[llvm-obcopy][MachO] Add --prefix-symbols support

[keith]

I must be missing some cases here, and also need some tests

[jhenderson]

Take a look at the equivalent ELF test case, to see what cases there are. I imagine the logic is going to be pretty similar.

[keith]

In D113735#3126545, @jhenderson wrote:

Take a look at the equivalent ELF test case, to see what cases there are. I imagine the logic is going to be pretty similar.

I did model this after that, I was surprised at how minimal the implementation seemed to be https://github.com/llvm/llvm-project/blob/aab1810006a6788e32ee04e7d40d0b2474754aa2/llvm/tools/llvm-objcopy/ELF/ELFObjcopy.cpp#L282-L283

[jhenderson]

In D113735#3128538, @keith wrote:

In D113735#3126545, @jhenderson wrote:

Take a look at the equivalent ELF test case, to see what cases there are. I imagine the logic is going to be pretty similar.

I did model this after that, I was surprised at how minimal the implementation seemed to be https://github.com/llvm/llvm-project/blob/aab1810006a6788e32ee04e7d40d0b2474754aa2/llvm/tools/llvm-objcopy/ELF/ELFObjcopy.cpp#L282-L283

Sorry, I meant that comment as a suggestion for how to test it - the existing ELF tests should provide a reasonable framework for how to test this in Mach-O, I imagine.

The implementation is simple because the symbol table is rewritten from scratch by llvm-objcopy, so all that has to be updated is the internal symbol's name.

[keith]

In D113735#3130625, @jhenderson wrote:

In D113735#3128538, @keith wrote:

In D113735#3126545, @jhenderson wrote:

Take a look at the equivalent ELF test case, to see what cases there are. I imagine the logic is going to be pretty similar.

I did model this after that, I was surprised at how minimal the implementation seemed to be https://github.com/llvm/llvm-project/blob/aab1810006a6788e32ee04e7d40d0b2474754aa2/llvm/tools/llvm-objcopy/ELF/ELFObjcopy.cpp#L282-L283

Sorry, I meant that comment as a suggestion for how to test it - the existing ELF tests should provide a reasonable framework for how to test this in Mach-O, I imagine.

The implementation is simple because the symbol table is rewritten from scratch by llvm-objcopy, so all that has to be updated is the internal symbol's name.

Ah got it thanks. Given this conversation https://groups.google.com/g/llvm-dev/c/A26kbQhZ9Po I'm going to drop this for now since this doesn't seem to do what I hoped. For others --redefine-syms may solve your use case instead.

llvm/tools/llvm-objcopy/ConfigManager.cpp

if (!Common.SplitDWO.empty() || !Common.SymbolsPrefix.empty() ||
     return createStringError(llvm::errc::invalid_argument,
                              "option not supported by llvm-objcopy for COFF");
   }
 
   return COFF;
 }
 
 Expected<const MachOConfig &> ConfigManager::getMachOConfig() const {
-  if (!Common.SplitDWO.empty() || !Common.SymbolsPrefix.empty() ||
-      !Common.AllocSectionsPrefix.empty() || !Common.KeepSection.empty() ||
-      !Common.SymbolsToGlobalize.empty() || !Common.SymbolsToKeep.empty() ||
-      !Common.SymbolsToLocalize.empty() || !Common.SymbolsToWeaken.empty() ||
-      !Common.SymbolsToKeepGlobal.empty() || !Common.SectionsToRename.empty() ||
+  if (!Common.SplitDWO.empty() || !Common.AllocSectionsPrefix.empty() ||
+      !Common.KeepSection.empty() || !Common.SymbolsToGlobalize.empty() ||
+      !Common.SymbolsToKeep.empty() || !Common.SymbolsToLocalize.empty() ||
+      !Common.SymbolsToWeaken.empty() || !Common.SymbolsToKeepGlobal.empty() ||
+      !Common.SectionsToRename.empty() ||
       !Common.UnneededSymbolsToRemove.empty() ||
       !Common.SetSectionAlignment.empty() || !Common.SetSectionFlags.empty() ||
       Common.ExtractDWO || Common.PreserveDates || Common.StripAllGNU ||
       Common.StripDWO || Common.StripNonAlloc || Common.StripSections ||
       Common.Weaken || Common.DecompressDebugSections || Common.StripUnneeded ||
       Common.DiscardMode == DiscardType::Locals ||
       !Common.SymbolsToAdd.empty()) {
     return createStringError(llvm::errc::invalid_argument,

llvm/tools/llvm-objcopy/MachO/MachOObjcopy.cpp

 
 static void updateAndRemoveSymbols(const CommonConfig &Config,
                                    const MachOConfig &MachOConfig,
                                    Object &Obj) {
   for (SymbolEntry &Sym : Obj.SymTable) {
     auto I = Config.SymbolsToRename.find(Sym.Name);
     if (I != Config.SymbolsToRename.end())
       Sym.Name = std::string(I->getValue());
+
+    if (!Config.SymbolsPrefix.empty() && !Sym.isUndefinedSymbol())
+      Sym.Name = (Config.SymbolsPrefix + Sym.Name).str();
   }
 
   auto RemovePred = [Config, MachOConfig,
                      &Obj](const std::unique_ptr<SymbolEntry> &N) {
     if (N->Referenced)
       return false;
     if (MachOConfig.KeepUndefined && N->isUndefinedSymbol())
       return false;