This patch improves the MCJIT runtime dynamic loader by adding new handling

of zero-initialized sections, virtual sections and common symbols
and preventing the loading of sections which are not required for
execution such as debug information.

Patch by Andy Kaylor!



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@154610 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/Object/COFF.h

@@ -126,6 +126,10 @@ protected:
   virtual error_code isSectionText(DataRefImpl Sec, bool &Res) const;
   virtual error_code isSectionData(DataRefImpl Sec, bool &Res) const;
   virtual error_code isSectionBSS(DataRefImpl Sec, bool &Res) const;
+  virtual error_code isSectionVirtual(DataRefImpl Sec, bool &Res) const;
+  virtual error_code isSectionZeroInit(DataRefImpl Sec, bool &Res) const;
+  virtual error_code isSectionRequiredForExecution(DataRefImpl Sec,
+                                                   bool &Res) const;
   virtual error_code sectionContainsSymbol(DataRefImpl Sec, DataRefImpl Symb,
                                            bool &Result) const;
   virtual relocation_iterator getSectionRelBegin(DataRefImpl Sec) const;

include/llvm/Object/ELF.h

@@ -33,6 +33,15 @@
 namespace llvm {
 namespace object {
 
+// Subclasses of ELFObjectFile may need this for template instantiation
+inline std::pair<unsigned char, unsigned char>
+getElfArchType(MemoryBuffer *Object) {
+  if (Object->getBufferSize() < ELF::EI_NIDENT)
+    return std::make_pair((uint8_t)ELF::ELFCLASSNONE,(uint8_t)ELF::ELFDATANONE);
+  return std::make_pair( (uint8_t)Object->getBufferStart()[ELF::EI_CLASS]
+                        , (uint8_t)Object->getBufferStart()[ELF::EI_DATA]);
+}
+
 // Templates to choose Elf_Addr and Elf_Off depending on is64Bits.
 template<support::endianness target_endianness>
 struct ELFDataTypeTypedefHelperCommon {
@@ -540,6 +549,10 @@ protected:
   virtual error_code isSectionText(DataRefImpl Sec, bool &Res) const;
   virtual error_code isSectionData(DataRefImpl Sec, bool &Res) const;
   virtual error_code isSectionBSS(DataRefImpl Sec, bool &Res) const;
+  virtual error_code isSectionRequiredForExecution(DataRefImpl Sec,
+                                                   bool &Res) const;
+  virtual error_code isSectionVirtual(DataRefImpl Sec, bool &Res) const;
+  virtual error_code isSectionZeroInit(DataRefImpl Sec, bool &Res) const;
   virtual error_code sectionContainsSymbol(DataRefImpl Sec, DataRefImpl Symb,
                                            bool &Result) const;
   virtual relocation_iterator getSectionRelBegin(DataRefImpl Sec) const;
@@ -1092,6 +1105,43 @@ error_code ELFObjectFile<target_endianness, is64Bits>
   return object_error::success;
 }
 
+template<support::endianness target_endianness, bool is64Bits>
+error_code ELFObjectFile<target_endianness, is64Bits>
+                        ::isSectionRequiredForExecution(DataRefImpl Sec,
+                                                        bool &Result) const {
+  const Elf_Shdr *sec = reinterpret_cast<const Elf_Shdr *>(Sec.p);
+  if (sec->sh_flags & ELF::SHF_ALLOC)
+    Result = true;
+  else
+    Result = false;
+  return object_error::success;
+}
+
+template<support::endianness target_endianness, bool is64Bits>
+error_code ELFObjectFile<target_endianness, is64Bits>
+                        ::isSectionVirtual(DataRefImpl Sec,
+                                           bool &Result) const {
+  const Elf_Shdr *sec = reinterpret_cast<const Elf_Shdr *>(Sec.p);
+  if (sec->sh_type == ELF::SHT_NOBITS)
+    Result = true;
+  else
+    Result = false;
+  return object_error::success;
+}
+
+template<support::endianness target_endianness, bool is64Bits>
+error_code ELFObjectFile<target_endianness, is64Bits>::isSectionZeroInit(DataRefImpl Sec,
+                                            bool &Result) const {
+  const Elf_Shdr *sec = reinterpret_cast<const Elf_Shdr *>(Sec.p);
+  // For ELF, all zero-init sections are virtual (that is, they occupy no space
+  //   in the object image) and vice versa.
+  if (sec->sh_flags & ELF::SHT_NOBITS)
+    Result = true;
+  else
+    Result = false;
+  return object_error::success;
+}
+
 template<support::endianness target_endianness, bool is64Bits>
 error_code ELFObjectFile<target_endianness, is64Bits>
                           ::sectionContainsSymbol(DataRefImpl Sec,

include/llvm/Object/MachO.h

@@ -72,6 +72,10 @@ protected:
   virtual error_code isSectionText(DataRefImpl Sec, bool &Res) const;
   virtual error_code isSectionData(DataRefImpl Sec, bool &Res) const;
   virtual error_code isSectionBSS(DataRefImpl Sec, bool &Res) const;
+  virtual error_code isSectionRequiredForExecution(DataRefImpl Sec,
+                                                   bool &Res) const;
+  virtual error_code isSectionVirtual(DataRefImpl Sec, bool &Res) const;
+  virtual error_code isSectionZeroInit(DataRefImpl Sec, bool &Res) const;
   virtual error_code sectionContainsSymbol(DataRefImpl DRI, DataRefImpl S,
                                            bool &Result) const;
   virtual relocation_iterator getSectionRelBegin(DataRefImpl Sec) const;

include/llvm/Object/ObjectFile.h

@@ -158,11 +158,16 @@ public:
   error_code isText(bool &Result) const;
   error_code isData(bool &Result) const;
   error_code isBSS(bool &Result) const;
+  error_code isRequiredForExecution(bool &Result) const;
+  error_code isVirtual(bool &Result) const;
+  error_code isZeroInit(bool &Result) const;
 
   error_code containsSymbol(SymbolRef S, bool &Result) const;
 
   relocation_iterator begin_relocations() const;
   relocation_iterator end_relocations() const;
+
+  DataRefImpl getRawDataRefImpl() const;
 };
 typedef content_iterator<SectionRef> section_iterator;
 
@@ -217,6 +222,9 @@ public:
   /// Get symbol flags (bitwise OR of SymbolRef::Flags)
   error_code getFlags(uint32_t &Result) const;
 
+  /// @brief Return true for common symbols such as uninitialized globals
+  error_code isCommon(bool &Result) const;
+
   /// @brief Get section this symbol is defined in reference to. Result is
   /// end_sections() if it is undefined or is an absolute symbol.
   error_code getSection(section_iterator &Result) const;
@@ -299,6 +307,11 @@ protected:
   virtual error_code isSectionText(DataRefImpl Sec, bool &Res) const = 0;
   virtual error_code isSectionData(DataRefImpl Sec, bool &Res) const = 0;
   virtual error_code isSectionBSS(DataRefImpl Sec, bool &Res) const = 0;
+  virtual error_code isSectionRequiredForExecution(DataRefImpl Sec,
+                                                   bool &Res) const = 0;
+  // A section is 'virtual' if its contents aren't present in the object image.
+  virtual error_code isSectionVirtual(DataRefImpl Sec, bool &Res) const = 0;
+  virtual error_code isSectionZeroInit(DataRefImpl Sec, bool &Res) const = 0;
   virtual error_code sectionContainsSymbol(DataRefImpl Sec, DataRefImpl Symb,
                                            bool &Result) const = 0;
   virtual relocation_iterator getSectionRelBegin(DataRefImpl Sec) const = 0;
@@ -481,6 +494,18 @@ inline error_code SectionRef::isBSS(bool &Result) const {
   return OwningObject->isSectionBSS(SectionPimpl, Result);
 }
 
+inline error_code SectionRef::isRequiredForExecution(bool &Result) const {
+  return OwningObject->isSectionRequiredForExecution(SectionPimpl, Result);
+}
+
+inline error_code SectionRef::isVirtual(bool &Result) const {
+  return OwningObject->isSectionVirtual(SectionPimpl, Result);
+}
+
+inline error_code SectionRef::isZeroInit(bool &Result) const {
+  return OwningObject->isSectionZeroInit(SectionPimpl, Result);
+}
+
 inline error_code SectionRef::containsSymbol(SymbolRef S, bool &Result) const {
   return OwningObject->sectionContainsSymbol(SectionPimpl, S.SymbolPimpl,
                                              Result);
@@ -494,6 +519,9 @@ inline relocation_iterator SectionRef::end_relocations() const {
   return OwningObject->getSectionRelEnd(SectionPimpl);
 }
 
+inline DataRefImpl SectionRef::getRawDataRefImpl() const {
+  return SectionPimpl;
+}
 
 /// RelocationRef
 inline RelocationRef::RelocationRef(DataRefImpl RelocationP,