[ARM][AArch64] SLSHardening: make non-comdat thunks possible

[danielkiss]

Summary

Linker scripts might not handle COMDAT sections. SLSHardeing adds
new section for each __llvm_slsblr_thunk_xN. This new option allows
the generation of the thunks into the normal text section to handle these
exceptional cases.
,comdat or ,noncomdat can be added to harden-sls to control the codegen.
-mharden-sls=[all|retbr|blr],nocomdat.

[tamas.petz]

llvm/include/llvm/CodeGen/IndirectThunks.h

56

NIT: tabs to spaces

[kristof.beyls]

Apart from maybe needing to run clang-format on the patch, the code changes look good to me.
Before this could be committed, this needs tests.

llvm/include/llvm/CodeGen/IndirectThunks.h

43–44

I'm not entirely sure, but is this how clang-format formats these lines?

[danielkiss]

Adding a fronted flag and tests.
comdat is still the default, feels fine but I'm not sure.

[danielkiss]

llvm/include/llvm/CodeGen/IndirectThunks.h

43–44

yes, patch went thru git clang-format

[tamas.petz]

I have just a few small comments.

llvm/include/llvm/CodeGen/IndirectThunks.h

31

Is the default argument really required?

57

There are still TABs there.

[danielkiss]

llvm/include/llvm/CodeGen/IndirectThunks.h

31

yes, this function is called from x86 backed and I'd not change that.

57

I think these are spaces, could you please take a look at the raw diff?

[kristof.beyls]

clang/lib/Driver/ToolChains/Arch/ARM.cpp

837–840

I think it would be better if comdat/nocomdat were also communicated through Features.
It keeps the interface on this part of the code base consistent (no need to introduce a CmdArgs feature); and also makes sure that LTO vs non-LTO builds keep on behaving the same way, as the feature is set per function, not per translation unit.

I haven't really thought about how to best specify that feature. Maybe just have an extra 2 features: +harden-sls-comdat and +harden-sls-nocomdat?

llvm/test/CodeGen/AArch64/speculation-hardening-sls.ll

218–220

Would it be possible to also have check lines for HARDEN-COMDAT-OFF, i.e. look for lines that HARDEN-COMDAT-OFF should produce?

llvm/test/CodeGen/ARM/speculation-hardening-sls.ll

249–251

Would it be possible to also have check lines for HARDEN-COMDAT-OFF, i.e. look for lines that HARDEN-COMDAT-OFF should produce?

[danielkiss]

clang/lib/Driver/ToolChains/Arch/ARM.cpp

837–840

I almost added a feature for the harden-sls-noncomdat but that is not really a HW feature so felt the backed flag is better.
One feature bit seems enough to describe the two states.

[danielkiss]

address review comments.

[kristof.beyls]

Thanks @danielkiss !
I only have a few nit picky remarks.
Overall looks good!

clang/lib/Driver/ToolChains/Arch/AArch64.cpp

275

I'm wondering if the '(EnableRetBr || EnableBlr)' condition is needed here?
Just dropping it would make this code a little bit simpler.
I'm assuming here of course that the semantics of the +harden-sls-comdat target feature is to not produce comdat sections in case any of the other sls-hardening target features would produce thunks.
I agree this is a bit of a nit pick though.

clang/lib/Driver/ToolChains/Arch/ARM.cpp

837

Same comment/thought on the "(EnableRetBr || EnableBlr)" condition as on the AArch64 side.

llvm/lib/Target/AArch64/AArch64.td

528

I think it would be more accurate if the word "thunk" would be present in the documentation.
What about the following:
"Generate thunk code for SLS mitigation in the normal text section"?

llvm/lib/Target/ARM/ARM.td

578

Same comment as on the AArch64 side on using the word "thunk" somewhere in the help text.

[danielkiss]

clang/lib/Driver/ToolChains/Arch/AArch64.cpp

275

the check is a bit overkill, the backend won't do anything anyway without the EnableRetBr || EnableBlr

[kristof.beyls]

LGTM.

clang/lib/Driver/ToolChains/Arch/AArch64.cpp

else if (Mtp != "el0")
       D.Diag(diag::err_drv_invalid_mtp) << A->getAsString(Args);
   }
 
   // Enable/disable straight line speculation hardening.
   if (Arg *A = Args.getLastArg(options::OPT_mharden_sls_EQ)) {
     StringRef Scope = A->getValue();
     bool EnableRetBr = false;
     bool EnableBlr = false;
-    if (Scope != "none" && Scope != "all") {
+    bool DisableComdat = false;
+    if (Scope != "none") {
       SmallVector<StringRef, 4> Opts;
       Scope.split(Opts, ",");
       for (auto Opt : Opts) {
         Opt = Opt.trim();
+        if (Opt == "all") {
+          EnableBlr = true;
+          EnableRetBr = true;
+          continue;
+        }
         if (Opt == "retbr") {
           EnableRetBr = true;
           continue;
         }
         if (Opt == "blr") {
           EnableBlr = true;
           continue;
         }
+        if (Opt == "comdat") {
+          DisableComdat = false;
+          continue;
+        }
+        if (Opt == "nocomdat") {
+          DisableComdat = true;
+          continue;
+        }
         D.Diag(diag::err_invalid_sls_hardening)
             << Scope << A->getAsString(Args);
         break;
       }
-    } else if (Scope == "all") {
-      EnableRetBr = true;
-      EnableBlr = true;
     }
 
     if (EnableRetBr)
       Features.push_back("+harden-sls-retbr");
     if (EnableBlr)
       Features.push_back("+harden-sls-blr");
+    if (DisableComdat) {
+      Features.push_back("+harden-sls-nocomdat");
+    }
   }
 
   // En/disable crc
   if (Arg *A = Args.getLastArg(options::OPT_mcrc, options::OPT_mnocrc)) {
     if (A->getOption().matches(options::OPT_mcrc))
       Features.push_back("+crc");
     else
       Features.push_back("-crc");

clang/lib/Driver/ToolChains/Arch/ARM.cpp

fp16_fml_fallthrough:
   if (Args.hasArg(options::OPT_mno_neg_immediates))
     Features.push_back("+no-neg-immediates");
 
   // Enable/disable straight line speculation hardening.
   if (Arg *A = Args.getLastArg(options::OPT_mharden_sls_EQ)) {
     StringRef Scope = A->getValue();
     bool EnableRetBr = false;
     bool EnableBlr = false;
-    if (Scope != "none" && Scope != "all") {
+    bool DisableComdat = false;
+    if (Scope != "none") {
       SmallVector<StringRef, 4> Opts;
       Scope.split(Opts, ",");
       for (auto Opt : Opts) {
         Opt = Opt.trim();
+        if (Opt == "all") {
+          EnableBlr = true;
+          EnableRetBr = true;
+          continue;
+        }
         if (Opt == "retbr") {
           EnableRetBr = true;
           continue;
         }
         if (Opt == "blr") {
           EnableBlr = true;
           continue;
         }
+        if (Opt == "comdat") {
+          DisableComdat = false;
+          continue;
+        }
+        if (Opt == "nocomdat") {
+          DisableComdat = true;
+          continue;
+        }
         D.Diag(diag::err_invalid_sls_hardening)
             << Scope << A->getAsString(Args);
         break;
       }
-    } else if (Scope == "all") {
-      EnableRetBr = true;
-      EnableBlr = true;
     }
 
     if (EnableRetBr || EnableBlr)
       if (!(isARMAProfile(Triple) && getARMSubArchVersionNumber(Triple) >= 7))
         D.Diag(diag::err_sls_hardening_arm_not_supported)
             << Scope << A->getAsString(Args);
 
     if (EnableRetBr)
       Features.push_back("+harden-sls-retbr");
     if (EnableBlr)
       Features.push_back("+harden-sls-blr");
+    if (DisableComdat) {
+      Features.push_back("+harden-sls-nocomdat");
+    }
   }
 
 }
 
 const std::string arm::getARMArch(StringRef Arch, const llvm::Triple &Triple) {
   std::string MArch;
   if (!Arch.empty())
     MArch = std::string(Arch);
   else

clang/test/Driver/sls-hardening-options.c

 // Check the -mharden-sls= option, which has a required argument to select
 // scope.
 // RUN: %clang -target aarch64--none-eabi -c %s -### 2>&1 | \
-// RUN: FileCheck %s --check-prefix=RETBR-OFF --check-prefix=BLR-OFF
+// RUN: FileCheck %s --check-prefix=RETBR-OFF --check-prefix=BLR-OFF --check-prefix=NOCOMDAT-OFF
 // RUN: %clang -target armv7a--none-eabi -c %s -### 2>&1 | \
-// RUN: FileCheck %s --check-prefix=RETBR-OFF --check-prefix=BLR-OFF
+// RUN: FileCheck %s --check-prefix=RETBR-OFF --check-prefix=BLR-OFF --check-prefix=NOCOMDAT-OFF
 
 // RUN: %clang -target aarch64--none-eabi -c %s -### -mharden-sls=none 2>&1 | \
-// RUN: FileCheck %s --check-prefix=RETBR-OFF --check-prefix=BLR-OFF
+// RUN: FileCheck %s --check-prefix=RETBR-OFF --check-prefix=BLR-OFF --check-prefix=NOCOMDAT-OFF
 // RUN: %clang -target armv7a--none-eabi -c %s -### -mharden-sls=none 2>&1 | \
-// RUN: FileCheck %s --check-prefix=RETBR-OFF --check-prefix=BLR-OFF
+// RUN: FileCheck %s --check-prefix=RETBR-OFF --check-prefix=BLR-OFF --check-prefix=NOCOMDAT-OFF
 
 // RUN: %clang -target aarch64--none-eabi -c %s -### -mharden-sls=retbr 2>&1 | \
-// RUN: FileCheck %s --check-prefix=RETBR-ON --check-prefix=BLR-OFF
+// RUN: FileCheck %s --check-prefix=RETBR-ON --check-prefix=BLR-OFF --check-prefix=NOCOMDAT-OFF
 // RUN: %clang -target armv7a--none-eabi -c %s -### -mharden-sls=retbr 2>&1 | \
-// RUN: FileCheck %s --check-prefix=RETBR-ON --check-prefix=BLR-OFF
+// RUN: FileCheck %s --check-prefix=RETBR-ON --check-prefix=BLR-OFF --check-prefix=NOCOMDAT-OFF
 
 // RUN: %clang -target aarch64--none-eabi -c %s -### -mharden-sls=blr 2>&1 | \
-// RUN: FileCheck %s --check-prefix=RETBR-OFF --check-prefix=BLR-ON
+// RUN: FileCheck %s --check-prefix=RETBR-OFF --check-prefix=BLR-ON --check-prefix=NOCOMDAT-OFF
 // RUN: %clang -target armv7a--none-eabi -c %s -### -mharden-sls=blr 2>&1 | \
-// RUN: FileCheck %s --check-prefix=RETBR-OFF --check-prefix=BLR-ON
+// RUN: FileCheck %s --check-prefix=RETBR-OFF --check-prefix=BLR-ON --check-prefix=NOCOMDAT-OFF
 
 // RUN: %clang -target aarch64--none-eabi -c %s -### -mharden-sls=blr -mharden-sls=none 2>&1 | \
-// RUN: FileCheck %s --check-prefix=RETBR-OFF --check-prefix=BLR-OFF
+// RUN: FileCheck %s --check-prefix=RETBR-OFF --check-prefix=BLR-OFF --check-prefix=NOCOMDAT-OFF
 // RUN: %clang -target armv7a--none-eabi -c %s -### -mharden-sls=blr -mharden-sls=none 2>&1 | \
-// RUN: FileCheck %s --check-prefix=RETBR-OFF --check-prefix=BLR-OFF
+// RUN: FileCheck %s --check-prefix=RETBR-OFF --check-prefix=BLR-OFF --check-prefix=NOCOMDAT-OFF
 
 // RUN: %clang -target aarch64--none-eabi -c %s -### -mharden-sls=blr -mharden-sls=retbr 2>&1 | \
-// RUN: FileCheck %s --check-prefix=RETBR-ON --check-prefix=BLR-OFF
+// RUN: FileCheck %s --check-prefix=RETBR-ON --check-prefix=BLR-OFF --check-prefix=NOCOMDAT-OFF
 // RUN: %clang -target armv7a--none-eabi -c %s -### -mharden-sls=blr -mharden-sls=retbr 2>&1 | \
-// RUN: FileCheck %s --check-prefix=RETBR-ON --check-prefix=BLR-OFF
+// RUN: FileCheck %s --check-prefix=RETBR-ON --check-prefix=BLR-OFF --check-prefix=NOCOMDAT-OFF
 
 // RUN: %clang -target aarch64--none-eabi -c %s -### -mharden-sls=retbr,blr 2>&1 | \
-// RUN: FileCheck %s --check-prefix=RETBR-ON --check-prefix=BLR-ON
+// RUN: FileCheck %s --check-prefix=RETBR-ON --check-prefix=BLR-ON --check-prefix=NOCOMDAT-OFF
 // RUN: %clang -target armv7a--none-eabi -c %s -### -mharden-sls=retbr,blr 2>&1 | \
-// RUN: FileCheck %s --check-prefix=RETBR-ON --check-prefix=BLR-ON
+// RUN: FileCheck %s --check-prefix=RETBR-ON --check-prefix=BLR-ON --check-prefix=NOCOMDAT-OFF
 
 // RUN: %clang -target aarch64--none-eabi -c %s -### -mharden-sls=all 2>&1 | \
-// RUN: FileCheck %s --check-prefix=RETBR-ON --check-prefix=BLR-ON
+// RUN: FileCheck %s --check-prefix=RETBR-ON --check-prefix=BLR-ON --check-prefix=NOCOMDAT-OFF
 // RUN: %clang -target armv7a--none-eabi -c %s -### -mharden-sls=all 2>&1 | \
-// RUN: FileCheck %s --check-prefix=RETBR-ON --check-prefix=BLR-ON
+// RUN: FileCheck %s --check-prefix=RETBR-ON --check-prefix=BLR-ON --check-prefix=NOCOMDAT-OFF
 
 // RUN: %clang -target aarch64--none-eabi -c %s -### -mharden-sls=retbr,blr,retbr 2>&1 | \
-// RUN: FileCheck %s --check-prefix=RETBR-ON --check-prefix=BLR-ON
+// RUN: FileCheck %s --check-prefix=RETBR-ON --check-prefix=BLR-ON --check-prefix=NOCOMDAT-OFF
 // RUN: %clang -target armv7a--none-eabi -c %s -### -mharden-sls=retbr,blr,retbr 2>&1 | \
-// RUN: FileCheck %s --check-prefix=RETBR-ON --check-prefix=BLR-ON
+// RUN: FileCheck %s --check-prefix=RETBR-ON --check-prefix=BLR-ON --check-prefix=NOCOMDAT-OFF
 
 // RUN: %clang -target aarch64--none-eabi -c %s -### -mharden-sls=retbr,blr,r 2>&1 | \
 // RUN: FileCheck %s --check-prefix=BAD-SLS-SPEC
 // RUN: %clang -target armv7a--none-eabi -c %s -### -mharden-sls=retbr,blr,r 2>&1 | \
 // RUN: FileCheck %s --check-prefix=BAD-SLS-SPEC
 
 // RUN: %clang -target aarch64--none-eabi -c %s -### -mharden-sls=none,blr 2>&1 | \
 // RUN: FileCheck %s --check-prefix=BAD-SLS-SPEC
 // RUN: %clang -target armv7a--none-eabi -c %s -### -mharden-sls=none,blr 2>&1 | \
 // RUN: FileCheck %s --check-prefix=BAD-SLS-SPEC
 
 // RUN: %clang -target aarch64--none-eabi -c %s -### -mharden-sls=all,-blr 2>&1 | \
 // RUN: FileCheck %s --check-prefix=BAD-SLS-SPEC
 // RUN: %clang -target armv7a--none-eabi -c %s -### -mharden-sls=all,-blr 2>&1 | \
 // RUN: FileCheck %s --check-prefix=BAD-SLS-SPEC
 
+// RUN: %clang -target aarch64--none-eabi -c %s -### -mharden-sls=retbr,blr,nocomdat 2>&1 | \
+// RUN: FileCheck %s --check-prefix=RETBR-ON --check-prefix=BLR-ON --check-prefix=NOCOMDAT
+// RUN: %clang -target armv7a--none-eabi -c %s -### -mharden-sls=retbr,blr,nocomdat 2>&1 | \
+// RUN: FileCheck %s --check-prefix=RETBR-ON --check-prefix=BLR-ON --check-prefix=NOCOMDAT
+
+// RUN: %clang -target aarch64--none-eabi -c %s -### -mharden-sls=all,nocomdat 2>&1 | \
+// RUN: FileCheck %s --check-prefix=RETBR-ON --check-prefix=BLR-ON --check-prefix=NOCOMDAT
+// RUN: %clang -target armv7a--none-eabi -c %s -### -mharden-sls=all,nocomdat 2>&1 | \
+// RUN: FileCheck %s --check-prefix=RETBR-ON --check-prefix=BLR-ON --check-prefix=NOCOMDAT
+
+// RUN: %clang -target aarch64--none-eabi -c %s -### -mharden-sls=retbr,blr,retbr,nocomdat 2>&1 | \
+// RUN: FileCheck %s --check-prefix=RETBR-ON --check-prefix=BLR-ON --check-prefix=NOCOMDAT
+// RUN: %clang -target armv7a--none-eabi -c %s -### -mharden-sls=retbr,blr,retbr,nocomdat 2>&1 | \
+// RUN: FileCheck %s --check-prefix=RETBR-ON --check-prefix=BLR-ON --check-prefix=NOCOMDAT
+
+// RUN: %clang -target aarch64--none-eabi -c %s -### -mharden-sls=retbr,comdat,r 2>&1 | \
+// RUN: FileCheck %s --check-prefix=BAD-SLS-SPEC
+// RUN: %clang -target armv7a--none-eabi -c %s -### -mharden-sls=retbr,comdat,r 2>&1 | \
+// RUN: FileCheck %s --check-prefix=BAD-SLS-SPEC
+
+// RUN: %clang -target aarch64--none-eabi -c %s -### -mharden-sls=none,comdat 2>&1 | \
+// RUN: FileCheck %s --check-prefix=BAD-SLS-SPEC
+// RUN: %clang -target armv7a--none-eabi -c %s -### -mharden-sls=none,comdat 2>&1 | \
+// RUN: FileCheck %s --check-prefix=BAD-SLS-SPEC
+
+// RUN: %clang -target aarch64--none-eabi -c %s -### -mharden-sls=all,-comdat 2>&1 | \
+// RUN: FileCheck %s --check-prefix=BAD-SLS-SPEC
+// RUN: %clang -target armv7a--none-eabi -c %s -### -mharden-sls=all,-comdat 2>&1 | \
+// RUN: FileCheck %s --check-prefix=BAD-SLS-SPEC
+
 // RETBR-OFF-NOT: "harden-sls-retbr"
 // RETBR-ON:  "+harden-sls-retbr"
 
 // BLR-OFF-NOT: "harden-sls-blr"
 // BLR-ON:  "+harden-sls-blr"
 
+// NOCOMDAT-OFF-NOT: "harden-sls-nocomdat"
+// NOCOMDAT: "+harden-sls-nocomdat"
+
 // BAD-SLS-SPEC: invalid sls hardening option '{{[^']+}}' in '-mharden-sls=
 
 // RUN: %clang -target armv6a--none-eabi -c %s -### -mharden-sls=all 2>&1 | \
 // RUN: FileCheck %s --check-prefix=SLS-NOT-SUPPORTED
 
 // RUN: %clang -target armv6a--none-eabi -c %s -### -mharden-sls=retbr 2>&1 | \
 // RUN: FileCheck %s --check-prefix=SLS-NOT-SUPPORTED
 

llvm/include/llvm/CodeGen/IndirectThunks.h

 namespace llvm {
 
 template <typename Derived> class ThunkInserter {
   Derived &getDerived() { return *static_cast<Derived *>(this); }
 
 protected:
   bool InsertedThunks;
   void doInitialization(Module &M) {}
-  void createThunkFunction(MachineModuleInfo &MMI, StringRef Name);
+  void createThunkFunction(MachineModuleInfo &MMI, StringRef Name,
+                           bool Comdat = true);
 
 public:
   void init(Module &M) {
     InsertedThunks = false;
     getDerived().doInitialization(M);
   }
   // return `true` if `MMI` or `MF` was modified
   bool run(MachineModuleInfo &MMI, MachineFunction &MF);
 };
 
 template <typename Derived>
 void ThunkInserter<Derived>::createThunkFunction(MachineModuleInfo &MMI,
-                                                 StringRef Name) {
+                                                 StringRef Name, bool Comdat) {
   assert(Name.startswith(getDerived().getThunkPrefix()) &&
          "Created a thunk with an unexpected prefix!");
 
   Module &M = const_cast<Module &>(*MMI.getModule());
   LLVMContext &Ctx = M.getContext();
   auto Type = FunctionType::get(Type::getVoidTy(Ctx), false);
-  Function *F =
-      Function::Create(Type, GlobalValue::LinkOnceODRLinkage, Name, &M);
+  Function *F = Function::Create(Type,
+                                 Comdat ? GlobalValue::LinkOnceODRLinkage
+                                        : GlobalValue::InternalLinkage,
+                                 Name, &M);
+  if (Comdat) {
     F->setVisibility(GlobalValue::HiddenVisibility);
     F->setComdat(M.getOrInsertComdat(Name));
+  }
 
   // Add Attributes so that we don't create a frame, unwind information, or
   // inline.
   AttrBuilder B;
   B.addAttribute(llvm::Attribute::NoUnwind);
   B.addAttribute(llvm::Attribute::Naked);
   F->addAttributes(llvm::AttributeList::FunctionIndex, B);
 

llvm/lib/Target/AArch64/AArch64.td

 //===----------------------------------------------------------------------===//
 
 def FeatureHardenSlsRetBr : SubtargetFeature<"harden-sls-retbr",
   "HardenSlsRetBr", "true",
   "Harden against straight line speculation across RET and BR instructions">;
 def FeatureHardenSlsBlr : SubtargetFeature<"harden-sls-blr",
   "HardenSlsBlr", "true",
   "Harden against straight line speculation across BLR instructions">;
+def FeatureHardenSlsNoComdat : SubtargetFeature<"harden-sls-nocomdat",
+  "HardenSlsNoComdat", "true",
+  "Generate thunk code for SLS mitigation in the normal text section">;
 
 //===----------------------------------------------------------------------===//
 // AArch64 Processors supported.
 //
 
 //===----------------------------------------------------------------------===//
 // Unsupported features to disable for scheduling models
 //===----------------------------------------------------------------------===//

llvm/lib/Target/AArch64/AArch64SLSHardening.cpp

static const struct ThunkNameAndReg {
   // missing.
   { "__llvm_slsblr_thunk_x31",  AArch64::XZR},
 };
 
 namespace {
 struct SLSBLRThunkInserter : ThunkInserter<SLSBLRThunkInserter> {
   const char *getThunkPrefix() { return SLSBLRNamePrefix; }
   bool mayUseThunk(const MachineFunction &MF) {
+    ComdatThunks &= !MF.getSubtarget<AArch64Subtarget>().hardenSlsNoComdat();
     // FIXME: This could also check if there are any BLRs in the function
     // to more accurately reflect if a thunk will be needed.
     return MF.getSubtarget<AArch64Subtarget>().hardenSlsBlr();
   }
   void insertThunks(MachineModuleInfo &MMI);
   void populateThunk(MachineFunction &MF);
+
+private:
+  bool ComdatThunks = true;
 };
 } // namespace
 
 void SLSBLRThunkInserter::insertThunks(MachineModuleInfo &MMI) {
   // FIXME: It probably would be possible to filter which thunks to produce
   // based on which registers are actually used in BLR instructions in this
   // function. But would that be a worthwhile optimization?
   for (auto T : SLSBLRThunks)
-    createThunkFunction(MMI, T.Name);
+    createThunkFunction(MMI, T.Name, ComdatThunks);
 }
 
 void SLSBLRThunkInserter::populateThunk(MachineFunction &MF) {
   // FIXME: How to better communicate Register number, rather than through
   // name and lookup table?
   assert(MF.getName().startswith(getThunkPrefix()));
   auto ThunkIt = llvm::find_if(
       SLSBLRThunks, [&MF](auto T) { return T.Name == MF.getName(); });

llvm/lib/Target/AArch64/AArch64Subtarget.h

protected:
   bool UseRSqrt = false;
   bool Force32BitJumpTables = false;
   bool UseEL1ForTP = false;
   bool UseEL2ForTP = false;
   bool UseEL3ForTP = false;
   bool AllowTaggedGlobals = false;
   bool HardenSlsRetBr = false;
   bool HardenSlsBlr = false;
+  bool HardenSlsNoComdat = false;
   uint8_t MaxInterleaveFactor = 2;
   uint8_t VectorInsertExtractBaseCost = 3;
   uint16_t CacheLineSize = 0;
   uint16_t PrefetchDistance = 0;
   uint16_t MinPrefetchStride = 1;
   unsigned MaxPrefetchIterationsAhead = UINT_MAX;
   unsigned PrefFunctionLogAlignment = 0;
   unsigned PrefLoopLogAlignment = 0;
public:
   bool hasFusion() const {
     return hasArithmeticBccFusion() || hasArithmeticCbzFusion() ||
            hasFuseAES() || hasFuseArithmeticLogic() ||
            hasFuseCCSelect() || hasFuseLiterals();
   }
 
   bool hardenSlsRetBr() const { return HardenSlsRetBr; }
   bool hardenSlsBlr() const { return HardenSlsBlr; }
+  bool hardenSlsNoComdat() const { return HardenSlsNoComdat; }
 
   bool useEL1ForTP() const { return UseEL1ForTP; }
   bool useEL2ForTP() const { return UseEL2ForTP; }
   bool useEL3ForTP() const { return UseEL3ForTP; }
 
   bool useRSqrt() const { return UseRSqrt; }
   bool force32BitJumpTables() const { return Force32BitJumpTables; }
   unsigned getMaxInterleaveFactor() const { return MaxInterleaveFactor; }

llvm/lib/Target/ARM/ARM.td

 
 def FeatureHardenSlsRetBr : SubtargetFeature<"harden-sls-retbr",
   "HardenSlsRetBr", "true",
   "Harden against straight line speculation across RETurn and BranchRegister "
   "instructions">;
 def FeatureHardenSlsBlr : SubtargetFeature<"harden-sls-blr",
   "HardenSlsBlr", "true",
   "Harden against straight line speculation across indirect calls">;
-
-
+def FeatureHardenSlsNoComdat : SubtargetFeature<"harden-sls-nocomdat",
+  "HardenSlsNoComdat", "true",
+  "Generate thunk code for SLS mitigation in the normal text section">;
 
 //===----------------------------------------------------------------------===//
 // ARM Processor subtarget features.
 //
 
 def ProcA5      : SubtargetFeature<"a5", "ARMProcFamily", "CortexA5",
                                    "Cortex-A5 ARM processors", []>;
 def ProcA7      : SubtargetFeature<"a7", "ARMProcFamily", "CortexA7",

llvm/lib/Target/ARM/ARMSLSHardening.cpp

bool isThumb;
     {"__llvm_slsblr_thunk_thumb_sp", ARM::SP, true},
     {"__llvm_slsblr_thunk_thumb_pc", ARM::PC, true},
 };
 
 namespace {
 struct SLSBLRThunkInserter : ThunkInserter<SLSBLRThunkInserter> {
   const char *getThunkPrefix() { return SLSBLRNamePrefix; }
   bool mayUseThunk(const MachineFunction &MF) {
+    ComdatThunks &= !MF.getSubtarget<ARMSubtarget>().hardenSlsNoComdat();
     // FIXME: This could also check if there are any indirect calls in the
     // function to more accurately reflect if a thunk will be needed.
     return MF.getSubtarget<ARMSubtarget>().hardenSlsBlr();
   }
   void insertThunks(MachineModuleInfo &MMI);
   void populateThunk(MachineFunction &MF);
+
+private:
+  bool ComdatThunks = true;
 };
 } // namespace
 
 void SLSBLRThunkInserter::insertThunks(MachineModuleInfo &MMI) {
   // FIXME: It probably would be possible to filter which thunks to produce
   // based on which registers are actually used in indirect calls in this
   // function. But would that be a worthwhile optimization?
   for (auto T : SLSBLRThunks)
-    createThunkFunction(MMI, T.Name);
+    createThunkFunction(MMI, T.Name, ComdatThunks);
 }
 
 void SLSBLRThunkInserter::populateThunk(MachineFunction &MF) {
   // FIXME: How to better communicate Register number, rather than through
   // name and lookup table?
   assert(MF.getName().startswith(getThunkPrefix()));
   auto ThunkIt = llvm::find_if(
       SLSBLRThunks, [&MF](auto T) { return T.Name == MF.getName(); });

llvm/lib/Target/ARM/ARMSubtarget.h

protected:
 
   /// Harden against Straight Line Speculation for Returns and Indirect
   /// Branches.
   bool HardenSlsRetBr = false;
 
   /// Harden against Straight Line Speculation for indirect calls.
   bool HardenSlsBlr = false;
 
+  /// Generate thunk code for SLS mitigation in the normal text section.
+  bool HardenSlsNoComdat = false;
+
   /// stackAlignment - The minimum alignment known to hold of the stack frame on
   /// entry to the function and which must be maintained by every function.
   Align stackAlignment = Align(4);
 
   /// CPUString - String name of used CPU.
   std::string CPUString;
 
   unsigned MaxInterleaveFactor = 1;
public:
   }
 
   bool ignoreCSRForAllocationOrder(const MachineFunction &MF,
                                    unsigned PhysReg) const override;
   unsigned getGPRAllocationOrder(const MachineFunction &MF) const;
 
   bool hardenSlsRetBr() const { return HardenSlsRetBr; }
   bool hardenSlsBlr() const { return HardenSlsBlr; }
+  bool hardenSlsNoComdat() const { return HardenSlsNoComdat; }
 };
 
 } // end namespace llvm
 
 #endif  // LLVM_LIB_TARGET_ARM_ARMSUBTARGET_H

llvm/test/CodeGen/AArch64/speculation-hardening-sls.ll

-; RUN: llc -mattr=harden-sls-retbr,harden-sls-blr -verify-machineinstrs -mtriple=aarch64-none-linux-gnu < %s | FileCheck %s --check-prefixes=CHECK,HARDEN,ISBDSB,ISBDSBDAGISEL
+; RUN: llc -mattr=harden-sls-retbr,harden-sls-blr -verify-machineinstrs -mtriple=aarch64-none-linux-gnu < %s | FileCheck %s --check-prefixes=CHECK,HARDEN,HARDEN-COMDAT,ISBDSB,ISBDSBDAGISEL
+; RUN: llc -mattr=harden-sls-retbr,harden-sls-blr,harden-sls-nocomdat -verify-machineinstrs -mtriple=aarch64-none-linux-gnu < %s | FileCheck %s --check-prefixes=CHECK,HARDEN,HARDEN-COMDAT-OFF,ISBDSB,ISBDSBDAGISEL
 ; RUN: llc -mattr=harden-sls-retbr,harden-sls-blr -mattr=+sb -verify-machineinstrs -mtriple=aarch64-none-linux-gnu < %s | FileCheck %s --check-prefixes=CHECK,HARDEN,SB,SBDAGISEL
+; RUN: llc -global-isel -global-isel-abort=0 -mattr=harden-sls-retbr,harden-sls-blr -verify-machineinstrs -mtriple=aarch64-none-linux-gnu < %s | FileCheck %s --check-prefixes=CHECK,HARDEN,HARDEN-COMDAT,ISBDSB
 ; RUN: llc -verify-machineinstrs -mtriple=aarch64-none-linux-gnu < %s | FileCheck %s --check-prefixes=CHECK,NOHARDEN
-; RUN: llc -global-isel -global-isel-abort=0 -mattr=harden-sls-retbr,harden-sls-blr -verify-machineinstrs -mtriple=aarch64-none-linux-gnu < %s | FileCheck %s --check-prefixes=CHECK,HARDEN,ISBDSB
+; RUN: llc -global-isel -global-isel-abort=0 -mattr=harden-sls-retbr,harden-sls-blr,harden-sls-nocomdat -verify-machineinstrs -mtriple=aarch64-none-linux-gnu < %s | FileCheck %s --check-prefixes=CHECK,HARDEN,HARDEN-COMDAT-OFF,ISBDSB
 ; RUN: llc -global-isel -global-isel-abort=0 -mattr=harden-sls-retbr,harden-sls-blr -mattr=+sb -verify-machineinstrs -mtriple=aarch64-none-linux-gnu < %s | FileCheck %s --check-prefixes=CHECK,HARDEN,SB
 
 ; Function Attrs: norecurse nounwind readnone
 define dso_local i32 @double_return(i32 %a, i32 %b) local_unnamed_addr {
 entry:
   %cmp = icmp sgt i32 %a, 0
   br i1 %cmp, label %if.then, label %if.else
 

 ; HARDEN-label: __llvm_slsblr_thunk_x0:
 ; HARDEN:    mov x16, x0
 ; HARDEN:    br x16
 ; ISBDSB-NEXT: dsb sy
 ; ISBDSB-NEXT: isb
 ; SB-NEXT:     dsb sy
 ; SB-NEXT:     isb
 ; HARDEN-NEXT: .Lfunc_end
+; HARDEN-COMDAT:  .section .text.__llvm_slsblr_thunk_x19
+; HARDEN-COMDAT:  .hidden __llvm_slsblr_thunk_x19
+; HARDEN-COMDAT:  .weak __llvm_slsblr_thunk_x19
+; HARDEN-COMDAT: .type  __llvm_slsblr_thunk_x19,@function
+; HARDEN-COMDAT-OFF-NOT:  .section .text.__llvm_slsblr_thunk_x19
+; HARDEN-COMDAT-OFF-NOT:  .hidden __llvm_slsblr_thunk_x19
+; HARDEN-COMDAT-OFF-NOT:  .weak __llvm_slsblr_thunk_x19
+; HARDEN-COMDAT-OFF:      .type __llvm_slsblr_thunk_x19,@function
 ; HARDEN-label: __llvm_slsblr_thunk_x19:
 ; HARDEN:    mov x16, x19
 ; HARDEN:    br x16
 ; ISBDSB-NEXT: dsb sy
 ; ISBDSB-NEXT: isb
 ; SB-NEXT:     dsb sy
 ; SB-NEXT:     isb
 ; HARDEN-NEXT: .Lfunc_end

llvm/test/CodeGen/ARM/speculation-hardening-sls.ll

-; RUN: llc -mattr=harden-sls-retbr -mattr=harden-sls-blr -verify-machineinstrs -mtriple=armv8-linux-gnueabi < %s | FileCheck %s --check-prefixes=CHECK,ARM,HARDEN,ISBDSB -dump-input-context=100
-; RUN: llc -mattr=harden-sls-retbr -mattr=harden-sls-blr -verify-machineinstrs -mtriple=thumbv8-linux-gnueabi < %s | FileCheck %s --check-prefixes=CHECK,THUMB,HARDENTHUMB,HARDEN,ISBDSB -dump-input-context=100
-; RUN: llc -mattr=harden-sls-retbr -mattr=harden-sls-blr -mattr=+sb -verify-machineinstrs -mtriple=armv8-linux-gnueabi < %s | FileCheck %s --check-prefixes=CHECK,ARM,HARDEN,SB -dump-input-context=100
-; RUN: llc -mattr=harden-sls-retbr -mattr=harden-sls-blr -mattr=+sb -verify-machineinstrs -mtriple=thumbv8-linux-gnueabi < %s | FileCheck %s --check-prefixes=CHECK,THUMB,HARDENTHUMB,HARDEN,SB -dump-input-context=100
+; RUN: llc -mattr=harden-sls-retbr -mattr=harden-sls-blr -verify-machineinstrs -mtriple=armv8-linux-gnueabi < %s | FileCheck %s --check-prefixes=CHECK,ARM,HARDEN,HARDEN-COMDAT,ISBDSB -dump-input-context=100
+; RUN: llc -mattr=harden-sls-retbr -mattr=harden-sls-blr -verify-machineinstrs -mtriple=thumbv8-linux-gnueabi < %s | FileCheck %s --check-prefixes=CHECK,THUMB,HARDENTHUMB,HARDEN,HARDEN-COMDAT,ISBDSB -dump-input-context=100
+; RUN: llc -mattr=harden-sls-retbr -mattr=harden-sls-blr -mattr=+sb -verify-machineinstrs -mtriple=armv8-linux-gnueabi < %s | FileCheck %s --check-prefixes=CHECK,ARM,HARDEN,HARDEN-COMDAT,SB -dump-input-context=100
+; RUN: llc -mattr=harden-sls-retbr -mattr=harden-sls-blr -mattr=+sb -verify-machineinstrs -mtriple=thumbv8-linux-gnueabi < %s | FileCheck %s --check-prefixes=CHECK,THUMB,HARDENTHUMB,HARDEN,HARDEN-COMDAT,SB -dump-input-context=100
+; RUN: llc -mattr=harden-sls-retbr -mattr=harden-sls-blr -mattr=harden-sls-nocomdat -verify-machineinstrs -mtriple=armv8-linux-gnueabi < %s | FileCheck %s --check-prefixes=CHECK,ARM,HARDEN,HARDEN-COMDAT-OFF,ISBDSB -dump-input-context=100
+; RUN: llc -mattr=harden-sls-retbr -mattr=harden-sls-blr -mattr=harden-sls-nocomdat -verify-machineinstrs -mtriple=thumbv8-linux-gnueabi < %s | FileCheck %s --check-prefixes=CHECK,THUMB,HARDENTHUMB,HARDEN,HARDEN-COMDAT-OFF,ISBDSB -dump-input-context=100
+; RUN: llc -mattr=harden-sls-retbr -mattr=harden-sls-blr -mattr=harden-sls-nocomdat -mattr=+sb -verify-machineinstrs -mtriple=armv8-linux-gnueabi < %s | FileCheck %s --check-prefixes=CHECK,ARM,HARDEN,HARDEN-COMDAT-OFF,SB -dump-input-context=100
+; RUN: llc -mattr=harden-sls-retbr -mattr=harden-sls-blr -mattr=harden-sls-nocomdat -mattr=+sb -verify-machineinstrs -mtriple=thumbv8-linux-gnueabi < %s | FileCheck %s --check-prefixes=CHECK,THUMB,HARDENTHUMB,HARDEN,HARDEN-COMDAT-OFF,SB -dump-input-context=100
 ; RUN: llc -verify-machineinstrs -mtriple=armv8-linux-gnueabi < %s | FileCheck %s --check-prefixes=CHECK,ARM,NOHARDENARM -dump-input-context=100
 ; RUN: llc -verify-machineinstrs -mtriple=thumbv8-linux-gnueabi < %s | FileCheck %s --check-prefixes=CHECK,THUMB,NOHARDENTHUMB
-; RUN: llc -global-isel -global-isel-abort=0 -mattr=harden-sls-retbr -mattr=harden-sls-blr -verify-machineinstrs -mtriple=armv8-linux-gnueabi < %s | FileCheck %s --check-prefixes=CHECK,ARM,HARDEN,ISBDSB
-; RUN: llc -global-isel -global-isel-abort=0 -mattr=harden-sls-retbr -mattr=harden-sls-blr -verify-machineinstrs -mtriple=thumbv8-linux-gnueabi < %s | FileCheck %s --check-prefixes=CHECK,THUMB,HARDENTHUMB,HARDEN,ISBDSB
+; RUN: llc -global-isel -global-isel-abort=0 -mattr=harden-sls-retbr -mattr=harden-sls-blr -verify-machineinstrs -mtriple=armv8-linux-gnueabi < %s | FileCheck %s --check-prefixes=CHECK,ARM,HARDEN,HARDEN-COMDAT,ISBDSB
+; RUN: llc -global-isel -global-isel-abort=0 -mattr=harden-sls-retbr -mattr=harden-sls-blr -verify-machineinstrs -mtriple=thumbv8-linux-gnueabi < %s | FileCheck %s --check-prefixes=CHECK,THUMB,HARDENTHUMB,HARDEN,HARDEN-COMDAT,ISBDSB
+; RUN: llc -global-isel -global-isel-abort=0 -mattr=harden-sls-retbr -mattr=harden-sls-nocomdat -mattr=harden-sls-blr -verify-machineinstrs -mtriple=armv8-linux-gnueabi < %s | FileCheck %s --check-prefixes=CHECK,ARM,HARDEN,HARDEN-COMDAT-OFF,ISBDSB
+; RUN: llc -global-isel -global-isel-abort=0 -mattr=harden-sls-retbr -mattr=harden-sls-nocomdat -mattr=harden-sls-blr -verify-machineinstrs -mtriple=thumbv8-linux-gnueabi < %s | FileCheck %s --check-prefixes=CHECK,THUMB,HARDENTHUMB,HARDEN,HARDEN-COMDAT-OFF,ISBDSB
 ; RUN: llc -global-isel -global-isel-abort=0 -mattr=harden-sls-retbr -mattr=harden-sls-blr -mattr=+sb -verify-machineinstrs -mtriple=armv8-linux-gnueabi < %s | FileCheck %s --check-prefixes=CHECK,ARM,HARDEN,SB
 ; RUN: llc -global-isel -global-isel-abort=0 -mattr=harden-sls-retbr -mattr=harden-sls-blr -mattr=+sb -verify-machineinstrs -mtriple=thumbv8-linux-gnueabi < %s | FileCheck %s --check-prefixes=CHECK,THUMB,HARDENTHUMB,HARDEN,SB
-; RUN: llc -fast-isel -mattr=harden-sls-retbr -mattr=harden-sls-blr -verify-machineinstrs -mtriple=armv8-linux-gnueabi < %s | FileCheck %s --check-prefixes=CHECK,ARM,HARDEN,ISBDSB
-; RUN: llc -fast-isel -mattr=harden-sls-retbr -mattr=harden-sls-blr -verify-machineinstrs -mtriple=thumbv8-linux-gnueabi < %s | FileCheck %s --check-prefixes=CHECK,THUMB,HARDENTHUMB,HARDEN,ISBDSB
+; RUN: llc -fast-isel -mattr=harden-sls-retbr -mattr=harden-sls-blr -verify-machineinstrs -mtriple=armv8-linux-gnueabi < %s | FileCheck %s --check-prefixes=CHECK,ARM,HARDEN,HARDEN-COMDAT,ISBDSB
+; RUN: llc -fast-isel -mattr=harden-sls-retbr -mattr=harden-sls-blr -verify-machineinstrs -mtriple=thumbv8-linux-gnueabi < %s | FileCheck %s --check-prefixes=CHECK,THUMB,HARDENTHUMB,HARDEN,HARDEN-COMDAT,ISBDSB
+; RUN: llc -fast-isel -mattr=harden-sls-retbr -mattr=harden-sls-blr -mattr=harden-sls-nocomdat -verify-machineinstrs -mtriple=armv8-linux-gnueabi < %s | FileCheck %s --check-prefixes=CHECK,ARM,HARDEN,HARDEN-COMDAT-OFF,ISBDSB
+; RUN: llc -fast-isel -mattr=harden-sls-retbr -mattr=harden-sls-blr -mattr=harden-sls-nocomdat -verify-machineinstrs -mtriple=thumbv8-linux-gnueabi < %s | FileCheck %s --check-prefixes=CHECK,THUMB,HARDENTHUMB,HARDEN,HARDEN-COMDAT-OFF,ISBDSB
 ; RUN: llc -fast-isel -mattr=harden-sls-retbr -mattr=harden-sls-blr -mattr=+sb -verify-machineinstrs -mtriple=armv8-linux-gnueabi < %s | FileCheck %s --check-prefixes=CHECK,ARM,HARDEN,SB
 ; RUN: llc -fast-isel -mattr=harden-sls-retbr -mattr=harden-sls-blr -mattr=+sb -verify-machineinstrs -mtriple=thumbv8-linux-gnueabi < %s | FileCheck %s --check-prefixes=CHECK,THUMB,HARDENTHUMB,HARDEN,SB
 
 ; Function Attrs: norecurse nounwind readnone
 define dso_local i32 @double_return(i32 %a, i32 %b) local_unnamed_addr {
 entry:
   %cmp = icmp sgt i32 %a, 0
   br i1 %cmp, label %if.then, label %if.else
; CHECK: blx r12
   ret void
 ; CHECK:       {{bx lr$}}
 ; ISBDSB-NEXT: dsb sy
 ; ISBDSB-NEXT: isb
 ; SB-NEXT:     {{ sb$}}
 ; CHECK: .Lfunc_end
 }
 
+; HARDEN-COMDAT:  .section {{.text.__llvm_slsblr_thunk_(arm|thumb)_r5}}
+; HARDEN-COMDAT:  .hidden {{__llvm_slsblr_thunk_(arm|thumb)_r5}}
+; HARDEN-COMDAT:  .weak {{__llvm_slsblr_thunk_(arm|thumb)_r5}}
+; HARDEN-COMDAT:  .type {{__llvm_slsblr_thunk_(arm|thumb)_r5}},%function
+; HARDEN-COMDAT-OFF-NOT:  .section {{.text.__llvm_slsblr_thunk_(arm|thumb)_r5}}
+; HARDEN-COMDAT-OFF-NOT:  .hidden {{__llvm_slsblr_thunk_(arm|thumb)_r5}}
+; HARDEN-COMDAT-OFF-NOT:  .weak {{__llvm_slsblr_thunk_(arm|thumb)_r5}}
+; HARDEN-COMDAT-OFF:      .type {{__llvm_slsblr_thunk_(arm|thumb)_r5}},%function
 ; HARDEN-label: {{__llvm_slsblr_thunk_(arm|thumb)_r5}}:
 ; HARDEN:    bx r5
 ; ISBDSB-NEXT: dsb sy
 ; ISBDSB-NEXT: isb
 ; SB-NEXT:     dsb sy
 ; SB-NEXT:     isb
 ; HARDEN-NEXT: .Lfunc_end