[Clang][Driver] Fix the missing Target-Triple-Level include path resolution in Baremetal Driver #165321

simpal01 · 2025-10-27T21:33:45Z

The current baremetal driver implementation does not have a way to derive the target-triple-level include path within the sysroot.

This feature is especially useful in setups where header paths deviate from the default bare-metal assumptions. For example, when headers are shared across target triples, it becomes necessary to organise them under target-triple-specific directories to ensure correct resolution..

…lution in Baremetal Driver The current baremetal driver implementation does not have a way to derive the target-triple-level include path within the sysroot. This feature is especially useful in setups where header paths deviate from the default bare-metal assumptions. For example, when headers are shared across target triples, it becomes necessary to organize them under target-triple-specific directories to ensure correct resolution..

llvmbot · 2025-10-27T21:34:18Z

@llvm/pr-subscribers-clang

Author: Simi Pallipurath (simpal01)

Changes

The current baremetal driver implementation does not have a way to derive the target-triple-level include path within the sysroot.

This feature is especially useful in setups where header paths deviate from the default bare-metal assumptions. For example, when headers are shared across target triples, it becomes necessary to organise them under target-triple-specific directories to ensure correct resolution..

Full diff: https://github.com/llvm/llvm-project/pull/165321.diff

1 Files Affected:

(modified) clang/lib/Driver/ToolChains/BareMetal.cpp (+14-1)

diff --git a/clang/lib/Driver/ToolChains/BareMetal.cpp b/clang/lib/Driver/ToolChains/BareMetal.cpp
index 9b7f58c392885..d048f228f4572 100644
--- a/clang/lib/Driver/ToolChains/BareMetal.cpp
+++ b/clang/lib/Driver/ToolChains/BareMetal.cpp
@@ -408,6 +408,8 @@ void BareMetal::AddClangSystemIncludeArgs(const ArgList &DriverArgs,
   if (DriverArgs.hasArg(options::OPT_nostdlibinc))
     return;
 
+  const Driver &D = getDriver();
+
   if (std::optional<std::string> Path = getStdlibIncludePath())
     addSystemInclude(DriverArgs, CC1Args, *Path);
 
@@ -418,6 +420,13 @@ void BareMetal::AddClangSystemIncludeArgs(const ArgList &DriverArgs,
       llvm::sys::path::append(Dir, M.includeSuffix());
       llvm::sys::path::append(Dir, "include");
       addSystemInclude(DriverArgs, CC1Args, Dir.str());
+
+      Dir = SysRootDir;
+      llvm::sys::path::append(Dir, getTripleString());
+      if (D.getVFS().exists(Dir)) {
+        llvm::sys::path::append(Dir, "include");
+        addSystemInclude(DriverArgs, CC1Args, Dir.str());
+      }
     }
   }
 }
@@ -498,9 +507,13 @@ void BareMetal::AddClangCXXStdlibIncludeArgs(const ArgList &DriverArgs,
         addSystemInclude(DriverArgs, CC1Args, TargetDir.str());
         break;
       }
-      // Add generic path if nothing else succeeded so far.
+      // Add generic paths if nothing else succeeded so far.
       llvm::sys::path::append(Dir, "include", "c++", "v1");
       addSystemInclude(DriverArgs, CC1Args, Dir.str());
+      Dir = SysRootDir;
+      llvm::sys::path::append(Dir, Target, "include", "c++", "v1");
+      if (D.getVFS().exists(Dir))
+        addSystemInclude(DriverArgs, CC1Args, Dir.str());
       break;
     }
     case ToolChain::CST_Libstdcxx: {

llvmbot · 2025-10-27T21:34:18Z

@llvm/pr-subscribers-clang-driver

Author: Simi Pallipurath (simpal01)

Changes

The current baremetal driver implementation does not have a way to derive the target-triple-level include path within the sysroot.

This feature is especially useful in setups where header paths deviate from the default bare-metal assumptions. For example, when headers are shared across target triples, it becomes necessary to organise them under target-triple-specific directories to ensure correct resolution..

Full diff: https://github.com/llvm/llvm-project/pull/165321.diff

1 Files Affected:

(modified) clang/lib/Driver/ToolChains/BareMetal.cpp (+14-1)

diff --git a/clang/lib/Driver/ToolChains/BareMetal.cpp b/clang/lib/Driver/ToolChains/BareMetal.cpp
index 9b7f58c392885..d048f228f4572 100644
--- a/clang/lib/Driver/ToolChains/BareMetal.cpp
+++ b/clang/lib/Driver/ToolChains/BareMetal.cpp
@@ -408,6 +408,8 @@ void BareMetal::AddClangSystemIncludeArgs(const ArgList &DriverArgs,
   if (DriverArgs.hasArg(options::OPT_nostdlibinc))
     return;
 
+  const Driver &D = getDriver();
+
   if (std::optional<std::string> Path = getStdlibIncludePath())
     addSystemInclude(DriverArgs, CC1Args, *Path);
 
@@ -418,6 +420,13 @@ void BareMetal::AddClangSystemIncludeArgs(const ArgList &DriverArgs,
       llvm::sys::path::append(Dir, M.includeSuffix());
       llvm::sys::path::append(Dir, "include");
       addSystemInclude(DriverArgs, CC1Args, Dir.str());
+
+      Dir = SysRootDir;
+      llvm::sys::path::append(Dir, getTripleString());
+      if (D.getVFS().exists(Dir)) {
+        llvm::sys::path::append(Dir, "include");
+        addSystemInclude(DriverArgs, CC1Args, Dir.str());
+      }
     }
   }
 }
@@ -498,9 +507,13 @@ void BareMetal::AddClangCXXStdlibIncludeArgs(const ArgList &DriverArgs,
         addSystemInclude(DriverArgs, CC1Args, TargetDir.str());
         break;
       }
-      // Add generic path if nothing else succeeded so far.
+      // Add generic paths if nothing else succeeded so far.
       llvm::sys::path::append(Dir, "include", "c++", "v1");
       addSystemInclude(DriverArgs, CC1Args, Dir.str());
+      Dir = SysRootDir;
+      llvm::sys::path::append(Dir, Target, "include", "c++", "v1");
+      if (D.getVFS().exists(Dir))
+        addSystemInclude(DriverArgs, CC1Args, Dir.str());
       break;
     }
     case ToolChain::CST_Libstdcxx: {

simpal01 · 2025-10-28T11:27:45Z

https://discourse.llvm.org/t/rfc-support-target-triple-specific-include-paths-derived-from-sysroot-via-multilib-yaml-or-driver-logic/86925/6?u=simpal01

simpal01 · 2025-11-12T15:21:59Z

@petrhosek Please review this patch. This is one of the solutions provided to support Target Triple–specific include paths in the bare-metal driver via hard coded path.

and another solution is via multilib.yaml which is added here #146651. This is more favourable both within the team and based on the feedback received in the RFC https://discourse.llvm.org/t/rfc-support-target-triple-specific-include-paths-derived-from-sysroot-via-multilib-yaml-or-driver-logic/86925/6

petrhosek · 2025-11-13T08:01:07Z

clang/lib/Driver/ToolChains/BareMetal.cpp

+      Dir = SysRootDir;
+      llvm::sys::path::append(Dir, Target, "include", "c++", "v1");
+      if (D.getVFS().exists(Dir))
+        addSystemInclude(DriverArgs, CC1Args, Dir.str());


Since this logic is unrelated to multilibs, this should be done inside AddCXXIncludePath.

AddCXXIncludePath(Path) is currently passed a path derived from a top-level include directory that isn’t rooted in the active --sysroot. What this PR is actually aiming for is to derive the target-triple-level include path within the sysroot itself. But here the sysroot computation happens after the AddCXXIncludePath(Path) call.

I see, I still think we need to move this logic outside of the multilib loop to avoid adding the include directory multiple times. I think this entire loop might need to be restructured since I don't think it's actually correct, so it might be probably easiest for now to just move the new logic outside.

petrhosek · 2025-11-13T08:01:44Z

clang/lib/Driver/ToolChains/BareMetal.cpp

+      Dir = SysRootDir;
+      llvm::sys::path::append(Dir, getTripleString());
+      if (D.getVFS().exists(Dir)) {
+        llvm::sys::path::append(Dir, "include");
+        addSystemInclude(DriverArgs, CC1Args, Dir.str());


This is unrelated to multilibs so should be done outside of the loop.

petrhosek · 2025-11-13T08:03:52Z

Would it be possible to also add a test case in clang/test/Driver/baremetal.cpp?

…th resolution in Baremetal Driver

github-actions · 2025-11-17T21:47:17Z

🐧 Linux x64 Test Results

111272 tests passed
4418 tests skipped

simpal01 · 2025-11-19T20:38:02Z

support Target Triple–specific include paths in the bare-metal driver

In this patch, the target-triple–specific header path is added only if the corresponding directory exists on the host system. Since the LLVM test environment doesn’t include such a layout, it’s not possible to test this behaviour purely within clang/test/Driver using the in-tree setup.

I did verify it locally using the Arm Toolchain for Embedded (ATFE), which provides exactly this header layout, and confirmed that the driver picks up the correct triple-specific include directory.

Separately, I have an alternate patch that adds support for target-triple-specific include paths in the bare-metal driver via multilib.yaml configuration, #146651 . That approach is what our team prefers, and in that case I was able to include appropriate driver tests, as the include paths are conditionally added based on entries available in the multilib.yaml file. Would you like to take a look at that patch too?

petrhosek · 2025-11-20T06:52:00Z

clang/lib/Driver/ToolChains/BareMetal.cpp

      llvm::sys::path::append(Dir, "include");
      addSystemInclude(DriverArgs, CC1Args, Dir.str());
    }
+    SmallString<128> Dir = SysRootDir;


Nit: I'd use copy constructor over assignment operator for consistency with the existing code.

Suggested change

SmallString<128> Dir = SysRootDir;

SmallString<128> Dir(SysRootDir);

petrhosek · 2025-11-20T06:55:43Z

support Target Triple–specific include paths in the bare-metal driver

In this patch, the target-triple–specific header path is added only if the corresponding directory exists on the host system. Since the LLVM test environment doesn’t include such a layout, it’s not possible to test this behaviour purely within clang/test/Driver using the in-tree setup.

The way we typically handle that is by constructing the artificial directory layout in https://github.com/llvm/llvm-project/tree/main/clang/test/Driver/Inputs for testing, see for example https://github.com/llvm/llvm-project/tree/main/clang/test/Driver/Inputs/basic_baremetal_tree.

Separately, I have an alternate patch that adds support for target-triple-specific include paths in the bare-metal driver via multilib.yaml configuration, #146651 . That approach is what our team prefers, and in that case I was able to include appropriate driver tests, as the include paths are conditionally added based on entries available in the multilib.yaml file. Would you like to take a look at that patch too?

Sure, but I'd like to merge this change as well since we have customers who don't use multilib.yaml and asked for this change.

llvmbot added clang Clang issues not falling into any other category clang:driver 'clang' and 'clang++' user-facing binaries. Not 'clang-cl' labels Oct 27, 2025

simpal01 requested a review from petrhosek October 28, 2025 10:56

simpal01 mentioned this pull request Nov 12, 2025

[Multilib] Extend the Multilib system to support an IncludeDirs field. #146651

Open

petrhosek reviewed Nov 13, 2025

View reviewed changes

simpal01 force-pushed the add-target-level-include-paths branch from ed2e69d to c664b02 Compare November 17, 2025 20:58

fixup! [Clang][Driver] Fix the missing Target-Triple-Level include pa…

a1e7c03

…th resolution in Baremetal Driver

petrhosek reviewed Nov 20, 2025

View reviewed changes

	SmallString<128> Dir = SysRootDir;
	SmallString<128> Dir(SysRootDir);

[Clang][Driver] Fix the missing Target-Triple-Level include path resolution in Baremetal Driver #165321

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[Clang][Driver] Fix the missing Target-Triple-Level include path resolution in Baremetal Driver #165321

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