[DWARFYAML][debug_ranges] Make the "Offset" field optional.

[Higuoxing]

Summary

Before this patch, we have to calculate the offset for the current range list entry. This patch helps make the "Offset" field optional.

[Higuoxing]

Add assert(*DebugRanges.Offset >= CurrOffset).

[Higuoxing]

Update.

[jhenderson]

You should also have a test case either in this test or D81217 that shows what happens when you use an offset that is either higher than where you are already, or lower.

llvm/lib/ObjectYAML/DWARFEmitter.cpp

122–124

I don't think this wants to be an assert - it should be an error, right? If you specify a lower offset than the current position (e.g. 0 for the second set), you want an error since you can't place it there.

[Higuoxing]

llvm/lib/ObjectYAML/DWARFEmitter.cpp

122–124

Yes, I think it should be an error as well. Currently, DWARFYAML doesn't support error handling. If we change one void EmitXXXSection() to Error EmitXXXSection(), we should change them all. Can I do it in a follow-up patch?

[jhenderson]

llvm/lib/ObjectYAML/DWARFEmitter.cpp

122–124

Oh, I missed that there's an assertion in this area already. Yes, leaving it to a follow-up is fine, but please add a FIXME note in this patch.

[Higuoxing]

I will wait until DWARFYAML supports error handling.

[Higuoxing]

Add one test case when we try to assign an offset that is greater than the number of bytes written already.

[jhenderson]

llvm/lib/ObjectYAML/DWARFEmitter.cpp

121–128

Can ZeroFillBytes cope with a size of zero? If so, this can be simplified to simply:

if (DebugRanges.Offset)
  ZeroFillBytes(OS, *DebugRanges.Offset - CurrOffset);

[Higuoxing]

• Address comment.
• Add one more testcase when we try to assign an offset that is equal to the number of bytes written.

[jhenderson]

LGTM, thanks!

llvm/include/llvm/ObjectYAML/DWARFYAML.h

 /// within a range list in the .debug_ranges section.
 struct RangeEntry {
   llvm::yaml::Hex64 LowOffset;
   llvm::yaml::Hex64 HighOffset;
 };
 
 /// Class that describes a single range list inside the .debug_ranges section.
 struct Ranges {
-  llvm::yaml::Hex32 Offset;
+  Optional<llvm::yaml::Hex64> Offset;
   llvm::yaml::Hex8 AddrSize;
   std::vector<RangeEntry> Entries;
 };
 
 struct PubEntry {
   llvm::yaml::Hex32 DieOffset;
   llvm::yaml::Hex8 Descriptor;
   StringRef Name;

llvm/lib/ObjectYAML/DWARFEmitter.cpp

for (auto Range : DI.ARanges) {
     ZeroFillBytes(OS, Range.AddrSize * 2);
   }
 }
 
 void DWARFYAML::EmitDebugRanges(raw_ostream &OS, const DWARFYAML::Data &DI) {
   const size_t RangesOffset = OS.tell();
   for (auto DebugRanges : DI.DebugRanges) {
     const size_t CurrOffset = OS.tell() - RangesOffset;
-    assert(DebugRanges.Offset <= CurrOffset);
-    if (DebugRanges.Offset > CurrOffset)
-      ZeroFillBytes(OS, DebugRanges.Offset - CurrOffset);
+    if (DebugRanges.Offset) {
+      assert(*DebugRanges.Offset >= CurrOffset &&
+             "Offset should be greater than or equal to the bytes that we have "
+             "written");
+      if (*DebugRanges.Offset > CurrOffset)
+        ZeroFillBytes(OS, *DebugRanges.Offset - CurrOffset);
+    }
     for (auto Entry : DebugRanges.Entries) {
       writeVariableSizedInteger(Entry.LowOffset, DebugRanges.AddrSize, OS,
                                 DI.IsLittleEndian);
       writeVariableSizedInteger(Entry.HighOffset, DebugRanges.AddrSize, OS,
                                 DI.IsLittleEndian);
     }
     ZeroFillBytes(OS, DebugRanges.AddrSize * 2);
   }
 }

llvm/lib/ObjectYAML/DWARFYAML.cpp

 void MappingTraits<DWARFYAML::RangeEntry>::mapping(
     IO &IO, DWARFYAML::RangeEntry &Descriptor) {
   IO.mapRequired("LowOffset", Descriptor.LowOffset);
   IO.mapRequired("HighOffset", Descriptor.HighOffset);
 }
 
 void MappingTraits<DWARFYAML::Ranges>::mapping(IO &IO,
                                                DWARFYAML::Ranges &DebugRanges) {
-  IO.mapRequired("Offset", DebugRanges.Offset);
+  IO.mapOptional("Offset", DebugRanges.Offset);
   IO.mapRequired("AddrSize", DebugRanges.AddrSize);
   IO.mapRequired("Entries", DebugRanges.Entries);
 }
 
 void MappingTraits<DWARFYAML::PubEntry>::mapping(IO &IO,
                                                  DWARFYAML::PubEntry &Entry) {
   IO.mapRequired("DieOffset", Entry.DieOffset);
   if (reinterpret_cast<DWARFYAML::PubSection *>(IO.getContext())->IsGNUStyle)

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

 ## Test that yaml2obj emits .debug_ranges section.
 
 ## a) Generate the .debug_ranges section from the "DWARF" entry.
 
 ## Generate and verify a little endian .debug_ranges section.
 
 # RUN: yaml2obj --docnum=1 -DENDIAN=ELFDATA2LSB %s -o %t.le.o
 # RUN: llvm-readobj --sections --section-data %t.le.o | \
-# RUN:   FileCheck %s -DSIZE=72 -DADDRALIGN=1 --check-prefixes=DWARF-HEADER,DWARF-LE-CONTENT
+# RUN:   FileCheck %s -DSIZE=88 -DADDRALIGN=1 --check-prefixes=DWARF-HEADER,DWARF-LE-CONTENT
 
 #         DWARF-HEADER: Index: 1
 #    DWARF-HEADER-NEXT: Name: .debug_ranges (1)
 #    DWARF-HEADER-NEXT: Type: SHT_PROGBITS (0x1)
 #    DWARF-HEADER-NEXT: Flags [ (0x0)
 #    DWARF-HEADER-NEXT: ]
 #    DWARF-HEADER-NEXT: Address: 0x0
 #    DWARF-HEADER-NEXT: Offset: 0x40

 # DWARF-LE-CONTENT-NEXT:   0020: 30000000 00000000 00000000 00000000
 ##                               |                 |
 ##                               |                 +---------------- LowOffset (8-byte) 0x00
 ##                               +---------------- HighOffset (8-byte) 0x30
 # DWARF-LE-CONTENT-NEXT:   0030: 40000000 00000000 00000000 00000000
 ##                               |                 |
 ##                               |                 +---------------- Terminating Entry (Lower bits, 8-byte)
 ##                               +---------------- HighOffset (8-byte) 0x40
-# DWARF-LE-CONTENT-NEXT:   0040: 00000000 00000000
-##                               |
+# DWARF-LE-CONTENT-NEXT:   0040: 00000000 00000000 00000000 10000000
+##                               |                 |        |
+##                               |                 |        +------- HighOffset (4-byte) 0x10
+##                               |                 +------- LowOffset (4-byte) 0x00
 ##                               +---------------- Terminating Entry (Higher bits, 8-byte)
+# DWARF-LE-CONTENT-NEXT:   0050: 00000000 00000000
+##                               |
+##                               +---------------- Terminating Entry (8-byte)
 # DWARF-LE-CONTENT-NEXT: )
 
 --- !ELF
 FileHeader:
   Class:   ELFCLASS64
   Data:    [[ENDIAN]]
   Type:    ET_EXEC
   Machine: EM_X86_64
 DWARF:
   debug_ranges:
     - Offset:   0
       AddrSize: 0x04
       Entries:
         - LowOffset:  0x00000000
           HighOffset: 0x00000010
         - LowOffset:  0x00000000
           HighOffset: 0x00000020
     - Offset:   24
       AddrSize: 0x08
       Entries:
         - LowOffset:  0x0000000000000000
           HighOffset: 0x0000000000000030
         - LowOffset:  0x0000000000000000
           HighOffset: 0x0000000000000040
+    - AddrSize: 0x04
+      Entries:
+        - LowOffset:  0x00000000
+          HighOffset: 0x00000010
 
 ## Generate and verify a big endian .debug_ranges section.
 
 # RUN: yaml2obj --docnum=1 -DENDIAN=ELFDATA2MSB %s -o %t.be.o
 # RUN: llvm-readobj --sections --section-data %t.be.o | \
-# RUN:   FileCheck %s -DSIZE=72 -DADDRALIGN=1 --check-prefixes=DWARF-HEADER,DWARF-BE-CONTENT
+# RUN:   FileCheck %s -DSIZE=88 -DADDRALIGN=1 --check-prefixes=DWARF-HEADER,DWARF-BE-CONTENT
 
 #      DWARF-BE-CONTENT: SectionData (
 # DWARF-BE-CONTENT-NEXT:   0000: 00000000 00000010 00000000 00000020
 ##                               |        |        |        |
 ##                               |        |        |        +------- HighOffset (4-byte) 0x20
 ##                               |        |        +------- LowOffset (4-byte) 0x00
 ##                               |        +------- HighOffset (4-byte) 0x10
 ##                               +------- LowOffset (4-byte) 0x00
 ##
 # DWARF-BE-CONTENT-NEXT:   0010: 00000000 00000000 00000000 00000000
 ##                               |                 |
 ##                               |                 +---------------- LowOffset (8-byte) 0x00
 ##                               +---------------- Terminating Entry (8-byte)
 # DWARF-BE-CONTENT-NEXT:   0020: 00000000 00000030 00000000 00000000
 ##                               |                 |
 ##                               |                 +---------------- LowOffset (8-byte) 0x00
 ##                               +---------------- HighOffset (8-byte) 0x30
 # DWARF-BE-CONTENT-NEXT:   0030: 00000000 00000040 00000000 00000000
 ##                               |                 |
 ##                               |                 +---------------- Terminating Entry (Lower bits, 8-byte)
 ##                               +---------------- HighOffset (8-byte) 0x40
-# DWARF-BE-CONTENT-NEXT:   0040: 00000000 00000000
-##                               |
+# DWARF-BE-CONTENT-NEXT:   0040: 00000000 00000000 00000000 00000010
+##                               |                 |        |
+##                               |                 |        +------- HighOffset (4-byte) 0x10
+##                               |                 +------- LowOffset (4-byte) 0x00
 ##                               +---------------- Terminating Entry (Higher bits, 8-byte)
+# DWARF-BE-CONTENT-NEXT:   0050: 00000000 00000000
+##                               |
+##                               +---------------- Terminating Entry (8-byte)
 # DWARF-BE-CONTENT-NEXT: )
 
 ## b) Generate the .debug_ranges section from raw section content.
 
 # RUN: yaml2obj --docnum=2 %s -o %t2.o
 # RUN: llvm-readobj --sections --section-data %t2.o | \
 # RUN:   FileCheck %s -DSIZE=3 -DADDRALIGN=0 --check-prefixes=DWARF-HEADER,ARBITRARY-CONTENT
 
FileHeader:
   Type:    ET_EXEC
   Machine: EM_X86_64
 Sections:
   - Name: .debug_ranges
     Type: SHT_PROGBITS
     Size: 0x10
 DWARF:
   debug_ranges:
-    - Offset:   0
-      AddrSize: 0x04
+    - AddrSize: 0x04
       Entries:
         - LowOffset:  0x00000000
           HighOffset: 0x00000000
 
 ## e) Test that yaml2obj emits an error message when both the "Content" and the
 ## "debug_ranges" entry are specified at the same time.
 
 # RUN: not yaml2obj --docnum=5 %s 2>&1 | FileCheck %s --check-prefix=ERROR
 
 --- !ELF
 FileHeader:
   Class:   ELFCLASS64
   Data:    ELFDATA2LSB
   Type:    ET_EXEC
   Machine: EM_X86_64
 Sections:
   - Name:    .debug_ranges
     Type:    SHT_PROGBITS
     Content: "00"
 DWARF:
   debug_ranges:
-    - Offset:   0
-      AddrSize: 0x04
+    - AddrSize: 0x04
       Entries:
         - LowOffset:  0x00000000
           HighOffset: 0x00000000
 
 ## f) Test that all the properties can be overridden by the section header when
 ## the "debug_ranges" entry doesn't exist.
 
 # RUN: yaml2obj --docnum=6 %s -o %t6.o
- Name:         .debug_ranges
     Info:         1                  # 0 by default.
     AddressAlign: 2                  # 1 by default.
     Address:      0x0000000000002020 # 0x00 by default.
     Offset:       0x00000050         # 0x40 for the first section.
   - Name:         .sec               # Linked by .debug_ranges.
     Type:         SHT_STRTAB
 DWARF:
   debug_ranges:
-    - Offset:   0
-      AddrSize: 0x04
+    - AddrSize: 0x04
       Entries:
         - LowOffset:  0x00000000
           HighOffset: 0x00000000
 
 ## h) Test that yaml2obj will not generate the .debug_ranges section when the "DWARF" entry
 ## exists but the "debug_ranges" entry doesn't exist in the "DWARF" entry or the "Sections" entry.
 
 # RUN: yaml2obj --docnum=8 %s -o %t8.o