[HLSL][DirectX] Add the Qdx-rootsignature-strip driver option #154454

inbelic · 2025-08-20T01:43:52Z

This pr adds the Qstrip-rootsignature as a DXC driver option.

To do so, this pr introduces the BinaryModifyJobClass as an Action to modify a produced object file before its final output.

Further, it registers llvm-objcopy as the tool to modify a produced DXContainer on the HLSL toolchain.

This allows us to specify the Qstrip-rootsignature option to clang-dxc which will invoke llvm-objcopy with a --remove-section=RTS0 argument to implement its functionality.

Resolves: #150275.

llvmbot · 2025-08-20T01:44:24Z

@llvm/pr-subscribers-hlsl
@llvm/pr-subscribers-clang

@llvm/pr-subscribers-clang-driver

Author: Finn Plummer (inbelic)

Changes

It pr adds the Qstrip-rootsignature as a DXC driver option.

To do so, this pr introduces the BinaryModifyJobClass as an Action to modify a produced object file before its final output.

Further, it registers llvm-objcopy as the tool to modify a produced DXContainer on the HLSL toolchain.

This allows us to specify the Qstrip-rootsignature option to clang-dxc which will invoke llvm-objcopy with a --remove-section=RTS0 argument to implement its functionality.

Resolves: #150275.

Full diff: https://github.com/llvm/llvm-project/pull/154454.diff

9 Files Affected:

(modified) clang/include/clang/Basic/CodeGenOptions.def (+3)
(modified) clang/include/clang/Driver/Action.h (+13-1)
(modified) clang/include/clang/Driver/Options.td (+6)
(modified) clang/lib/Driver/Action.cpp (+7)
(modified) clang/lib/Driver/Driver.cpp (+10)
(modified) clang/lib/Driver/ToolChain.cpp (+1)
(modified) clang/lib/Driver/ToolChains/HLSL.cpp (+39-2)
(modified) clang/lib/Driver/ToolChains/HLSL.h (+15)
(added) clang/test/Driver/dxc_strip_rootsignature.hlsl (+22)

diff --git a/clang/include/clang/Basic/CodeGenOptions.def b/clang/include/clang/Basic/CodeGenOptions.def
index 423b696785500..89e9f5b5853bb 100644
--- a/clang/include/clang/Basic/CodeGenOptions.def
+++ b/clang/include/clang/Basic/CodeGenOptions.def
@@ -479,6 +479,9 @@ CODEGENOPT(StaticClosure, 1, 0, Benign)
 /// Assume that UAVs/SRVs may alias
 CODEGENOPT(ResMayAlias, 1, 0, Benign)
 
+/// Omit the root signature from produced DXContainer
+CODEGENOPT(HLSLRootSigStrip, 1, 0, Benign)
+
 /// Controls how unwind v2 (epilog) information should be generated for x64
 /// Windows.
 ENUM_CODEGENOPT(WinX64EHUnwindV2, WinX64EHUnwindV2Mode,
diff --git a/clang/include/clang/Driver/Action.h b/clang/include/clang/Driver/Action.h
index 7aecfd886adb8..6fc515f9e4049 100644
--- a/clang/include/clang/Driver/Action.h
+++ b/clang/include/clang/Driver/Action.h
@@ -76,9 +76,10 @@ class Action {
     StaticLibJobClass,
     BinaryAnalyzeJobClass,
     BinaryTranslatorJobClass,
+    BinaryModifyJobClass,
 
     JobClassFirst = PreprocessJobClass,
-    JobClassLast = BinaryTranslatorJobClass
+    JobClassLast = BinaryModifyJobClass
   };
 
   // The offloading kind determines if this action is binded to a particular
@@ -687,6 +688,17 @@ class BinaryTranslatorJobAction : public JobAction {
   }
 };
 
+class BinaryModifyJobAction : public JobAction {
+  void anchor() override;
+
+public:
+  BinaryModifyJobAction(Action *Input, types::ID Type);
+
+  static bool classof(const Action *A) {
+    return A->getKind() == BinaryModifyJobClass;
+  }
+};
+
 } // namespace driver
 } // namespace clang
 
diff --git a/clang/include/clang/Driver/Options.td b/clang/include/clang/Driver/Options.td
index 6aab43c9ed57f..1bd3f09ae1df1 100644
--- a/clang/include/clang/Driver/Options.td
+++ b/clang/include/clang/Driver/Options.td
@@ -9381,6 +9381,12 @@ def res_may_alias : Option<["/", "-"], "res-may-alias", KIND_FLAG>,
   Visibility<[DXCOption, ClangOption, CC1Option]>,
   HelpText<"Assume that UAVs/SRVs may alias">,
   MarshallingInfoFlag<CodeGenOpts<"ResMayAlias">>;
+def dxc_strip_rootsignature :
+  Option<["/", "-"], "Qstrip-rootsignature", KIND_FLAG>,
+  Group<dxc_Group>,
+  Visibility<[DXCOption]>,
+  HelpText<"Omit the root signature from produced DXContainer">,
+  MarshallingInfoFlag<CodeGenOpts<"HLSLRootSigStrip">>;
 def target_profile : DXCJoinedOrSeparate<"T">, MetaVarName<"<profile>">,
   HelpText<"Set target profile">,
   Values<"ps_6_0, ps_6_1, ps_6_2, ps_6_3, ps_6_4, ps_6_5, ps_6_6, ps_6_7,"
diff --git a/clang/lib/Driver/Action.cpp b/clang/lib/Driver/Action.cpp
index ec09726044812..fbf80b3c6f124 100644
--- a/clang/lib/Driver/Action.cpp
+++ b/clang/lib/Driver/Action.cpp
@@ -52,6 +52,8 @@ const char *Action::getClassName(ActionClass AC) {
     return "binary-analyzer";
   case BinaryTranslatorJobClass:
     return "binary-translator";
+  case BinaryModifyJobClass:
+    return "binary-modifier";
   }
 
   llvm_unreachable("invalid class");
@@ -467,3 +469,8 @@ void BinaryTranslatorJobAction::anchor() {}
 BinaryTranslatorJobAction::BinaryTranslatorJobAction(Action *Input,
                                                      types::ID Type)
     : JobAction(BinaryTranslatorJobClass, Input, Type) {}
+
+void BinaryModifyJobAction::anchor() {}
+
+BinaryModifyJobAction::BinaryModifyJobAction(Action *Input, types::ID Type)
+    : JobAction(BinaryModifyJobClass, Input, Type) {}
diff --git a/clang/lib/Driver/Driver.cpp b/clang/lib/Driver/Driver.cpp
index 586f287843f3e..59a4eadcd5d85 100644
--- a/clang/lib/Driver/Driver.cpp
+++ b/clang/lib/Driver/Driver.cpp
@@ -4601,6 +4601,16 @@ void Driver::BuildActions(Compilation &C, DerivedArgList &Args,
         Actions.push_back(C.MakeAction<BinaryTranslatorJobAction>(
             LastAction, types::TY_DX_CONTAINER));
     }
+    if (TC.requiresObjcopy(Args)) {
+      Action *LastAction = Actions.back();
+      // llvm-objcopy expects a DXIL container, which can either be
+      // validated (in which case they are TY_DX_CONTAINER), or unvalidated
+      // (TY_OBJECT).
+      if (LastAction->getType() == types::TY_DX_CONTAINER ||
+          LastAction->getType() == types::TY_Object)
+        Actions.push_back(C.MakeAction<BinaryModifyJobAction>(
+            LastAction, types::TY_DX_CONTAINER));
+    }
   }
 
   // Claim ignored clang-cl options.
diff --git a/clang/lib/Driver/ToolChain.cpp b/clang/lib/Driver/ToolChain.cpp
index 25c6b5a486fd5..713bda1d7244d 100644
--- a/clang/lib/Driver/ToolChain.cpp
+++ b/clang/lib/Driver/ToolChain.cpp
@@ -652,6 +652,7 @@ Tool *ToolChain::getTool(Action::ActionClass AC) const {
   case Action::VerifyDebugInfoJobClass:
   case Action::BinaryAnalyzeJobClass:
   case Action::BinaryTranslatorJobClass:
+  case Action::BinaryModifyJobClass:
     llvm_unreachable("Invalid tool kind.");
 
   case Action::CompileJobClass:
diff --git a/clang/lib/Driver/ToolChains/HLSL.cpp b/clang/lib/Driver/ToolChains/HLSL.cpp
index 38f4643abad98..a554c15f1e7c6 100644
--- a/clang/lib/Driver/ToolChains/HLSL.cpp
+++ b/clang/lib/Driver/ToolChains/HLSL.cpp
@@ -247,6 +247,30 @@ void tools::hlsl::MetalConverter::ConstructJob(
                                          Exec, CmdArgs, Inputs, Input));
 }
 
+void tools::hlsl::LLVMObjcopy::ConstructJob(Compilation &C, const JobAction &JA,
+                                            const InputInfo &Output,
+                                            const InputInfoList &Inputs,
+                                            const ArgList &Args,
+                                            const char *LinkingOutput) const {
+
+  std::string ObjcopyPath = getToolChain().GetProgramPath("llvm-objcopy");
+  const char *Exec = Args.MakeArgString(ObjcopyPath);
+
+  ArgStringList CmdArgs;
+  assert(Inputs.size() == 1 && "Unable to handle multiple inputs.");
+  const InputInfo &Input = Inputs[0];
+  CmdArgs.push_back(Input.getFilename());
+  CmdArgs.push_back(Output.getFilename());
+
+  if (Args.hasArg(options::OPT_dxc_strip_rootsignature)) {
+    const char *Frs = Args.MakeArgString("--remove-section=RTS0");
+    CmdArgs.push_back(Frs);
+  }
+
+  C.addCommand(std::make_unique<Command>(JA, *this, ResponseFileSupport::None(),
+                                         Exec, CmdArgs, Inputs, Input));
+}
+
 /// DirectX Toolchain
 HLSLToolChain::HLSLToolChain(const Driver &D, const llvm::Triple &Triple,
                              const ArgList &Args)
@@ -267,6 +291,10 @@ Tool *clang::driver::toolchains::HLSLToolChain::getTool(
     if (!MetalConverter)
       MetalConverter.reset(new tools::hlsl::MetalConverter(*this));
     return MetalConverter.get();
+  case Action::BinaryModifyJobClass:
+    if (!LLVMObjcopy)
+      LLVMObjcopy.reset(new tools::hlsl::LLVMObjcopy(*this));
+    return LLVMObjcopy.get();
   default:
     return ToolChain::getTool(AC);
   }
@@ -404,16 +432,25 @@ bool HLSLToolChain::requiresBinaryTranslation(DerivedArgList &Args) const {
   return Args.hasArg(options::OPT_metal) && Args.hasArg(options::OPT_dxc_Fo);
 }
 
+bool HLSLToolChain::requiresObjcopy(DerivedArgList &Args) const {
+  return Args.hasArg(options::OPT_dxc_Fo) &&
+         Args.hasArg(options::OPT_dxc_strip_rootsignature);
+}
+
 bool HLSLToolChain::isLastJob(DerivedArgList &Args,
                               Action::ActionClass AC) const {
   bool HasTranslation = requiresBinaryTranslation(Args);
   bool HasValidation = requiresValidation(Args);
+  bool HasObjcopy = requiresObjcopy(Args);
   // If translation and validation are not required, we should only have one
   // action.
-  if (!HasTranslation && !HasValidation)
+  if (!HasTranslation && !HasValidation && !HasObjcopy)
     return true;
   if ((HasTranslation && AC == Action::BinaryTranslatorJobClass) ||
-      (!HasTranslation && HasValidation && AC == Action::BinaryAnalyzeJobClass))
+      (!HasTranslation && HasValidation &&
+       AC == Action::BinaryAnalyzeJobClass) ||
+      (!HasTranslation && !HasValidation && HasObjcopy &&
+       AC == Action::BinaryModifyJobClass))
     return true;
   return false;
 }
diff --git a/clang/lib/Driver/ToolChains/HLSL.h b/clang/lib/Driver/ToolChains/HLSL.h
index 3824b4252324b..b81141b26b4e6 100644
--- a/clang/lib/Driver/ToolChains/HLSL.h
+++ b/clang/lib/Driver/ToolChains/HLSL.h
@@ -42,6 +42,19 @@ class LLVM_LIBRARY_VISIBILITY MetalConverter : public Tool {
                     const llvm::opt::ArgList &TCArgs,
                     const char *LinkingOutput) const override;
 };
+
+class LLVM_LIBRARY_VISIBILITY LLVMObjcopy : public Tool {
+public:
+  LLVMObjcopy(const ToolChain &TC)
+      : Tool("hlsl::LLVMObjcopy", "llvm-objcopy", TC) {}
+
+  bool hasIntegratedCPP() const override { return false; }
+
+  void ConstructJob(Compilation &C, const JobAction &JA,
+                    const InputInfo &Output, const InputInfoList &Inputs,
+                    const llvm::opt::ArgList &TCArgs,
+                    const char *LinkingOutput) const override;
+};
 } // namespace hlsl
 } // namespace tools
 
@@ -65,6 +78,7 @@ class LLVM_LIBRARY_VISIBILITY HLSLToolChain : public ToolChain {
   static std::optional<std::string> parseTargetProfile(StringRef TargetProfile);
   bool requiresValidation(llvm::opt::DerivedArgList &Args) const;
   bool requiresBinaryTranslation(llvm::opt::DerivedArgList &Args) const;
+  bool requiresObjcopy(llvm::opt::DerivedArgList &Args) const;
   bool isLastJob(llvm::opt::DerivedArgList &Args, Action::ActionClass AC) const;
 
   // Set default DWARF version to 4 for DXIL uses version 4.
@@ -73,6 +87,7 @@ class LLVM_LIBRARY_VISIBILITY HLSLToolChain : public ToolChain {
 private:
   mutable std::unique_ptr<tools::hlsl::Validator> Validator;
   mutable std::unique_ptr<tools::hlsl::MetalConverter> MetalConverter;
+  mutable std::unique_ptr<tools::hlsl::LLVMObjcopy> LLVMObjcopy;
 };
 
 } // end namespace toolchains
diff --git a/clang/test/Driver/dxc_strip_rootsignature.hlsl b/clang/test/Driver/dxc_strip_rootsignature.hlsl
new file mode 100644
index 0000000000000..b4af1f4b1541d
--- /dev/null
+++ b/clang/test/Driver/dxc_strip_rootsignature.hlsl
@@ -0,0 +1,22 @@
+// RUN: %clang_dxc -Qstrip-rootsignature -T cs_6_0 -HV 202x -Vd /Fo %t %s
+// RUN: obj2yaml %t | FileCheck %s
+// RUN: obj2yaml %t | FileCheck %s --check-prefix=OTHERS
+
+// Test to demonstrate that we specify to the root signature with the
+// -Qstrip-rootsignature option
+
+// CHECK-NOT: RTS0
+
+// OTHERS: FileSize:       1964
+// OTHERS-NEXT: PartCount:      6
+// OTHERS: Parts:
+// OTHERS: Name:            DXIL
+// OTHERS: Name:            SFI0
+// OTHERS: Name:            HASH
+// OTHERS: Name:            ISG1
+// OTHERS: Name:            OSG1
+// OTHERS: Name:            PSV0
+
+[shader("compute"), RootSignature("")]
+[numthreads(1,1,1)]
+void EmptyEntry() {}

clang/include/clang/Driver/Action.h

llvm-beanz · 2025-08-21T13:39:03Z

clang/lib/Driver/Driver.cpp

+      // llvm-objcopy expects a DXIL container, which can either be
+      // validated (in which case they are TY_DX_CONTAINER), or unvalidated
+      // (TY_OBJECT).
+      if (LastAction->getType() == types::TY_DX_CONTAINER ||


Should we be running this before validation rather than after? What does DXC do?

Yep, DXC will construct the final output blob before running the validator. So it would validate with the parts removed.

clang/lib/Driver/ToolChains/HLSL.cpp

clang/lib/Driver/ToolChains/HLSL.h

- DXC will invoke the validator after the final blob has been generated (in this case after the part is removed)

bogner · 2025-08-22T15:45:28Z

clang/lib/Driver/Driver.cpp

@@ -4647,6 +4647,16 @@ void Driver::BuildDefaultActions(Compilation &C, DerivedArgList &Args,
    // Only add action when needValidation.


The comments around the isDXIL block look like they're out of date or at least misplaced (both this one and the "Call validator" one above.

bogner · 2025-08-22T15:46:51Z

clang/lib/Driver/ToolChains/HLSL.h

+class LLVM_LIBRARY_VISIBILITY LLVMObjcopy : public Tool {
+public:
+  LLVMObjcopy(const ToolChain &TC) : Tool("LLVMObjcopy", "llvm-objcopy", TC) {}
+
+  bool hasIntegratedCPP() const override { return false; }
+
+  void ConstructJob(Compilation &C, const JobAction &JA,
+                    const InputInfo &Output, const InputInfoList &Inputs,
+                    const llvm::opt::ArgList &TCArgs,
+                    const char *LinkingOutput) const override;
+};


LLVMObjcopy fairly generic, even if we are only using it in the HLSL toolchain right now. Should this class be defined somewhere less toolchain specific?

While it is generic, the logic of ConstructJob is specific to just the hlsl toolchain.

It is convention for the other toolchains to each redefine their own version of the struct with their namespace prefixed. See Linker etc.

So I have added back the hlsl namespace to this struct.

clang/lib/Driver/ToolChains/HLSL.cpp

clang/lib/Driver/Driver.cpp

farzonl · 2025-08-22T16:16:54Z

Wait for Justin or Chris, this isn't my area of expertise.

- following convention used from other toolchains (eg. `Linker`), each toolchain will need to define a custom override of `ConstructJob` so that it converts the applicable arguments accordingly - since this will be toolchain specific, it is convention to prefix it with the toolchain namespace (hlsl::)

bogner · 2025-08-25T16:28:43Z

clang/lib/Driver/ToolChains/HLSL.cpp

-  if (!HasTranslation && !HasValidation)
+  if (!HasTranslation && !HasValidation && !HasObjcopy)
    return true;
  if ((HasTranslation && AC == Action::BinaryTranslatorJobClass) ||
-      (!HasTranslation && HasValidation && AC == Action::BinaryAnalyzeJobClass))
+      (!HasTranslation && HasValidation &&
+       AC == Action::BinaryAnalyzeJobClass) ||
+      (!HasTranslation && !HasValidation && HasObjcopy &&
+       AC == Action::ObjcopyJobClass))
    return true;
  return false;


This logic is getting a bit unweildy. Would it simplify things to work from the last job backwards? That is,

if (HasObjcopy) return AC == Action::ObjcopyJobClass; if (HasValidation) return AC == Action::BinaryAnalyzeJobClass; if (HasTranslation) return AC == Action::BinaryTranslatorJobClass; // If none of translation, validation, or objcopy are required, we should only // have one action return true;

bogner · 2025-08-25T16:31:12Z

clang/include/clang/Basic/CodeGenOptions.def

+/// Omit the root signature from produced DXContainer
+CODEGENOPT(HLSLRootSigStrip, 1, 0, Benign)


Do we need this anymore? I don't see it being used, and I would think that making this a separate tool's job would make this unnecessary.

llvmbot added clang Clang issues not falling into any other category clang:driver 'clang' and 'clang++' user-facing binaries. Not 'clang-cl' clang:frontend Language frontend issues, e.g. anything involving "Sema" HLSL HLSL Language Support labels Aug 20, 2025

inbelic linked an issue Aug 20, 2025 that may be closed by this pull request

[HLSL][RootSignature] Add support for Qstrip_rootsignature compiler flag #150275

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llvm-beanz reviewed Aug 21, 2025

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inbelic and others added 3 commits August 21, 2025 11:01

add BinaryModifyJobClass

0f11eb0

[HLSL] Add the Qstrip-rootsignature DXC driver option

acfd4d5

review: use terminology directed for objcopy

f3f3a07

inbelic changed the base branch from users/inbelic/pr-153246 to main August 21, 2025 18:53

inbelic force-pushed the inbelic/rs-strip branch from 644f3b1 to 4830024 Compare August 21, 2025 18:53

inbelic added 2 commits August 21, 2025 11:54

review: add assert

f8ff016

review: apply objcopy before validation

154c2b0

- DXC will invoke the validator after the final blob has been generated (in this case after the part is removed)

inbelic force-pushed the inbelic/rs-strip branch from 4830024 to 154c2b0 Compare August 21, 2025 18:54

bogner reviewed Aug 22, 2025

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farzonl reviewed Aug 22, 2025

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farzonl approved these changes Aug 22, 2025

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llvm-beanz reviewed Aug 22, 2025

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inbelic added 2 commits August 22, 2025 10:35

review: improve comments

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bogner reviewed Aug 25, 2025

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inbelic added 2 commits August 25, 2025 17:31

review: remove unused marshalling

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review: clarify isLastJob check

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inbelic force-pushed the inbelic/rs-strip branch from 6bdf65e to 7dd6205 Compare August 25, 2025 18:18

inbelic added 2 commits August 25, 2025 18:19

self-review: little clean-up

514063b

review: correct job order and add test that validation occurs after

2945de4

bogner approved these changes Aug 26, 2025

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inbelic merged commit 74a4d81 into llvm:main Aug 26, 2025
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aemerson mentioned this pull request Aug 30, 2025

[NFC] [clangd] [Modules] remove dot in log #156207

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		@@ -4647,6 +4647,16 @@ void Driver::BuildDefaultActions(Compilation &C, DerivedArgList &Args,
		// Only add action when needValidation.

		/// Omit the root signature from produced DXContainer
		CODEGENOPT(HLSLRootSigStrip, 1, 0, Benign)

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