Fix PR36793

[• espindola]

Summary

With this patch lld will iterate over compile units to file the line tables instead of assuming there is only one at offset 0.

[arichardson]

ELF/InputFiles.cpp

138

Maybe use .get() instead of &*?

[• espindola]

address review comments.

[grimar]

It turns out this can be simplified slightly. I attached the patch.

patch.patch69 KBDownload

ELF/InputFiles.cpp

134

Code above duplicates code from DWARFContext::getLineTableForUnit.
Since we now do not explicitly support case when there is no .debug_info (D44760),
we do not need to parse line tables explicitly here I think, so I would suggest the
different approach:

We could have DWARFContext as a member of ObjectFile. And here it could be just:

template <class ELFT> void ObjFile<ELFT>::initializeDwarf() {
  Dwarf = llvm::make_unique<DWARFContext>(
      llvm::make_unique<LLDDwarfObj<ELFT>>(this));
  for (std::unique_ptr<DWARFCompileUnit> &CU : Dwarf->compile_units()) {
    const DWARFDebugLine::LineTable *LT = Dwarf->getLineTableForUnit(CU.get());
...

203

getFileLineInfoForAddress returns true on success according to specification.
It can be the following I think:

for (const llvm::DWARFDebugLine::LineTable *LT : LineTables)
  if (LT->getFileLineInfoForAddress(
      S->getOffsetInFile() + Offset, nullptr,
      DILineInfoSpecifier::FileLineInfoKind::AbsoluteFilePath, Info))
  return Info;

[jhenderson]

ELF/InputFiles.cpp

134

@grimar is probably right, although it looks like it would mean I'd have to propagate the Errors I'm adding to getOrParseLineTableUnit further up the stack than they currently need to be (see D44560).

ELF/InputFiles.h

20

Do we need this header here? All I see that has changed is the use of pointers in a vector, which can be forward declared, can't they?

test/ELF/Inputs/multiple-cu.s

18

Nit: comment doesn't line up here (also in test/ELF/multiple-cu.s).

[• espindola]

ELF/InputFiles.h

20

I don't think it is possible to forward declare an inner class (llvm::DWARFDebugLine::LineTable).

[• espindola]

Use getLineTableForUnit.

[ruiu]

LGTM

[• espindola]

328284

ELF/InputFiles.h

 
 #include "Config.h"
 #include "lld/Common/ErrorHandler.h"
 #include "lld/Common/LLVM.h"
 #include "lld/Common/Reproduce.h"
 #include "llvm/ADT/CachedHashString.h"
 #include "llvm/ADT/DenseSet.h"
 #include "llvm/ADT/STLExtras.h"
+#include "llvm/DebugInfo/DWARF/DWARFDebugLine.h"
 #include "llvm/IR/Comdat.h"
 #include "llvm/Object/Archive.h"
 #include "llvm/Object/ELF.h"
 #include "llvm/Object/IRObjectFile.h"
 #include "llvm/Support/Threading.h"
 #include <map>
 
 namespace llvm {
-class DWARFDebugLine;
 class TarWriter;
 struct DILineInfo;
 namespace lto {
 class InputFile;
 }
 } // namespace llvm
 
 namespace lld {
private:
 
   // .shstrtab contents.
   StringRef SectionStringTable;
 
   // Debugging information to retrieve source file and line for error
   // reporting. Linker may find reasonable number of errors in a
   // single object file, so we cache debugging information in order to
   // parse it only once for each object file we link.
+  std::vector<const llvm::DWARFDebugLine::LineTable *> LineTables;
   std::unique_ptr<llvm::DWARFDebugLine> DwarfLine;
   struct VarLoc {
+    const llvm::DWARFDebugLine::LineTable *LT;
     unsigned File;
     unsigned Line;
   };
   llvm::DenseMap<StringRef, VarLoc> VariableLoc;
   llvm::once_flag InitDwarfLine;
 };
 
 // LazyObjFile is analogous to ArchiveFile in the sense that

ELF/InputFiles.cpp

 
 template <class ELFT> void ObjFile<ELFT>::initializeDwarf() {
   DWARFContext Dwarf(make_unique<LLDDwarfObj<ELFT>>(this));
   const DWARFObject &Obj = Dwarf.getDWARFObj();
   DwarfLine.reset(new DWARFDebugLine);
   DWARFDataExtractor LineData(Obj, Obj.getLineSection(), Config->IsLE,
                               Config->Wordsize);
 
-  // The second parameter is offset in .debug_line section
-  // for compilation unit (CU) of interest. We have only one
-  // CU (object file), so offset is always 0.
+  for (std::unique_ptr<DWARFCompileUnit> &CU : Dwarf.compile_units()) {
+    DWARFDie UnitDIE = CU->getUnitDIE();
+    Optional<uint64_t> Offset =
+        dwarf::toSectionOffset(UnitDIE.find(dwarf::DW_AT_stmt_list));
+    if (!Offset)
+      continue;
     const DWARFDebugLine::LineTable *LT =
-      DwarfLine->getOrParseLineTable(LineData, 0, Dwarf, nullptr);
+        DwarfLine->getOrParseLineTable(LineData, *Offset, Dwarf, nullptr);
     if (!LT)
-    return;
-
-  // Return if there is no debug information about CU available.
-  if (!Dwarf.getNumCompileUnits())
-    return;
+      continue;
+    LineTables.push_back(LT);
 
     // Loop over variable records and insert them to VariableLoc.
-  DWARFCompileUnit *CU = Dwarf.getCompileUnitAtIndex(0);
     for (const auto &Entry : CU->dies()) {
-    DWARFDie Die(CU, &Entry);
+      DWARFDie Die(CU.get(), &Entry);
       // Skip all tags that are not variables.
       if (Die.getTag() != dwarf::DW_TAG_variable)
         continue;
 
-    // Skip if a local variable because we don't need them for generating error
-    // messages. In general, only non-local symbols can fail to be linked.
+      // Skip if a local variable because we don't need them for generating
+      // error messages. In general, only non-local symbols can fail to be
+      // linked.
       if (!dwarf::toUnsigned(Die.find(dwarf::DW_AT_external), 0))
         continue;
 
       // Get the source filename index for the variable.
       unsigned File = dwarf::toUnsigned(Die.find(dwarf::DW_AT_decl_file), 0);
       if (!LT->hasFileAtIndex(File))
         continue;
 
       // Get the line number on which the variable is declared.
       unsigned Line = dwarf::toUnsigned(Die.find(dwarf::DW_AT_decl_line), 0);
 
       // Get the name of the variable and add the collected information to
-    // VariableLoc. Usually Name is non-empty, but it can be empty if the input
-    // object file lacks some debug info.
+      // VariableLoc. Usually Name is non-empty, but it can be empty if the
+      // input object file lacks some debug info.
       StringRef Name = dwarf::toString(Die.find(dwarf::DW_AT_name), "");
       if (!Name.empty())
-      VariableLoc.insert({Name, {File, Line}});
+        VariableLoc.insert({Name, {LT, File, Line}});
+    }
   }
 }
 
 // Returns the pair of file name and line number describing location of data
 // object (variable, array, etc) definition.
 template <class ELFT>
 Optional<std::pair<std::string, unsigned>>
 ObjFile<ELFT>::getVariableLoc(StringRef Name) {
   llvm::call_once(InitDwarfLine, [this]() { initializeDwarf(); });
 
-  // There is always only one CU so it's offset is 0.
-  const DWARFDebugLine::LineTable *LT = DwarfLine->getLineTable(0);
-  if (!LT)
-    return None;
-
   // Return if we have no debug information about data object.
   auto It = VariableLoc.find(Name);
   if (It == VariableLoc.end())
     return None;
 
   // Take file name string from line table.
   std::string FileName;
-  if (!LT->getFileNameByIndex(
+  if (!It->second.LT->getFileNameByIndex(
           It->second.File, nullptr,
           DILineInfoSpecifier::FileLineInfoKind::AbsoluteFilePath, FileName))
     return None;
 
   return std::make_pair(FileName, It->second.Line);
 }
 
 // Returns source line information for a given offset
 // using DWARF debug info.
 template <class ELFT>
 Optional<DILineInfo> ObjFile<ELFT>::getDILineInfo(InputSectionBase *S,
                                                   uint64_t Offset) {
   llvm::call_once(InitDwarfLine, [this]() { initializeDwarf(); });
 
-  // The offset to CU is 0.
-  const DWARFDebugLine::LineTable *Tbl = DwarfLine->getLineTable(0);
-  if (!Tbl)
-    return None;
-
   // Use fake address calcuated by adding section file offset and offset in
   // section. See comments for ObjectInfo class.
   DILineInfo Info;
-  Tbl->getFileLineInfoForAddress(
+  for (const llvm::DWARFDebugLine::LineTable *LT : LineTables) {
+    LT->getFileLineInfoForAddress(
         S->getOffsetInFile() + Offset, nullptr,
         DILineInfoSpecifier::FileLineInfoKind::AbsoluteFilePath, Info);
-  if (Info.Line == 0)
-    return None;
+    if (Info.Line != 0)
       return Info;
   }
+  return None;
+}
 
 // Returns source line information for a given offset using DWARF debug info.
 template <class ELFT>
 std::string ObjFile<ELFT>::getLineInfo(InputSectionBase *S, uint64_t Offset) {
   if (Optional<DILineInfo> Info = getDILineInfo(S, Offset))
     return Info->FileName + ":" + std::to_string(Info->Line);
   return "";
 }

test/ELF/Inputs/multiple-cu.s

+  .file 1 "test2.c"
+  .loc  1 2 0
+  jmp bar
+
+  .section  .debug_abbrev,"",@progbits
+  .byte 1                       # Abbreviation Code
+  .byte 17                      # DW_TAG_compile_unit
+  .byte 0                       # DW_CHILDREN_no
+  .byte 16                      # DW_AT_stmt_list
+  .byte 23                      # DW_FORM_sec_offset
+  .byte 0                       # EOM(1)
+  .byte 0                       # EOM(2)
+  .byte 0                       # EOM(3)
+
+  .section  .debug_info,"",@progbits
+  .long .Lend0 - .Lbegin0       # Length of Unit
+.Lbegin0:
+  .short  4                       # DWARF version number
+  .long .debug_abbrev           # Offset Into Abbrev. Section
+  .byte 8                       # Address Size (in bytes)
+  .byte 1                       # Abbrev [1] 0xb:0x1f DW_TAG_compile_unit
+  .long .debug_line             # DW_AT_stmt_list
+.Lend0:
+  .section  .debug_line,"",@progbits

test/ELF/multiple-cu.s

+# REQUIRES: x86
+# RUN: llvm-mc -filetype=obj -triple=x86_64-pc-linux %s -o %t1.o
+# RUN: llvm-mc -filetype=obj -triple=x86_64-pc-linux %p/Inputs/multiple-cu.s -o %t2.o
+# RUN: ld.lld -r -o %t.o %t1.o %t2.o
+# RUN: not ld.lld %t.o -o %t 2>&1 | FileCheck %s
+
+# CHECK:      error: undefined symbol: foo
+# CHECK-NEXT: referenced by test1.c:2
+
+# CHECK:      error: undefined symbol: bar
+# CHECK-NEXT: referenced by test2.c:2
+
+  .globl  _start
+_start:
+  .file 1 "test1.c"
+  .loc  1 2 0
+  jmp foo
+
+  .section  .debug_abbrev,"",@progbits
+  .byte 1                       # Abbreviation Code
+  .byte 17                      # DW_TAG_compile_unit
+  .byte 0                       # DW_CHILDREN_no
+  .byte 16                      # DW_AT_stmt_list
+  .byte 23                      # DW_FORM_sec_offset
+  .byte 0                       # EOM(1)
+  .byte 0                       # EOM(2)
+  .byte 0                       # EOM(3)
+
+  .section  .debug_info,"",@progbits
+  .long .Lend0 - .Lbegin0       # Length of Unit
+.Lbegin0:
+  .short  4                       # DWARF version number
+  .long .debug_abbrev           # Offset Into Abbrev. Section
+  .byte 8                       # Address Size (in bytes)
+  .byte 1                       # Abbrev [1] 0xb:0x1f DW_TAG_compile_unit
+  .long .debug_line             # DW_AT_stmt_list
+.Lend0:
+  .section  .debug_line,"",@progbits