[obj2yaml,yaml2obj] - Fix issues with creating/dumping group sections.

[grimar]

Summary

We have the following issues related to group sections:

1. yaml2obj is unable to set the custom sh_entsize value, because the EntSize key is currently ignored.
2. obj2yaml is unable to dump the group section which sh_entsize != 4.
3. obj2yaml always dumps the "EntSize" for group sections, though usually we are trying to omit dumping default values when dumping keys. I.e. we should not print the "EntSize" key when sh_entsize == 4.

This patch fixes (1),(3) and adds the test case to document the behavior of (2).

Depends on D93753

[jhenderson]

Seems to me like you should have a dedicate yaml2obj test that shows the sh_entsize can be set for group sections?

[grimar]

• Added dedicated yaml2obj test.

[jhenderson]

LGTM.

llvm/lib/ObjectYAML/ELFEmitter.cpp

void ELFState<ELFT>::writeSectionContent(Elf_Shdr &SHeader,
   assert(Section.Type == llvm::ELF::SHT_GROUP &&
          "Section type is not SHT_GROUP");
 
   unsigned Link = 0;
   if (!Section.Link && !ExcludedSectionHeaders.count(".symtab") &&
       SN2I.lookup(".symtab", Link))
     SHeader.sh_link = Link;
 
-  SHeader.sh_entsize = 4;
+  if (Section.EntSize)
+    SHeader.sh_entsize = *Section.EntSize;
+  else
+    SHeader.sh_entsize = sizeof(typename ELFT::Word);
 
   if (Section.Signature)
     SHeader.sh_info =
         toSymbolIndex(*Section.Signature, Section.Name, /*IsDynamic=*/false);
 
   if (!Section.Members)
     return;
 

llvm/test/tools/obj2yaml/ELF/section-group.yaml

 ## Checks that the tool is able to read section groups from ELF.
 
+## Check how groups sections are dumped.
+## Check we don't dump the "EntSize" key when sh_entsize == 4.
+
 # RUN: yaml2obj %s -o %t1.o
 # RUN: obj2yaml %t1.o | FileCheck %s -DSEC=.rodata
 
-# CHECK:      - Name:    .group
-# CHECK-NEXT:   Type:    SHT_GROUP
-# CHECK-NEXT:   Link:    .symtab
-# CHECK-NEXT:   EntSize: 0x4
-# CHECK-NEXT:   Info:    signature
+# CHECK:      - Name: .group
+# CHECK-NEXT:   Type: SHT_GROUP
+# CHECK-NEXT:   Link: .symtab
+# CHECK-NEXT:   Info: signature
 # CHECK-NEXT:   Members:
 # CHECK-NEXT:     - SectionOrType: GRP_COMDAT
 # CHECK-NEXT:     - SectionOrType: [[SEC]]
 # CHECK-NEXT: - Name:
 
 --- !ELF
 FileHeader:
   Class: ELFCLASS64
   Data:  ELFDATA2LSB
   Type:  ET_REL
 Sections:
-  - Name: .group
-    Type: SHT_GROUP
-    Link: .symtab
-    Info: [[INFO=signature]]
+  - Name:    .group
+    Type:    SHT_GROUP
+    Link:    .symtab
+    Info:    [[INFO=signature]]
+    EntSize: [[ENTSIZE=<none>]]
     Members:
       - SectionOrType: GRP_COMDAT
       - SectionOrType: [[SEC=.rodata]]
   - Name: .rodata
     Type: SHT_PROGBITS
 Symbols:
   - Name:    signature
     Type:    STT_OBJECT
     Section: .rodata
 
+## Document that yaml2obj can't dump the SHT_GROUP section when its sh_entsize != 4.
+
+# RUN: yaml2obj %s -DENTSIZE=0xfe -o %t1.entsize.o
+# RUN: not obj2yaml %t1.entsize.o 2>&1 | \
+# RUN:   FileCheck %s -DFILE=%t1.entsize.o --check-prefix=ENTSIZE
+
+# ENTSIZE: Error reading file: [[FILE]]: section [index 1] has invalid sh_entsize: expected 4, but got 254
+
 ## Check we are able to dump members of the SHT_GROUP section even when
 ## one of them has section index 0.
 
 # RUN: yaml2obj -DSEC=0 %s -o %tnull.o
 # RUN: obj2yaml %tnull.o | FileCheck %s -DSEC="''"
 
 ## Check obj2yaml report an error when sh_info field of
 ## group section contains invalid (too large) signature symbol index.
 
 # RUN: yaml2obj -DINFO=0xFF %s -o %t2.o
 # RUN: not obj2yaml %t2.o 2>&1 | FileCheck %s -DFILE=%t2.o --check-prefix=ERR
 
 # ERR: Error reading file: [[FILE]]: unable to get symbol from section [index 3]: invalid symbol index (255)

llvm/test/tools/yaml2obj/ELF/group.yaml

FileHeader:
   Class: ELFCLASS64
   Data:  ELFDATA2LSB
   Type:  ET_DYN
 Sections:
   - Name:    .group
     Type:    SHT_GROUP
     Link:    0x1
     Info:    0x2
+    EntSize: [[ENTSIZE=<none>]]
     Size:    [[SIZE=<none>]]
     Content: [[CONTENT=<none>]]
     Members: [[MEMBERS=<none>]]
 
 # RUN: yaml2obj -DSIZE=2 -DCONTENT="'0011'" %s -o %t.cont.size.eq.o
 # RUN: llvm-readobj --sections --section-data %t.cont.size.eq.o | \
 # RUN:   FileCheck %s --check-prefix=CHECK-CONTENT -DDATA="0011"
 

 # RUN: not yaml2obj -DSIZE=0 -DMEMBERS="[]" %s 2>&1 | \
 # RUN:   FileCheck %s --check-prefix=MEMBERS-ERR
 # RUN: not yaml2obj -DCONTENT="'00'" -DMEMBERS="[]" %s 2>&1 | \
 # RUN:   FileCheck %s --check-prefix=MEMBERS-ERR
 
 # MEMBERS-ERR: error: "Members" cannot be used with "Content" or "Size"
 
 ## Check we create an empty section when none of "Size", "Content" or "Members" are specified.
+## Check that the default value of sh_entsize is 4.
 
 # RUN: yaml2obj %s -o %t.empty.o
 # RUN: llvm-readelf --sections --section-data %t.empty.o | \
 # RUN:   FileCheck %s --check-prefix=EMPTY-SEC
 
-# EMPTY-SEC: [Nr] Name   Type  Address          Off    Size
-# EMPTY-SEC: [ 1] .group GROUP 0000000000000000 000040 000000
+# EMPTY-SEC: [Nr] Name   Type  Address          Off    Size   ES Flg
+# EMPTY-SEC: [ 1] .group GROUP 0000000000000000 000040 000000 04 1
+
+## Check that we are able to set an arbitrary entry size for the group section.
+
+# RUN: yaml2obj %s -DENTSIZE=0xFE -o %t.entsize.o
+# RUN: llvm-readelf --sections %t.entsize.o | FileCheck %s --check-prefix=ENTSIZE
+
+# ENTSIZE: [Nr] Name   Type  Address          Off    Size   ES Flg
+# ENTSIZE: [ 1] .group GROUP 0000000000000000 000040 000000 fe 1

llvm/tools/obj2yaml/elf2yaml.cpp

Error ELFDumper<ELFT>::dumpRelocation(const RelT *Rel, const Elf_Shdr *SymTab,
 
   return Error::success();
 }
 
 template <class ELFT>
 static unsigned getDefaultShEntSize(ELFYAML::ELF_SHT SecType,
                                     StringRef SecName) {
   switch (SecType) {
+  case ELF::SHT_GROUP:
+    return sizeof(typename ELFT::Word);
   case ELF::SHT_REL:
     return sizeof(typename ELFT::Rel);
   case ELF::SHT_RELA:
     return sizeof(typename ELFT::Rela);
   case ELF::SHT_RELR:
     return sizeof(typename ELFT::Relr);
   case ELF::SHT_DYNAMIC:
     return sizeof(typename ELFT::Dyn);