clang-cl: Support /guard:cf,nochecks

[hans]

Summary

This extension emits the guard cf table without inserting the instrumentation. Currently that's what clang-cl does with /guard:cf anyway, but this allows a user to request that explicitly.

[hans]

lib/CodeGen/CodeGenModule.cpp

463 ↗

(On Diff #159927)

I'll update the LLVM side before landing this, but I think this name better explains what's being emitted.

[rnk]

lgtm!

There is some additional work to do to put .gfids$y sections into appropriate comdat sections, but that's future work.

cfe/trunk/include/clang/Driver/CLCompatOptions.td

def _SLASH_Fe : CLJoined<"Fe">,
   HelpText<"Set output executable file or directory (ends in / or \\)">,
   MetaVarName<"<file or directory>">;
 def _SLASH_Fi : CLCompileJoined<"Fi">,
   HelpText<"Set preprocess output file name (with /P)">,
   MetaVarName<"<file>">;
 def _SLASH_Fo : CLCompileJoined<"Fo">,
   HelpText<"Set output object file, or directory (ends in / or \\) (with /c)">,
   MetaVarName<"<file or directory>">;
-def _SLASH_Guard : CLJoined<"guard:">,
-  HelpText<"Enable Control Flow Guard with /guard:cf">;
+def _SLASH_guard : CLJoined<"guard:">,
+  HelpText<"Enable Control Flow Guard with /guard:cf, or only the table with /guard:cf,nochecks">;
 def _SLASH_GX : CLFlag<"GX">,
   HelpText<"Enable exception handling">;
 def _SLASH_GX_ : CLFlag<"GX-">,
   HelpText<"Disable exception handling">;
 def _SLASH_imsvc : CLJoinedOrSeparate<"imsvc">,
   HelpText<"Add directory to system include search path, as if part of %INCLUDE%">,
   MetaVarName<"<dir>">;
 def _SLASH_LD : CLFlag<"LD">, HelpText<"Create DLL">;

cfe/trunk/lib/CodeGen/CodeGenModule.cpp

getModule().addModuleFlag(llvm::Module::Warning, "Dwarf Version",
                               CodeGenOpts.DwarfVersion);
   }
   if (CodeGenOpts.EmitCodeView) {
     // Indicate that we want CodeView in the metadata.
     getModule().addModuleFlag(llvm::Module::Warning, "CodeView", 1);
   }
   if (CodeGenOpts.ControlFlowGuard) {
     // We want function ID tables for Control Flow Guard.
-    getModule().addModuleFlag(llvm::Module::Warning, "cfguard", 1);
+    getModule().addModuleFlag(llvm::Module::Warning, "cfguardtable", 1);
   }
   if (CodeGenOpts.OptimizationLevel > 0 && CodeGenOpts.StrictVTablePointers) {
     // We don't support LTO with 2 with different StrictVTablePointers
     // FIXME: we could support it by stripping all the information introduced
     // by StrictVTablePointers.
 
     getModule().addModuleFlag(llvm::Module::Error, "StrictVTablePointers",1);
 

cfe/trunk/lib/Driver/ToolChains/Clang.cpp

void Clang::AddClangCLArgs(const ArgList &Args, types::ID InputType,
   if (!Args.hasArg(options::OPT_fdiagnostics_format_EQ)) {
     CmdArgs.push_back("-fdiagnostics-format");
     if (Args.hasArg(options::OPT__SLASH_fallback))
       CmdArgs.push_back("msvc-fallback");
     else
       CmdArgs.push_back("msvc");
   }
 
-  if (Args.hasArg(options::OPT__SLASH_Guard) &&
-      Args.getLastArgValue(options::OPT__SLASH_Guard).equals_lower("cf"))
+  if (Arg *A = Args.getLastArg(options::OPT__SLASH_guard)) {
+    SmallVector<StringRef, 1> SplitArgs;
+    StringRef(A->getValue()).split(SplitArgs, ",");
+    bool Instrument = false;
+    bool NoChecks = false;
+    for (StringRef Arg : SplitArgs) {
+      if (Arg.equals_lower("cf"))
+        Instrument = true;
+      else if (Arg.equals_lower("cf-"))
+        Instrument = false;
+      else if (Arg.equals_lower("nochecks"))
+        NoChecks = true;
+      else if (Arg.equals_lower("nochecks-"))
+        NoChecks = false;
+      else
+        D.Diag(diag::err_drv_invalid_value) << A->getSpelling() << Arg;
+    }
+    // Currently there's no support emitting CFG instrumentation; the flag only
+    // emits the table of address-taken functions.
+    if (Instrument || NoChecks)
       CmdArgs.push_back("-cfguard");
   }
+}
 
 visualstudio::Compiler *Clang::getCLFallback() const {
   if (!CLFallback)
     CLFallback.reset(new visualstudio::Compiler(getToolChain()));
   return CLFallback.get();
 }
 
 

cfe/trunk/test/CodeGen/cfguardtable.c

+// RUN: %clang_cc1 -cfguard -emit-llvm %s -o - | FileCheck %s
+
+void f() {}
+
+// Check that the cfguardtable metadata flag gets set on the module.
+// CHECK: !"cfguardtable", i32 1}

cfe/trunk/test/Driver/cl-options.c

 // RUN:     /GH \
 // RUN:     /GL \
 // RUN:     /GL- \
 // RUN:     /Gm \
 // RUN:     /Gm- \
 // RUN:     /Gr \
 // RUN:     /GS \
 // RUN:     /GT \
-// RUN:     /guard:cf \
-// RUN:     /guard:cf- \
 // RUN:     /GX \
 // RUN:     /Gv \
 // RUN:     /Gz \
 // RUN:     /GZ \
 // RUN:     /H \
 // RUN:     /homeparams \
 // RUN:     /hotpatch \
 // RUN:     /JMC \

 // LTO: -flto
 
 // RUN: %clang_cl -### /c -flto=thin -- %s 2>&1 | FileCheck -check-prefix=LTO-THIN %s
 // LTO-THIN: -flto=thin
 
 // RUN: %clang_cl -### -Fe%t.exe -entry:main -flto -- %s 2>&1 | FileCheck -check-prefix=LTO-WITHOUT-LLD %s
 // LTO-WITHOUT-LLD: LTO requires -fuse-ld=lld
 
+// RUN: %clang_cl  -### -- %s 2>&1 | FileCheck -check-prefix=NOCFGUARD %s
+// RUN: %clang_cl /guard:cf- -### -- %s 2>&1 | FileCheck -check-prefix=NOCFGUARD %s
+// NOCFGUARD-NOT: -guardcf
+
+// RUN: %clang_cl /guard:cf -### -- %s 2>&1 | FileCheck -check-prefix=CFGUARD %s
+// RUN: %clang_cl /guard:cf,nochecks -### -- %s 2>&1 | FileCheck -check-prefix=CFGUARD %s
+// RUN: %clang_cl /guard:nochecks -### -- %s 2>&1 | FileCheck -check-prefix=CFGUARD %s
+// CFGUARD: -cfguard
+
+// RUN: %clang_cl /guard:foo -### -- %s 2>&1 | FileCheck -check-prefix=CFGUARDINVALID %s
+// CFGUARDINVALID: invalid value 'foo' in '/guard:'
+
 // Accept "core" clang options.
 // (/Zs is for syntax-only, -Werror makes it fail hard on unknown options)
 // RUN: %clang_cl \
 // RUN:     --driver-mode=cl \
 // RUN:     -fblocks \
 // RUN:     -fno-blocks \
 // RUN:     -fbuiltin \
 // RUN:     -fno-builtin \