[ELF2] Add --sysroot command line switch

[ruiu]

ELF/Config.h

23

In the GNU ld manual, sysroot is used as a single word, so I'd name it Sysroot.

ELF/Driver.cpp

66–67

I'm generally not happy about the use of SmallString in sys::path. It seems to be able to be replaced by std::string without noticeable performance penalty. At least we don't need any speed here. Can you return std::string from this function to make this function functional?

[ikudrin]

• SysRoot -> Sysroot
• Made the buildSysrootedPath function functional

[ruiu]

LGTM

ELF/Config.h

 namespace lld {
 namespace elf2 {
 
 struct Configuration {
   llvm::StringRef OutputFile;
   llvm::StringRef DynamicLinker;
   std::string RPath;
   std::vector<llvm::StringRef> InputSearchPaths;
+  llvm::StringRef SysRoot;
   bool Shared = false;
   bool DiscardAll = false;
   bool DiscardLocals = false;
   bool DiscardNone = false;
   bool ExportDynamic = false;
   bool NoInhibitExec = false;
 };
 
 extern Configuration *Config;
 
 } // namespace elf2
 } // namespace lld
 
 #endif

ELF/Driver.cpp

if (Magic == file_magic::archive)
     return make_unique<ArchiveFile>(MB);
 
   if (Magic == file_magic::elf_shared_object)
     return createELFFile<SharedFile>(MB);
 
   return createELFFile<ObjectFile>(MB);
 }
 
+// Makes a path by concatenating Dir and File.
+// If Dir starts with "=" the result will be preceded by SysRoot,
+// which can be set with --sysroot command line switch.
+static void buildSysRootedPath(SmallString<128> &Path, StringRef Dir,
+                               StringRef File) {
+  if (Dir.startswith("=")) {
+    Path.assign(Config->SysRoot);
+    sys::path::append(Path, Dir.substr(1), File);
+  } else {
+    Path.assign(Dir);
+    sys::path::append(Path, File);
+  }
+}
+
 // Searches a given library from input search paths, which are filled
 // from -L command line switches. Returns a path to an existent library file.
 static std::string searchLibrary(StringRef Path) {
   std::vector<std::string> Names;
   if (Path[0] == ':') {
     Names.push_back(Path.drop_front().str());
   } else {
     Names.push_back((Twine("lib") + Path + ".so").str());
     Names.push_back((Twine("lib") + Path + ".a").str());
   }
   SmallString<128> FullPath;
   for (StringRef Dir : Config->InputSearchPaths) {
     for (const std::string &Name : Names) {
-      FullPath = Dir;
-      sys::path::append(FullPath, Name);
+      buildSysRootedPath(FullPath, Dir, Name);
       if (sys::fs::exists(FullPath.str()))
         return FullPath.str().str();
     }
   }
   error(Twine("Unable to find library -l") + Path);
 }
 
 void LinkerDriver::link(ArrayRef<const char *> ArgsArr) {
   // Parse command line options.
   opt::InputArgList Args = Parser.parse(ArgsArr);
 
   // Handle -o
   if (auto *Arg = Args.getLastArg(OPT_output))
     Config->OutputFile = Arg->getValue();
   if (Config->OutputFile.empty())
     error("-o must be specified.");
 
   // Handle -dynamic-linker
   if (auto *Arg = Args.getLastArg(OPT_dynamic_linker))
     Config->DynamicLinker = Arg->getValue();
 
+  if (auto *Arg = Args.getLastArg(OPT_sysroot))
+    Config->SysRoot = Arg->getValue();
+
   std::vector<StringRef> RPaths;
   for (auto *Arg : Args.filtered(OPT_rpath))
     RPaths.push_back(Arg->getValue());
   if (!RPaths.empty())
     Config->RPath = llvm::join(RPaths.begin(), RPaths.end(), ":");
 
   for (auto *Arg : Args.filtered(OPT_L))
     Config->InputSearchPaths.push_back(Arg->getValue());

ELF/Options.td

 def alias_L : Joined<["--"], "library-path=">,
      Alias<L>;
 
 def l : Joined<["-"], "l">, MetaVarName<"<libName>">,
      HelpText<"Root name of library to use">;
 
 def alias_l : Joined<["--"], "library=">,
      Alias<l>;
+
+def sysroot : Joined<["--"], "sysroot=">,
+     HelpText<"Set the system root">;

test/elf2/sysroot.s

+// RUN: mkdir -p %t/lib
+// RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %s -o %t/m.o
+// RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux \
+// RUN:     %p/Inputs/libsearch-st.s -o %t/st.o
+// RUN: rm -f %t/lib/libls.a
+// RUN: llvm-ar rcs %t/lib/libls.a %t/st.o
+// REQUIRES: x86
+
+// Should not link because of undefined symbol _bar
+// RUN: not lld -flavor gnu2 -o %t/r %t/m.o 2>&1 \
+// RUN:     | FileCheck --check-prefix=UNDEFINED %s
+// UNDEFINED: undefined symbol: _bar
+
+// We need to be sure that there is no suitable library in the /lib directory
+// RUN: not lld -flavor gnu2 -o %t/r %t/m.o -L/lib -l:libls.a 2>&1 \
+// RUN:     | FileCheck --check-prefix=NOLIB %s
+// NOLIB: Unable to find library -l:libls.a
+
+// Should just remove the '=' symbol if --sysroot is not specified.
+// Case 1: relative path
+// RUN: cd %t && lld -flavor gnu2 -o %t/r %t/m.o -L=lib -l:libls.a
+// Case 2: absolute path
+// RUN: cd %p && lld -flavor gnu2 -o %t/r %t/m.o -L=%t/lib -l:libls.a
+
+// RUN: cd %p
+
+// Should substitute SysRoot if specified
+// RUN: lld -flavor gnu2 -o %t/r %t/m.o --sysroot=%t -L=lib -l:libls.a
+// RUN: lld -flavor gnu2 -o %t/r %t/m.o --sysroot=%t -L=/lib -l:libls.a
+
+// Should not substitute SysRoot if the directory name does not start with '='
+// RUN: not lld -flavor gnu2 -o %t/r %r/m.o --sysroot=%t -Llib -l:libls.a
+// RUN: not lld -flavor gnu2 -o %t/r %r/m.o --sysroot=%t -L/lib -l:libls.a
+
+.globl _start,_bar;
+_start: