Merge pull request #898 from adamjseitz/reloc-symbol-table

Utilize SH_LINK section metadata to resolve relocation's target symbol table

api/python/src/ELF/objects/pyRelocation.cpp

@@ -106,6 +106,13 @@ void create<Relocation>(py::module& m) {
         )delim",
         py::return_value_policy::reference)
 
+    .def_property_readonly("symbol_table",
+      static_cast<Section* (Relocation::*)(void)>(&Relocation::symbol_table),
+      R"delim(
+      the symbol table :class:`~lief.ELF.Section` which the relocation references
+      )delim",
+      py::return_value_policy::reference)
+
     .def_property_readonly("is_rela",
       static_cast<getter_t<bool>>(&Relocation::is_rela),
       "``True`` if the relocation **uses** the :attr:`~lief.ELF.Relocation.addend` proprety")

doc/sphinx/changelog.rst

@@ -1,6 +1,13 @@
 Changelog
 =========
 
+0.14.0 - Not Released Yet
+-------------------------
+
+:ELF:
+
+  * Fix relocation issue when using `-Wl,--emit-relocs` (c.f. :issue:`897` / :pr:`898` by :github_user:`adamjseitz`)
+
 0.13.0 - April 9, 2023
 ----------------------
 

include/LIEF/ELF/Relocation.hpp

@@ -119,17 +119,23 @@ class LIEF_API Relocation : public LIEF::Relocation {
   //! True if the relocation has an associated section
   bool has_section() const;
 
-  //! Section associated with this relocation.
-  //! If no section is tied to this relocation, it returns a nullptr
+  //! The section to which the relocation applies.
+  //! If no section to which the relocation applies is associtated to this relocation, it returns a nullptr
   Section*       section();
   const Section* section() const;
 
+  //! The associated symbol table.
+  //! If no symbol table section is associated with this relocation, it returns a nullptr
+  Section*       symbol_table();
+  const Section* symbol_table() const;
+
   void addend(int64_t addend);
   void type(uint32_t type);
   void purpose(RELOCATION_PURPOSES purpose);
   void info(uint32_t v);
   void symbol(Symbol* symbol);
   void section(Section* section);
+  void symbol_table(Section* section);
 
   void accept(Visitor& visitor) const override;
 
@@ -146,6 +152,7 @@ class LIEF_API Relocation : public LIEF::Relocation {
   ARCH                architecture_ = ARCH::EM_NONE;
   RELOCATION_PURPOSES purpose_ = RELOCATION_PURPOSES::RELOC_PURPOSE_NONE;
   Section*            section_{nullptr};
+  Section*            symbol_table_{nullptr};
   uint32_t            info_ = 0;
 };
 

src/ELF/Parser.tcc

@@ -1342,21 +1342,20 @@ ok_error_t Parser::parse_section_relocations(const Section& section) {
                 std::is_same<REL_T, Elf_Rela>::value, "REL_T must be Elf_Rel || Elf_Rela");
 
   // A relocation section can reference two other sections: a symbol table,
-  // identified by the sh_info section header entry, and a section to modify,
-  // identified by the sh_link
-  // BUT: in practice sh_info and sh_link are inverted
+  // identified by the sh_link section header entry, and a section to modify,
+  // identified by the sh_info
+  // See Figure 4-12 in https://refspecs.linuxbase.org/elf/gabi4+/ch4.sheader.html#sh_link
   Section* applies_to = nullptr;
   const size_t sh_info = section.information();
   if (sh_info > 0 && sh_info < binary_->sections_.size()) {
     applies_to = binary_->sections_[sh_info].get();
   }
 
-  // FIXME: Use it
-  // Section* section_associated = nullptr;
-  // if (section.link() > 0 and section.link() < binary_->sections_.size()) {
-  //   const size_t sh_link = section.link();
-  //   section_associated = binary_->sections_[sh_link];
-  // }
+  Section* symbol_table = nullptr;
+  if (section.link() > 0 and section.link() < binary_->sections_.size()) {
+    const size_t sh_link = section.link();
+    symbol_table = binary_->sections_[sh_link].get();
+  }
 
   const uint64_t offset_relocations = section.file_offset();
   const uint8_t shift = std::is_same<ELF_T, details::ELF32>::value ? 8 : 32;
@@ -1375,15 +1374,16 @@ ok_error_t Parser::parse_section_relocations(const Section& section) {
     auto reloc = std::make_unique<Relocation>(*rel_hdr);
     reloc->architecture_ = binary_->header_.machine_type();
     reloc->section_      = applies_to;
+    reloc->symbol_table_ = symbol_table;
     if (binary_->header().file_type() == ELF::E_TYPE::ET_REL &&
         binary_->segments().size() == 0) {
       reloc->purpose(RELOCATION_PURPOSES::RELOC_PURPOSE_OBJECT);
     }
 
     const auto idx  = static_cast<uint32_t>(rel_hdr->r_info >> shift);
-    if (idx > 0 && idx < binary_->dynamic_symbols_.size()) {
+    if (idx > 0 && idx < binary_->dynamic_symbols_.size() && (symbol_table == nullptr || symbol_table->type() == LIEF::ELF::ELF_SECTION_TYPES::SHT_DYNSYM)) {
       reloc->symbol_ = binary_->dynamic_symbols_[idx].get();
-    } else if (idx < binary_->static_symbols_.size()) {
+    } else if (idx < binary_->static_symbols_.size() && (symbol_table == nullptr || symbol_table->type() == LIEF::ELF::ELF_SECTION_TYPES::SHT_SYMTAB)) {
       reloc->symbol_ = binary_->static_symbols_[idx].get();
     }
     if (reloc_hash.insert(reloc.get()).second) {

src/ELF/Relocation.cpp

@@ -129,6 +129,14 @@ Section* Relocation::section() {
   return const_cast<Section*>(static_cast<const Relocation*>(this)->section());
 }
 
+const Section* Relocation::symbol_table() const {
+  return symbol_table_;
+}
+
+Section* Relocation::symbol_table() {
+  return const_cast<Section*>(static_cast<const Relocation*>(this)->symbol_table());
+}
+
 bool Relocation::is_rela() const {
   return isRela_;
 }

tests/elf/test_parser.py

@@ -60,3 +60,16 @@ def test_issue_845():
     target = lief.parse(get_sample('ELF/issue_845.elf'))
     assert len(target.segments) > 1
     assert len(target.segments[1].content) == 0
+
+def test_issue_897():
+    """
+    Issue #897 / PR: #898
+    """
+    target = lief.parse(get_sample('ELF/test_897.elf'))
+    rel1 = target.get_relocation(0x1b39)
+    assert rel1.symbol.name == "__init_array_start"
+    assert rel1.symbol_table.name == ".symtab"
+
+    rel2 = target.get_relocation(0x1b50)
+    assert rel2.symbol.name == "__init_array_end"
+    assert rel2.symbol_table.name == ".symtab"