[ELF] Mark linker defined symbols as .hidden when needed.

[davide]

Summary

I noticed that gold mark these as hidden.
Also, this depends on D9416.

[davide]

While at it I rewrote the test for this feature to use yaml rather than an object file as input.

[ruiu]

LGTM

lld/trunk/lib/ReaderWriter/ELF/ELFFile.h

 /// for adding absolute symbols and undefined symbols
 template <class ELFT> class RuntimeFile : public ELFFile<ELFT> {
 public:
   typedef llvm::object::Elf_Sym_Impl<ELFT> Elf_Sym;
   RuntimeFile(ELFLinkingContext &ctx, StringRef name)
       : ELFFile<ELFT>(name, ctx) {}
 
   /// \brief add a global absolute atom
-  virtual void addAbsoluteAtom(StringRef symbolName);
+  virtual void addAbsoluteAtom(StringRef symbolName, bool isHidden = false);
 
   /// \brief add an undefined atom
   virtual void addUndefinedAtom(StringRef symbolName);
 };
 
 } // end namespace elf
 } // end namespace lld
 
 #endif // LLD_READER_WRITER_ELF_FILE_H

lld/trunk/lib/ReaderWriter/ELF/ELFFile.cpp

bool ELFFile<ELFT>::redirectReferenceUsingUndefAtom(
   // If the source and child are from the same group, we dont need the
   // relocation to go through a undefined symbol.
   if (groupChildSource->second.second == groupChildTarget->second.second)
     return false;
   return true;
 }
 
 template <class ELFT>
-void RuntimeFile<ELFT>::addAbsoluteAtom(StringRef symbolName) {
+void RuntimeFile<ELFT>::addAbsoluteAtom(StringRef symbolName, bool isHidden) {
   assert(!symbolName.empty() && "AbsoluteAtoms must have a name");
   Elf_Sym *sym = new (this->_readerStorage) Elf_Sym;
   sym->st_name = 0;
   sym->st_value = 0;
   sym->st_shndx = llvm::ELF::SHN_ABS;
   sym->setBindingAndType(llvm::ELF::STB_GLOBAL, llvm::ELF::STT_OBJECT);
+  if (isHidden)
+    sym->setVisibility(llvm::ELF::STV_HIDDEN);
+  else
     sym->setVisibility(llvm::ELF::STV_DEFAULT);
   sym->st_size = 0;
   ELFAbsoluteAtom<ELFT> *atom = this->createAbsoluteAtom(symbolName, sym, -1);
   this->addAtom(*atom);
 }
 
 template <class ELFT>
 void RuntimeFile<ELFT>::addUndefinedAtom(StringRef symbolName) {
   assert(!symbolName.empty() && "UndefinedAtoms must have a name");

lld/trunk/lib/ReaderWriter/ELF/ExecutableWriter.h

 template<class ELFT>
 std::unique_ptr<RuntimeFile<ELFT>> ExecutableWriter<ELFT>::createRuntimeFile() {
   auto file = llvm::make_unique<RuntimeFile<ELFT>>(this->_ctx, "C runtime");
   file->addUndefinedAtom(this->_ctx.entrySymbolName());
   file->addAbsoluteAtom("__bss_start");
   file->addAbsoluteAtom("__bss_end");
   file->addAbsoluteAtom("_end");
   file->addAbsoluteAtom("end");
-  file->addAbsoluteAtom("__preinit_array_start");
-  file->addAbsoluteAtom("__preinit_array_end");
-  file->addAbsoluteAtom("__init_array_start");
-  file->addAbsoluteAtom("__init_array_end");
+  file->addAbsoluteAtom("__preinit_array_start", true);
+  file->addAbsoluteAtom("__preinit_array_end", true);
+  file->addAbsoluteAtom("__init_array_start", true);
+  file->addAbsoluteAtom("__init_array_end", true);
   if (this->_ctx.isRelaOutputFormat()) {
     file->addAbsoluteAtom("__rela_iplt_start");
     file->addAbsoluteAtom("__rela_iplt_end");
   } else {
     file->addAbsoluteAtom("__rel_iplt_start");
     file->addAbsoluteAtom("__rel_iplt_end");
   }
-  file->addAbsoluteAtom("__fini_array_start");
-  file->addAbsoluteAtom("__fini_array_end");
+  file->addAbsoluteAtom("__fini_array_start", true);
+  file->addAbsoluteAtom("__fini_array_end", true);
   return file;
 }
 
 /// \brief Hook in lld to add CRuntime file
 template <class ELFT>
 void ExecutableWriter<ELFT>::createImplicitFiles(
     std::vector<std::unique_ptr<File> > &result) {
   OutputELFWriter<ELFT>::createImplicitFiles(result);

lld/trunk/test/elf/X86_64/omagic.test

 OMAGICSECTIONS:    Name: .symtab
 OMAGICSECTIONS:    Type: SHT_SYMTAB (0x2)
 OMAGICSECTIONS:    Flags [ (0x0)
 OMAGICSECTIONS:    ]
 OMAGICSECTIONS:    Address: 0x0
 OMAGICSECTIONS:    Offset: 0x1E8
 OMAGICSECTIONS:    Size: 504
 OMAGICSECTIONS:    Link: 13
-OMAGICSECTIONS:    Info: 2
+OMAGICSECTIONS:    Info: 8
 OMAGICSECTIONS:    AddressAlignment: 8
 OMAGICSECTIONS:    EntrySize: 24
 OMAGICSECTIONS:  }
 OMAGICSECTIONS:  Section {
 OMAGICSECTIONS:    Name: .strtab
 OMAGICSECTIONS:    Type: SHT_STRTAB (0x3)
 OMAGICSECTIONS:    Flags [ (0x0)
 OMAGICSECTIONS:    ]

lld/trunk/test/elf/init_array.test

-RUN: lld -flavor gnu -target x86_64-linux -o %t %p/Inputs/init_array.x86-64 \
-RUN:  -e __init_array_start
-RUN: llvm-objdump -t -section-headers %t | FileCheck %s
+#RUN: yaml2obj -format=elf %s -o=%t.o
+#RUN: lld -flavor gnu -target x86_64-linux %t.o -o %t1 -e=main
+#RUN: llvm-objdump -t -section-headers %t | FileCheck %s
 
-CHECK: .init_array {{[0-9]+}} [[ADDR:[0-9]+]]
-CHECK: [[ADDR]] g *ABS* {{[0-9]+}} __init_array_start
+#CHECK: .init_array {{[0-9]+}} [[ADDR:[0-9]+]]
+#CHECK: [[ADDR]] l *ABS* {{[0-9]+}} .hidden __init_array_start
+
+---
+FileHeader:
+  Class:           ELFCLASS64
+  Data:            ELFDATA2LSB
+  OSABI:           ELFOSABI_FREEBSD
+  Type:            ET_REL
+  Machine:         EM_X86_64
+Sections:
+  - Name:            .text
+    Type:            SHT_PROGBITS
+    Flags:           [ SHF_ALLOC, SHF_EXECINSTR ]
+    AddressAlign:    0x0000000000000010
+    Content:         554889E5B800000000C745FC000000008B0C2500000000894DF85DC3
+  - Name:            .rela.text
+    Type:            SHT_RELA
+    Link:            .symtab
+    AddressAlign:    0x0000000000000008
+    Info:            .text
+    Relocations:
+      - Offset:          0x0000000000000013
+        Symbol:          a
+        Type:            R_X86_64_32S
+  - Name:            .data
+    Type:            SHT_PROGBITS
+    Flags:           [ SHF_WRITE, SHF_ALLOC ]
+    AddressAlign:    0x0000000000000004
+    Content:         '05000000'
+  - Name:            .bss
+    Type:            SHT_NOBITS
+    Flags:           [ SHF_WRITE, SHF_ALLOC ]
+    AddressAlign:    0x0000000000000004
+    Content:         ''
+  - Name:            .comment
+    Type:            SHT_PROGBITS
+    Flags:           [ SHF_MERGE, SHF_STRINGS ]
+    AddressAlign:    0x0000000000000001
+    Content:         004672656542534420636C616E672076657273696F6E20332E342E312028746167732F52454C454153455F33342F646F74312D66696E616C203230383033322920323031343035313200
+  - Name:            .note.GNU-stack
+    Type:            SHT_PROGBITS
+    AddressAlign:    0x0000000000000001
+    Content:         ''
+  - Name:            .eh_frame
+    Type:            SHT_PROGBITS
+    Flags:           [ SHF_ALLOC ]
+    AddressAlign:    0x0000000000000008
+    Content:         1400000000000000017A5200017810011B0C0708900100001C0000001C000000000000001C00000000410E108602430D0600000000000000
+  - Name:            .rela.eh_frame
+    Type:            SHT_RELA
+    Link:            .symtab
+    AddressAlign:    0x0000000000000008
+    Info:            .eh_frame
+    Relocations:
+      - Offset:          0x0000000000000020
+        Symbol:          .text
+        Type:            R_X86_64_PC32
+Symbols:
+  Local:
+    - Name:            .text
+      Type:            STT_SECTION
+      Section:         .text
+    - Name:            .data
+      Type:            STT_SECTION
+      Section:         .data
+    - Name:            .bss
+      Type:            STT_SECTION
+      Section:         .bss
+    - Name:            .comment
+      Type:            STT_SECTION
+      Section:         .comment
+    - Name:            .note.GNU-stack
+      Type:            STT_SECTION
+      Section:         .note.GNU-stack
+    - Name:            .eh_frame
+      Type:            STT_SECTION
+      Section:         .eh_frame
+  Global:
+    - Name:            a
+      Type:            STT_OBJECT
+      Section:         .data
+      Size:            0x0000000000000004
+    - Name:            main
+      Type:            STT_FUNC
+      Section:         .text
+      Size:            0x000000000000001C
+...