Cleanup .gnu.version_r after removing symbol version

src/patchelf.cc

@@ -1709,6 +1709,82 @@ void ElfFile<ElfFileParamNames>::addDebugTag()
     changed = true;
 }
 
+/* Remove any unused dependency symbol versions from .gnu.version_r */
+template<ElfFileParams>
+void ElfFile<ElfFileParamNames>::cleanDependencySymbolVersions()
+{
+    auto shdrVersym = findSectionHeader(".gnu.version");
+    auto shdrVersymR = findSectionHeader(".gnu.version_r");
+
+    auto versyms = reinterpret_cast<Elf_Versym *>(fileContents->data() + rdi(shdrVersym.sh_offset));
+    checkPointer(fileContents, versyms, sizeof(Elf_Versym));
+    size_t count = rdi(shdrVersym.sh_size) / sizeof(Elf_Versym);
+
+    /* Set of versions actually used. */
+    std::set<Elf_Versym> allVersions;
+
+    for (size_t i = 0; i < count; i++) {
+        allVersions.insert(versyms[i]);
+    }
+
+    /* Strings associated with .gnu_version_r section: used for debug only. */
+    Elf_Shdr & shdrVersionRStrings = shdrs.at(rdi(shdrVersymR.sh_link));
+    char * verStrTab = reinterpret_cast<char *>(fileContents->data() + rdi(shdrVersionRStrings.sh_offset));
+
+    auto ver_r = reinterpret_cast<Elf_Verneed *>(fileContents->data() + rdi(shdrVersymR.sh_offset));
+    checkPointer(fileContents, ver_r, sizeof(Elf_Verneed));
+
+    while (true) {
+        auto prev = (Elf_Vernaux *)nullptr;
+        auto vern_aux = reinterpret_cast<Elf_Vernaux *>((char *)ver_r + rdi(ver_r->vn_aux));
+        checkPointer(fileContents, vern_aux, sizeof(Elf_Vernaux));
+
+        char * file = verStrTab + rdi(ver_r->vn_file);
+        for (size_t j = 0; j < ver_r->vn_cnt ; j++) {
+            char * ver_name = verStrTab + rdi(vern_aux->vna_name);
+            // FIXME: add proper check for null-terminated string
+            checkPointer(fileContents, ver_name, sizeof(char));
+
+            auto next = reinterpret_cast<Elf_Vernaux *>((char *)vern_aux + rdi(vern_aux->vna_next));
+            checkPointer(fileContents, next, sizeof(Elf_Vernaux));
+
+            if (!allVersions.count(rdi(vern_aux->vna_other) & ~0x8000)) {
+                debug("Removing version identifier %d %s@%s\n", rdi(vern_aux->vna_other), file, ver_name);
+                /* Symbol version is no longer used, unlink it. */
+                if (!prev) {
+                    auto next_off = (intptr_t)(vern_aux) + rdi(vern_aux->vna_next) - (intptr_t)(ver_r);
+                    wri(ver_r->vn_aux, next_off);
+                } else {
+                    auto next_off = (intptr_t)(vern_aux) + rdi(vern_aux->vna_next) - (intptr_t)(prev);
+                    wri(prev->vna_next, next_off);
+                }
+                wri(ver_r->vn_cnt, rdi(ver_r->vn_cnt) - 1);
+            } else {
+                prev = vern_aux;
+            }
+
+            if (vern_aux == next) {
+                if (j != rdi(ver_r->vn_cnt)) {
+                    debug("Section missing elements! Ended on element %d, expected %d\n", j, rdi(ver_r->vn_cnt));
+                }
+                break;
+            }
+            vern_aux = next;
+        }
+
+        /* If this was the last entry, we're done. */
+        if (!rdi(ver_r->vn_next)) {
+            break;
+        }
+
+        ver_r = reinterpret_cast<Elf_Verneed *>(((char *) ver_r) + rdi(ver_r->vn_next));
+        checkPointer(fileContents, ver_r, sizeof(Elf_Verneed));
+    }
+
+    changed = true;
+    this->rewriteSections();
+}
+
 template<ElfFileParams>
 void ElfFile<ElfFileParamNames>::clearSymbolVersions(const std::set<std::string> & syms)
 {
@@ -1734,6 +1810,10 @@ void ElfFile<ElfFileParamNames>::clearSymbolVersions(const std::set<std::string>
             wri(versyms[i], 1);
         }
     }
+
+    /* Remove entries in the .gnu.versions_r table which are no;-longer required. */
+    cleanDependencySymbolVersions();
+
     changed = true;
     this->rewriteSections();
 }
@@ -1817,9 +1897,9 @@ static void patchElf()
         const std::string & outputFileName2 = outputFileName.empty() ? fileName : outputFileName;
 
         if (getElfType(fileContents).is32Bit)
-            patchElf2(ElfFile<Elf32_Ehdr, Elf32_Phdr, Elf32_Shdr, Elf32_Addr, Elf32_Off, Elf32_Dyn, Elf32_Sym, Elf32_Verneed, Elf32_Versym>(fileContents), fileContents, outputFileName2);
+            patchElf2(ElfFile<Elf32_Ehdr, Elf32_Phdr, Elf32_Shdr, Elf32_Addr, Elf32_Off, Elf32_Dyn, Elf32_Sym, Elf32_Verneed, Elf32_Vernaux, Elf32_Versym>(fileContents), fileContents, outputFileName2);
         else
-            patchElf2(ElfFile<Elf64_Ehdr, Elf64_Phdr, Elf64_Shdr, Elf64_Addr, Elf64_Off, Elf64_Dyn, Elf64_Sym, Elf64_Verneed, Elf64_Versym>(fileContents), fileContents, outputFileName2);
+            patchElf2(ElfFile<Elf64_Ehdr, Elf64_Phdr, Elf64_Shdr, Elf64_Addr, Elf64_Off, Elf64_Dyn, Elf64_Sym, Elf64_Verneed, Elf64_Vernaux, Elf64_Versym>(fileContents), fileContents, outputFileName2);
     }
 }
 

src/patchelf.h

@@ -1,7 +1,7 @@
 using FileContents = std::shared_ptr<std::vector<unsigned char>>;
 
-#define ElfFileParams class Elf_Ehdr, class Elf_Phdr, class Elf_Shdr, class Elf_Addr, class Elf_Off, class Elf_Dyn, class Elf_Sym, class Elf_Verneed, class Elf_Versym
-#define ElfFileParamNames Elf_Ehdr, Elf_Phdr, Elf_Shdr, Elf_Addr, Elf_Off, Elf_Dyn, Elf_Sym, Elf_Verneed, Elf_Versym
+#define ElfFileParams class Elf_Ehdr, class Elf_Phdr, class Elf_Shdr, class Elf_Addr, class Elf_Off, class Elf_Dyn, class Elf_Sym, class Elf_Verneed, class Elf_Vernaux, class Elf_Versym
+#define ElfFileParamNames Elf_Ehdr, Elf_Phdr, Elf_Shdr, Elf_Addr, Elf_Off, Elf_Dyn, Elf_Sym, Elf_Verneed, Elf_Vernaux, Elf_Versym
 
 template<ElfFileParams>
 class ElfFile
@@ -133,6 +133,8 @@ class ElfFile
 
     void addDebugTag();
 
+    void cleanDependencySymbolVersions();
+
     void clearSymbolVersions(const std::set<std::string> & syms);
 
 private:

tests/Makefile.am

@@ -41,7 +41,8 @@ src_TESTS = \
   phdr-corruption.sh \
   replace-needed.sh \
   replace-add-needed.sh \
-  add-debug-tag.sh
+  add-debug-tag.sh \
+  clear-symver.sh
 
 build_TESTS = \
   $(no_rpath_arch_TESTS)

tests/clear-symver.sh

@@ -0,0 +1,33 @@
+#! /bin/sh -e
+SCRATCH=scratch/$(basename $0 .sh)
+
+rm -rf ${SCRATCH}
+mkdir -p ${SCRATCH}
+
+cp main ${SCRATCH}/
+
+SYMBOL_TO_REMOVE=__libc_start_main
+VERSION_TO_REMOVE=GLIBC_2.34a
+
+readelfData=$(readelf -V ${SCRATCH}/main 2>&1)
+
+if [ $(echo "$readelfData" | grep --count "$VERSION_TO_REMOVE") -lt 2 ]; then
+    # We expect this to appear at least twice: once for the symbol entry,
+    # and once for verneed entry.
+    echo "Warning: Couldn't find expected versioned symbol."
+    echo "This is probably because you're either not using glibc, or"
+    echo "${SYMBOL_TO_REMOVE} is no longer at version ${VERSION_TO_REMOVE}"
+    echo "Reporting a pass anyway, as the test result is invalid."
+    exit 0
+fi
+
+../src/patchelf --clear-symbol-version ${SYMBOL_TO_REMOVE} ${SCRATCH}/main
+
+readelfData=$(readelf -V ${SCRATCH}/main 2>&1)
+
+if [ $(echo "$readelfData" | grep --count "$VERSION_TO_REMOVE") -ne 0 ]; then
+    # We expect this to appear at least twice: once for the symbol entry,
+    # and once for verneed entry.
+    echo "The symbol version ${SYMBOL_TO_REMOVE} remained behind!"
+    exit 1
+fi