef mbref = *buffer;
   for (StringRef path : args::getLines(mbref))
     addFile(path);
 }
 
+// Returns slices of MB by parsing MB as an archive file.
+// Each slice consists of a member file in the archive.
+static std::vector<MemoryBufferRef> getArchiveMembers(MemoryBufferRef mb) {
+  std::unique_ptr<Archive> file =
+      CHECK(Archive::create(mb),
+            mb.getBufferIdentifier() + ": failed to parse archive");
+
+  std::vector<MemoryBufferRef> v;
+  Error err = Error::success();
+  for (const Archive::Child &c : file->children(err)) {
+    MemoryBufferRef mbref =
+        CHECK(c.getMemoryBufferRef(),
+              mb.getBufferIdentifier() +
+                  ": could not get the buffer for a child of the archive");
+    v.push_back(mbref);
+  }
+  if (err)
+    fatal(mb.getBufferIdentifier() +
+          ": Archive::children failed: " + toString(std::move(err)));
+
+  return v;
+}
+
+static void forceLoadArchive(StringRef path) {
+  if (Optional<MemoryBufferRef> buffer = readFile(path))
+    for (MemoryBufferRef member : getArchiveMembers(*buffer))
+      inputFiles.push_back(make<ObjFile>(member));
+}
+
 static std::array<StringRef, 6> archNames{"arm",    "arm64", "i386",
                                           "x86_64", "ppc",   "ppc64"};
 static bool isArchString(StringRef s) {
   static DenseSet<StringRef> archNamesSet(archNames.begin(), archNames.end());
   return archNamesSet.find(s) != archNamesSet.end();
 }
 
 // An order file has one entry per line, in the following format:
 //
 //   <arch>:<object file>:<symbol name>
for (const auto &arg : args) {
     warnIfDeprecatedOption(opt);
     switch (arg->getOption().getID()) {
     case OPT_INPUT:
       addFile(arg->getValue());
       break;
     case OPT_filelist:
       addFileList(arg->getValue());
       break;
+    case OPT_force_load:
+      forceLoadArchive(arg->getValue());
+      break;
     case OPT_l: {
       StringRef name = arg->getValue();
       if (Optional<std::string> path = findLibrary(name)) {
         addFile(*path);
         break;
       }
       error("library not found for -l" + name);
       break;

lld/test/MachO/force-load.s

+# REQUIRES: x86
+# RUN: mkdir -p %t
+# RUN: echo ".section __TEXT,archive; .globl _foo; .weak_definition _foo; _foo:" | llvm-mc -filetype=obj -triple=x86_64-apple-darwin -o %t/archive-foo.o
+# RUN: rm -f %t/foo.a
+# RUN: llvm-ar rcs %t/foo.a %t/archive-foo.o
+# RUN: echo ".section __TEXT,obj; .globl _foo; .weak_definition _foo; _foo:" | llvm-mc -filetype=obj -triple=x86_64-apple-darwin -o %t/foo.o
+# RUN: llvm-mc -filetype=obj -triple=x86_64-apple-darwin %s -o %t/test.o
+
+# RUN: lld -flavor darwinnew -force_load %t/foo.a %t/foo.o %t/test.o -o %t/test-force-load-first
+# FORCE-LOAD-FIRST:  __TEXT,archive _foo
+# RUN: llvm-objdump --syms %t/test-force-load-first | FileCheck %s --check-prefix=FORCE-LOAD-FIRST
+
+# RUN: lld -flavor darwinnew %t/foo.o -force_load %t/foo.a %t/test.o -o %t/test-force-load-second
+# RUN: llvm-objdump --syms %t/test-force-load-second | FileCheck %s --check-prefix=FORCE-LOAD-SECOND
+# FORCE-LOAD-SECOND: __TEXT,obj _foo
+
+.globl _main
+_main:
+  ret

lld/test/MachO/invalid/bad-archive.s

 # REQUIRES: x86
 # RUN: echo "!<arch>" > %t.a
 # RUN: echo "foo" >> %t.a
 # RUN: llvm-mc -filetype=obj -triple=x86_64-apple-darwin %s -o %t.o
 
 # RUN: not lld -flavor darwinnew %t.o %t.a -o /dev/null 2>&1 | FileCheck -DFILE=%t.a %s
+# RUN: not lld -flavor darwinnew %t.o -force_load %t.a -o /dev/null 2>&1 | FileCheck -DFILE=%t.a %s
 # CHECK: error: [[FILE]]: failed to parse archive: truncated or malformed archive (remaining size of archive too small for next archive member header at offset 8)
 
 .global _main
 _main:
   ret