Start symbol.

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Summary

Start symbol.

[ruiu]

• Simplify

ELF/Config.h

struct Configuration {
   bool ZRelro;
   DiscardPolicy Discard;
   StripPolicy Strip = StripPolicy::None;
   UnresolvedPolicy UnresolvedSymbols;
   BuildIdKind BuildId = BuildIdKind::None;
   ELFKind EKind = ELFNoneKind;
   uint16_t DefaultSymbolVersion = llvm::ELF::VER_NDX_GLOBAL;
   uint16_t EMachine = llvm::ELF::EM_NONE;
-  uint64_t EntryAddr = -1;
+  uint64_t EntryAddr = 0;
   uint64_t ImageBase;
   uint64_t ZStackSize = -1;
   unsigned LtoJobs;
   unsigned LtoO;
   unsigned Optimize;
 };
 
 // The only instance of Configuration struct.
 extern Configuration *Config;
 
 } // namespace elf
 } // namespace lld
 
 #endif

ELF/Driver.cpp

template <class ELFT> void LinkerDriver::link(opt::InputArgList &Args) {
   Target = TI.get();
   LinkerScript<ELFT> LS;
   Script<ELFT>::X = &LS;
 
   Config->Rela = ELFT::Is64Bits || Config->EMachine == EM_X86_64;
   Config->Mips64EL =
       (Config->EMachine == EM_MIPS && Config->EKind == ELF64LEKind);
 
-  // Add entry symbol. Note that AMDGPU binaries have no entry points.
-  if (Config->Entry.empty() && !Config->Shared && !Config->Relocatable &&
-      Config->EMachine != EM_AMDGPU)
-    Config->Entry = (Config->EMachine == EM_MIPS) ? "__start" : "_start";
-
   // Default output filename is "a.out" by the Unix tradition.
   if (Config->OutputFile.empty())
     Config->OutputFile = "a.out";
 
   // Handle --trace-symbol.
   for (auto *Arg : Args.filtered(OPT_trace_symbol))
     Symtab.trace(Arg->getValue());
 
-  // Set either EntryAddr (if S is a number) or EntrySym (otherwise).
-  if (!Config->Entry.empty()) {
-    StringRef S = Config->Entry;
-    if (S.getAsInteger(0, Config->EntryAddr))
-      Config->EntrySym = Symtab.addUndefined(S);
-  }
-
   // Initialize Config->ImageBase.
   if (auto *Arg = Args.getLastArg(OPT_image_base)) {
     StringRef S = Arg->getValue();
     if (S.getAsInteger(0, Config->ImageBase))
       error(Arg->getSpelling() + ": number expected, but got " + S);
     else if ((Config->ImageBase % Target->PageSize) != 0)
       warning(Arg->getSpelling() + ": address isn't multiple of page size");
   } else {
     Config->ImageBase = Config->Pic ? 0 : Target->DefaultImageBase;
   }
 
+  // Add all files to the symbol table. After this, the symbol table
+  // contains all known names except a few linker-synthesized symbols.
   for (std::unique_ptr<InputFile> &F : Files)
     Symtab.addFile(std::move(F));
+
+  // Add the start symbol.
+  // It initializes either Config->Entry or Config->EntryAddr.
+  // Note that AMDGPU binaries have no entries.
+  if (!Config->Entry.empty()) {
+    // It is either "-e <addr>" or "-e <symbol>".
+    if (Config->Entry.getAsInteger(0, Config->EntryAddr))
+      Config->EntrySym = Symtab.addUndefined(Config->Entry);
+  } else if (!Config->Shared && !Config->Relocatable &&
+             Config->EMachine != EM_AMDGPU) {
+    // -e was not specified. Use the default start symbol name
+    // if it is resolvable.
+    StringRef Start = (Config->EMachine == EM_MIPS) ? "__start" : "_start";
+    if (Symtab.find(Start))
+      Config->EntrySym = Symtab.addUndefined(Start);
+  }
+
   if (HasError)
     return; // There were duplicate symbols or incompatible files
 
   Symtab.scanUndefinedFlags();
   Symtab.scanShlibUndefined();
   Symtab.scanDynamicList();
   Symtab.scanVersionScript();
 

ELF/Writer.cpp

if (H.p_type == PT_TLS) {
         H.p_memsz = alignTo(H.p_memsz, H.p_align);
     }
   }
 }
 
 template <class ELFT> static typename ELFT::uint getEntryAddr() {
   if (Symbol *S = Config->EntrySym)
     return S->body()->getVA<ELFT>();
-  if (Config->EntryAddr != uint64_t(-1))
-    return Config->EntryAddr;
-  return 0;
 }
 
 template <class ELFT> static uint8_t getELFEncoding() {
   if (ELFT::TargetEndianness == llvm::support::little)
     return ELFDATA2LSB;
   return ELFDATA2MSB;
 }