3 files changed, 78 insertions(+), 0 deletions(-)

M patchelf.1
M src/patchelf.cc
M src/patchelf.h

@@ 88,6 88,11 @@ option can be given multiple times.
 .IP --print-needed
 Prints all DT_NEEDED entries of the executable.
 
+.IP "--replace-symbol SYMBOL_ORIG SYMBOL_NEW"
+Replaces the name of a symbol with another one (.dynsym). The new symbol will
+not have a version associated with it.
+This option can be given multiple times.
+
 .IP "--no-default-lib"
 Marks the object so that the search for dependencies of this object will ignore any
 default library search paths.

@@ 1638,6 1638,69 @@ void ElfFile<ElfFileParamNames>::printNeededLibs() // const
 
 
 template<ElfFileParams>
+void ElfFile<ElfFileParamNames>::replaceSymbols(const std::map<std::string, std::string> & syms)
+{
+    if (syms.empty()) return;
+
+    auto shdrDynStr = findSectionHeader(".dynstr");
+    auto shdrDynSym = findSectionHeader(".dynsym");
+    auto shdrVersion = tryFindSectionHeader(".gnu.version");
+    char * strTab = (char *) fileContents->data() + rdi(shdrDynStr.sh_offset);
+
+    auto symStart = (Elf_Sym *)(fileContents->data() + rdi(shdrDynSym.sh_offset));
+    auto symCount = rdi(shdrDynSym.sh_size) / rdi(shdrDynSym.sh_entsize);
+    auto version = shdrVersion
+        ? (Elf_Versym *) (fileContents->data() + rdi(shdrVersion->get().sh_offset))
+        : nullptr;
+
+    unsigned int dynStrAddedBytes = 0;
+    std::unordered_map<std::string, Elf_Off> addedStrings;
+
+    for ( size_t symNum = 0; symNum < symCount; symNum++ ) {
+        auto sym = symStart + symNum;
+        char * name = strTab + rdi(sym->st_name);
+        auto i = syms.find(name);
+        if (i != syms.end() && name != i->second) {
+            auto replacement = i->second;
+
+            debug("replacing .dynsym entry '%s' with '%s'\n", name, replacement.c_str());
+
+            if (version) {
+                debug("setting version of symbol %d from %d to %d\n", symNum, version[symNum], VER_NDX_GLOBAL);
+                wri(version[symNum], VER_NDX_GLOBAL);
+            }
+
+            auto a = addedStrings.find(replacement);
+            // the same replacement string has already been added, reuse it
+            if (a != addedStrings.end()) {
+                wri(sym->st_name, a->second);
+                continue;
+            }
+
+            // technically, the string referred by d_val could be used otherwise, too (although unlikely)
+            // we'll therefore add a new string
+            debug("resizing .dynstr ...\n");
+
+            // relative location of the new string
+            Elf_Off strOffset = rdi(shdrDynStr.sh_size) + dynStrAddedBytes;
+            std::string & newDynStr = replaceSection(".dynstr",
+                strOffset + replacement.size() + 1);
+            setSubstr(newDynStr, strOffset, replacement + '\0');
+
+            wri(sym->st_name, strOffset);
+            addedStrings[replacement] = strOffset;
+
+            dynStrAddedBytes += replacement.size() + 1;
+
+            changed = true;
+        }
+    }
+
+    this->rewriteSections();
+}
+
+
+template<ElfFileParams>
 void ElfFile<ElfFileParamNames>::noDefaultLib()
 {
     auto shdrDynamic = findSectionHeader(".dynamic");


@@ 1754,6 1817,7 @@ static std::string newRPath;
 static std::set<std::string> neededLibsToRemove;
 static std::map<std::string, std::string> neededLibsToReplace;
 static std::set<std::string> neededLibsToAdd;
+static std::map<std::string, std::string> symbolsToReplace;
 static std::set<std::string> symbolsToClearVersion;
 static bool printNeeded = false;
 static bool noDefaultLib = false;


@@ 1790,6 1854,7 @@ static void patchElf2(ElfFile && elfFile, const FileContents & fileContents, con
     elfFile.removeNeeded(neededLibsToRemove);
     elfFile.replaceNeeded(neededLibsToReplace);
     elfFile.addNeeded(neededLibsToAdd);
+    elfFile.replaceSymbols(symbolsToReplace);
     elfFile.clearSymbolVersions(symbolsToClearVersion);
 
     if (noDefaultLib)


@@ 1852,6 1917,7 @@ void showHelp(const std::string & progName)
   [--remove-needed LIBRARY]\n\
   [--replace-needed LIBRARY NEW_LIBRARY]\n\
   [--print-needed]\n\
+  [--replace-symbol SYMBOL OLD_SYMBOL]\n\
   [--no-default-lib]\n\
   [--no-sort]\t\tDo not sort program+section headers; useful for debugging patchelf.\n\
   [--clear-symbol-version SYMBOL]\n\


@@ 1952,6 2018,11 @@ int mainWrapped(int argc, char * * argv)
             neededLibsToReplace[ argv[i+1] ] = argv[i+2];
             i += 2;
         }
+        else if (arg == "--replace-symbol") {
+            if (i+2 >= argc) error("missing argument(s)");
+            symbolsToReplace[ argv[i+1] ] = argv[i+2];
+            i += 2;
+        }
         else if (arg == "--clear-symbol-version") {
             if (++i == argc) error("missing argument");
             symbolsToClearVersion.insert(resolveArgument(argv[i]));

@@ 127,6 127,8 @@ public:
 
     void replaceNeeded(const std::map<std::string, std::string> & libs);
 
+    void replaceSymbols(const std::map<std::string, std::string> & syms);
+
     void printNeededLibs() /* should be const */;
 
     void noDefaultLib();