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

[antoniofrighetto]

Allow verdaux entry offset to be user-defined. First commit to be landed separately.

[llvmbot]

@llvm/pr-subscribers-objectyaml

Author: Antonio Frighetto (antoniofrighetto)

Changes

Allow verdaux entry offset to be user-defined. First commit to be landed separately.

---

Full diff: https://github.com/llvm/llvm-project/pull/115343.diff

5 Files Affected:

• (modified) llvm/include/llvm/ObjectYAML/ELFYAML.h (+1)
• (modified) llvm/lib/ObjectYAML/ELFEmitter.cpp (+6-6)
• (modified) llvm/lib/ObjectYAML/ELFYAML.cpp (+1)
• (modified) llvm/test/tools/obj2yaml/ELF/verdef-section.yaml (+8)
• (modified) llvm/tools/obj2yaml/elf2yaml.cpp (+8)

diff --git a/llvm/include/llvm/ObjectYAML/ELFYAML.h b/llvm/include/llvm/ObjectYAML/ELFYAML.h
index 8f045d6383623b..dfdfa055d65fa6 100644
--- a/llvm/include/llvm/ObjectYAML/ELFYAML.h
+++ b/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;
 };
 
diff --git a/llvm/lib/ObjectYAML/ELFEmitter.cpp b/llvm/lib/ObjectYAML/ELFEmitter.cpp
index fc234581a45a70..bf19e81933cab7 100644
--- a/llvm/lib/ObjectYAML/ELFEmitter.cpp
+++ b/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;
@@ -1665,13 +1665,13 @@ void ELFState<ELFT>::writeSectionContent(Elf_Shdr &SHeader,
     CBA.write((const char *)&VerDef, sizeof(Elf_Verdef));
 
     for (size_t J = 0; J < E.VerNames.size(); ++J, ++AuxCnt) {
-      Elf_Verdaux VernAux;
-      VernAux.vda_name = DotDynstr.getOffset(E.VerNames[J]);
+      Elf_Verdaux VerdAux;
+      VerdAux.vda_name = DotDynstr.getOffset(E.VerNames[J]);
       if (J == E.VerNames.size() - 1)
-        VernAux.vda_next = 0;
+        VerdAux.vda_next = 0;
       else
-        VernAux.vda_next = sizeof(Elf_Verdaux);
-      CBA.write((const char *)&VernAux, sizeof(Elf_Verdaux));
+        VerdAux.vda_next = sizeof(Elf_Verdaux);
+      CBA.write((const char *)&VerdAux, sizeof(Elf_Verdaux));
     }
   }
 
diff --git a/llvm/lib/ObjectYAML/ELFYAML.cpp b/llvm/lib/ObjectYAML/ELFYAML.cpp
index e97248cbcf5682..bd816a6d704d44 100644
--- a/llvm/lib/ObjectYAML/ELFYAML.cpp
+++ b/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);
 }
 
diff --git a/llvm/test/tools/obj2yaml/ELF/verdef-section.yaml b/llvm/test/tools/obj2yaml/ELF/verdef-section.yaml
index fc3e0f7ae22d9c..0eb81d7cfffab4 100644
--- a/llvm/test/tools/obj2yaml/ELF/verdef-section.yaml
+++ b/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]]: vd_aux value 100 in section verdef points past end of the section, corrupted section
diff --git a/llvm/tools/obj2yaml/elf2yaml.cpp b/llvm/tools/obj2yaml/elf2yaml.cpp
index 9b4644bde36c0b..111e25294fa5ba 100644
--- a/llvm/tools/obj2yaml/elf2yaml.cpp
+++ b/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,
+                               "vd_aux value " + Twine(Verdef->vd_aux) +
+                                   " in section verdef points past end of the "
+                                   "section, corrupted section");
     while (BufAux) {
       const Elf_Verdaux *Verdaux =
           reinterpret_cast<const Elf_Verdaux *>(BufAux);

[antoniofrighetto]

I'm don't think adding support in yaml2elf should be desirable too. To achieve that we would need to add VDAux too in struct VerDef in Object/ELF.h, and this looks quite of an invasive change.

In general, as the original report mentions, this is a crash-on-invalid, and I don't think the user should be able to modify the vd_aux themselves (unless manually modifying the binary), but it's fine to have it elsewhere for testing purpose for #115284.