[llvm] Reapply "[llvm/DWARF] Recursively resolve DW_AT_signature references"… (PR #99495)

Pavel Labath via llvm-commits llvm-commits at lists.llvm.org
Thu Jul 18 07:12:31 PDT 2024


https://github.com/labath created https://github.com/llvm/llvm-project/pull/99495

… (#99444)

The previous version introduced a bug (caught by cross-project tests). Explicit signature resolution is still necessary when one wants to access the children (not attributes) of a given DIE.

In the new version of the patch, I keep the `resolveTypeUnitReference` function, and call it in the function doing child iteration.

I've also extended the prettyprint_type_units test case to cover this scenario (and also reduced it to remove irrelevant details).

>From ad42e60fd9e3a42f2260d852c809203c4bd54a5f Mon Sep 17 00:00:00 2001
From: Pavel Labath <pavel at labath.sk>
Date: Thu, 18 Jul 2024 11:23:56 +0200
Subject: [PATCH] Reapply "[llvm/DWARF] Recursively resolve DW_AT_signature
 references" (#99444)

The previous version introduced a bug (caught by cross-project tests).
Explicit signature resolution is still necessary when one wants to
access the children (not attributes) of a given DIE.

In the new version of the patch, I keep the `resolveTypeUnitReference`
function, and call it in the function doing child iteration.

I've also extended the prettyprint_type_units test case to cover this
scenario (and also reduced it to remove irrelevant details).
---
 llvm/lib/DebugInfo/DWARF/DWARFDie.cpp         |  26 +-
 llvm/lib/DebugInfo/DWARF/DWARFTypePrinter.cpp |  54 +-
 .../X86/prettyprint_type_units.s              | 616 +++++++-----------
 3 files changed, 279 insertions(+), 417 deletions(-)

diff --git a/llvm/lib/DebugInfo/DWARF/DWARFDie.cpp b/llvm/lib/DebugInfo/DWARF/DWARFDie.cpp
index 72e7464b68971..7ae6af5dfe496 100644
--- a/llvm/lib/DebugInfo/DWARF/DWARFDie.cpp
+++ b/llvm/lib/DebugInfo/DWARF/DWARFDie.cpp
@@ -103,10 +103,6 @@ static void dumpLocationExpr(raw_ostream &OS, const DWARFFormValue &FormValue,
       .print(OS, DumpOpts, U);
 }
 
-static DWARFDie resolveReferencedType(DWARFDie D, DWARFFormValue F) {
-  return D.getAttributeValueAsReferencedDie(F).resolveTypeUnitReference();
-}
-
 static void dumpAttribute(raw_ostream &OS, const DWARFDie &Die,
                           const DWARFAttribute &AttrValue, unsigned Indent,
                           DIDumpOptions DumpOpts) {
@@ -198,8 +194,8 @@ static void dumpAttribute(raw_ostream &OS, const DWARFDie &Die,
                 DINameKind::LinkageName))
       OS << Space << "\"" << Name << '\"';
   } else if (Attr == DW_AT_type || Attr == DW_AT_containing_type) {
-    DWARFDie D = resolveReferencedType(Die, FormValue);
-    if (D && !D.isNULL()) {
+    if (DWARFDie D = Die.getAttributeValueAsReferencedDie(FormValue);
+        D && !D.isNULL()) {
       OS << Space << "\"";
       dumpTypeQualifiedName(D, OS);
       OS << '"';
@@ -291,13 +287,12 @@ DWARFDie::findRecursively(ArrayRef<dwarf::Attribute> Attrs) const {
     if (auto Value = Die.find(Attrs))
       return Value;
 
-    if (auto D = Die.getAttributeValueAsReferencedDie(DW_AT_abstract_origin))
-      if (Seen.insert(D).second)
-        Worklist.push_back(D);
-
-    if (auto D = Die.getAttributeValueAsReferencedDie(DW_AT_specification))
-      if (Seen.insert(D).second)
-        Worklist.push_back(D);
+    for (dwarf::Attribute Attr :
+         {DW_AT_abstract_origin, DW_AT_specification, DW_AT_signature}) {
+      if (auto D = Die.getAttributeValueAsReferencedDie(Attr))
+        if (Seen.insert(D).second)
+          Worklist.push_back(D);
+    }
   }
 
   return std::nullopt;
@@ -319,6 +314,10 @@ DWARFDie::getAttributeValueAsReferencedDie(const DWARFFormValue &V) const {
   } else if (Offset = V.getAsDebugInfoReference(); Offset) {
     if (DWARFUnit *SpecUnit = U->getUnitVector().getUnitForOffset(*Offset))
       Result = SpecUnit->getDIEForOffset(*Offset);
+  } else if (std::optional<uint64_t> Sig = V.getAsSignatureReference()) {
+    if (DWARFTypeUnit *TU = U->getContext().getTypeUnitForHash(
+            U->getVersion(), *Sig, U->isDWOUnit()))
+      Result = TU->getDIEForOffset(TU->getTypeOffset() + TU->getOffset());
   }
   return Result;
 }
@@ -333,7 +332,6 @@ DWARFDie DWARFDie::resolveTypeUnitReference() const {
   }
   return *this;
 }
-
 std::optional<uint64_t> DWARFDie::getRangesBaseAttribute() const {
   return toSectionOffset(find({DW_AT_rnglists_base, DW_AT_GNU_ranges_base}));
 }
diff --git a/llvm/lib/DebugInfo/DWARF/DWARFTypePrinter.cpp b/llvm/lib/DebugInfo/DWARF/DWARFTypePrinter.cpp
index a26431e8313f6..cc38bc6197eb8 100644
--- a/llvm/lib/DebugInfo/DWARF/DWARFTypePrinter.cpp
+++ b/llvm/lib/DebugInfo/DWARF/DWARFTypePrinter.cpp
@@ -62,17 +62,10 @@ void DWARFTypePrinter::appendArrayType(const DWARFDie &D) {
   EndedWithTemplate = false;
 }
 
-static DWARFDie resolveReferencedType(DWARFDie D,
-                                      dwarf::Attribute Attr = DW_AT_type) {
-  return D.getAttributeValueAsReferencedDie(Attr).resolveTypeUnitReference();
-}
-static DWARFDie resolveReferencedType(DWARFDie D, DWARFFormValue F) {
-  return D.getAttributeValueAsReferencedDie(F).resolveTypeUnitReference();
-}
 DWARFDie DWARFTypePrinter::skipQualifiers(DWARFDie D) {
   while (D && (D.getTag() == DW_TAG_const_type ||
                D.getTag() == DW_TAG_volatile_type))
-    D = resolveReferencedType(D);
+    D = D.getAttributeValueAsReferencedDie(DW_AT_type);
   return D;
 }
 
@@ -103,7 +96,9 @@ DWARFTypePrinter::appendUnqualifiedNameBefore(DWARFDie D,
     return DWARFDie();
   }
   DWARFDie InnerDIE;
-  auto Inner = [&] { return InnerDIE = resolveReferencedType(D); };
+  auto Inner = [&] {
+    return InnerDIE = D.getAttributeValueAsReferencedDie(DW_AT_type);
+  };
   const dwarf::Tag T = D.getTag();
   switch (T) {
   case DW_TAG_pointer_type: {
@@ -134,7 +129,8 @@ DWARFTypePrinter::appendUnqualifiedNameBefore(DWARFDie D,
       OS << '(';
     else if (Word)
       OS << ' ';
-    if (DWARFDie Cont = resolveReferencedType(D, DW_AT_containing_type)) {
+    if (DWARFDie Cont =
+            D.getAttributeValueAsReferencedDie(DW_AT_containing_type)) {
       appendQualifiedName(Cont);
       EndedWithTemplate = false;
       OS << "::";
@@ -173,7 +169,8 @@ DWARFTypePrinter::appendUnqualifiedNameBefore(DWARFDie D,
   case DW_TAG_base_type:
   */
   default: {
-    const char *NamePtr = dwarf::toString(D.find(DW_AT_name), nullptr);
+    const char *NamePtr =
+        dwarf::toString(D.findRecursively(DW_AT_name), nullptr);
     if (!NamePtr) {
       appendTypeTagName(D.getTag());
       return DWARFDie();
@@ -235,9 +232,9 @@ void DWARFTypePrinter::appendUnqualifiedNameAfter(
   case DW_TAG_pointer_type: {
     if (needsParens(Inner))
       OS << ')';
-    appendUnqualifiedNameAfter(Inner, resolveReferencedType(Inner),
-                               /*SkipFirstParamIfArtificial=*/D.getTag() ==
-                                   DW_TAG_ptr_to_member_type);
+    appendUnqualifiedNameAfter(
+        Inner, Inner.getAttributeValueAsReferencedDie(DW_AT_type),
+        /*SkipFirstParamIfArtificial=*/D.getTag() == DW_TAG_ptr_to_member_type);
     break;
   }
   case DW_TAG_LLVM_ptrauth_type: {
@@ -326,7 +323,7 @@ bool DWARFTypePrinter::appendTemplateParameters(DWARFDie D,
   bool IsTemplate = false;
   if (!FirstParameter)
     FirstParameter = &FirstParameterValue;
-  for (const DWARFDie &C : D) {
+  for (const DWARFDie &C : D.resolveTypeUnitReference()) {
     auto Sep = [&] {
       if (*FirstParameter)
         OS << '<';
@@ -341,7 +338,7 @@ bool DWARFTypePrinter::appendTemplateParameters(DWARFDie D,
       appendTemplateParameters(C, FirstParameter);
     }
     if (C.getTag() == dwarf::DW_TAG_template_value_parameter) {
-      DWARFDie T = resolveReferencedType(C);
+      DWARFDie T = C.getAttributeValueAsReferencedDie(DW_AT_type);
       Sep();
       if (T.getTag() == DW_TAG_enumeration_type) {
         OS << '(';
@@ -461,7 +458,7 @@ bool DWARFTypePrinter::appendTemplateParameters(DWARFDie D,
       continue;
     auto TypeAttr = C.find(DW_AT_type);
     Sep();
-    appendQualifiedName(TypeAttr ? resolveReferencedType(C, *TypeAttr)
+    appendQualifiedName(TypeAttr ? C.getAttributeValueAsReferencedDie(*TypeAttr)
                                  : DWARFDie());
   }
   if (IsTemplate && *FirstParameter && FirstParameter == &FirstParameterValue) {
@@ -473,15 +470,15 @@ bool DWARFTypePrinter::appendTemplateParameters(DWARFDie D,
 void DWARFTypePrinter::decomposeConstVolatile(DWARFDie &N, DWARFDie &T,
                                               DWARFDie &C, DWARFDie &V) {
   (N.getTag() == DW_TAG_const_type ? C : V) = N;
-  T = resolveReferencedType(N);
+  T = N.getAttributeValueAsReferencedDie(DW_AT_type);
   if (T) {
     auto Tag = T.getTag();
     if (Tag == DW_TAG_const_type) {
       C = T;
-      T = resolveReferencedType(T);
+      T = T.getAttributeValueAsReferencedDie(DW_AT_type);
     } else if (Tag == DW_TAG_volatile_type) {
       V = T;
-      T = resolveReferencedType(T);
+      T = T.getAttributeValueAsReferencedDie(DW_AT_type);
     }
   }
 }
@@ -491,10 +488,11 @@ void DWARFTypePrinter::appendConstVolatileQualifierAfter(DWARFDie N) {
   DWARFDie T;
   decomposeConstVolatile(N, T, C, V);
   if (T && T.getTag() == DW_TAG_subroutine_type)
-    appendSubroutineNameAfter(T, resolveReferencedType(T), false, C.isValid(),
-                              V.isValid());
+    appendSubroutineNameAfter(T, T.getAttributeValueAsReferencedDie(DW_AT_type),
+                              false, C.isValid(), V.isValid());
   else
-    appendUnqualifiedNameAfter(T, resolveReferencedType(T));
+    appendUnqualifiedNameAfter(T,
+                               T.getAttributeValueAsReferencedDie(DW_AT_type));
 }
 void DWARFTypePrinter::appendConstVolatileQualifierBefore(DWARFDie N) {
   DWARFDie C;
@@ -504,7 +502,7 @@ void DWARFTypePrinter::appendConstVolatileQualifierBefore(DWARFDie N) {
   bool Subroutine = T && T.getTag() == DW_TAG_subroutine_type;
   DWARFDie A = T;
   while (A && A.getTag() == DW_TAG_array_type)
-    A = resolveReferencedType(A);
+    A = A.getAttributeValueAsReferencedDie(DW_AT_type);
   bool Leading =
       (!A || (A.getTag() != DW_TAG_pointer_type &&
               A.getTag() != llvm::dwarf::DW_TAG_ptr_to_member_type)) &&
@@ -546,7 +544,7 @@ void DWARFTypePrinter::appendSubroutineNameAfter(
     if (P.getTag() != DW_TAG_formal_parameter &&
         P.getTag() != DW_TAG_unspecified_parameters)
       return;
-    DWARFDie T = resolveReferencedType(P);
+    DWARFDie T = P.getAttributeValueAsReferencedDie(DW_AT_type);
     if (SkipFirstParamIfArtificial && RealFirst && P.find(DW_AT_artificial)) {
       FirstParamIfArtificial = T;
       RealFirst = false;
@@ -567,7 +565,7 @@ void DWARFTypePrinter::appendSubroutineNameAfter(
     if (DWARFDie P = FirstParamIfArtificial) {
       if (P.getTag() == DW_TAG_pointer_type) {
         auto CVStep = [&](DWARFDie CV) {
-          if (DWARFDie U = resolveReferencedType(CV)) {
+          if (DWARFDie U = CV.getAttributeValueAsReferencedDie(DW_AT_type)) {
             Const |= U.getTag() == DW_TAG_const_type;
             Volatile |= U.getTag() == DW_TAG_volatile_type;
             return U;
@@ -653,7 +651,8 @@ void DWARFTypePrinter::appendSubroutineNameAfter(
   if (D.find(DW_AT_rvalue_reference))
     OS << " &&";
 
-  appendUnqualifiedNameAfter(Inner, resolveReferencedType(Inner));
+  appendUnqualifiedNameAfter(
+      Inner, Inner.getAttributeValueAsReferencedDie(DW_AT_type));
 }
 void DWARFTypePrinter::appendScopes(DWARFDie D) {
   if (D.getTag() == DW_TAG_compile_unit)
@@ -666,7 +665,6 @@ void DWARFTypePrinter::appendScopes(DWARFDie D) {
     return;
   if (D.getTag() == DW_TAG_lexical_block)
     return;
-  D = D.resolveTypeUnitReference();
   if (DWARFDie P = D.getParent())
     appendScopes(P);
   appendUnqualifiedName(D);
diff --git a/llvm/test/tools/llvm-dwarfdump/X86/prettyprint_type_units.s b/llvm/test/tools/llvm-dwarfdump/X86/prettyprint_type_units.s
index aad748a301e6b..0893889dbc259 100644
--- a/llvm/test/tools/llvm-dwarfdump/X86/prettyprint_type_units.s
+++ b/llvm/test/tools/llvm-dwarfdump/X86/prettyprint_type_units.s
@@ -1,403 +1,269 @@
 # RUN: llvm-mc < %s -filetype obj -triple x86_64 -o - \
 # RUN:   | llvm-dwarfdump - | FileCheck %s
 
-# Significantly modified assembly generated from this source:
+# Hand-written assembly roughly equivalent to this source code:
 #
 # struct t1 { };
 # struct t2 { };
 # template<typename ...T>
-# void f1() { }
-# int main() {
-#   f1<t1, t2>();
-# }
+# struct S {};
+# S<t1, t2, t1> s;
 #
-# $ clang++-tot test.cpp -g -S -fdebug-types-section -gdwarf-5 -o test.5.s -fstandalone-debug
-#
-# I inserted a DWARFv4 copy of the first type unit ("t1") to replace the
-# DWARFv5 type unit - to test both v4 and v5 type unit support.  This test
-# doesn't really need templates - two local variables would've sufficed
-# (anything that references the type units) but I was working on something else
-# and this seemed minimal enough.
+# To various scenarios, the test uses a mixture of DWARF v4 and v5 type units,
+# and of llvm and gcc styles of referring to them.
+
 
+# CHECK:      DW_TAG_variable
+# CHECK-NEXT:   DW_AT_name ("s")
+# CHECK-NEXT:   DW_AT_type ({{.*}} "S<t1, t2, t1>")
+# CHECK:      DW_TAG_template_type_parameter
+# CHECK-NEXT:   DW_AT_type ({{.*}} "t1")
+# CHECK:      DW_TAG_template_type_parameter
+# CHECK-NEXT:   DW_AT_type ({{.*}} "t2")
+# CHECK:      DW_TAG_template_type_parameter
+# CHECK-NEXT:   DW_AT_type (0xdeadbeef00000001 "t1")
 
-# CHECK: DW_TAG_template_type_parameter
-# CHECK:   DW_AT_type ({{.*}} "t1")
-# CHECK: DW_TAG_template_type_parameter
-# CHECK:   DW_AT_type ({{.*}} "t2")
+.set S_sig,  0xdeadbeef00000000
+.set t1_sig, 0xdeadbeef00000001
+.set t2_sig, 0xdeadbeef00000002
 
-	.text
-	.file	"test.cpp"
-	.globl	main                            # -- Begin function main
-	.p2align	4, 0x90
-	.type	main, at function
-main:                                   # @main
-.Lfunc_begin0:
-	.file	0 "/usr/local/google/home/blaikie/dev/scratch" "test.cpp" md5 0xafee1e55f64a0b86063fa85c8c456dba
-	.loc	0 5 0                           # test.cpp:5:0
-	.cfi_startproc
-# %bb.0:                                # %entry
-	pushq	%rbp
-	.cfi_def_cfa_offset 16
-	.cfi_offset %rbp, -16
-	movq	%rsp, %rbp
-	.cfi_def_cfa_register %rbp
-.Ltmp0:
-	.loc	0 6 3 prologue_end              # test.cpp:6:3
-	callq	_Z2f1IJ2t12t2EEvv
-	.loc	0 7 1                           # test.cpp:7:1
-	xorl	%eax, %eax
-	popq	%rbp
-	.cfi_def_cfa %rsp, 8
-	retq
-.Ltmp1:
-.Lfunc_end0:
-	.size	main, .Lfunc_end0-main
-	.cfi_endproc
-                                        # -- End function
-	.section	.text._Z2f1IJ2t12t2EEvv,"axG", at progbits,_Z2f1IJ2t12t2EEvv,comdat
-	.weak	_Z2f1IJ2t12t2EEvv               # -- Begin function _Z2f1IJ2t12t2EEvv
-	.p2align	4, 0x90
-	.type	_Z2f1IJ2t12t2EEvv, at function
-_Z2f1IJ2t12t2EEvv:                      # @_Z2f1IJ2t12t2EEvv
-.Lfunc_begin1:
-	.loc	0 4 0                           # test.cpp:4:0
-	.cfi_startproc
-# %bb.0:                                # %entry
-	pushq	%rbp
-	.cfi_def_cfa_offset 16
-	.cfi_offset %rbp, -16
-	movq	%rsp, %rbp
-	.cfi_def_cfa_register %rbp
-.Ltmp2:
-	.loc	0 4 13 prologue_end             # test.cpp:4:13
-	popq	%rbp
-	.cfi_def_cfa %rsp, 8
-	retq
-.Ltmp3:
-.Lfunc_end1:
-	.size	_Z2f1IJ2t12t2EEvv, .Lfunc_end1-_Z2f1IJ2t12t2EEvv
-	.cfi_endproc
-                                        # -- End function
-	.section	.debug_types,"G", at progbits,14297044602779165170,comdat
-	.long	.Ldebug_info_end0-.Ldebug_info_start0 # Length of Unit
+        .section        .debug_types,"G", at progbits,t1_sig,comdat
+.Ltu_begin0:
+        .long   .Ldebug_info_end0-.Ldebug_info_start0 # Length of Unit
 .Ldebug_info_start0:
-	.short	4                               # DWARF version number
-	.long	.debug_abbrev                   # Offset Into Abbrev. Section
-	.byte	8                               # Address Size (in bytes)
-	.quad	-4149699470930386446            # Type Signature
-	.long	30                              # Type DIE Offset
-	.byte	10                              # Abbrev [1] 0x17:0x11 DW_TAG_type_unit
-	.short	33                              # DW_AT_language
-	.long	.Lline_table_start0             # DW_AT_stmt_list
-	.byte	11                              # Abbrev [2] 0x1e:0x9 DW_TAG_structure_type
-	.byte	5                               # DW_AT_calling_convention
-	.long	.Linfo_string6                  # DW_AT_name
-	.byte	1                               # DW_AT_byte_size
-	.byte	1                               # DW_AT_decl_file
-	.byte	1                               # DW_AT_decl_line
-	.byte	0                               # End Of Children Mark
+        .short  4                               # DWARF version number
+        .long   .debug_abbrev                   # Offset Into Abbrev. Section
+        .byte   8                               # Address Size (in bytes)
+        .quad   t1_sig                          # Type Signature
+        .long   .Lt1_def-.Ltu_begin0            # Type DIE Offset
+        .byte   10                              # Abbrev [10] DW_TAG_type_unit
+        .short  33                              # DW_AT_language
+.Lt1_def:
+        .byte   11                              # Abbrev [11] DW_TAG_structure_type
+        .long   .Linfo_string6                  # DW_AT_name
+        .byte   1                               # DW_AT_byte_size
+        .byte   0                               # End Of Children Mark
 .Ldebug_info_end0:
-	.section	.debug_info,"G", at progbits,5649318945901130368,comdat
-	.long	.Ldebug_info_end1-.Ldebug_info_start1 # Length of Unit
+        .section        .debug_info,"G", at progbits,t2_sig,comdat
+.Ltu_begin1:
+        .long   .Ldebug_info_end1-.Ldebug_info_start1 # Length of Unit
 .Ldebug_info_start1:
-	.short	5                               # DWARF version number
-	.byte	2                               # DWARF Unit Type
-	.byte	8                               # Address Size (in bytes)
-	.long	.debug_abbrev                   # Offset Into Abbrev. Section
-	.quad	5649318945901130368             # Type Signature
-	.long	35                              # Type DIE Offset
-	.byte	1                               # Abbrev [1] 0x18:0x12 DW_TAG_type_unit
-	.short	33                              # DW_AT_language
-	.long	.Lline_table_start0             # DW_AT_stmt_list
-	.long	.Lstr_offsets_base0             # DW_AT_str_offsets_base
-	.byte	2                               # Abbrev [2] 0x23:0x6 DW_TAG_structure_type
-	.byte	5                               # DW_AT_calling_convention
-	.byte	7                               # DW_AT_name
-	.byte	1                               # DW_AT_byte_size
-	.byte	0                               # DW_AT_decl_file
-	.byte	2                               # DW_AT_decl_line
-	.byte	0                               # End Of Children Mark
+        .short  5                               # DWARF version number
+        .byte   2                               # DWARF Unit Type
+        .byte   8                               # Address Size (in bytes)
+        .long   .debug_abbrev                   # Offset Into Abbrev. Section
+        .quad   t2_sig                          # Type Signature
+        .long   .Lt2_def-.Ltu_begin1            # Type DIE Offset
+        .byte   1                               # Abbrev [1] 0x18:0x12 DW_TAG_type_unit
+        .short  33                              # DW_AT_language
+        .long   .Lstr_offsets_base0             # DW_AT_str_offsets_base
+.Lt2_def:
+        .byte   2                               # Abbrev [2] 0x23:0x6 DW_TAG_structure_type
+        .byte   7                               # DW_AT_name
+        .byte   1                               # DW_AT_byte_size
+        .byte   0                               # End Of Children Mark
 .Ldebug_info_end1:
-	.section	.debug_abbrev,"", at progbits
-	.byte	1                               # Abbreviation Code
-	.byte	65                              # DW_TAG_type_unit
-	.byte	1                               # DW_CHILDREN_yes
-	.byte	19                              # DW_AT_language
-	.byte	5                               # DW_FORM_data2
-	.byte	16                              # DW_AT_stmt_list
-	.byte	23                              # DW_FORM_sec_offset
-	.byte	114                             # DW_AT_str_offsets_base
-	.byte	23                              # DW_FORM_sec_offset
-	.byte	0                               # EOM(1)
-	.byte	0                               # EOM(2)
-	.byte	2                               # Abbreviation Code
-	.byte	19                              # DW_TAG_structure_type
-	.byte	0                               # DW_CHILDREN_no
-	.byte	54                              # DW_AT_calling_convention
-	.byte	11                              # DW_FORM_data1
-	.byte	3                               # DW_AT_name
-	.byte	37                              # DW_FORM_strx1
-	.byte	11                              # DW_AT_byte_size
-	.byte	11                              # DW_FORM_data1
-	.byte	58                              # DW_AT_decl_file
-	.byte	11                              # DW_FORM_data1
-	.byte	59                              # DW_AT_decl_line
-	.byte	11                              # DW_FORM_data1
-	.byte	0                               # EOM(1)
-	.byte	0                               # EOM(2)
-	.byte	3                               # Abbreviation Code
-	.byte	17                              # DW_TAG_compile_unit
-	.byte	1                               # DW_CHILDREN_yes
-	.byte	37                              # DW_AT_producer
-	.byte	37                              # DW_FORM_strx1
-	.byte	19                              # DW_AT_language
-	.byte	5                               # DW_FORM_data2
-	.byte	3                               # DW_AT_name
-	.byte	37                              # DW_FORM_strx1
-	.byte	114                             # DW_AT_str_offsets_base
-	.byte	23                              # DW_FORM_sec_offset
-	.byte	16                              # DW_AT_stmt_list
-	.byte	23                              # DW_FORM_sec_offset
-	.byte	27                              # DW_AT_comp_dir
-	.byte	37                              # DW_FORM_strx1
-	.byte	17                              # DW_AT_low_pc
-	.byte	1                               # DW_FORM_addr
-	.byte	85                              # DW_AT_ranges
-	.byte	35                              # DW_FORM_rnglistx
-	.byte	115                             # DW_AT_addr_base
-	.byte	23                              # DW_FORM_sec_offset
-	.byte	116                             # DW_AT_rnglists_base
-	.byte	23                              # DW_FORM_sec_offset
-	.byte	0                               # EOM(1)
-	.byte	0                               # EOM(2)
-	.byte	4                               # Abbreviation Code
-	.byte	46                              # DW_TAG_subprogram
-	.byte	0                               # DW_CHILDREN_no
-	.byte	17                              # DW_AT_low_pc
-	.byte	27                              # DW_FORM_addrx
-	.byte	18                              # DW_AT_high_pc
-	.byte	6                               # DW_FORM_data4
-	.byte	64                              # DW_AT_frame_base
-	.byte	24                              # DW_FORM_exprloc
-	.byte	3                               # DW_AT_name
-	.byte	37                              # DW_FORM_strx1
-	.byte	58                              # DW_AT_decl_file
-	.byte	11                              # DW_FORM_data1
-	.byte	59                              # DW_AT_decl_line
-	.byte	11                              # DW_FORM_data1
-	.byte	73                              # DW_AT_type
-	.byte	19                              # DW_FORM_ref4
-	.byte	63                              # DW_AT_external
-	.byte	25                              # DW_FORM_flag_present
-	.byte	0                               # EOM(1)
-	.byte	0                               # EOM(2)
-	.byte	5                               # Abbreviation Code
-	.byte	46                              # DW_TAG_subprogram
-	.byte	1                               # DW_CHILDREN_yes
-	.byte	17                              # DW_AT_low_pc
-	.byte	27                              # DW_FORM_addrx
-	.byte	18                              # DW_AT_high_pc
-	.byte	6                               # DW_FORM_data4
-	.byte	64                              # DW_AT_frame_base
-	.byte	24                              # DW_FORM_exprloc
-	.byte	110                             # DW_AT_linkage_name
-	.byte	37                              # DW_FORM_strx1
-	.byte	3                               # DW_AT_name
-	.byte	37                              # DW_FORM_strx1
-	.byte	58                              # DW_AT_decl_file
-	.byte	11                              # DW_FORM_data1
-	.byte	59                              # DW_AT_decl_line
-	.byte	11                              # DW_FORM_data1
-	.byte	63                              # DW_AT_external
-	.byte	25                              # DW_FORM_flag_present
-	.byte	0                               # EOM(1)
-	.byte	0                               # EOM(2)
-	.byte	6                               # Abbreviation Code
-	.ascii	"\207\202\001"                  # DW_TAG_GNU_template_parameter_pack
-	.byte	1                               # DW_CHILDREN_yes
-	.byte	3                               # DW_AT_name
-	.byte	37                              # DW_FORM_strx1
-	.byte	0                               # EOM(1)
-	.byte	0                               # EOM(2)
-	.byte	7                               # Abbreviation Code
-	.byte	47                              # DW_TAG_template_type_parameter
-	.byte	0                               # DW_CHILDREN_no
-	.byte	73                              # DW_AT_type
-	.byte	19                              # DW_FORM_ref4
-	.byte	0                               # EOM(1)
-	.byte	0                               # EOM(2)
-	.byte	8                               # Abbreviation Code
-	.byte	36                              # DW_TAG_base_type
-	.byte	0                               # DW_CHILDREN_no
-	.byte	3                               # DW_AT_name
-	.byte	37                              # DW_FORM_strx1
-	.byte	62                              # DW_AT_encoding
-	.byte	11                              # DW_FORM_data1
-	.byte	11                              # DW_AT_byte_size
-	.byte	11                              # DW_FORM_data1
-	.byte	0                               # EOM(1)
-	.byte	0                               # EOM(2)
-	.byte	9                               # Abbreviation Code
-	.byte	19                              # DW_TAG_structure_type
-	.byte	0                               # DW_CHILDREN_no
-	.byte	60                              # DW_AT_declaration
-	.byte	25                              # DW_FORM_flag_present
-	.byte	105                             # DW_AT_signature
-	.byte	32                              # DW_FORM_ref_sig8
-	.byte	0                               # EOM(1)
-	.byte	0                               # EOM(2)
-	.byte	10                              # Abbreviation Code
-	.byte	65                              # DW_TAG_type_unit
-	.byte	1                               # DW_CHILDREN_yes
-	.byte	19                              # DW_AT_language
-	.byte	5                               # DW_FORM_data2
-	.byte	16                              # DW_AT_stmt_list
-	.byte	23                              # DW_FORM_sec_offset
-	.byte	0                               # EOM(1)
-	.byte	0                               # EOM(2)
-	.byte	11                              # Abbreviation Code
-	.byte	19                              # DW_TAG_structure_type
-	.byte	0                               # DW_CHILDREN_no
-	.byte	54                              # DW_AT_calling_convention
-	.byte	11                              # DW_FORM_data1
-	.byte	3                               # DW_AT_name
-	.byte	14                              # DW_FORM_strp
-	.byte	11                              # DW_AT_byte_size
-	.byte	11                              # DW_FORM_data1
-	.byte	58                              # DW_AT_decl_file
-	.byte	11                              # DW_FORM_data1
-	.byte	59                              # DW_AT_decl_line
-	.byte	11                              # DW_FORM_data1
-	.byte	0                               # EOM(1)
-	.byte	0                               # EOM(2)
-	.byte	0                               # EOM(3)
-	.section	.debug_info,"", at progbits
+        .section        .debug_abbrev,"", at progbits
+        .byte   1                               # Abbreviation Code
+        .byte   65                              # DW_TAG_type_unit
+        .byte   1                               # DW_CHILDREN_yes
+        .byte   19                              # DW_AT_language
+        .byte   5                               # DW_FORM_data2
+        .byte   114                             # DW_AT_str_offsets_base
+        .byte   23                              # DW_FORM_sec_offset
+        .byte   0                               # EOM(1)
+        .byte   0                               # EOM(2)
+        .byte   2                               # Abbreviation Code
+        .byte   19                              # DW_TAG_structure_type
+        .byte   0                               # DW_CHILDREN_no
+        .byte   3                               # DW_AT_name
+        .byte   37                              # DW_FORM_strx1
+        .byte   11                              # DW_AT_byte_size
+        .byte   11                              # DW_FORM_data1
+        .byte   0                               # EOM(1)
+        .byte   0                               # EOM(2)
+        .byte   3                               # Abbreviation Code
+        .byte   17                              # DW_TAG_compile_unit
+        .byte   1                               # DW_CHILDREN_yes
+        .byte   37                              # DW_AT_producer
+        .byte   37                              # DW_FORM_strx1
+        .byte   19                              # DW_AT_language
+        .byte   5                               # DW_FORM_data2
+        .byte   3                               # DW_AT_name
+        .byte   37                              # DW_FORM_strx1
+        .byte   114                             # DW_AT_str_offsets_base
+        .byte   23                              # DW_FORM_sec_offset
+        .byte   27                              # DW_AT_comp_dir
+        .byte   37                              # DW_FORM_strx1
+        .byte   0                               # EOM(1)
+        .byte   0                               # EOM(2)
+        .byte   4                               # Abbreviation Code
+        .byte   52                              # DW_TAG_variable
+        .byte   0                               # DW_CHILDREN_no
+        .byte   3                               # DW_AT_name
+        .byte   8                               # DW_FORM_string
+        .byte   73                              # DW_AT_type
+        .byte   19                              # DW_FORM_ref4
+        .byte   0                               # EOM(1)
+        .byte   0                               # EOM(2)
+        .byte   6                               # Abbreviation Code
+        .ascii  "\207\202\001"                  # DW_TAG_GNU_template_parameter_pack
+        .byte   1                               # DW_CHILDREN_yes
+        .byte   3                               # DW_AT_name
+        .byte   37                              # DW_FORM_strx1
+        .byte   0                               # EOM(1)
+        .byte   0                               # EOM(2)
+        .byte   7                               # Abbreviation Code
+        .byte   47                              # DW_TAG_template_type_parameter
+        .byte   0                               # DW_CHILDREN_no
+        .byte   73                              # DW_AT_type
+        .byte   19                              # DW_FORM_ref4
+        .byte   0                               # EOM(1)
+        .byte   0                               # EOM(2)
+        .byte   8                               # Abbreviation Code
+        .byte   36                              # DW_TAG_base_type
+        .byte   0                               # DW_CHILDREN_no
+        .byte   3                               # DW_AT_name
+        .byte   37                              # DW_FORM_strx1
+        .byte   62                              # DW_AT_encoding
+        .byte   11                              # DW_FORM_data1
+        .byte   11                              # DW_AT_byte_size
+        .byte   11                              # DW_FORM_data1
+        .byte   0                               # EOM(1)
+        .byte   0                               # EOM(2)
+        .byte   9                               # Abbreviation Code
+        .byte   19                              # DW_TAG_structure_type
+        .byte   0                               # DW_CHILDREN_no
+        .byte   60                              # DW_AT_declaration
+        .byte   25                              # DW_FORM_flag_present
+        .byte   105                             # DW_AT_signature
+        .byte   32                              # DW_FORM_ref_sig8
+        .byte   0                               # EOM(1)
+        .byte   0                               # EOM(2)
+        .byte   10                              # Abbreviation Code
+        .byte   65                              # DW_TAG_type_unit
+        .byte   1                               # DW_CHILDREN_yes
+        .byte   19                              # DW_AT_language
+        .byte   5                               # DW_FORM_data2
+        .byte   0                               # EOM(1)
+        .byte   0                               # EOM(2)
+        .byte   11                              # Abbreviation Code
+        .byte   19                              # DW_TAG_structure_type
+        .byte   0                               # DW_CHILDREN_no
+        .byte   3                               # DW_AT_name
+        .byte   14                              # DW_FORM_strp
+        .byte   11                              # DW_AT_byte_size
+        .byte   11                              # DW_FORM_data1
+        .byte   0                               # EOM(1)
+        .byte   0                               # EOM(2)
+        .byte   12                              # Abbreviation Code
+        .byte   47                              # DW_TAG_template_type_parameter
+        .byte   0                               # DW_CHILDREN_no
+        .byte   73                              # DW_AT_type
+        .byte   32                              # DW_FORM_ref_sig8
+        .byte   0                               # EOM(1)
+        .byte   0                               # EOM(2)
+        .byte   13                              # Abbreviation Code
+        .byte   19                              # DW_TAG_structure_type
+        .byte   1                               # DW_CHILDREN_yes
+        .byte   3                               # DW_AT_name
+        .byte   8                               # DW_FORM_string
+        .byte   0                               # EOM(1)
+        .byte   0                               # EOM(2)
+        .byte   0                               # EOM(3)
+        .section        .debug_info,"", at progbits
 .Lcu_begin0:
-	.long	.Ldebug_info_end2-.Ldebug_info_start2 # Length of Unit
+        .long   .Ldebug_info_end2-.Ldebug_info_start2 # Length of Unit
 .Ldebug_info_start2:
-	.short	5                               # DWARF version number
-	.byte	1                               # DWARF Unit Type
-	.byte	8                               # Address Size (in bytes)
-	.long	.debug_abbrev                   # Offset Into Abbrev. Section
-	.byte	3                               # Abbrev [3] 0xc:0x5f DW_TAG_compile_unit
-	.byte	0                               # DW_AT_producer
-	.short	33                              # DW_AT_language
-	.byte	1                               # DW_AT_name
-	.long	.Lstr_offsets_base0             # DW_AT_str_offsets_base
-	.long	.Lline_table_start0             # DW_AT_stmt_list
-	.byte	2                               # DW_AT_comp_dir
-	.quad	0                               # DW_AT_low_pc
-	.byte	0                               # DW_AT_ranges
-	.long	.Laddr_table_base0              # DW_AT_addr_base
-	.long	.Lrnglists_table_base0          # DW_AT_rnglists_base
-	.byte	4                               # Abbrev [4] 0x2b:0xf DW_TAG_subprogram
-	.byte	0                               # DW_AT_low_pc
-	.long	.Lfunc_end0-.Lfunc_begin0       # DW_AT_high_pc
-	.byte	1                               # DW_AT_frame_base
-	.byte	86
-	.byte	3                               # DW_AT_name
-	.byte	0                               # DW_AT_decl_file
-	.byte	5                               # DW_AT_decl_line
-	.long	84                              # DW_AT_type
-                                        # DW_AT_external
-	.byte	5                               # Abbrev [5] 0x3a:0x1a DW_TAG_subprogram
-	.byte	1                               # DW_AT_low_pc
-	.long	.Lfunc_end1-.Lfunc_begin1       # DW_AT_high_pc
-	.byte	1                               # DW_AT_frame_base
-	.byte	86
-	.byte	8                               # DW_AT_linkage_name
-	.byte	9                               # DW_AT_name
-	.byte	0                               # DW_AT_decl_file
-	.byte	4                               # DW_AT_decl_line
-                                        # DW_AT_external
-	.byte	6                               # Abbrev [6] 0x46:0xd DW_TAG_GNU_template_parameter_pack
-	.byte	5                               # DW_AT_name
-	.byte	7                               # Abbrev [7] 0x48:0x5 DW_TAG_template_type_parameter
-	.long	88                              # DW_AT_type
-	.byte	7                               # Abbrev [7] 0x4d:0x5 DW_TAG_template_type_parameter
-	.long	97                              # DW_AT_type
-	.byte	0                               # End Of Children Mark
-	.byte	0                               # End Of Children Mark
-	.byte	8                               # Abbrev [8] 0x54:0x4 DW_TAG_base_type
-	.byte	4                               # DW_AT_name
-	.byte	5                               # DW_AT_encoding
-	.byte	4                               # DW_AT_byte_size
-	.byte	9                               # Abbrev [9] 0x58:0x9 DW_TAG_structure_type
+        .short  5                               # DWARF version number
+        .byte   1                               # DWARF Unit Type
+        .byte   8                               # Address Size (in bytes)
+        .long   .debug_abbrev                   # Offset Into Abbrev. Section
+        .byte   3                               # Abbrev [3] 0xc:0x5f DW_TAG_compile_unit
+        .byte   0                               # DW_AT_producer
+        .short  33                              # DW_AT_language
+        .byte   1                               # DW_AT_name
+        .long   .Lstr_offsets_base0             # DW_AT_str_offsets_base
+        .byte   2                               # DW_AT_comp_dir
+        .byte   4                               # Abbrev [4] DW_TAG_variable
+        .asciz  "s"                             # DW_AT_name
+        .long   .LS_decl-.Lcu_begin0            # DW_AT_type
+.LS_decl:
+        .byte   9                               # Abbrev [9] DW_TAG_structure_type
+        .quad   S_sig                           # DW_AT_signature
+        .byte   8                               # Abbrev [8] 0x54:0x4 DW_TAG_base_type
+        .byte   4                               # DW_AT_name
+        .byte   5                               # DW_AT_encoding
+        .byte   4                               # DW_AT_byte_size
+        .byte   0                               # End Of Children Mark
+.Ldebug_info_end2:
+        .section        .debug_info,"G", at progbits,S_sig,comdat
+.Ltu_begin2:
+        .long   .Ldebug_info_end3-.Ldebug_info_start3 # Length of Unit
+.Ldebug_info_start3:
+        .short  5                               # DWARF version number
+        .byte   2                               # DWARF Unit Type
+        .byte   8                               # Address Size (in bytes)
+        .long   .debug_abbrev                   # Offset Into Abbrev. Section
+        .quad   S_sig                           # Type Signature
+        .long   .LS_def-.Ltu_begin2             # Type DIE Offset
+        .byte   1                               # Abbrev [1] DW_TAG_type_unit
+        .short  33                              # DW_AT_language
+        .long   .Lstr_offsets_base0             # DW_AT_str_offsets_base
+.LS_def:
+        .byte   13                              # Abbrev [13] DW_TAG_structure_type
+        .asciz  "S"                             # DW_AT_name (simplified template name)
+        .byte   6                               # Abbrev [6] 0x46:0xd DW_TAG_GNU_template_parameter_pack
+        .byte   5                               # DW_AT_name
+        .byte   7                               # Abbrev [7] 0x48:0x5 DW_TAG_template_type_parameter
+        .long   .Lt1_decl-.Ltu_begin2           # DW_AT_type
+        .byte   7                               # Abbrev [7] 0x4d:0x5 DW_TAG_template_type_parameter
+        # Simulate DWARF emitted by GCC where the signature is directly in the type attribute.
+        .long   .Lt2_decl-.Ltu_begin2           # DW_AT_type
+        .byte   12                              # Abbrev [12] DW_TAG_template_type_parameter
+        .quad   t1_sig                          # DW_AT_type
+        .byte   0                               # End Of Children Mark
+        .byte   0                               # End Of Children Mark
+.Lt1_decl:
+        .byte   9                               # Abbrev [9] 0x58:0x9 DW_TAG_structure_type
                                         # DW_AT_declaration
-	.quad	-4149699470930386446            # DW_AT_signature
-	.byte	9                               # Abbrev [9] 0x61:0x9 DW_TAG_structure_type
+        .quad   t1_sig                          # DW_AT_signature
+.Lt2_decl:
+        .byte   9                               # Abbrev [9] 0x61:0x9 DW_TAG_structure_type
                                         # DW_AT_declaration
-	.quad	5649318945901130368             # DW_AT_signature
-	.byte	0                               # End Of Children Mark
-.Ldebug_info_end2:
-	.section	.debug_rnglists,"", at progbits
-	.long	.Ldebug_list_header_end0-.Ldebug_list_header_start0 # Length
-.Ldebug_list_header_start0:
-	.short	5                               # Version
-	.byte	8                               # Address size
-	.byte	0                               # Segment selector size
-	.long	1                               # Offset entry count
-.Lrnglists_table_base0:
-	.long	.Ldebug_ranges0-.Lrnglists_table_base0
-.Ldebug_ranges0:
-	.byte	3                               # DW_RLE_startx_length
-	.byte	0                               #   start index
-	.uleb128 .Lfunc_end0-.Lfunc_begin0      #   length
-	.byte	3                               # DW_RLE_startx_length
-	.byte	1                               #   start index
-	.uleb128 .Lfunc_end1-.Lfunc_begin1      #   length
-	.byte	0                               # DW_RLE_end_of_list
-.Ldebug_list_header_end0:
-	.section	.debug_str_offsets,"", at progbits
-	.long	44                              # Length of String Offsets Set
-	.short	5
-	.short	0
+        .quad   t2_sig                          # DW_AT_signature
+        .byte   0                               # End Of Children Mark
+.Ldebug_info_end3:
+        .section        .debug_str_offsets,"", at progbits
+        .long   .Lstr_offsets_end-.Lstr_offsets_start # Length of String Offsets Set
+.Lstr_offsets_start:
+        .short  5
+        .short  0
 .Lstr_offsets_base0:
-	.section	.debug_str,"MS", at progbits,1
+        .section        .debug_str,"MS", at progbits,1
 .Linfo_string0:
-	.asciz	"clang version 14.0.0 (git at github.com:llvm/llvm-project.git 22a1aa5a43cbdaf9dde014ba1f120e0f7ca1788b)" # string offset=0
+        .asciz  "hand-written DWARF"
 .Linfo_string1:
-	.asciz	"test.cpp"                      # string offset=101
+        .asciz  "test.cpp"
 .Linfo_string2:
-	.asciz	"/usr/local/google/home/blaikie/dev/scratch" # string offset=110
+        .asciz  "/tmp"
 .Linfo_string3:
-	.asciz	"main"                          # string offset=153
+        .asciz  "S"
 .Linfo_string4:
-	.asciz	"int"                           # string offset=158
+        .asciz  "int"
 .Linfo_string5:
-	.asciz	"T"                             # string offset=162
+        .asciz  "T"
 .Linfo_string6:
-	.asciz	"t1"                            # string offset=164
+        .asciz  "t1"
 .Linfo_string7:
-	.asciz	"t2"                            # string offset=167
-.Linfo_string8:
-	.asciz	"_Z2f1IJ2t12t2EEvv"             # string offset=170
-.Linfo_string9:
-	.asciz	"f1<t1, t2>"                    # string offset=188
-	.section	.debug_str_offsets,"", at progbits
-	.long	.Linfo_string0
-	.long	.Linfo_string1
-	.long	.Linfo_string2
-	.long	.Linfo_string3
-	.long	.Linfo_string4
-	.long	.Linfo_string5
-	.long	.Linfo_string6
-	.long	.Linfo_string7
-	.long	.Linfo_string8
-	.long	.Linfo_string9
-	.section	.debug_addr,"", at progbits
-	.long	.Ldebug_addr_end0-.Ldebug_addr_start0 # Length of contribution
-.Ldebug_addr_start0:
-	.short	5                               # DWARF version number
-	.byte	8                               # Address size
-	.byte	0                               # Segment selector size
-.Laddr_table_base0:
-	.quad	.Lfunc_begin0
-	.quad	.Lfunc_begin1
-.Ldebug_addr_end0:
-	.ident	"clang version 14.0.0 (git at github.com:llvm/llvm-project.git 22a1aa5a43cbdaf9dde014ba1f120e0f7ca1788b)"
-	.section	".note.GNU-stack","", at progbits
-	.addrsig
-	.addrsig_sym _Z2f1IJ2t12t2EEvv
-	.section	.debug_line,"", at progbits
-.Lline_table_start0:
+        .asciz  "t2"
+        .section        .debug_str_offsets,"", at progbits
+        .long   .Linfo_string0
+        .long   .Linfo_string1
+        .long   .Linfo_string2
+        .long   .Linfo_string3
+        .long   .Linfo_string4
+        .long   .Linfo_string5
+        .long   .Linfo_string6
+        .long   .Linfo_string7
+.Lstr_offsets_end:



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