[MCDwarf] Respect -fdebug-prefix-map= for generated assembly debug in…

…fo (DWARF v5)

For generated assembly debug info, MCDwarfLineTableHeader::CompilationDir is an
unmapped path set in MCContext::setGenDwarfRootFile. Remap it.

A relative destination path of -fdebug-prefix-map= exposes a llvm-dwarfdump bug
which joins relative DW_AT_comp_dir and directories[0].

Fix #56609

Reviewed By: dblaikie

Differential Revision: https://reviews.llvm.org/D131749

(cherry picked from commit f62e60f)

llvm/include/llvm/MC/MCContext.h

@@ -698,6 +698,9 @@ class MCContext {
   /// Add an entry to the debug prefix map.
   void addDebugPrefixMapEntry(const std::string &From, const std::string &To);
 
+  /// Remap one path in-place as per the debug prefix map.
+  void remapDebugPath(SmallVectorImpl<char> &Path);
+
   // Remaps all debug directory paths in-place as per the debug prefix map.
   void RemapDebugPaths();
 

llvm/include/llvm/MC/MCDwarf.h

@@ -22,6 +22,7 @@
 #include "llvm/MC/StringTableBuilder.h"
 #include "llvm/Support/Error.h"
 #include "llvm/Support/MD5.h"
+#include "llvm/Support/StringSaver.h"
 #include <cassert>
 #include <cstdint>
 #include <string>
@@ -48,6 +49,8 @@ MCSymbol *emitListsTableHeaderStart(MCStreamer &S);
 
 /// Manage the .debug_line_str section contents, if we use it.
 class MCDwarfLineStr {
+  BumpPtrAllocator Alloc;
+  StringSaver Saver{Alloc};
   MCSymbol *LineStrLabel = nullptr;
   StringTableBuilder LineStrings{StringTableBuilder::DWARF};
   bool UseRelocs = false;
@@ -57,6 +60,8 @@ class MCDwarfLineStr {
   /// v5 line table).
   explicit MCDwarfLineStr(MCContext &Ctx);
 
+  StringSaver &getSaver() { return Saver; }
+
   /// Emit a reference to the string.
   void emitRef(MCStreamer *MCOS, StringRef Path);
 

llvm/lib/MC/MCContext.cpp

@@ -855,30 +855,29 @@ void MCContext::addDebugPrefixMapEntry(const std::string &From,
   DebugPrefixMap.insert(std::make_pair(From, To));
 }
 
+void MCContext::remapDebugPath(SmallVectorImpl<char> &Path) {
+  for (const auto &[From, To] : DebugPrefixMap)
+    if (llvm::sys::path::replace_path_prefix(Path, From, To))
+      break;
+}
+
 void MCContext::RemapDebugPaths() {
   const auto &DebugPrefixMap = this->DebugPrefixMap;
   if (DebugPrefixMap.empty())
     return;
 
-  const auto RemapDebugPath = [&DebugPrefixMap](std::string &Path) {
-    SmallString<256> P(Path);
-    for (const auto &Entry : DebugPrefixMap) {
-      if (llvm::sys::path::replace_path_prefix(P, Entry.first, Entry.second)) {
-        Path = P.str().str();
-        break;
-      }
-    }
-  };
-
   // Remap compilation directory.
-  std::string CompDir = std::string(CompilationDir.str());
-  RemapDebugPath(CompDir);
-  CompilationDir = CompDir;
+  remapDebugPath(CompilationDir);
 
   // Remap MCDwarfDirs in all compilation units.
-  for (auto &CUIDTablePair : MCDwarfLineTablesCUMap)
-    for (auto &Dir : CUIDTablePair.second.getMCDwarfDirs())
-      RemapDebugPath(Dir);
+  SmallString<256> P;
+  for (auto &CUIDTablePair : MCDwarfLineTablesCUMap) {
+    for (auto &Dir : CUIDTablePair.second.getMCDwarfDirs()) {
+      P = Dir;
+      remapDebugPath(P);
+      Dir = std::string(P);
+    }
+  }
 }
 
 //===----------------------------------------------------------------------===//

llvm/lib/MC/MCDwarf.cpp

@@ -416,9 +416,15 @@ void MCDwarfLineTableHeader::emitV5FileDirTables(
                                     : dwarf::DW_FORM_string);
   MCOS->emitULEB128IntValue(MCDwarfDirs.size() + 1);
   // Try not to emit an empty compilation directory.
-  const StringRef CompDir = CompilationDir.empty()
-                                ? MCOS->getContext().getCompilationDir()
-                                : StringRef(CompilationDir);
+  SmallString<256> Dir;
+  StringRef CompDir = MCOS->getContext().getCompilationDir();
+  if (!CompilationDir.empty()) {
+    Dir = CompilationDir;
+    MCOS->getContext().remapDebugPath(Dir);
+    CompDir = Dir.str();
+    if (LineStr)
+      CompDir = LineStr->getSaver().save(CompDir);
+  }
   if (LineStr) {
     // Record path strings, emit references here.
     LineStr->emitRef(MCOS, CompDir);

llvm/test/MC/ELF/debug-prefix-map.s

@@ -31,19 +31,19 @@ f:
 # MAP_V4:      DW_AT_decl_file [DW_FORM_data4] ("src_root{{(/|\\)+}}src.s")
 # MAP_V4-NOT:  .foo
 
-## FIXME DW_AT_decl_file and include_directories are not mapped
 # MAP_V5:      DW_AT_name [DW_FORM_string] ("src.s")
 # MAP_V5:      DW_AT_comp_dir [DW_FORM_string] ("src_root")
-# MAP_V5:      DW_AT_decl_file [DW_FORM_data4] ("{{.*}}.foo{{(/|\\)+}}src.s")
-# MAP_V5:      include_directories[ 0] = .debug_line_str[0x00000000] = "{{.*}}.foo"
+## FIXME llvm-dwarfdump incorrectly joins include_directories[0] to DW_AT_comp_dir,
+## so there are two src_root path components.
+# MAP_V5:      DW_AT_decl_file [DW_FORM_data4] ("src_root{{(/|\\)+}}src_root{{(/|\\)+}}src.s")
+# MAP_V5:      include_directories[ 0] = .debug_line_str[0x00000000] = "src_root"
 
 # MAPABS_V4:      DW_AT_name [DW_FORM_string] ("src.s")
 # MAPABS_V4:      DW_AT_comp_dir [DW_FORM_string] ("{{(/|\\)+}}src_root")
 # MAPABS_V4:      DW_AT_decl_file [DW_FORM_data4] ("{{(/|\\)+}}src_root{{(/|\\)+}}src.s")
 # MAPABS_V4-NOT:  .foo
 
-## FIXME DW_AT_decl_file and include_directories are not mapped
 # MAPABS_V5:      DW_AT_name [DW_FORM_string] ("src.s")
 # MAPABS_V5:      DW_AT_comp_dir [DW_FORM_string] ("{{(/|\\)+}}src_root")
-# MAPABS_V5:      DW_AT_decl_file [DW_FORM_data4] ("{{.*}}.foo{{(/|\\)+}}src.s")
-# MAPABS_V5:      include_directories[ 0] = .debug_line_str[0x00000000] = "{{.*}}.foo"
+# MAPABS_V5:      DW_AT_decl_file [DW_FORM_data4] ("/src_root{{(/|\\)+}}src.s")
+# MAPABS_V5:      include_directories[ 0] = .debug_line_str[0x00000000] = "/src_root"