[PDB] Better support for posix style paths in PDBs.

[zturner]

Summary

While it doesn't make a *ton* of sense for POSIX paths to be
in PDBs, it's possible to occur in real scenarios involving
cross compilation.

The tools need to be able to handle this, because certain types
of debugging scenarios are possible without a running process
and so don't necessarily require you to be on a Windows system.
These include post-mortem debugging and binary forensics (e.g.
using a debugger to disassemble functions and examine symbols
without running the process).

There's changes in clang, LLD, and lldb in this patch.  After
this the cross-platform disassembly and source-list tests pass
on Linux.

[stella.stamenova]

A couple of comments, but looks good otherwise.

lldb/source/Plugins/SymbolFile/NativePDB/CompileUnitIndex.cpp

156 ↗

(On Diff #169245)

This looks unused

lldb/source/Plugins/SymbolFile/NativePDB/SymbolFileNativePDB.cpp

533 ↗

(On Diff #169245)

Is it possible that it would start with a letter? Like D:\ etc...

[rnk]

I agree with the direction, but please update the commit message to make it clear what the new expected behavior of our tools is. Basically, they should generate native paths unless we have command line flags telling us to do something else.

lld/COFF/PDB.cpp

221–239 ↗

(On Diff #169245)

Please clean up these comments to make it clear that we have a new, simple rule for what we're doing: Creating absolute paths that work on the linker's host filesystem. If you want any other kind of behavior, the user should use /pdbsourcepath:.

COFF/PDB.cpp

public:
   void finish();
 };
 }
 
 // Visual Studio's debugger requires absolute paths in various places in the
 // PDB to work without additional configuration:
 // https://docs.microsoft.com/en-us/visualstudio/debugger/debug-source-files-common-properties-solution-property-pages-dialog-box
 static void pdbMakeAbsolute(SmallVectorImpl<char> &FileName) {
-  if (sys::path::is_absolute(FileName, sys::path::Style::windows))
+  // The default behavior is to produce paths that are valid within the context
+  // of the machine that you perform the link on.  If the linker is running on
+  // a POSIX system, we will output absolute POSIX paths.  If the linker is
+  // running on a Windows system, we will output absolute Windows paths.  If the
+  // user desires any other kind of behavior, they should explicitly pass
+  // /pdbsourcepath and/or /pdbaltpath.
+  if (sys::path::is_absolute(FileName))
     return;
   if (Config->PDBSourcePath.empty()) {
-    // Debuggers generally want that PDB files contain absolute, Windows-style
-    // paths. On POSIX hosts, this here will produce an absolute POSIX-style
-    // path, which is weird -- but it's not clear what else to do.
-    // People doing cross builds should probably just always pass
-    // /pbdsourcepath: and make sure paths to input obj files and to lld-link
-    // itself are relative.
     sys::fs::make_absolute(FileName);
     return;
   }
-  // Using /pdbsourcepath: with absolute POSIX paths will prepend
-  // PDBSourcePath to the absolute POSIX path. Since absolute POSIX paths
-  // don't make sense in PDB files anyways, this is gargabe-in-garbage-out.
   SmallString<128> AbsoluteFileName = Config->PDBSourcePath;
-  sys::path::append(AbsoluteFileName, sys::path::Style::windows, FileName);
-  sys::path::native(AbsoluteFileName, sys::path::Style::windows);
-  sys::path::remove_dots(AbsoluteFileName, /*remove_dot_dots=*/true,
-                         sys::path::Style::windows);
+  sys::path::append(AbsoluteFileName, FileName);
+  sys::path::native(AbsoluteFileName);
+  sys::path::remove_dots(AbsoluteFileName, /*remove_dot_dots=*/true);
   FileName = std::move(AbsoluteFileName);
 }
 
 static SectionChunk *findByName(ArrayRef<SectionChunk *> Sections,
                                 StringRef Name) {
   for (SectionChunk *C : Sections)
     if (C->getSectionName() == Name)
       return C;
PDBLinker::maybeMergeTypeServerPDB(ObjFile *File, TypeServer2Record &TS) {
   // 1. The given file path
   // 2. Next to the object file or archive file
   auto ExpectedSession = handleExpected(
       tryToLoadPDB(TSId, TSPath),
       [&]() {
         StringRef LocalPath =
             !File->ParentName.empty() ? File->ParentName : File->getName();
         SmallString<128> Path = sys::path::parent_path(LocalPath);
-        sys::path::append(
-            Path, sys::path::filename(TSPath, sys::path::Style::windows));
+        sys::path::append(Path, sys::path::filename(TSPath));
         return tryToLoadPDB(TSId, Path);
       },
       [&](std::unique_ptr<ECError> EC) -> Error {
         auto SysErr = EC->convertToErrorCode();
         // Only re-try loading if the previous error was "No such file or
         // directory"
         if (SysErr.category() == std::generic_category() &&
             SysErr.value() == ENOENT)

 void PDBLinker::addObjFile(ObjFile *File) {
   // Add a module descriptor for every object file. We need to put an absolute
   // path to the object into the PDB. If this is a plain object, we make its
   // path absolute. If it's an object in an archive, we make the archive path
   // absolute.
   bool InArchive = !File->ParentName.empty();
   SmallString<128> Path = InArchive ? File->ParentName : File->getName();
   pdbMakeAbsolute(Path);
-  sys::path::native(Path, sys::path::Style::windows);
+  sys::path::native(Path);
   StringRef Name = InArchive ? File->getName() : StringRef(Path);
 
   pdb::DbiStreamBuilder &DbiBuilder = Builder.getDbiBuilder();
   File->ModuleDBI = &ExitOnErr(DbiBuilder.addModuleInfo(Name));
   File->ModuleDBI->setObjFileName(Path);
 
   auto Chunks = File->getChunks();
   uint32_t Modi = File->ModuleDBI->getModuleIndex();

 }
 
 void PDBLinker::addSections(ArrayRef<OutputSection *> OutputSections,
                             ArrayRef<uint8_t> SectionTable) {
   // It's not entirely clear what this is, but the * Linker * module uses it.
   pdb::DbiStreamBuilder &DbiBuilder = Builder.getDbiBuilder();
   NativePath = Config->PDBPath;
   pdbMakeAbsolute(NativePath);
-  sys::path::native(NativePath, sys::path::Style::windows);
+  sys::path::native(NativePath);
   uint32_t PdbFilePathNI = DbiBuilder.addECName(NativePath);
   auto &LinkerModule = ExitOnErr(DbiBuilder.addModuleInfo("* Linker *"));
   LinkerModule.setPdbFilePathNI(PdbFilePathNI);
   addCommonLinkerModuleSymbols(NativePath, LinkerModule, Alloc);
 
   // Add section contributions. They must be ordered by ascending RVA.
   for (OutputSection *OS : OutputSections) {
     addLinkerModuleSectionSymbol(LinkerModule, *OS, Alloc);