[LLD] Tombstone LocalTU entry in .debug_names

lld/ELF/InputSection.cpp

@@ -20,8 +20,7 @@
 #include "llvm/Support/Compression.h"
 #include "llvm/Support/Endian.h"
 #include "llvm/Support/xxhash.h"
-#include <algorithm>
-#include <mutex>
+#include <optional>
 #include <vector>
 
 using namespace llvm;
@@ -886,16 +885,25 @@ void InputSection::relocateNonAlloc(uint8_t *buf, ArrayRef<RelTy> rels) {
   const unsigned bits = sizeof(typename ELFT::uint) * 8;
   const TargetInfo &target = *elf::target;
   const bool isDebug = isDebugSection(*this);
-  const bool isDebugLocOrRanges =
-      isDebug && (name == ".debug_loc" || name == ".debug_ranges");
   const bool isDebugLine = isDebug && name == ".debug_line";
-  std::optional<uint64_t> tombstone;
+  std::optional<uint64_t> tombstone = std::nullopt;
+  std::optional<uint64_t> tombstoneValueToUse = std::nullopt;
   for (const auto &patAndValue : llvm::reverse(config->deadRelocInNonAlloc))
     if (patAndValue.first.match(this->name)) {
       tombstone = patAndValue.second;
       break;
     }
 
+  const uint64_t debugTombstone = StringSwitch<uint64_t>(name)
+                                      .Case(".debug_ranges", 1)
+                                      .Case(".debug_loc", 1)
+                                      .Case(".debug_names", llvm::maxUIntN(32))
+                                      .Default(0);
+  // If -z dead-reloc-in-nonalloc= is specified, respect it.
+  if (!tombstone && isDebug)
+    tombstoneValueToUse = debugTombstone;
+  else if (tombstone)
+    tombstoneValueToUse = SignExtend64<bits>(*tombstone);
   for (const RelTy &rel : rels) {
     RelType type = rel.getType(config->isMips64EL);
 
@@ -917,8 +925,9 @@ void InputSection::relocateNonAlloc(uint8_t *buf, ArrayRef<RelTy> rels) {
     if (expr == R_NONE)
       continue;
 
-    if (tombstone ||
-        (isDebug && (type == target.symbolicRel || expr == R_DTPREL))) {
+    auto *ds = dyn_cast<Defined>(&sym);
+    if (tombstoneValueToUse &&
+        (!sym.getOutputSection() || (ds && ds->folded && !isDebugLine))) {
       // Resolve relocations in .debug_* referencing (discarded symbols or ICF
       // folded section symbols) to a tombstone value. Resolving to addend is
       // unsatisfactory because the result address range may collide with a
@@ -947,14 +956,13 @@ void InputSection::relocateNonAlloc(uint8_t *buf, ArrayRef<RelTy> rels) {
       //
       // TODO To reduce disruption, we use 0 instead of -1 as the tombstone
       // value. Enable -1 in a future release.
-      auto *ds = dyn_cast<Defined>(&sym);
-      if (!sym.getOutputSection() || (ds && ds->folded && !isDebugLine)) {
-        // If -z dead-reloc-in-nonalloc= is specified, respect it.
-        const uint64_t value = tombstone ? SignExtend64<bits>(*tombstone)
-                                         : (isDebugLocOrRanges ? 1 : 0);
-        target.relocateNoSym(bufLoc, type, value);
-        continue;
-      }
+
+      // Extending 32bit MAX value to 64bit MAX value..
+      // One usage example is in .debug_names LocatTU tombstoning.
+      if (!tombstone && type == target.symbolicRel)
+        tombstoneValueToUse = SignExtend64<32>(*tombstoneValueToUse);
+      target.relocateNoSym(bufLoc, type, *tombstoneValueToUse);
+      continue;
     }
 
     // For a relocatable link, content relocated by RELA remains unchanged and

lld/test/ELF/debug-dead-reloc.s

@@ -17,8 +17,8 @@
 # CHECK-NEXT:  0000 {{.*}}000 00000000 {{.*}}000 00000000
 # CHECK-NEXT:  0010 00000000  00000000 {{.*}}000 00000000
 # CHECK:      Contents of section .debug_foo:
-# CHECK-NEXT:  0000 00000000 00000000 08000000 00000000
-# CHECK-NEXT:  0010 00000000 00000000 08000000 00000000
+# CHECK-NEXT:  0000 00000000 00000000 00000000 00000000
+# CHECK-NEXT:  0010 00000000 00000000 00000000 00000000
 
 # REL:      Relocations [
 # REL-NEXT:   .rela.text {
@@ -80,8 +80,6 @@ group:
 .section .debug_foo
   .quad .text.1+8
 
-## We only deal with DW_FORM_addr. Don't special case short-range absolute
-## relocations. Treat them like regular absolute relocations referencing
-## discarded symbols, which are resolved to the addend.
+## Treat short-range absolute relocations the same as DW_FORM_addr.
   .long .text.1+8
   .long 0

lld/test/ELF/x86-64-dwarf5-64-debug-names-type-comdat.test

@@ -0,0 +1,97 @@
+# REQUIRES: x86
+
+# RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux --defsym DWARF32=1 %s -o %t.o
+# RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux --defsym DWARF32=1 %s -o %t1.o
+# RUN: ld.lld %t.o %t1.o -o %t1
+# RUN: llvm-objdump -s %t1 | FileCheck %s --check-prefix=CHECK32
+
+# Test checks that LLD tombstones TU section that was de-duplicated using COMDAT to the maxium value.
+
+# CHECK32:Contents of section .debug_names:
+# CHECK32-NEXT: 0000 37000000 05000000 00000000 01000000  7...............
+# CHECK32-NEXT: 0010 00000000 00000000 00000000 03000000  ................
+# CHECK32-NEXT: 0020 08000000 4c4c564d 30373030 00000000  ....LLVM0700....
+# CHECK32-NEXT: 0030 00000000 00000000 00000037 00000005  ...........7....
+# CHECK32-NEXT: 0040 00000000 00000001 00000000 00000000  ................
+# CHECK32-NEXT: 0050 00000000 00000003 00000008 0000004c  ...............L
+# CHECK32-NEXT: 0060 4c564d30 37303000 000000ff ffffff00  LVM0700.........
+
+
+# RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux --defsym DWARF64=1 %s -o %t.o
+# RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux --defsym DWARF64=1 %s -o %t1.o
+# RUN: ld.lld %t.o %t1.o -o %t1
+# RUN: llvm-objdump -s %t1 | FileCheck %s --check-prefix=CHECK64
+
+# Test checks that LLD tombstones TU section that was de-duplicated using COMDAT to the maxium value.
+
+# CHECK64: Contents of section .debug_names:
+# CHECK64-NEXT:  0000 ffffffff 3f000000 00000000 05000000  ....?...........
+# CHECK64-NEXT:  0010 00000000 01000000 00000000 00000000  ................
+# CHECK64-NEXT:  0020 00000000 03000000 08000000 4c4c564d  ............LLVM
+# CHECK64-NEXT:  0030 30373030 00000000 00000000 00000000  0700............
+# CHECK64-NEXT:  0040 00000000 00000000 000000ff ffffff3f  ...............?
+# CHECK64-NEXT:  0050 00000000 00000005 00000000 00000001  ................
+# CHECK64-NEXT:  0060 00000000 00000000 00000000 00000003  ................
+# CHECK64-NEXT:  0070 00000008 0000004c 4c564d30 37303000  .......LLVM0700.
+# CHECK64-NEXT:  0080 00000000 000000ff ffffffff ffffff00  ................
+
+# Test generated with clang++ -g2 -gdwarf-5 -gpubnames -fdebug-types-section -S and then manually reduced.
+.ifdef DWARF32
+	.section	.debug_info,"G",@progbits,1175092228111723119,comdat
+.Ltu_begin0:
+	.section	.debug_names,"",@progbits
+	.long	.Lnames_end0-.Lnames_start0     # Header: unit length
+.Lnames_start0:
+	.short	5                               # Header: version
+	.short	0                               # Header: padding
+	.long	0                               # Header: compilation unit count
+	.long	1                               # Header: local type unit count
+	.long	0                               # Header: foreign type unit count
+	.long	0                               # Header: bucket count
+	.long	0                               # Header: name count
+	.long	.Lnames_abbrev_end0-.Lnames_abbrev_start0 # Header: abbreviation table size
+	.long	8                               # Header: augmentation string size
+	.ascii	"LLVM0700"                      # Header: augmentation string
+	.long	0                               # Compilation unit 0
+	.long	.Ltu_begin0                     # Type unit 0
+	.long	0                               # Bucket 0
+
+.Lnames_abbrev_start0:
+	.byte	0                               # End of abbrev
+	.byte	0                               # End of abbrev
+	.byte	0                               # End of abbrev list
+.Lnames_abbrev_end0:
+.Lnames_entries0:
+.Lnames_end0:
+.endif
+
+# Test generated with clang++ -g2 -gdwarf-5 -gdwarf64 -gpubnames -fdebug-types-section -S and then manually reduced.
+.ifdef DWARF64
+	.section	.debug_info,"G",@progbits,1175092228111723119,comdat
+.Ltu_begin0:
+	.section	.debug_names,"",@progbits
+	.long	4294967295                      # DWARF64 Mark
+	.quad	.Lnames_end0-.Lnames_start0     # Header: unit length
+.Lnames_start0:
+	.short	5                               # Header: version
+	.short	0                               # Header: padding
+	.long	0                               # Header: compilation unit count
+	.long	1                               # Header: local type unit count
+	.long	0                               # Header: foreign type unit count
+	.long	0                               # Header: bucket count
+	.long	0                               # Header: name count
+	.long	.Lnames_abbrev_end0-.Lnames_abbrev_start0 # Header: abbreviation table size
+	.long	8                               # Header: augmentation string size
+	.ascii	"LLVM0700"                      # Header: augmentation string
+	.quad	0                               # Compilation unit 0
+	.quad	.Ltu_begin0                     # Type unit 0
+	.long	0                               # Bucket 0
+
+.Lnames_abbrev_start0:
+	.byte	0                               # End of abbrev
+	.byte	0                               # End of abbrev
+	.byte	0                               # End of abbrev list
+.Lnames_abbrev_end0:
+.Lnames_entries0:
+.Lnames_end0:
+.endif