commit b36fbbc3ec9fe0e1636c16d38083c65aefbafa7e
author Saleem Abdulrasool <compnerd@compnerd.org> Tue Jan 30 16:29:29 2018 +0000
committer Saleem Abdulrasool <compnerd@compnerd.org> Tue Jan 30 16:29:29 2018 +0000
tree e4a489e2da9b07654a99ce57df8dacb7456aef50
parent f1d01645a76285e53dff50feca1a5791685d946f

CodeGen: support an extension to pass linker options on ELF

Introduce an extension to support passing linker options to the linker.
These would be ignored by older linkers, but newer linkers which support
this feature would be able to process the linker.

Emit a special discarded section `.linker-option`.  The content of this
section is a pair of strings (key, value).  The key is a type identifier for
the parameter.  This allows for an argument free parameter that will be
processed by the linker with the value being the parameter.  As an example,
`lib` identifies a library to be linked against, traditionally the `-l`
argument for Unix-based linkers with the parameter being the library name.

Thanks to James Henderson, Cary Coutant, Rafael Espinolda, Sean Silva
for the valuable discussion on the design of this feature.

llvm-svn: 323783

llvm/tools/llvm-readobj/ELFDumper.cpp

diff --git a/llvm/tools/llvm-readobj/ELFDumper.cpp b/llvm/tools/llvm-readobj/ELFDumper.cpp
index dfc5560..dd81c0b 100644
--- a/llvm/tools/llvm-readobj/ELFDumper.cpp
+++ b/llvm/tools/llvm-readobj/ELFDumper.cpp
@@ -164,6 +164,8 @@
 
   void printNotes() override;
 
+  void printELFLinkerOptions() override;
+
 private:
   std::unique_ptr<DumpStyle<ELFT>> ELFDumperStyle;
 
@@ -316,6 +318,7 @@
   virtual void printProgramHeaders(const ELFFile<ELFT> *Obj) = 0;
   virtual void printHashHistogram(const ELFFile<ELFT> *Obj) = 0;
   virtual void printNotes(const ELFFile<ELFT> *Obj) = 0;
+  virtual void printELFLinkerOptions(const ELFFile<ELFT> *Obj) = 0;
   virtual void printMipsGOT(const MipsGOTParser<ELFT> &Parser) = 0;
   virtual void printMipsPLT(const MipsGOTParser<ELFT> &Parser) = 0;
   const ELFDumper<ELFT> *dumper() const { return Dumper; }
@@ -345,6 +348,7 @@
   void printProgramHeaders(const ELFO *Obj) override;
   void printHashHistogram(const ELFFile<ELFT> *Obj) override;
   void printNotes(const ELFFile<ELFT> *Obj) override;
+  void printELFLinkerOptions(const ELFFile<ELFT> *Obj) override;
   void printMipsGOT(const MipsGOTParser<ELFT> &Parser) override;
   void printMipsPLT(const MipsGOTParser<ELFT> &Parser) override;
 
@@ -405,6 +409,7 @@
   void printProgramHeaders(const ELFO *Obj) override;
   void printHashHistogram(const ELFFile<ELFT> *Obj) override;
   void printNotes(const ELFFile<ELFT> *Obj) override;
+  void printELFLinkerOptions(const ELFFile<ELFT> *Obj) override;
   void printMipsGOT(const MipsGOTParser<ELFT> &Parser) override;
   void printMipsPLT(const MipsGOTParser<ELFT> &Parser) override;
 
@@ -1501,6 +1506,10 @@
   ELFDumperStyle->printNotes(Obj);
 }
 
+template <class ELFT> void ELFDumper<ELFT>::printELFLinkerOptions() {
+  ELFDumperStyle->printELFLinkerOptions(Obj);
+}
+
 #define LLVM_READOBJ_TYPE_CASE(name) \
   case DT_##name: return #name
 
@@ -2694,6 +2703,8 @@
     return "SYMTAB SECTION INDICES";
   case SHT_LLVM_ODRTAB:
     return "LLVM_ODRTAB";
+  case SHT_LLVM_LINKER_OPTIONS:
+    return "LLVM_LINKER_OPTIONS";
   // FIXME: Parse processor specific GNU attributes
   case SHT_GNU_ATTRIBUTES:
     return "ATTRIBUTES";
@@ -3555,6 +3566,11 @@
 }
 
 template <class ELFT>
+void GNUStyle<ELFT>::printELFLinkerOptions(const ELFFile<ELFT> *Obj) {
+  OS << "printELFLinkerOptions not implemented!\n";
+}
+
+template <class ELFT>
 void GNUStyle<ELFT>::printMipsGOT(const MipsGOTParser<ELFT> &Parser) {
   size_t Bias = ELFT::Is64Bits ? 8 : 0;
   auto PrintEntry = [&](const Elf_Addr *E, StringRef Purpose) {
@@ -4063,6 +4079,27 @@
 }
 
 template <class ELFT>
+void LLVMStyle<ELFT>::printELFLinkerOptions(const ELFFile<ELFT> *Obj) {
+  ListScope L(W, "LinkerOptions");
+
+  for (const Elf_Shdr &Shdr : unwrapOrError(Obj->sections())) {
+    if (Shdr.sh_type != ELF::SHT_LLVM_LINKER_OPTIONS)
+      continue;
+
+    ArrayRef<uint8_t> Contents = unwrapOrError(Obj->getSectionContents(&Shdr));
+    for (const uint8_t *P = Contents.begin(), *E = Contents.end(); P < E; ) {
+      StringRef Key = StringRef(reinterpret_cast<const char *>(P));
+      StringRef Value =
+          StringRef(reinterpret_cast<const char *>(P) + Key.size() + 1);
+
+      W.printString(Key, Value);
+
+      P = P + Key.size() + Value.size() + 2;
+    }
+  }
+}
+
+template <class ELFT>
 void LLVMStyle<ELFT>::printMipsGOT(const MipsGOTParser<ELFT> &Parser) {
   auto PrintEntry = [&](const Elf_Addr *E) {
     W.printHex("Address", Parser.getGotAddress(E));