[ObjectYAML][ELF] Allow verdaux entry offset to be user-defined

llvm/include/llvm/ObjectYAML/ELFYAML.h

@@ -582,6 +582,7 @@ struct VerdefEntry {
   std::optional<uint16_t> Flags;
   std::optional<uint16_t> VersionNdx;
   std::optional<uint32_t> Hash;
+  std::optional<uint16_t> VDAux;
   std::vector<StringRef> VerNames;
 };
 

llvm/lib/ObjectYAML/ELFEmitter.cpp

@@ -1655,7 +1655,7 @@ void ELFState<ELFT>::writeSectionContent(Elf_Shdr &SHeader,
     VerDef.vd_flags = E.Flags.value_or(0);
     VerDef.vd_ndx = E.VersionNdx.value_or(0);
     VerDef.vd_hash = E.Hash.value_or(0);
-    VerDef.vd_aux = sizeof(Elf_Verdef);
+    VerDef.vd_aux = E.VDAux.value_or(sizeof(Elf_Verdef));
     VerDef.vd_cnt = E.VerNames.size();
     if (I == Section.Entries->size() - 1)
       VerDef.vd_next = 0;

llvm/lib/ObjectYAML/ELFYAML.cpp

@@ -1921,6 +1921,7 @@ void MappingTraits<ELFYAML::VerdefEntry>::mapping(IO &IO,
   IO.mapOptional("Flags", E.Flags);
   IO.mapOptional("VersionNdx", E.VersionNdx);
   IO.mapOptional("Hash", E.Hash);
+  IO.mapOptional("VDAux", E.VDAux);
   IO.mapRequired("Names", E.VerNames);
 }
 

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

@@ -48,12 +48,14 @@ Sections:
         Flags:      0
         VersionNdx: 0
         Hash:       0
+        VDAux:      20
         Names:
           - VERSION_0
 ## An entry with arbitrary values.
       - Flags:      2
         VersionNdx: 2
         Hash:       108387921
+        VDAux:      [[VDAUX=20]]
         Names:
           - VERSION_1
 ## Another entry with arbitrary values and version predecessors.
@@ -81,3 +83,9 @@ DynamicSymbols: []
 # RUN:   FileCheck %s -DFILE=%t.version --check-prefix=VERSION-ERR
 
 # VERSION-ERR: Error reading file: [[FILE]]: invalid SHT_GNU_verdef section version: 2
+
+# RUN: yaml2obj %s -DVDAUX=100 -o %t.vdaux
+# RUN: not obj2yaml %t.vdaux 2>&1 | \
+# RUN:   FileCheck %s -DFILE=%t.vdaux --check-prefix=VDAUX-ERR
+
+# VDAUX-ERR: Error reading file: [[FILE]]: corrupted section: vd_aux value 100 in section verdef points past end of the section

llvm/tools/obj2yaml/elf2yaml.cpp

@@ -1451,7 +1451,15 @@ ELFDumper<ELFT>::dumpVerdefSection(const Elf_Shdr *Shdr) {
     if (Verdef->vd_hash != 0)
       Entry.Hash = Verdef->vd_hash;
 
+    if (Verdef->vd_aux != sizeof(Elf_Verdef))
+      Entry.VDAux = Verdef->vd_aux;
+
     const uint8_t *BufAux = Buf + Verdef->vd_aux;
+    if (BufAux > Data.end())
+      return createStringError(
+          errc::invalid_argument,
+          "corrupted section: vd_aux value " + Twine(Verdef->vd_aux) +
+              " in section verdef points past end of the section");
     while (BufAux) {
       const Elf_Verdaux *Verdaux =
           reinterpret_cast<const Elf_Verdaux *>(BufAux);