From 3b5a9be6b95f33f04244e6df26905578a9081d82 Mon Sep 17 00:00:00 2001
From: Stefano Sanfilippo <a.little.coder@gmail.com>
Date: Sun, 16 Sep 2018 14:09:18 +0200
Subject: [PATCH] Emit position independent code by default, to enable support
 for shared libraries and PIE.

PIE is now default on Ubuntu LTS. PIC can be disabled with --no-pic.
---
 src/asmgen.cpp  | 4 ++--
 src/asmgen.h    | 2 +-
 src/main.cpp    | 3 ++-
 src/options.cpp | 5 +++++
 src/options.h   | 4 +++-
 5 files changed, 13 insertions(+), 5 deletions(-)

diff --git a/src/asmgen.cpp b/src/asmgen.cpp
index 8ec6742..7b4a2a2 100644
--- a/src/asmgen.cpp
+++ b/src/asmgen.cpp
@@ -32,7 +32,7 @@ void registerTargets() {
 }
 
 llvm::TargetMachine* getTargetMachine(const std::string& triple, const std::string& cpu,
-                                      const std::string& features) {
+                                      const std::string& features, bool emit_pic) {
   std::string error;
   auto target = llvm::TargetRegistry::lookupTarget(triple, error);
 
@@ -42,7 +42,7 @@ llvm::TargetMachine* getTargetMachine(const std::string& triple, const std::stri
   }
 
   llvm::TargetOptions opt;
-  auto reloc_model = llvm::Reloc::Model::Static;
+  auto reloc_model = emit_pic ? llvm::Reloc::Model::PIC_ : llvm::Reloc::Model::Static;
   return target->createTargetMachine(triple, cpu, features, opt, reloc_model);
 }
 
diff --git a/src/asmgen.h b/src/asmgen.h
index 7c39123..4d40def 100644
--- a/src/asmgen.h
+++ b/src/asmgen.h
@@ -15,7 +15,7 @@ namespace monicelli {
 void registerTargets();
 
 llvm::TargetMachine* getTargetMachine(const std::string& triple, const std::string& cpu,
-                                      const std::string& features);
+                                      const std::string& features, bool emit_pic);
 
 void writeAssembly(const std::string& to_filename, llvm::Module* module,
                    llvm::TargetMachine* target_machine);
diff --git a/src/main.cpp b/src/main.cpp
index 7c502ac..12ff167 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -30,7 +30,8 @@ int main(int argc, char** argv) {
   registerTargets();
 
   auto triple = llvm::sys::getDefaultTargetTriple();
-  auto target_machine = getTargetMachine(triple, options.getCPU(), options.getCPUFeatures());
+  auto target_machine =
+      getTargetMachine(triple, options.getCPU(), options.getCPUFeatures(), options.shouldEmitPIC());
 
 #ifdef MONICELLI_ENABLE_LINKER
   std::vector<std::string> object_filenames;
diff --git a/src/options.cpp b/src/options.cpp
index 394cd35..07a954c 100644
--- a/src/options.cpp
+++ b/src/options.cpp
@@ -37,6 +37,10 @@ ProgramOptions ProgramOptions::fromCommandLine(int argc, char** argv) {
       options.skip_compile_ = true;
       continue;
     }
+    if (strcmp(argv[i], "--no-pic") == 0) {
+      options.emit_pic_ = false;
+      continue;
+    }
 #ifdef MONICELLI_ENABLE_LINKER
     if (strcmp(argv[i], "-c") == 0 || strcmp(argv[i], "--only-compile") == 0) {
       options.compile_only_ = true;
@@ -88,6 +92,7 @@ void ProgramOptions::printHelp(const char* program_name) {
                "  --print-ir, -s          : Print the IR of the code.\n"
                "  --cpu, -m model         : Set the CPU model to this (default: generic).\n"
                "  --cpu-features, -f feat : Enable these CPU features (default: none).\n"
+               "  --no-pic                : Disable position independent code.\n"
                "  --help, -h              : Print this message.\n"
                "\n";
   exit(0);
diff --git a/src/options.h b/src/options.h
index add7d92..4420724 100644
--- a/src/options.h
+++ b/src/options.h
@@ -34,13 +34,14 @@ public:
 
   const std::string& getCPU() const { return cpu_; }
   const std::string& getCPUFeatures() const { return cpu_features_; }
+  bool shouldEmitPIC() const { return emit_pic_; }
 
 private:
   static void printHelp(const char* program_name);
 
   ProgramOptions()
       : print_ir_(false), print_ast_(false), trace_lexer_(false), compile_only_(false),
-        skip_compile_(false), cpu_("generic") {}
+        skip_compile_(false), cpu_("generic"), emit_pic_(true) {}
 
   bool print_ir_;
   bool print_ast_;
@@ -51,6 +52,7 @@ private:
   std::string output_filename_;
   std::string cpu_;
   std::string cpu_features_;
+  bool emit_pic_;
 };
 
 } // namespace monicelli