[lldb] Try to find relative DWO files by file name only, as a last resort

[DavidSpickett]

Summary

Relative DWO files are normally found at some/path/to/file.dwo.
Currently lldb will find the file by adding that path to the
binary's location and to any debug search paths that are set.

This patch adds a fallback on top of that where lldb will look
for just the filename (file.dwo) in those same places.

So if you had flattened a build directory before distribution,
you could still get symbols. Or perhaps you send out a DWO file
on demand, and don't want people to have to recreate the directory
layout.

For example if you were built:
program
obj/program.dwo

And changed to:
program
program.dwo

<binary dir>/obj/program.dwo is not found.
<binary dir>/program.dwo is.

If the layout was changed to:
program
mydebuginfo/progam.dwo

And we had a debug search path of <binary dir>/mydebuginfo:

• <binary dir>/mydebuginfo/obj/program.dwo is not found.
• <binary dir>/mydebuginfo/program.dwo is found.

[DavidSpickett]

@clayborg This is I think what you meant. I'm not 100% sure it's safe because I keep wondering if we could find the wrong files this way, but with 1 DWO file per program it seems unlikely.

I've reduced the nesting in the new tests compared to the previous patch. Also this version builds all the possible paths first, then tries them all. I can try to rework that so we do it as we go, but tell me what you think of the functionality first.

[clayborg]

lldb/source/Plugins/SymbolFile/DWARF/SymbolFileDWARF.cpp

1784–1804

Would it be better to move this out of the "if (!dwo_file.IsRelative())" and else statement?

1815

Maybe move it here? That way even if we have a non-relative path to a .dwo file, it could find it locally or in the search paths?

[DavidSpickett]

Squashed into previous review.

lldb/source/Plugins/SymbolFile/DWARF/SymbolFileDWARF.cpp

 //===-- SymbolFileDWARF.cpp -----------------------------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
if (!dwo_file.IsRelative()) {
         FileSystem::Instance().Resolve(dirspec);
         if (!FileSystem::Instance().IsDirectory(dirspec))
           continue;
 
         dirspec.AppendPathComponent(dwo_name);
         dwo_paths.Append(dirspec);
       }
 
+      FileSpec spec_to_get_name(dwo_name);
+      llvm::StringRef filename_only = spec_to_get_name.GetFilename();
+
+      // Try binary dir plus DWO filename only.
+      FileSpec filename_next_to_binary(
+          m_objfile_sp->GetFileSpec().GetDirectory().GetStringRef());
+      FileSystem::Instance().Resolve(filename_next_to_binary);
+      filename_next_to_binary.AppendPathComponent(filename_only);
+      dwo_paths.Append(filename_next_to_binary);
+
+      // Try adding just the filename to each of the search paths.
+      for (size_t idx = 0; idx < num_directories; ++idx) {
+        FileSpec dirspec = debug_file_search_paths.GetFileSpecAtIndex(idx);
+        FileSystem::Instance().Resolve(dirspec);
+        if (!FileSystem::Instance().IsDirectory(dirspec))
+          continue;
+
+        dirspec.AppendPathComponent(filename_only);
+        dwo_paths.Append(dirspec);
+      }
+
       size_t num_possible = dwo_paths.GetSize();
       for (size_t idx = 0; idx < num_possible && !found; ++idx) {
         FileSpec dwo_spec = dwo_paths.GetFileSpecAtIndex(idx);
         if (FileSystem::Instance().Exists(dwo_spec)) {
           dwo_file = dwo_spec;
           found = true;
         }
       }
     }
   }
 
   if (!found) {
     unit.SetDwoError(Status::createWithFormat(
         "unable to locate .dwo debug file \"{0}\" for skeleton DIE "
         "{1:x16}",
         dwo_file.GetPath().c_str(), cu_die.GetOffset()));
 
     if (m_dwo_warning_issued.test_and_set(std::memory_order_relaxed) == false) {
       GetObjectFile()->GetModule()->ReportWarning(

lldb/test/Shell/SymbolFile/DWARF/dwo-debug-file-search-paths-filename-only.c

+/// Check that when LLDB is looking for a relative DWO it uses the debug search
+/// paths setting. If it doesn't find it by adding the whole relative path to
+/// of DWO it should try adding just the filename (e.g. main.dwo) to each debug
+/// search path.
+// RUN: rm -rf %t.compdir/
+// RUN: mkdir -p %t.compdir/a/b/
+// RUN: cp %s %t.compdir/a/b/main.c
+// RUN: cd %t.compdir/a/
+/// The produced DWO is named /b//main-main.dwo, with a DW_AT_comp_dir of a/.
+// RUN: %clang_host -g -gsplit-dwarf -fdebug-prefix-map=%t.compdir=. b/main.c -o b/main
+// RUN: cd ../..
+/// Move the DWO file away from the expected location.
+// RUN: mv %t.compdir/a/b/main-main.dwo %t.compdir/
+/// LLDB won't find the DWO next to the binary or by adding the relative path
+/// to any of the search paths. So it should find the DWO file at
+/// %t.compdir/main-main.dwo.
+// RUN: %lldb --no-lldbinit %t.compdir/a/b/main \
+// RUN:   -O "settings append target.debug-file-search-paths %t.compdir" \
+// RUN:   -o "b main.c:26" -o "run" -o "frame variable" --batch 2>&1 | FileCheck %s
+
+// CHECK-NOT: warning: {{.*}}main unable to locate separate debug file (dwo, dwp). Debugging will be degraded.
+// CHECK: (int) num = 5
+
+int main(void) {
+  int num = 5;
+  return 0;
+}
 No newline at end of file

lldb/test/Shell/SymbolFile/DWARF/dwo-relative-filename-only-binary-dir.c

+/// Check that LLDB can find a relative DWO file next to a binary just using the
+/// filename of that DWO. For example "main.dwo" not "a/b/main.dwo".
+// RUN: rm -rf %t.compdir/
+// RUN: mkdir -p %t.compdir/a/b/
+// RUN: cp %s %t.compdir/a/b/main.c
+// RUN: cd %t.compdir/a/
+/// The produced DWO is named b/main-main.dwo, with a DW_AT_comp_dir of a/.
+// RUN: %clang_host -g -gsplit-dwarf -fdebug-prefix-map=%t.compdir=. b/main.c -o b/main
+// RUN: cd ../..
+/// Move binary and DWO out of expected locations.
+// RUN: mv %t.compdir/a/b/main %t.compdir/
+// RUN: mv %t.compdir/a/b/main-main.dwo %t.compdir/
+// RUN: %lldb --no-lldbinit %t.compdir/main \
+// RUN:   -o "b main.c:21" -o "run" -o "frame variable" --batch 2>&1 | FileCheck %s
+
+// CHECK-NOT: warning: {{.*}}main unable to locate separate debug file (dwo, dwp). Debugging will be degraded.
+// CHECK: (int) num = 5
+
+int main(void) {
+  int num = 5;
+  return 0;
+}
 No newline at end of file