Add the --chroot option for --reproduce.

[ruiu]

Summary

If the linker is invoked with --chroot /foo and /bar/baz.o, it
tries to read the file from /foo/bar/baz.o. This feature is useful
when you are dealing with files created by the --reproduce option.

[grimar]

I uploaded reproduce for which this patch fails currently here: https://drive.google.com/file/d/0B_OWr6ld9gUmSXhjM0g4Y3I3d3c/view

In short- reproduce contains script that tries to open "/lib/x86_64-linux-gnu/libc.so.6" file. When running under windows,
callstack is

 	lld.exe!lld::elf::error(const llvm::Twine & Msg) Line 100	C++
 	lld.exe!lld::elf::ScriptLexer::setError(const llvm::Twine & Msg) Line 89	C++
>	lld.exe!`anonymous namespace'::ScriptParser::addFile(llvm::StringRef S) Line 275	C++
 	lld.exe!`anonymous namespace'::ScriptParser::readGroup() Line 310	C++
 	lld.exe!`anonymous namespace'::ScriptParser::readLinkerScript() Line 222	C++

That happens because sys::patch::is_absolute called from addFile uses native style by default and
returns false for /lib/x86_64-linux-gnu/libc.so.6" under windows.

With a little modification for above, patch works for me though. I uploaded changed version:

patch.patch150 KBDownload

It looks fine for me.

[emaste]

Approach LGTM, modulo @grimar's issue. I wonder if we should call the option --sysroot (and make it available to users) though? We'd have a little more work to do to handle a user-supplied sysroot when creating reproducers.

[ruiu]

• Always handle paths in linker scripts as Unix paths.
• Add a test for linker scripts.

[grimar]

LGTM

lld/ELF/Config.h

 // Most fields are direct mapping from the command line options
 // and such fields have the same name as the corresponding options.
 // Most fields are initialized by the driver.
 struct Configuration {
   InputFile *FirstElf = nullptr;
   uint8_t OSABI = 0;
   llvm::CachePruningPolicy ThinLTOCachePolicy;
   llvm::StringMap<uint64_t> SectionStartMap;
+  llvm::StringRef Chroot;
   llvm::StringRef DynamicLinker;
   llvm::StringRef Entry;
   llvm::StringRef Emulation;
   llvm::StringRef Fini;
   llvm::StringRef Init;
   llvm::StringRef LTOAAPipeline;
   llvm::StringRef LTONewPmPasses;
   llvm::StringRef MapFile;

lld/ELF/Driver.cpp

 }
 
 // Initializes Config members by the command line options.
 void LinkerDriver::readConfigs(opt::InputArgList &Args) {
   Config->AllowMultipleDefinition = Args.hasArg(OPT_allow_multiple_definition);
   Config->AuxiliaryList = getArgs(Args, OPT_auxiliary);
   Config->Bsymbolic = Args.hasArg(OPT_Bsymbolic);
   Config->BsymbolicFunctions = Args.hasArg(OPT_Bsymbolic_functions);
+  Config->Chroot = Args.getLastArgValue(OPT_chroot);
   Config->CompressDebugSections = getCompressDebugSections(Args);
   Config->DefineCommon = getArg(Args, OPT_define_common, OPT_no_define_common,
                                 !Args.hasArg(OPT_relocatable));
   Config->Demangle = getArg(Args, OPT_demangle, OPT_no_demangle, true);
   Config->DisableVerify = Args.hasArg(OPT_disable_verify);
   Config->Discard = getDiscard(Args);
   Config->DynamicLinker = getDynamicLinker(Args);
   Config->EhFrameHdr = Args.hasArg(OPT_eh_frame_hdr);

lld/ELF/DriverUtils.cpp

outs() << Argv0 << ": supported targets: "
          << "elf64-tradlittlemips elf64-x86-64\n";
 }
 
 // Reconstructs command line arguments so that so that you can re-run
 // the same command with the same inputs. This is for --reproduce.
 std::string elf::createResponseFile(const opt::InputArgList &Args) {
   SmallString<0> Data;
   raw_svector_ostream OS(Data);
+  OS << "--chroot .\n";
 
   // Copy the command line to the output while rewriting paths.
   for (auto *Arg : Args) {
     switch (Arg->getOption().getUnaliasedOption().getID()) {
     case OPT_reproduce:
       break;
     case OPT_INPUT:
       OS << quote(rewritePath(Arg->getValue())) << "\n";

lld/ELF/InputFiles.cpp

 using namespace lld;
 using namespace lld::elf;
 
 TarWriter *elf::Tar;
 
 InputFile::InputFile(Kind K, MemoryBufferRef M) : MB(M), FileKind(K) {}
 
 Optional<MemoryBufferRef> elf::readFile(StringRef Path) {
+  // The --chroot option changes our virtual root directory.
+  // This is useful when you are dealing with files created by --reproduce.
+  if (!Config->Chroot.empty() && Path.startswith("/"))
+    Path = Saver.save(Config->Chroot + Path);
+
   log(Path);
+
   auto MBOrErr = MemoryBuffer::getFile(Path);
   if (auto EC = MBOrErr.getError()) {
     error("cannot open " + Path + ": " + EC.message());
     return None;
   }
 
   std::unique_ptr<MemoryBuffer> &MB = *MBOrErr;
   MemoryBufferRef MBRef = MB->getMemBufferRef();

lld/ELF/Options.td

 def Ttext: S<"Ttext">, HelpText<"Same as --section-start with .text as the sectionname">;
 
 def allow_multiple_definition: F<"allow-multiple-definition">,
   HelpText<"Allow multiple definitions">;
 
 def as_needed: F<"as-needed">,
   HelpText<"Only set DT_NEEDED for shared libraries if used">;
 
+// -chroot doesn't have a help text because it is an internal option.
+def chroot: S<"chroot">;
+
 def color_diagnostics: F<"color-diagnostics">,
   HelpText<"Use colors in diagnostics">;
 
 def color_diagnostics_eq: J<"color-diagnostics=">,
   HelpText<"Use colors in diagnostics">;
 
 def define_common: F<"define-common">,
   HelpText<"Assign space to common symbols">;

lld/ELF/ScriptParser.cpp

if (IsUnderSysroot && S.startswith("/")) {
     SmallString<128> PathData;
     StringRef Path = (Config->Sysroot + S).toStringRef(PathData);
     if (sys::fs::exists(Path)) {
       Driver->addFile(Saver.save(Path), /*WithLOption=*/false);
       return;
     }
   }
 
-  if (sys::path::is_absolute(S)) {
+  if (S.startswith("/")) {
     Driver->addFile(S, /*WithLOption=*/false);
   } else if (S.startswith("=")) {
     if (Config->Sysroot.empty())
       Driver->addFile(S.substr(1), /*WithLOption=*/false);
     else
       Driver->addFile(Saver.save(Config->Sysroot + "/" + S.substr(1)),
                       /*WithLOption=*/false);
   } else if (S.startswith("-l")) {

lld/test/ELF/chroot.s

+# REQUIRES: x86
+# RUN: rm -rf %t.dir
+# RUN: mkdir %t.dir
+# RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %s -o %t.dir/chroot.o
+# RUN: ld.lld --chroot %t.dir -o %t.exe /chroot.o
+
+# RUN: echo 'INPUT(/chroot.o)' > %t.dir/scr
+# RUN: ld.lld --chroot %t.dir -o %t.exe /scr
+
+.globl _start
+_start:
+  ret

lld/test/ELF/reproduce.s

 # RUN: echo > file
 # RUN: echo > file2
 # RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %s -o 'foo bar'
 # RUN: ld.lld --reproduce repro2.tar 'foo bar' -L"foo bar" -Lfile -Tfile2 \
 # RUN:   --dynamic-list dyn -rpath file --script=file --version-script ver \
 # RUN:   --dynamic-linker "some unusual/path" -soname 'foo bar' -soname='foo bar'
 # RUN: tar xf repro2.tar
 # RUN: FileCheck %s --check-prefix=RSP2 < repro2/response.txt
+# RSP2:      --chroot .
 # RSP2:      "{{.*}}foo bar"
 # RSP2-NEXT: -L "{{.*}}foo bar"
 # RSP2-NEXT: -L {{.+}}file
 # RSP2-NEXT: --script {{.+}}file2
 # RSP2-NEXT: --dynamic-list {{.+}}dyn
 # RSP2-NEXT: -rpath {{.+}}file
 # RSP2-NEXT: --script {{.+}}file
 # RSP2-NEXT: --version-script [[PATH:.*]]ver