MachO: support `-syslibroot`

This adds support for the `-syslibroot` option.  This is required to
make the library search order actually function.  With this, it is now
possible to link a test Darwin x86_64 program with lld on Darwin.

Differential Revision: https://reviews.llvm.org/D82252
Reviewed By: Jez Ng

lld/MachO/Driver.cpp

@@ -152,28 +152,49 @@ static bool isDirectory(StringRef option, StringRef path) {
 
 static void getSearchPaths(std::vector<StringRef> &paths, unsigned optionCode,
                            opt::InputArgList &args,
+                           const std::vector<StringRef> &roots,
                            const SmallVector<StringRef, 2> &systemPaths) {
   StringRef optionLetter{(optionCode == OPT_F ? "F" : "L")};
   for (auto const &path : args::getStrings(args, optionCode)) {
-    if (isDirectory(optionLetter, path))
-      paths.push_back(path);
-  }
-  if (!args.hasArg(OPT_Z) && Triple(sys::getProcessTriple()).isOSDarwin()) {
-    for (auto const &path : systemPaths) {
+    // NOTE: only absolute paths are re-rooted to syslibroot(s)
+    if (llvm::sys::path::is_absolute(path, llvm::sys::path::Style::posix)) {
+      for (StringRef root : roots) {
+        SmallString<261> buffer(root);
+        llvm::sys::path::append(buffer, path);
+        // Do not warn about paths that are computed via the syslib roots
+        if (llvm::sys::fs::is_directory(buffer))
+          paths.push_back(saver.save(buffer.str()));
+      }
+    } else {
       if (isDirectory(optionLetter, path))
         paths.push_back(path);
     }
   }
+
+  // `-Z` suppresses the standard "system" search paths.
+  if (args.hasArg(OPT_Z))
+    return;
+
+  for (auto const &path : systemPaths) {
+    for (auto root : roots) {
+      SmallString<261> buffer(root);
+      llvm::sys::path::append(buffer, path);
+      if (isDirectory(optionLetter, buffer))
+        paths.push_back(saver.save(buffer.str()));
+    }
+  }
 }
 
-static void getLibrarySearchPaths(std::vector<StringRef> &paths,
-                                  opt::InputArgList &args) {
-  getSearchPaths(paths, OPT_L, args, {"/usr/lib", "/usr/local/lib"});
+static void getLibrarySearchPaths(opt::InputArgList &args,
+                                  const std::vector<StringRef> &roots,
+                                  std::vector<StringRef> &paths) {
+  getSearchPaths(paths, OPT_L, args, roots, {"/usr/lib", "/usr/local/lib"});
 }
 
-static void getFrameworkSearchPaths(std::vector<StringRef> &paths,
-                                    opt::InputArgList &args) {
-  getSearchPaths(paths, OPT_F, args,
+static void getFrameworkSearchPaths(opt::InputArgList &args,
+                                    const std::vector<StringRef> &roots,
+                                    std::vector<StringRef> &paths) {
+  getSearchPaths(paths, OPT_F, args, roots,
                  {"/Library/Frameworks", "/System/Library/Frameworks"});
 }
 
@@ -397,10 +418,22 @@ bool macho::link(llvm::ArrayRef<const char *> argsArr, bool canExitEarly,
   config->installName =
       args.getLastArgValue(OPT_install_name, config->outputFile);
   config->headerPad = args::getHex(args, OPT_headerpad, /*Default=*/32);
-  getLibrarySearchPaths(config->librarySearchPaths, args);
-  getFrameworkSearchPaths(config->frameworkSearchPaths, args);
   config->outputType = args.hasArg(OPT_dylib) ? MH_DYLIB : MH_EXECUTE;
 
+  std::vector<StringRef> roots;
+  for (const Arg *arg : args.filtered(OPT_syslibroot))
+    roots.push_back(arg->getValue());
+  // NOTE: the final `-syslibroot` being `/` will ignore all roots
+  if (roots.size() && roots.back() == "/")
+    roots.clear();
+  // NOTE: roots can never be empty - add an empty root to simplify the library
+  // and framework search path computation.
+  if (roots.empty())
+    roots.emplace_back("");
+
+  getLibrarySearchPaths(args, roots, config->librarySearchPaths);
+  getFrameworkSearchPaths(args, roots, config->frameworkSearchPaths);
+
   if (args.hasArg(OPT_v)) {
     message(getLLDVersion());
     message(StringRef("Library search paths:") +
@@ -455,6 +488,7 @@ bool macho::link(llvm::ArrayRef<const char *> argsArr, bool canExitEarly,
     case OPT_install_name:
     case OPT_Z:
     case OPT_arch:
+    case OPT_syslibroot:
       // handled elsewhere
       break;
     default:

lld/test/MachO/search-paths.test

@@ -2,13 +2,13 @@ UNSUPPORTED: darwin
 
 RUN: mkdir -p %t1 %t2
 
-RUN: lld -flavor darwinnew -v -L%t1 -F%t2 2>&1 | FileCheck -DLDIR=%t1 -DFDIR=%t2 %s
+RUN: lld -flavor darwinnew -Z -v -L%t1 -F%t2 2>&1 | FileCheck -DLDIR=%t1 -DFDIR=%t2 %s
 CHECK:      Library search paths:
 CHECK-NEXT: [[LDIR]]
 CHECK-NEXT: Framework search paths:
 CHECK-NEXT: [[FDIR]]
 
-RUN: lld -flavor darwinnew -v -L%t1 -F%t2 -Z 2>&1 | FileCheck -DLDIR=%t1 -DFDIR=%t2 --check-prefix=CHECK_Z %s
+RUN: lld -flavor darwinnew -Z -v -L%t1 -F%t2 -Z 2>&1 | FileCheck -DLDIR=%t1 -DFDIR=%t2 --check-prefix=CHECK_Z %s
 CHECK_Z:      Library search paths:
 CHECK_Z-NEXT: [[LDIR]]
 CHECK_Z-NEXT: Framework search paths:

lld/test/MachO/syslibroot.test

@@ -0,0 +1,55 @@
+# Ensure that a nonexistent path is ignored with a syslibroot
+
+RUN: lld -flavor darwinnew -v -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: lld -flavor darwinnew -v -syslibroot %t | FileCheck %s -check-prefix CHECK-SYSLIBROOT -DROOT=%t
+
+CHECK-SYSLIBROOT: Library search paths:
+CHECK-SYSLIBROOT-NEXT: [[ROOT]]/usr/lib
+
+RUN: mkdir -p %t/Library/libxml2-development
+RUN: lld -flavor darwinnew -v -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
+
+# NOTE: the match here is fuzzy because the default search paths exist on Linux
+# and macOS, but not on Windows (that is we ignore `/var/empty`).  This allows
+# us to run the test uniformly on all the platforms.
+RUN: lld -flavor darwinnew -v -syslibroot /var/empty -syslibroot / 2>&1 | FileCheck %s -check-prefix CHECK-SYSLIBROOT-IGNORED
+
+CHECK-SYSLIBROOT-IGNORED: /usr/lib
+CHECK-SYSLIBROOT-IGNORED: /usr/local/lib
+
+RUN: mkdir -p %t.2/usr/lib
+RUN: lld -flavor darwinnew -v -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: mkdir -p %t/System/Library/Frameworks
+RUN: lld -flavor darwinnew -v -syslibroot %t | FileCheck %s -check-prefix CHECK-SYSLIBROOT-FRAMEWORK -DROOT=%t
+
+CHECK-SYSLIBROOT-FRAMEWORK: Framework search paths:
+CHECK-SYSLIBROOT-FRAMEWORK: [[ROOT]]/System/Library/Frameworks
+
+# NOTE: the match here is fuzzy because the default search paths exist on Linux
+# and macOS, but not on Windows (that is we ignore `/var/empty`).  This allows
+# us to run the test uniformly on all the platforms.
+RUN: lld -flavor darwinnew -v -syslibroot /var/empty -syslibroot / 2>&1 | FileCheck %s -check-prefix CHECK-SYSLIBROOT-FRAMEWORK-IGNORED
+
+CHECK-SYSLIBROOT-FRAMEWORK-IGNORED: /System/Library/Framework
+
+RUN: mkdir -p %t/Library/Frameworks
+RUN: mkdir -p %t.2/Library/Frameworks
+RUN: lld -flavor darwinnew -v -syslibroot %t -syslibroot %t.2 -F /Library/Frameworks | 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