New clang option -fno-plt which avoids the PLT and lazy binding while…

… making external calls. Differential Revision: https://reviews.llvm.org/D39079 llvm-svn: 317605
llvm · Nov 7, 2017 · 5c65148 · 5c65148
1 parent 4e8ce02
commit 5c65148
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diff --git a/clang/include/clang/Driver/Options.td b/clang/include/clang/Driver/Options.td
@@ -1384,6 +1384,10 @@ def fpic : Flag<["-"], "fpic">, Group<f_Group>;
 def fno_pic : Flag<["-"], "fno-pic">, Group<f_Group>;
 def fpie : Flag<["-"], "fpie">, Group<f_Group>;
 def fno_pie : Flag<["-"], "fno-pie">, Group<f_Group>;
+def fplt : Flag<["-"], "fplt">, Group<f_Group>, Flags<[CC1Option]>,
+  HelpText<"Use the PLT to make function calls">;
+def fno_plt : Flag<["-"], "fno-plt">, Group<f_Group>, Flags<[CC1Option]>,
+  HelpText<"Do not use the PLT to make function calls">;
 def fropi : Flag<["-"], "fropi">, Group<f_Group>;
 def fno_ropi : Flag<["-"], "fno-ropi">, Group<f_Group>;
 def frwpi : Flag<["-"], "frwpi">, Group<f_Group>;

diff --git a/clang/include/clang/Frontend/CodeGenOptions.def b/clang/include/clang/Frontend/CodeGenOptions.def
@@ -297,6 +297,8 @@ CODEGENOPT(PreserveVec3Type, 1, 0)
 /// Whether to emit .debug_gnu_pubnames section instead of .debug_pubnames.
 CODEGENOPT(GnuPubnames, 1, 0)
 
+CODEGENOPT(NoPLT, 1, 0)
+
 #undef CODEGENOPT
 #undef ENUM_CODEGENOPT
 #undef VALUE_CODEGENOPT

diff --git a/clang/lib/CodeGen/CGCall.cpp b/clang/lib/CodeGen/CGCall.cpp
@@ -1855,6 +1855,16 @@ void CodeGenModule::ConstructAttributeList(
       !(TargetDecl && TargetDecl->hasAttr<NoSplitStackAttr>()))
     FuncAttrs.addAttribute("split-stack");
 
+  // Add NonLazyBind attribute to function declarations when -fno-plt
+  // is used.
+  if (TargetDecl && CodeGenOpts.NoPLT) {
+    if (auto *Fn = dyn_cast<FunctionDecl>(TargetDecl)) {
+      if (!Fn->isDefined() && !AttrOnCallSite) {
+        FuncAttrs.addAttribute(llvm::Attribute::NonLazyBind);
+      }
+    }
+  }
+
   if (!AttrOnCallSite) {
     bool DisableTailCalls =
         CodeGenOpts.DisableTailCalls ||

diff --git a/clang/lib/Driver/ToolChains/Clang.cpp b/clang/lib/Driver/ToolChains/Clang.cpp
@@ -3423,6 +3423,10 @@ void Clang::ConstructJob(Compilation &C, const JobAction &JA,
     CmdArgs.push_back("-mpie-copy-relocations");
   }
 
+  if (Args.hasFlag(options::OPT_fno_plt, options::OPT_fplt, false)) {
+    CmdArgs.push_back("-fno-plt");
+  }
+
   // -fhosted is default.
   // TODO: Audit uses of KernelOrKext and see where it'd be more appropriate to
   // use Freestanding.

diff --git a/clang/lib/Frontend/CompilerInvocation.cpp b/clang/lib/Frontend/CompilerInvocation.cpp
@@ -653,6 +653,7 @@ static bool ParseCodeGenArgs(CodeGenOptions &Opts, ArgList &Args, InputKind IK,
       Args.hasArg(OPT_mincremental_linker_compatible);
   Opts.PIECopyRelocations =
       Args.hasArg(OPT_mpie_copy_relocations);
+  Opts.NoPLT = Args.hasArg(OPT_fno_plt);
   Opts.OmitLeafFramePointer = Args.hasArg(OPT_momit_leaf_frame_pointer);
   Opts.SaveTempLabels = Args.hasArg(OPT_msave_temp_labels);
   Opts.NoDwarfDirectoryAsm = Args.hasArg(OPT_fno_dwarf_directory_asm);

diff --git a/clang/test/CodeGen/noplt.c b/clang/test/CodeGen/noplt.c
@@ -0,0 +1,9 @@
+// RUN: %clang_cc1 -emit-llvm -fno-plt %s -o - | FileCheck %s -check-prefix=CHECK-NOPLT
+
+// CHECK-NOPLT: Function Attrs: nonlazybind
+// CHECK-NOPLT-NEXT: declare i32 @foo
+int foo();
+
+int bar() {
+  return foo();
+}