[PATCH] D76081: [Object] object::ELFObjectFile::dynamic_symbol_begin(): skip symbol index 0

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Higuoxing created this revision.
Higuoxing added reviewers: grimar, jhenderson, MaskRay.
Herald added subscribers: llvm-commits, arphaman.
Herald added a project: LLVM.
Higuoxing edited the summary of this revision.

Note: This revision is very similar to D62296 <https://reviews.llvm.org/D62296>.

In D75756 <https://reviews.llvm.org/D75756>, we need `getDynamicSymbolIterators()` to skip first NULL symbol in `.dynsym`. And I believe it might be worth pointing this out in a separate patch to gather you experts' opinions.

I have checked that current code base will not be affected by this change.

  dynamic_symbol_begin()
  |- dynamic_symbol_end(): Ok
  `- getDynamicSymbolIterators()
     |- addDynamicElfSymbols(): llvm/tools/llvm-objdump/llvm-objdump.cpp, Line 934
     |                          Ok, NULL symbol will be omitted by Line 945-947
     |                          StringRef Name = unwrapOrError(Symbol.getName(), Obj->getName());
     |                          if (Name.empty()) continue;
     |- dumpSymbolNameFromObject(): llvm/tools/llvm-nm/llvm-nm.cpp, Line 1192
     |                          There's no test for dumping dynamic debugging symbol. This patch helps improve llvm-nm behavior. (we should add test for this later)
     `- computeSymbolSizes(): llvm/lib/Object/SymbolSize.cpp, Line 52
        |- OProfileJITEventListener::notifyObjectLoaded(): llvm/lib/ExecutionEngine/OProfileJIT/OProfileJITEventListener.cpp, Line 92
        |                                                  Ok, NULL symbol will be omitted by Line 94-95
        |                                                  if (!Sym.getType() || *Sym.getType() != SF_Function) continue;
        |- IntelJITEventListener::notifyObjectLoaded(): llvm/lib/ExecutionEngine/IntelJITEvents/IntelJITEventListener.cpp, Line 98
        |                                               Ok, NULL symbol will be omitted by Line 124-126 (same as previous one)
        |- PerfJITEventListener::notifyObjectLoaded(): llvm/lib/ExecutionEngine/PerfJITEvents/PerfJITEventListener.cpp, Line 244
        |                                              Ok, NULL symbol will be omitted by Line 254-256, (same as previous one)
        |- SymbolizableObjectFile::create(): llvm/lib/DebugInfo/Symbolize/SymbolizableObjectFile.cpp, Line 73
        |                                    Ok, NULL symbol will be omitted by Line 75
        |                                    res->addSymbol()
        |                                    In addSymbol(), Line 167-168
        |                                    if (!Sec || (Obj && Obj->section_end() == *Sec)) return std::error_code();
        |- dumpCXXData(): llvm/tools/llvm-cxxdump/llvm-cxxdump.cpp, Line 189
        |                 Ok, NULL symbol will be omitted by Line 199-202
        |                 object::section_iterator SecI = *SecIOrErr;
        |                 // Skip external symbols.
        |                 if (SecI == Obj->section_end())
        |                   continue;
        `- printLineInfoForInput(): llvm/tools/llvm-rtdyld/llvm-rtdyld.cpp, Line 418
                                    Ok, NULL symbol will be omitted by Line 430-477
                                    if (Type == object::SymbolRef::ST_Function) {
                                      ...
                                    }


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D76081

Files:
  llvm/include/llvm/Object/ELFObjectFile.h


Index: llvm/include/llvm/Object/ELFObjectFile.h
===================================================================
--- llvm/include/llvm/Object/ELFObjectFile.h
+++ llvm/include/llvm/Object/ELFObjectFile.h
@@ -1019,7 +1019,9 @@
 
 template <class ELFT>
 elf_symbol_iterator ELFObjectFile<ELFT>::dynamic_symbol_begin() const {
-  DataRefImpl Sym = toDRI(DotDynSymSec, 0);
+  DataRefImpl Sym =
+      toDRI(DotDynSymSec,
+            DotDynSymSec && DotDynSymSec->sh_size >= sizeof(Elf_Sym) ? 1 : 0);
   return symbol_iterator(SymbolRef(Sym, this));
 }
 


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