rewriter: Define call gates for function pointers in source defining …

…the pointee

We previously defined call gates for pointers to static functions by appending a
macro to the rewritten source files. In that case we had to do this because the
static function may not be referenced from outside the translation unit. For
pointers to globally-visible functions we defined the call gates in the call
gate .so for simplicity. This commit changes the latter call gates so they're
defined like the former. This change simplifies control-flow since the call gate
no longer requires cross-DSO calls and makes it possible to support programs
that are intended to be compiled with -fvisibility=hidden since functions that
may have hidden visibility are only referenced by call gates within the DSO that
defines them. Closes #435.

tools/rewriter/SourceRewriter.cpp

@@ -661,31 +661,26 @@ class FnPtrExpr : public RefactoringCallback {
     OpaqueStruct new_type = kFnPtrTypePrefix + mangled_type;
 
     auto linkage = fn_decl->getFormalLinkage();
-    if (clang::isExternallyVisible(linkage)) {
-      addr_taken_fns[fn_name] = new_type;
-    } else {
-
-      auto [it, new_fn] = internal_addr_taken_fns[filename].insert(
-          std::make_pair(fn_name, new_type));
-
-      // TODO: Note that this only checks if a function is added to the
-      // internal_addr_taken_fns map. To make the rewriter idempotent we should
-      // check for an existing used attribute.
-      if (new_fn) {
-        auto static_fn_range = fn_decl->getSourceRange();
-        auto expansion_range = sm.getExpansionRange(static_fn_range);
-        if (!expansion_range.getBegin().isFileID()) {
-          llvm::errs() << "Error: non-file loc for function " << fn_name << '\n';
-        } else {
-          auto decl_start = expansion_range.getBegin();
-          Filename decl_filename = get_filename(decl_start, sm);
-          Replacement old_used_attr(sm, decl_start, 0,
-                                    llvm::StringRef("__attribute__((used)) "));
-          Replacement used_attr = replace_new_file(decl_filename, old_used_attr);
-          auto err = file_replacements[decl_filename].add(used_attr);
-          if (err) {
-            llvm::errs() << "Error adding replacements: " << err << '\n';
-          }
+    auto [it, new_fn] = addr_taken_fns[filename].insert(
+        std::make_pair(fn_name, new_type));
+
+    // TODO: Note that this only checks if a function is added to the
+    // addr_taken_fns map. To make the rewriter idempotent we should
+    // check for an existing used attribute.
+    if (new_fn) {
+      auto static_fn_range = fn_decl->getSourceRange();
+      auto expansion_range = sm.getExpansionRange(static_fn_range);
+      if (!expansion_range.getBegin().isFileID()) {
+        llvm::errs() << "Error: non-file loc for function " << fn_name << '\n';
+      } else {
+        auto decl_start = expansion_range.getBegin();
+        Filename decl_filename = get_filename(decl_start, sm);
+        Replacement old_used_attr(sm, decl_start, 0,
+                                  llvm::StringRef("__attribute__((used)) "));
+        Replacement used_attr = replace_new_file(decl_filename, old_used_attr);
+        auto err = file_replacements[decl_filename].add(used_attr);
+        if (err) {
+          llvm::errs() << "Error adding replacements: " << err << '\n';
         }
       }
     }
@@ -715,9 +710,8 @@ class FnPtrExpr : public RefactoringCallback {
     return;
   }
 
-  std::map<Function, OpaqueStruct> addr_taken_fns;
   std::map<Filename, std::set<std::pair<Function, OpaqueStruct>>>
-      internal_addr_taken_fns;
+      addr_taken_fns;
 
 private:
   std::map<std::string, Replacements> &file_replacements;
@@ -1418,51 +1412,22 @@ int main(int argc, const char **argv) {
   }
 
   std::cout << "Generating function pointer wrappers\n";
-  // Define wrappers for function pointers (i.e. those referenced by IA2_FN)
-  for (const auto &[fn_name, opaque] : ptr_expr_pass.addr_taken_fns) {
-    /*
-     * Declare these wrapper in the output header so that IA2_FN can reference
-     * them. e.g. extern struct IA2_fnptr_ZTSFiiE __ia2_foo;
-     *
-     * The type used in these declarations is arbitrary and chosen to make it
-     * easy to go from a function's name to its mangled type in IA2_FN.
-     */
-    std::string wrapper_name = "__ia2_"s + fn_name;
-    header_out << "extern " << opaque << " " << wrapper_name << ";\n";
-
-    Pkey target_pkey = fn_decl_pass.fn_pkeys[fn_name];
-    if (target_pkey != 0) {
-      AbiSignature c_abi_sig = fn_decl_pass.abi_signatures[fn_name];
-      std::string asm_wrapper =
-          emit_asm_wrapper(c_abi_sig, wrapper_name, fn_name,
-                           WrapperKind::Pointer, 0, target_pkey, Target);
-      wrapper_out << "asm(\n";
-      wrapper_out << asm_wrapper;
-      wrapper_out << ");\n";
-    } else {
-      header_out << "asm(\n";
-      header_out << "  \".set " << wrapper_name << ", __real_" << fn_name << "\\n\"\n";
-      header_out << ");\n";
-    }
-  }
-
-  std::cout << "Generating function pointer wrappers for static functions\n";
-  // Define wrappers for pointers to static functions (also those referenced by
-  // IA2_FN)
+  // Define wrappers for pointers to static functions (those referenced by IA2_FN)
   std::string static_wrappers;
-  for (const auto &[filename, addr_taken_fns] :
-       ptr_expr_pass.internal_addr_taken_fns) {
+  for (const auto &[filename, addr_taken_fns_in_file] :
+       ptr_expr_pass.addr_taken_fns) {
 
     // Open each file that took the address of a static function
     std::ofstream source_file(filename, std::ios::app);
 
     // For each static function, define a macro to define the wrapper in the
     // output header and invoke it in the source file
-    for (const auto [fn_name, opaque] : addr_taken_fns) {
+    for (const auto [fn_name, opaque] : addr_taken_fns_in_file) {
       std::string wrapper_name = "__ia2_"s + fn_name;
       // TODO: These wrapper go from pkey 0 to the target pkey so if the target
       // also has pkey 0 then it just needs call the original function
       Pkey target_pkey = fn_decl_pass.fn_pkeys[fn_name];
+      header_out << "extern " << opaque << " " << wrapper_name << ";\n";
       if (target_pkey != 0) {
         AbiSignature c_abi_sig = fn_decl_pass.abi_signatures[fn_name];
 
@@ -1474,9 +1439,11 @@ int main(int argc, const char **argv) {
         static_wrappers += asm_wrapper;
         static_wrappers += ");\n";
 
-        header_out << "extern " << opaque << " " << wrapper_name << ";\n";
-
         source_file << "IA2_DEFINE_WRAPPER(" << fn_name << ")\n";
+      } else {
+        header_out << "asm(\n";
+        header_out << "  \".set " << wrapper_name << ", __real_" << fn_name << "\\n\"\n";
+        header_out << ");\n";
       }
     }
   }