[yaml2obj] - Allow specifying no tags to create empty sections in few cases.

[grimar]

Summary

Currently we have a few sections that
does not support specifying no keys for them. E.g. it is required that one
of "Content", "Size" or "Entries" key is present. There is no reason to
have this restriction. We can allow this and emit an empty section instead.

This opens road for a simplification and generalization of the code in validate()
that is discussed in the D89039 thread.

Depends on D89039.

[MaskRay]

Reasonable simplification. Thanks!

[jhenderson]

Some comment nits from me.

llvm/test/tools/yaml2obj/ELF/llvm-addrsig-section.yaml

121

(or "none of X, Y, or Z were set")

Same below.

llvm/lib/ObjectYAML/ELFEmitter.cpp

 void ELFState<ELFT>::writeSectionContent(
     Elf_Shdr &SHeader, const ELFYAML::StackSizesSection &Section,
     ContiguousBlobAccumulator &CBA) {
   if (Section.Content || Section.Size) {
     SHeader.sh_size = writeContent(CBA, Section.Content, Section.Size);
     return;
   }
 
+  if (!Section.Entries)
+    return;
+
   for (const ELFYAML::StackSizeEntry &E : *Section.Entries) {
     CBA.write<uintX_t>(E.Address, ELFT::TargetEndianness);
     SHeader.sh_size += sizeof(uintX_t) + CBA.writeULEB128(E.Size);
   }
 }
 
 template <class ELFT>
 void ELFState<ELFT>::writeSectionContent(
void ELFState<ELFT>::writeSectionContent(Elf_Shdr &SHeader,
   else
     SHeader.sh_entsize = sizeof(typename ELFT::Word);
 
   if (Section.Content || Section.Size) {
     SHeader.sh_size = writeContent(CBA, Section.Content, Section.Size);
     return;
   }
 
+  if (!Section.Bucket)
+    return;
+
   CBA.write<uint32_t>(
       Section.NBucket.getValueOr(llvm::yaml::Hex64(Section.Bucket->size())),
       ELFT::TargetEndianness);
   CBA.write<uint32_t>(
       Section.NChain.getValueOr(llvm::yaml::Hex64(Section.Chain->size())),
       ELFT::TargetEndianness);
 
   for (uint32_t Val : *Section.Bucket)
if (Section.Link.empty() && !ExcludedSectionHeaders.count(".symtab") &&
       SN2I.lookup(".symtab", Link))
     SHeader.sh_link = Link;
 
   if (Section.Content || Section.Size) {
     SHeader.sh_size = writeContent(CBA, Section.Content, Section.Size);
     return;
   }
 
+  if (!Section.Symbols)
+    return;
+
   for (StringRef Sym : *Section.Symbols)
     SHeader.sh_size +=
         CBA.writeULEB128(toSymbolIndex(Sym, Section.Name, /*IsDynamic=*/false));
 }
 
 template <class ELFT>
 void ELFState<ELFT>::writeSectionContent(Elf_Shdr &SHeader,
                                          const ELFYAML::NoteSection &Section,
                                          ContiguousBlobAccumulator &CBA) {
   uint64_t Offset = CBA.tell();
   if (Section.Content || Section.Size) {
     SHeader.sh_size = writeContent(CBA, Section.Content, Section.Size);
     return;
   }
 
+  if (!Section.Notes)
+    return;
+
   for (const ELFYAML::NoteEntry &NE : *Section.Notes) {
     // Write name size.
     if (NE.Name.empty())
       CBA.write<uint32_t>(0, ELFT::TargetEndianness);
     else
       CBA.write<uint32_t>(NE.Name.size() + 1, ELFT::TargetEndianness);
 
     // Write description size.
if (Section.Link.empty() && !ExcludedSectionHeaders.count(".dynsym") &&
       SN2I.lookup(".dynsym", Link))
     SHeader.sh_link = Link;
 
   if (Section.Content || Section.Size) {
     SHeader.sh_size = writeContent(CBA, Section.Content, Section.Size);
     return;
   }
 
+  if (!Section.Header)
+    return;
+
   // We write the header first, starting with the hash buckets count. Normally
   // it is the number of entries in HashBuckets, but the "NBuckets" property can
   // be used to override this field, which is useful for producing broken
   // objects.
   if (Section.Header->NBuckets)
     CBA.write<uint32_t>(*Section.Header->NBuckets, ELFT::TargetEndianness);
   else
     CBA.write<uint32_t>(Section.HashBuckets->size(), ELFT::TargetEndianness);

llvm/lib/ObjectYAML/ELFYAML.cpp

StringRef MappingTraits<std::unique_ptr<ELFYAML::Chunk>>::validate(
 
   if (const auto *RawSection = dyn_cast<ELFYAML::RawContentSection>(C.get())) {
     if (RawSection->Flags && RawSection->ShFlags)
       return "ShFlags and Flags cannot be used together";
     return {};
   }
 
   if (const auto *SS = dyn_cast<ELFYAML::StackSizesSection>(C.get())) {
-    if (!SS->Entries && !SS->Content && !SS->Size)
-      return ".stack_sizes: one of Content, Entries and Size must be specified";
-
-    // We accept Content, Size or both together when there are no Entries.
-    if (!SS->Entries)
-      return {};
-
-    if (SS->Size)
-      return ".stack_sizes: Size and Entries cannot be used together";
-    if (SS->Content)
-      return ".stack_sizes: Content and Entries cannot be used together";
+    if ((SS->Content || SS->Size) && SS->Entries)
+      return "\"Entries\" cannot be used with \"Content\" or \"Size\"";
     return {};
   }
 
   if (const auto *HS = dyn_cast<ELFYAML::HashSection>(C.get())) {
-    if (!HS->Content && !HS->Bucket && !HS->Chain && !HS->Size)
-      return "one of \"Content\", \"Size\", \"Bucket\" or \"Chain\" must be "
-             "specified";
-
-    if (HS->Content || HS->Size) {
-      if (HS->Bucket)
-        return "\"Bucket\" cannot be used with \"Content\" or \"Size\"";
-      if (HS->Chain)
-        return "\"Chain\" cannot be used with \"Content\" or \"Size\"";
-      return {};
-    }
-
+    if ((HS->Content || HS->Size) && (HS->Bucket || HS->Chain))
+      return "\"Bucket\" and \"Chain\" cannot be used with \"Content\" or "
+             "\"Size\"";
     if ((HS->Bucket && !HS->Chain) || (!HS->Bucket && HS->Chain))
       return "\"Bucket\" and \"Chain\" must be used together";
     return {};
   }
 
   if (const auto *Sec = dyn_cast<ELFYAML::AddrsigSection>(C.get())) {
-    if (!Sec->Symbols && !Sec->Content && !Sec->Size)
-      return "one of \"Content\", \"Size\" or \"Symbols\" must be specified";
-
     if ((Sec->Content || Sec->Size) && Sec->Symbols)
       return "\"Symbols\" cannot be used with \"Content\" or \"Size\"";
     return {};
   }
 
   if (const auto *NS = dyn_cast<ELFYAML::NoteSection>(C.get())) {
-    if (!NS->Content && !NS->Size && !NS->Notes)
-      return "one of \"Content\", \"Size\" or \"Notes\" must be "
-             "specified";
-
     if ((NS->Content || NS->Size) && NS->Notes)
       return "\"Notes\" cannot be used with \"Content\" or \"Size\"";
     return {};
   }
 
   if (const auto *Sec = dyn_cast<ELFYAML::GnuHashSection>(C.get())) {
-    if (!Sec->Content && !Sec->Size && !Sec->Header && !Sec->BloomFilter &&
-        !Sec->HashBuckets && !Sec->HashValues)
-      return "either \"Content\", \"Size\" or \"Header\", \"BloomFilter\", "
-             "\"HashBuckets\" and \"HashBuckets\" must be specified";
-
-    if (Sec->Header || Sec->BloomFilter || Sec->HashBuckets ||
-        Sec->HashValues) {
-      if (!Sec->Header || !Sec->BloomFilter || !Sec->HashBuckets ||
-          !Sec->HashValues)
-        return "\"Header\", \"BloomFilter\", "
-               "\"HashBuckets\" and \"HashValues\" must be used together";
-      if (Sec->Content || Sec->Size)
-        return "\"Header\", \"BloomFilter\", "
-               "\"HashBuckets\" and \"HashValues\" can't be used together with "
-               "\"Content\" or \"Size\"";
-      return {};
-    }
+    const bool HasSpecialFields =
+        Sec->Header || Sec->BloomFilter || Sec->HashBuckets || Sec->HashValues;
+    if (HasSpecialFields && (Sec->Content || Sec->Size))
 
-    // Only Content is specified.
+    if (HasSpecialFields && (!Sec->Header || !Sec->BloomFilter ||
+                             !Sec->HashBuckets || !Sec->HashValues))
+      return "\"Header\", \"BloomFilter\", "
+             "\"HashBuckets\" and \"HashValues\" must be used together";
     return {};
   }
 
   if (const auto *Sec = dyn_cast<ELFYAML::LinkerOptionsSection>(C.get())) {
     if ((Sec->Content || Sec->Size) && Sec->Options)
       return "\"Options\" cannot be used with \"Content\" or \"Size\"";
     return {};
   }

llvm/test/tools/yaml2obj/ELF/gnu-hash-section.yaml

FileHeader:
   Data:  ELFDATA2LSB
   Type:  ET_DYN
 Sections:
   - Name:  .gnu.hash
     Type:  SHT_GNU_HASH
     Header:
       SymNdx: 0x0
 
-## Either "Content" or "Header", "BloomFilter", "HashBuckets" and "HashBuckets" must be
-## specified when declaring a SHT_GNU_HASH section.
+## Check we emit an empty section if neither "Content", "Header",
+## "BloomFilter", "HashBuckets" nor "HashBuckets" were set.
 
-# RUN: not yaml2obj --docnum=10 %s -o %t10 2>&1 | FileCheck %s --check-prefix=NOKEYS
+# NOKEYS: Section Headers:
+# NOKEYS:  [Nr] Name      Type     Address          Off    Size
+# NOKEYS:  [ 1] .gnu.hash GNU_HASH 0000000000000000 000040 000000
 
-# NOKEYS: error: either "Content", "Size" or "Header", "BloomFilter", "HashBuckets" and "HashBuckets" must be specified
+# RUN: yaml2obj --docnum=10 %s -o %t10
+# RUN: llvm-readelf --sections %t10 | FileCheck %s --check-prefix=NOKEYS
 
 --- !ELF
 FileHeader:
   Class: ELFCLASS64
   Data:  ELFDATA2LSB
   Type:  ET_DYN
 Sections:
   - Name:  .gnu.hash

llvm/test/tools/yaml2obj/ELF/hash-section.yaml

- Name:   .hash
     Type:   SHT_HASH
     Bucket: [ 1, 2 ]
     Chain:  [ 3, 4, 5 ]
 
 ## Check we can't use "Content" and "Bucket" tags together.
 
 # RUN: not yaml2obj --docnum=3 %s 2>&1 | FileCheck %s --check-prefix=CONTENT-BUCKET
 
-# CONTENT-BUCKET: "Bucket" cannot be used with "Content" or "Size"
+# CONTENT-BUCKET: "Bucket" and "Chain" cannot be used with "Content" or "Size"
 
 --- !ELF
 FileHeader:
   Class: ELFCLASS32
   Data:  ELFDATA2LSB
   Type:  ET_DYN
 Sections:
   - Name:   .hash
FileHeader:
   Class: ELFCLASS32
   Data:  ELFDATA2LSB
   Type:  ET_DYN
 Sections:
   - Name:  .hash
     Type:  SHT_HASH
     Chain: [ 1 ]
 
-## Check we report an error if neither "Bucket", "Chain" nor "Content" were set.
+## Check we emit an empty section if neither "Bucket", "Chain",
+## "Content" nor "Size" were set.
 
-# RUN: not yaml2obj --docnum=7 %s 2>&1 | FileCheck %s --check-prefix=NO-TAGS
+# RUN: yaml2obj --docnum=7 %s -o %t7
+# RUN: llvm-readelf --sections %t7 | FileCheck %s --check-prefix=NO-TAGS
 
-# NO-TAGS: error: one of "Content", "Size", "Bucket" or "Chain" must be specified
+# NO-TAGS: [Nr] Name  Type Address  Off    Size
+# NO-TAGS: [ 1] .hash HASH 00000000 000034 000000
 
 --- !ELF
 FileHeader:
   Class: ELFCLASS32
   Data:  ELFDATA2LSB
   Type:  ET_DYN
 Sections:
   - Name:  .hash

llvm/test/tools/yaml2obj/ELF/llvm-addrsig-section.yaml

FileHeader:
   Class: ELFCLASS64
   Data:  ELFDATA2LSB
   Type:  ET_DYN
 Sections:
   - Name: .llvm_addrsig
     Type: SHT_LLVM_ADDRSIG
     Content: "1122334455"
 
-## Either "Content" or "Symbols" must be specifed for SHT_LLVM_ADDRSIG sections.
+## Check we emit an empty section if neither "Content", "Size" not "Symbols" were set.
 
-# RUN: not yaml2obj --docnum=6 %s 2>&1 | FileCheck %s --check-prefix=NO-TAGS
+# RUN: yaml2obj --docnum=6 %s -o %t6
+# RUN: llvm-readelf --sections %t6 | FileCheck %s --check-prefix=NO-TAGS
 
-# NO-TAGS: error: one of "Content", "Size" or "Symbols" must be specified
+# NO-TAGS: [Nr] Name          Type         Address          Off    Size
+# NO-TAGS: [ 1] .llvm_addrsig LLVM_ADDRSIG 0000000000000000 000040 000000
 
 --- !ELF
 FileHeader:
   Class: ELFCLASS64
   Data:  ELFDATA2LSB
   Type:  ET_DYN
 Sections:
   - Name: .llvm_addrsig

llvm/test/tools/yaml2obj/ELF/note-section.yaml

FileHeader:
   Class: ELFCLASS64
   Data:  ELFDATA2LSB
   Type:  ET_DYN
 Sections:
   - Name:    .note.foo
     Type:    SHT_NOTE
     Content: "1122334455"
 
-## Either "Content", "Size" or "Notes" must be specifed for SHT_NOTE sections.
+## Check we emit an empty section if neither "Content", "Size" not "Notes" were set.
 
-# RUN: not yaml2obj --docnum=8 %s 2>&1 | FileCheck %s --check-prefix=NO-TAGS
+# RUN: yaml2obj --docnum=8 %s -o %t8
+# RUN: llvm-readelf --sections %t8 | FileCheck %s --check-prefix=NO-TAGS
 
-# NO-TAGS: error: one of "Content", "Size" or "Notes" must be specified
+# NO-TAGS: [Nr] Name      Type Address          Off    Size
+# NO-TAGS: [ 1] .note.foo NOTE 0000000000000000 000040 000000
 
 --- !ELF
 FileHeader:
   Class: ELFCLASS64
   Data:  ELFDATA2LSB
   Type:  ET_DYN
 Sections:
   - Name: .note.foo

llvm/test/tools/yaml2obj/ELF/stack-sizes.yaml

- Name:    .stack_sizes
     Type:    SHT_PROGBITS
     Entries:
        - Address: 0x10
 
 ## Check we can't use both "Content" and "Entries" tags at the same time.
 
 # RUN: not yaml2obj --docnum=5 %s 2>&1 | FileCheck %s --check-prefix=ENTRIES-AND-CONTENT
 
-# ENTRIES-AND-CONTENT: error: .stack_sizes: Content and Entries cannot be used together
+# ENTRIES-AND-CONTENT: error: "Entries" cannot be used with "Content" or "Size"
 
 --- !ELF
 FileHeader:
   Class: ELFCLASS64
   Data:  ELFDATA2LSB
   Type:  ET_EXEC
 Sections:
   - Name:    .stack_sizes
     Type:    SHT_PROGBITS
     Content: "00"
     Entries:
       - Address: 0x10
         Size:    0x20
 
-## Check we must specify either "Content", "Entries" or "Size" tag when describing .stack_sizes.
+## Check we emit an empty section if neither "Content", "Size" nor "Entries" were set.
 
-# RUN: not yaml2obj --docnum=6 %s 2>&1 | FileCheck %s --check-prefix=NO-TAGS
+# RUN: yaml2obj --docnum=6 %s -o %t6
+# RUN: llvm-readelf --sections %t6 | FileCheck %s --check-prefix=NO-TAGS
 
-# NO-TAGS: .stack_sizes: one of Content, Entries and Size must be specified
+# NO-TAGS: [Nr] Name         Type     Address          Off    Size
+# NO-TAGS: [ 1] .stack_sizes PROGBITS 0000000000000000 000040 000000
 
 --- !ELF
 FileHeader:
   Class: ELFCLASS64
   Data:  ELFDATA2LSB
   Type:  ET_EXEC
 Sections:
   - Name: .stack_sizes
     Type: SHT_PROGBITS
 
 ## Check we can't use both "Size" and "Entries" tags at the same time.
 
 # RUN: not yaml2obj --docnum=7 %s 2>&1 | FileCheck %s --check-prefix=ENTRIES-AND-SIZE
 
-# ENTRIES-AND-SIZE: .stack_sizes: Size and Entries cannot be used together
+# ENTRIES-AND-SIZE: error: "Entries" cannot be used with "Content" or "Size"
 
 --- !ELF
 FileHeader:
   Class: ELFCLASS64
   Data:  ELFDATA2LSB
   Type:  ET_EXEC
 Sections:
   - Name: .stack_sizes