[DWARFYAML][debug_info] Teach yaml2obj emit correct DWARF64 unit header.

[Higuoxing]

Summary

This patch helps teach yaml2obj emit correct DWARF64 unit header of the .debug_info section.

[jhenderson]

LGTM. The DWARF64 nature of an object also affects any DW_FORM_sec_offset attributes in the body of the table. Is that something that is already correct and covered by testing? If not, that should be done in a separate change.

[Higuoxing]

In D82621#2116226, @jhenderson wrote:

LGTM. The DWARF64 nature of an object also affects any DW_FORM_sec_offset attributes in the body of the table. Is that something that is already correct and covered by testing? If not, that should be done in a separate change.

The body of the table isn't tested yet, I will do it in a separate change.

[Higuoxing]

Thanks for reviewing!

llvm/include/llvm/ObjectYAML/DWARFYAML.h

struct Entry {
   llvm::yaml::Hex32 AbbrCode;
   std::vector<FormValue> Values;
 };
 
 struct Unit {
   InitialLength Length;
   uint16_t Version;
   llvm::dwarf::UnitType Type; // Added in DWARF 5
-  uint32_t AbbrOffset;
+  yaml::Hex64 AbbrOffset;
   uint8_t AddrSize;
   std::vector<Entry> Entries;
 };
 
 struct File {
   StringRef Name;
   uint64_t DirIdx;
   uint64_t ModTime;

llvm/lib/ObjectYAML/DWARFEmitter.cpp

 
 protected:
   void onStartCompileUnit(const DWARFYAML::Unit &CU) override {
     writeInitialLength(CU.Length, OS, DebugInfo.IsLittleEndian);
     writeInteger((uint16_t)CU.Version, OS, DebugInfo.IsLittleEndian);
     if (CU.Version >= 5) {
       writeInteger((uint8_t)CU.Type, OS, DebugInfo.IsLittleEndian);
       writeInteger((uint8_t)CU.AddrSize, OS, DebugInfo.IsLittleEndian);
-      writeInteger((uint32_t)CU.AbbrOffset, OS, DebugInfo.IsLittleEndian);
+      cantFail(writeVariableSizedInteger(CU.AbbrOffset,
+                                         CU.Length.isDWARF64() ? 8 : 4, OS,
+                                         DebugInfo.IsLittleEndian));
     } else {
-      writeInteger((uint32_t)CU.AbbrOffset, OS, DebugInfo.IsLittleEndian);
+      cantFail(writeVariableSizedInteger(CU.AbbrOffset,
+                                         CU.Length.isDWARF64() ? 8 : 4, OS,
+                                         DebugInfo.IsLittleEndian));
       writeInteger((uint8_t)CU.AddrSize, OS, DebugInfo.IsLittleEndian);
     }
   }
 
   void onStartDIE(const DWARFYAML::Unit &CU,
                   const DWARFYAML::Entry &DIE) override {
     encodeULEB128(DIE.AbbrCode, OS);
   }

llvm/test/tools/yaml2obj/ELF/DWARF/debug-info.yaml

- Length:
       Version:    5
       UnitType:   DW_UT_type
       AbbrOffset: 0x1234
       AddrSize:   4
       Entries:
         - AbbrCode: 1
           Values:
             - Value: 0x1234
+
+## j) Test that yaml2obj emits the correct DWARF64 unit headers.
+
+## DWARFv5 unit header.
+
+# RUN: yaml2obj --docnum=11 %s -o %t11.o
+# RUN: llvm-readelf --hex-dump=.debug_info %t11.o | \
+# RUN:   FileCheck %s --check-prefix=DWARFV5-HEADER
+
+#      DWARFV5-HEADER: Hex dump of section '.debug_info':
+# DWARFV5-HEADER-NEXT: 0x00000000 ffffffff 0c000000 00000000 05000208 ................
+##                                ^-------------------------          unit_length (12-byte)
+##                                                           ^---     version (2-byte)
+##                                                               ^-   unit_type (1-byte)
+##                                                                 ^- address_size (1-byte)
+# DWARFV5-HEADER-NEXT: 0x00000010 34120000 00000000                   4.......
+##                                ^----------------                   debug_abbrev_offset (8-byte)
+
+--- !ELF
+FileHeader:
+  Class:   ELFCLASS64
+  Data:    ELFDATA2LSB
+  Type:    ET_EXEC
+  Machine: EM_X86_64
+DWARF:
+  debug_info:
+    - Length:
+        TotalLength:   0xffffffff
+        TotalLength64: 0x0c
+      Version:    5
+      UnitType:   DW_UT_type
+      AbbrOffset: 0x1234
+      AddrSize:   8
+      Entries:    []
+
+## DWARFv4 unit header.
+
+# RUN: yaml2obj --docnum=12 %s -o %t12.o
+# RUN: llvm-readelf --hex-dump=.debug_info %t12.o | \
+# RUN:   FileCheck %s --check-prefix=DWARFV4-HEADER
+
+#      DWARFV4-HEADER: Hex dump of section '.debug_info':
+# DWARFV4-HEADER-NEXT: 0x00000000 ffffffff 0c000000 00000000 04003412 ..............4.
+##                                ^-------------------------          unit_length (12-byte)
+##                                                           ^---     version (2-byte)
+##                                                               ^--- debug_abbrev_offset (8-byte)
+# DWARFV4-HEADER-NEXT: 0x00000010 00000000 000008                     .......
+##                                -------------
+##                                             ^-                     address_size (1-byte)
+
+--- !ELF
+FileHeader:
+  Class:   ELFCLASS64
+  Data:    ELFDATA2LSB
+  Type:    ET_EXEC
+  Machine: EM_X86_64
+DWARF:
+  debug_info:
+    - Length:
+        TotalLength:   0xffffffff
+        TotalLength64: 0x0c
+      Version:    4
+      AbbrOffset: 0x1234
+      AddrSize:   8
+      Entries:    []