Overriding llvmPackage source with local checkout in flake for clang-tools package

5chmidti · August 2, 2025, 9:35am

I am trying to create a dev environment where I can use clang-tools from a locally modified LLVM checkout.
I am not trying to do anything with a special stdenv, I only want to add a customized clang-tools package to the dev env.

My current flake is (flake used via direnv, with --impure due to the path):

{
  description = "A very basic flake";

  inputs = {
    nixpkgs.url = "github:nixos/nixpkgs?ref=nixos-unstable";
  };

  outputs =
    {
      self,
      nixpkgs,
    }:
    let
      system = "x86_64-linux";
      overlays = [
        (final: prev: {
          llvmPackages_custom = prev.llvmPackages_git.override (prev: {
            src = /home/user/dev/llvm/;
            doCheck = false;
            dontUnpack = true;
          });
        })
      ];
      pkgs = import nixpkgs {
        inherit system overlays;
      };
    in
    {
      packages.${system}.default = pkgs.stdenv.mkDerivation {
        name = "test";
        src = ./.;
        buildInputs = [
          pkgs.llvmPackages_custom.clang-tools
          pkgs.spdlog
        ];

      };
    };
}

But it looks like this is not actually overriding the source like I want it to. Instead, it is just llvmPackages_git. I’ve also tried a few permutations of src vs monorepoSrc, override vs overrideAttrs, and llvmPackages_custom vs llvmPackages_custom.clang-tools with no success. I must be doing something wrong here. Can anyone tell me what the correct way to do this would be?

5chmidti · August 7, 2025, 8:26pm

CC @Patryk27 as the maintainer of the clang-tools package. Do you know how I could do this? Or would someone else from the maintainers listed for clang-tools in the nixpkgs search know (I didn’t want to ping 8 people)?

Patryk27 · August 7, 2025, 9:05pm

Hi!

llvmPackages doesn’t have an argument called src, it’s monorepoSrc:

github.com/NixOS/nixpkgs

pkgs/development/compilers/llvm/common/default.nix

71f346c9c


      
            targetLlvmLibraries, # libraries, but from the next stage, for cross
            targetLlvm,
            # This is the default binutils, but with *this* version of LLD rather
            # than the default LLVM version's, if LLD is the choice. We use these for
            # the `useLLVM` bootstrapping below.
            bootBintoolsNoLibc ? if stdenv.targetPlatform.linker == "lld" then null else pkgs.bintoolsNoLibc,
            bootBintools ? if stdenv.targetPlatform.linker == "lld" then null else pkgs.bintools,
            darwin,
            gitRelease ? null,
            officialRelease ? null,
            monorepoSrc ? null,
            version ? null,
            patchesFn ? lib.id,
            # Allows passthrough to packages via newScope. This makes it possible to
            # do `(llvmPackages.override { <someLlvmDependency> = bar; }).clang` and get
            # an llvmPackages whose packages are overridden in an internally consistent way.
            ...
          }@args:
          
          assert lib.assertMsg (lib.xor (gitRelease != null) (officialRelease != null)) (
            "must specify `gitRelease` or `officialRelease`"

… so try doing monorepoSrc = /home/user/dev/llvm;

Let me know if it works - if it still doesn’t, will try to figure it out.

5chmidti · August 7, 2025, 9:32pm

Thanks for the quick reply. That sadly did not work (s/src = /monorepoSrc = ):

user@nixos ~/d/l/flake-test [1]> nix build .
error:
       … while calling the 'derivationStrict' builtin
         at <nix/derivation-internal.nix>:37:12:
           36|
           37|   strict = derivationStrict drvAttrs;
             |            ^
           38|

       … while evaluating derivation 'test'
         whose name attribute is located at /nix/store/9x1a429wj6sy54bfr028820n5mgyvdri-source/pkgs/stdenv/generic/make-derivation.nix:482:13

       … while evaluating attribute 'buildInputs' of derivation 'test'
         at /nix/store/9x1a429wj6sy54bfr028820n5mgyvdri-source/pkgs/stdenv/generic/make-derivation.nix:537:13:
          536|             depsHostHost = elemAt (elemAt dependencies 1) 0;
          537|             buildInputs = elemAt (elemAt dependencies 1) 1;
             |             ^
          538|             depsTargetTarget = elemAt (elemAt dependencies 2) 0;

       (stack trace truncated; use '--show-trace' to show the full, detailed trace)

       error: expected a set but found a path: «unknown»/home/user/dev/llvm

Patryk27 · August 8, 2025, 8:54pm

Okie, approach v2.0:

monorepoSrc = (fetchGit /home/user/dev/llvm) // {
  passthru = {
    owner = "";
    repo = "";
    rev = "";
  };
};

We can’t use a plain path, because LLVM expects for monorepoSrc to be a derivation that builds the source (using fetchGit is the easiest way if you happen to use a Git-based checkout of LLVM), and the seemingly random owner, repo and rev come from here:

github.com/NixOS/nixpkgs

pkgs/development/compilers/llvm/common/common-let.nix

91ad9f491


      
                monorepoSrc'
              else
                let
                  sha256 = releaseInfo.original.sha256;
                  rev = if gitRelease != null then gitRelease.rev else "llvmorg-${releaseInfo.version}";
                in
                fetchFromGitHub rec {
                  owner = "llvm";
                  repo = "llvm-project";
                  inherit rev sha256;
                  passthru = { inherit owner repo rev; };
                };
          
          }

… and are probably used to build some sort of VERSION="..." string later compiled into LLVM for debugging purposes, I guess; but it seems they are not validated whatsoever, so empty strings are good as any.

5chmidti · August 8, 2025, 9:26pm

I think this might be ‘working’, as in getting the right source, but I had to change llvmPackages_git to llvmPackages_21 because it complained about the major version, but I am now stuck at

error: builder for '/nix/store/ds3s71kichv3c7p5zln6xpmflfmyxyms-llvm-21.1.0-rc2.drv' failed with exit code 3;
       last 25 log lines:
       > -- Performing Test HAVE_CXX_FLAG_WTHREAD_SAFETY - Failed
       > -- Performing Test HAVE_CXX_FLAG_COVERAGE
       > -- Performing Test HAVE_CXX_FLAG_COVERAGE - Success
       > -- Compiling and running to test HAVE_GNU_POSIX_REGEX
       > -- Performing Test HAVE_GNU_POSIX_REGEX -- failed to compile
       > -- Compiling and running to test HAVE_POSIX_REGEX
       > -- Performing Test HAVE_POSIX_REGEX -- success
       > -- Compiling and running to test HAVE_STEADY_CLOCK
       > -- Performing Test HAVE_STEADY_CLOCK -- success
       > -- Compiling and running to test HAVE_PTHREAD_AFFINITY
       > -- Performing Test HAVE_PTHREAD_AFFINITY -- success
       > -- Configuring done (8.9s)
       > -- Generating done (1.6s)
       > CMake Warning:
       >   Manually-specified variables were not used by the project:
       >
       >     CMAKE_EXPORT_NO_PACKAGE_REGISTRY
       >     CMAKE_POLICY_DEFAULT_CMP0025
       >     LLVM_ENABLE_TERMINFO
       >
       > 
       > -- Build files have been written to: /build/llvm-src-21.1.0-rc2/llvm/build
       > cmake: enabled parallel building
       > cmake: enabled parallel installing
       > mismatch in the minor version! we have version 21.1.0-rc2 and expected the minor version to be '1'; the source has '0' instead
       For full logs, run:
         nix log /nix/store/ds3s71kichv3c7p5zln6xpmflfmyxyms-llvm-21.1.0-rc2.drv

Is this what you mean with VERSION?
Setting version in override to e.g., "21.1" errors out.

Current flake

{
  description = "A very basic flake";

  inputs = {
    nixpkgs.url = "github:nixos/nixpkgs?ref=nixos-unstable";
  };

  outputs =
    {
      self,
      nixpkgs,
    }:
    let
      system = "x86_64-linux";
      overlays = [
        (final: prev: {
          llvmPackages_custom = prev.llvmPackages_21.override (prev: {
            monorepoSrc = (fetchGit /home/user/dev/llvm) // {
              passthru = {
                owner = "";
                repo = "";
                rev = "";
              };
            };
            doCheck = false;
            dontUnpack = true;
          });
        })
      ];
      pkgs = import nixpkgs {
        inherit system overlays;
      };
    in
    {
      packages.${system}.default = pkgs.stdenv.mkDerivation {
        name = "test";
        src = ./.;
        buildInputs = [
          pkgs.llvmPackages_custom.clang-tools
        ];

      };
    };
}

Patryk27 · August 8, 2025, 9:31pm

How about version = "21.0.0";, then?

5chmidti · August 8, 2025, 9:54pm

That worked (I do get a build error that’s unrelated to my changes though, not sure what the issue would be)

llvm> [381/4817] Building CXX object lib/MC/CMakeFiles/LLVMMC.dir/MCAsmInfoWasm.cpp.o
llvm> [382/4817] Building CXX object lib/IR/CMakeFiles/LLVMCore.dir/RuntimeLibcalls.cpp.o
llvm> FAILED: lib/IR/CMakeFiles/LLVMCore.dir/RuntimeLibcalls.cpp.o
llvm> /nix/store/354j0fc7cccsdlxq7zwbj9d6l59bx6p4-ccache-links-wrapper-4.11.3/bin/g++ -DLLVM_EXPORTS -D_GNU_SOURCE -D__STDC_CONSTANT_MACROS -D__STDC_FORMAT_MACROS -D__STDC_LIMIT_MACROS -I/build/llvm-src-22.0.0-unstable-2025-07-28/llvm/build/lib/IR -I/build/llvm-src-22.0.0-unstable-2025-07-28/llvm/lib/IR -I/build/llvm-src-22.0.0-unstable-2025-07-28/llvm/build/include -I/build/llvm-src-22.0.0-unstable-2025-07-28/llvm/include -fPIC -fno-semantic-interposition -fvisibility-inlines-hidden -Werror=date-time -Wall -Wextra -Wno-unused-parameter -Wwrite-strings -Wcast-qual -Wno-missing-field-initializers -pedantic -Wno-long-long -Wimplicit-fallthrough -Wno-uninitialized -Wno-nonnull -Wno-class-memaccess -Wno-redundant-move -Wno-pessimizing-move -Wno-noexcept-type -Wdelete-non-virtual-dtor -Wsuggest-override -Wno-comment -Wno-misleading-indentation -Wctad-maybe-unsupported -fdiagnostics-color -ffunction-sections -fdata-sections -O3 -DNDEBUG -std=c++17  -fno-exceptions -funwind-tables -MD -MT lib/IR/CMakeFiles/LLVMCore.dir/RuntimeLibcalls.cpp.o -MF lib/IR/CMakeFiles/LLVMCore.dir/RuntimeLibcalls.cpp.o.d -o lib/IR/CMakeFiles/LLVMCore.dir/RuntimeLibcalls.cpp.o -c /build/llvm-src-22.0.0-unstable-2025-07-28/llvm/lib/IR/RuntimeLibcalls.cpp
llvm> In file included from /build/llvm-src-22.0.0-unstable-2025-07-28/llvm/lib/IR/RuntimeLibcalls.cpp:20:
llvm> /build/llvm-src-22.0.0-unstable-2025-07-28/llvm/build/include/llvm/IR/RuntimeLibcalls.inc:2565:26: error: 'const llvm::RTLIB::LibcallImpl llvm::RTLIB::RuntimeLibcallsInfo::DefaultLibcallImpls [814]' is not a static data member of 'struct llvm::RTLIB::RuntimeLibcallsInfo'
llvm>  2565 | const RTLIB::LibcallImpl llvm::RTLIB::RuntimeLibcallsInfo::DefaultLibcallImpls[RTLIB::UNKNOWN_LIBCALL + 1] = {
llvm>       |                          ^~~~
llvm> /build/llvm-src-22.0.0-unstable-2025-07-28/llvm/build/include/llvm/IR/RuntimeLibcalls.inc: In member function 'void llvm::RTLIB::RuntimeLibcallsInfo::setTargetRuntimeLibcallSets(const llvm::Triple&, llvm::FloatABI::ABIType)':
llvm> /build/llvm-src-22.0.0-unstable-2025-07-28/llvm/build/include/llvm/IR/RuntimeLibcalls.inc:17171:3: error: 'initDefaultLibCallImpls' was not declared in this scope
llvm> 17171 |   initDefaultLibCallImpls();
llvm>       |   ^~~~~~~~~~~~~~~~~~~~~~~
llvm> [383/4817] Building CXX object lib/MC/CMakeFiles/LLVMMC.dir/MCAsmInfoXCOFF.cpp.o
llvm> [384/4817] Building CXX object lib/MC/CMakeFiles/LLVMMC.dir/MCInstrInfo.cpp.o
llvm> [385/4817] Building CXX object lib/MC/CMakeFiles/LLVMMC.dir/MCLabel.cpp.o

I’ll try my best to figure it out (unless you have ideas).

Thanks to @Patryk27, here is the flake that almost works:

{
  description = "A very basic flake";

  inputs = {
    nixpkgs.url = "github:nixos/nixpkgs?ref=nixos-unstable";
  };

  outputs =
    {
      self,
      nixpkgs,
    }:
    let
      system = "x86_64-linux";
      overlays = [
        (final: super: {
          llvmPackages_custom = super.llvmPackages_git.override (prev: {
            monorepoSrc = (fetchGit /home/user/dev/llvm) // {
              passthru = {
                owner = "";
                repo = "";
                rev = "";
              };
            };
            version = "22.0.0";
            doCheck = false;
            dontUnpack = true;
          });
        })
      ];
      pkgs = import nixpkgs {
        inherit system overlays;
      };
    in
    {
      packages.${system}.default = pkgs.stdenv.mkDerivation {
        name = "test";
        src = ./.;
        buildInputs = [
          pkgs.llvmPackages_custom.clang-tools
        ];

      };
    };
}

Patryk27 · August 9, 2025, 12:28pm

When you were making those changes to LLVM, have you added any new files to /home/user/dev/llvm?

fetchGit only fetches files that were committed or at least git added to the index.

Patryk27 · August 9, 2025, 12:29pm

I’ve tried to reproduce it locally, on my own copy of LLVM - and in my case the build succeeded:

error: builder for '/nix/store/xzjavw6lfqny1ryzrq7z34paja0nc7bj-test.drv' failed to produce output path for output 'out' at '/nix/store/xzjavw6lfqny1ryzrq7z34paja0nc7bj-test.drv.chroot/root/nix/store/c4ffavhnh9asal54bnmzgrzgk21d9jn4-test'

I mean, it failed, because that test derivation of yours doesn’t produce any output, but the LLVM itself built successfully.

5chmidti · August 9, 2025, 2:51pm

I just tried it with a clean fetch from main (7fb8630e71c4) with no additinal changes and it also fails:

[1533/4817] Building CXX object lib/Transforms/Coroutines/CMakeFiles/LLVMCoroutines.dir/Coroutines.cpp.o
[1534/4817] Building R600GenAsmWriter.inc...
[1535/4817] Building CXX object lib/Transforms/Coroutines/CMakeFiles/LLVMCoroutines.dir/CoroEarly.cpp.o
[1536/4817] Building CXX object lib/Transforms/Coroutines/CMakeFiles/LLVMCoroutines.dir/CoroFrame.cpp.o
[1537/4817] Building CXX object lib/ExecutionEngine/Orc/Shared/CMakeFiles/LLVMOrcShared.dir/SimpleRemoteEPCUtils.cpp.o
[1538/4817] Building CXX object lib/Transforms/CFGuard/CMakeFiles/LLVMCFGuard.dir/CFGuard.cpp.o
[1539/4817] Building CXX object lib/Transforms/HipStdPar/CMakeFiles/LLVMHipStdPar.dir/HipStdPar.cpp.o
[1540/4817] Building R600GenCallingConv.inc...
[1541/4817] Building R600GenSubtargetInfo.inc...
[1542/4817] Building R600GenMCCodeEmitter.inc...
[1543/4817] Building R600GenDAGISel.inc...
FAILED: lib/Target/AMDGPU/R600GenDAGISel.inc /build/llvm-src-22.0.0-unstable-2025-08-03/llvm/build/lib/Target/AMDGPU/R600GenDAGISel.inc 
cd /build/llvm-src-22.0.0-unstable-2025-08-03/llvm/build/lib/Target/AMDGPU && /nix/store/gcc4gk5ayaxpnxvm8pajsxpsw54wwqjj-llvm-tblgen-22.0.0-unstable-2025-08-03/bin/llvm-tblgen -gen-dag-isel -I/build/llvm-src-22.0.0-unstable-2025-08-03>
Included from /build/llvm-src-22.0.0-unstable-2025-08-03/llvm/lib/Target/AMDGPU/R600.td:40:
/build/llvm-src-22.0.0-unstable-2025-08-03/llvm/lib/Target/AMDGPU/R600Instructions.td:1692:1: error: Type set is empty for each HW mode in 'anonymous_8907'
def : ExtractVerticalPat <R600_EXTRACT_ELT_V2, v2i32, i32>;
^
[1544/4817] Building R600GenDFAPacketizer.inc...
[1545/4817] Building HexagonGenAsmMatcher.inc...
[1546/4817] Building R600GenRegisterInfo.inc...
[1547/4817] Building HexagonGenCallingConv.inc...
[1548/4817] Building R600GenInstrInfo.inc...
FAILED: lib/Target/AMDGPU/R600GenInstrInfo.inc /build/llvm-src-22.0.0-unstable-2025-08-03/llvm/build/lib/Target/AMDGPU/R600GenInstrInfo.inc 
cd /build/llvm-src-22.0.0-unstable-2025-08-03/llvm/build/lib/Target/AMDGPU && /nix/store/gcc4gk5ayaxpnxvm8pajsxpsw54wwqjj-llvm-tblgen-22.0.0-unstable-2025-08-03/bin/llvm-tblgen -gen-instr-info -I/build/llvm-src-22.0.0-unstable-2025-08->
Included from /build/llvm-src-22.0.0-unstable-2025-08-03/llvm/lib/Target/AMDGPU/R600.td:40:
/build/llvm-src-22.0.0-unstable-2025-08-03/llvm/lib/Target/AMDGPU/R600Instructions.td:1692:1: error: Type set is empty for each HW mode in 'anonymous_8907'
def : ExtractVerticalPat <R600_EXTRACT_ELT_V2, v2i32, i32>;
^
[1549/4817] Building HexagonGenAsmWriter.inc...
[1550/4817] Building HexagonGenDAGISel.inc...
FAILED: lib/Target/Hexagon/HexagonGenDAGISel.inc /build/llvm-src-22.0.0-unstable-2025-08-03/llvm/build/lib/Target/Hexagon/HexagonGenDAGISel.inc 
cd /build/llvm-src-22.0.0-unstable-2025-08-03/llvm/build/lib/Target/Hexagon && /nix/store/gcc4gk5ayaxpnxvm8pajsxpsw54wwqjj-llvm-tblgen-22.0.0-unstable-2025-08-03/bin/llvm-tblgen -gen-dag-isel -I/build/llvm-src-22.0.0-unstable-2025-08-0>
Included from /build/llvm-src-22.0.0-unstable-2025-08-03/llvm/lib/Target/Hexagon/Hexagon.td:402:
/build/llvm-src-22.0.0-unstable-2025-08-03/llvm/lib/Target/Hexagon/HexagonPatterns.td:526:1: error: Type set is empty for each HW mode in 'anonymous_9818'
def: Pat<(v2i16 (sext V2I1:$Pu)), (S2_vtrunehb (C2_mask V2I1:$Pu))>;
^
[1551/4817] Building AMDGPUGenPostLegalizeGICombiner.inc...
[1552/4817] Building AMDGPUGenDisassemblerTables.inc...
[1553/4817] Building AMDGPUGenGlobalISel.inc...
FAILED: lib/Target/AMDGPU/AMDGPUGenGlobalISel.inc /build/llvm-src-22.0.0-unstable-2025-08-03/llvm/build/lib/Target/AMDGPU/AMDGPUGenGlobalISel.inc 
cd /build/llvm-src-22.0.0-unstable-2025-08-03/llvm/build/lib/Target/AMDGPU && /nix/store/gcc4gk5ayaxpnxvm8pajsxpsw54wwqjj-llvm-tblgen-22.0.0-unstable-2025-08-03/bin/llvm-tblgen -gen-global-isel -I/build/llvm-src-22.0.0-unstable-2025-08>
Included from /build/llvm-src-22.0.0-unstable-2025-08-03/llvm/lib/Target/AMDGPU/AMDGPUGISel.td:13:
Included from /build/llvm-src-22.0.0-unstable-2025-08-03/llvm/lib/Target/AMDGPU/AMDGPU.td:2897:
Included from /build/llvm-src-22.0.0-unstable-2025-08-03/llvm/lib/Target/AMDGPU/SIInstrInfo.td:3439:
Included from /build/llvm-src-22.0.0-unstable-2025-08-03/llvm/lib/Target/AMDGPU/SIInstructions.td:26:
Included from /build/llvm-src-22.0.0-unstable-2025-08-03/llvm/lib/Target/AMDGPU/VOPInstructions.td:2195:
/build/llvm-src-22.0.0-unstable-2025-08-03/llvm/lib/Target/AMDGPU/VOPCInstructions.td:384:7: error: Type set is empty for each HW mode in 'V_CMP_F_F32_e64'
  def _e64 : VOP3_Pseudo<opName, P, getVOPCPat64<cond, P>.ret, /*IsVOP3P*/false, P.HasOpSel>,
      ^
Included from /build/llvm-src-22.0.0-unstable-2025-08-03/llvm/lib/Target/AMDGPU/AMDGPUGISel.td:13:
Included from /build/llvm-src-22.0.0-unstable-2025-08-03/llvm/lib/Target/AMDGPU/AMDGPU.td:2897:
Included from /build/llvm-src-22.0.0-unstable-2025-08-03/llvm/lib/Target/AMDGPU/SIInstrInfo.td:3439:
Included from /build/llvm-src-22.0.0-unstable-2025-08-03/llvm/lib/Target/AMDGPU/SIInstructions.td:26:
Included from /build/llvm-src-22.0.0-unstable-2025-08-03/llvm/lib/Target/AMDGPU/VOPInstructions.td:2195:
/build/llvm-src-22.0.0-unstable-2025-08-03/llvm/lib/Target/AMDGPU/VOPCInstructions.td:587:20: note: instantiated from multiclass
defm V_CMP_F_F32 : VOPC_F32 <"v_cmp_f_f32">;
                   ^
[1554/4817] Building AMDGPUGenMCCodeEmitter.inc...
[1555/4817] Building AMDGPUGenAsmWriter.inc...
[1556/4817] Building AMDGPUGenInstrInfo.inc...
FAILED: lib/Target/AMDGPU/AMDGPUGenInstrInfo.inc /build/llvm-src-22.0.0-unstable-2025-08-03/llvm/build/lib/Target/AMDGPU/AMDGPUGenInstrInfo.inc 
cd /build/llvm-src-22.0.0-unstable-2025-08-03/llvm/build/lib/Target/AMDGPU && /nix/store/gcc4gk5ayaxpnxvm8pajsxpsw54wwqjj-llvm-tblgen-22.0.0-unstable-2025-08-03/bin/llvm-tblgen -gen-instr-info -I/build/llvm-src-22.0.0-unstable-2025-08->
Included from /build/llvm-src-22.0.0-unstable-2025-08-03/llvm/lib/Target/AMDGPU/AMDGPU.td:2897:
Included from /build/llvm-src-22.0.0-unstable-2025-08-03/llvm/lib/Target/AMDGPU/SIInstrInfo.td:3439:
Included from /build/llvm-src-22.0.0-unstable-2025-08-03/llvm/lib/Target/AMDGPU/SIInstructions.td:26:
Included from /build/llvm-src-22.0.0-unstable-2025-08-03/llvm/lib/Target/AMDGPU/VOPInstructions.td:2195:
/build/llvm-src-22.0.0-unstable-2025-08-03/llvm/lib/Target/AMDGPU/VOPCInstructions.td:384:7: error: Type set is empty for each HW mode in 'V_CMP_F_F32_e64'
  def _e64 : VOP3_Pseudo<opName, P, getVOPCPat64<cond, P>.ret, /*IsVOP3P*/false, P.HasOpSel>,
      ^
Included from /build/llvm-src-22.0.0-unstable-2025-08-03/llvm/lib/Target/AMDGPU/AMDGPU.td:2897:
Included from /build/llvm-src-22.0.0-unstable-2025-08-03/llvm/lib/Target/AMDGPU/SIInstrInfo.td:3439:
Included from /build/llvm-src-22.0.0-unstable-2025-08-03/llvm/lib/Target/AMDGPU/SIInstructions.td:26:
Included from /build/llvm-src-22.0.0-unstable-2025-08-03/llvm/lib/Target/AMDGPU/VOPInstructions.td:2195:
/build/llvm-src-22.0.0-unstable-2025-08-03/llvm/lib/Target/AMDGPU/VOPCInstructions.td:587:20: note: instantiated from multiclass
defm V_CMP_F_F32 : VOPC_F32 <"v_cmp_f_f32">;
                   ^
[1557/4817] Building AMDGPUGenMCPseudoLowering.inc...
[1558/4817] Building AMDGPUGenPreLegalizeGICombiner.inc...
[1559/4817] Building AMDGPUGenCallingConv.inc...
[1560/4817] Building AMDGPUGenRegBankGICombiner.inc...
[1561/4817] Building AMDGPUGenSubtargetInfo.inc...
[1562/4817] Building AMDGPUGenAsmMatcher.inc...
[1563/4817] Building AMDGPUGenRegisterInfo.inc...
[1564/4817] Building AMDGPUGenSearchableTables.inc...
[1565/4817] Building AMDGPUGenDAGISel.inc...
FAILED: lib/Target/AMDGPU/AMDGPUGenDAGISel.inc /build/llvm-src-22.0.0-unstable-2025-08-03/llvm/build/lib/Target/AMDGPU/AMDGPUGenDAGISel.inc 
cd /build/llvm-src-22.0.0-unstable-2025-08-03/llvm/build/lib/Target/AMDGPU && /nix/store/gcc4gk5ayaxpnxvm8pajsxpsw54wwqjj-llvm-tblgen-22.0.0-unstable-2025-08-03/bin/llvm-tblgen -gen-dag-isel -I/build/llvm-src-22.0.0-unstable-2025-08-03>
Included from /build/llvm-src-22.0.0-unstable-2025-08-03/llvm/lib/Target/AMDGPU/AMDGPU.td:2897:
Included from /build/llvm-src-22.0.0-unstable-2025-08-03/llvm/lib/Target/AMDGPU/SIInstrInfo.td:3439:
Included from /build/llvm-src-22.0.0-unstable-2025-08-03/llvm/lib/Target/AMDGPU/SIInstructions.td:26:
Included from /build/llvm-src-22.0.0-unstable-2025-08-03/llvm/lib/Target/AMDGPU/VOPInstructions.td:2195:
/build/llvm-src-22.0.0-unstable-2025-08-03/llvm/lib/Target/AMDGPU/VOPCInstructions.td:384:7: error: Type set is empty for each HW mode in 'V_CMP_F_F32_e64'
  def _e64 : VOP3_Pseudo<opName, P, getVOPCPat64<cond, P>.ret, /*IsVOP3P*/false, P.HasOpSel>,
      ^
Included from /build/llvm-src-22.0.0-unstable-2025-08-03/llvm/lib/Target/AMDGPU/AMDGPU.td:2897:
Included from /build/llvm-src-22.0.0-unstable-2025-08-03/llvm/lib/Target/AMDGPU/SIInstrInfo.td:3439:
Included from /build/llvm-src-22.0.0-unstable-2025-08-03/llvm/lib/Target/AMDGPU/SIInstructions.td:26:
Included from /build/llvm-src-22.0.0-unstable-2025-08-03/llvm/lib/Target/AMDGPU/VOPInstructions.td:2195:
/build/llvm-src-22.0.0-unstable-2025-08-03/llvm/lib/Target/AMDGPU/VOPCInstructions.td:587:20: note: instantiated from multiclass
defm V_CMP_F_F32 : VOPC_F32 <"v_cmp_f_f32">;
                   ^
[1566/4817] Building AMDGPUGenRegisterBank.inc...
ninja: build stopped: subcommand failed.

{
  description = "A very basic flake";

  inputs = {
    nixpkgs.url = "github:nixos/nixpkgs?ref=nixos-unstable";
  };

  outputs =
    {
      self,
      nixpkgs,
    }:
    let
      system = "x86_64-linux";
      overlays = [
        (self: super: {
          ccacheWrapper = super.ccacheWrapper.override {
            extraConfig = ''
              export CCACHE_COMPRESS=1
              export CCACHE_DIR="/var/cache/ccache"
              export CCACHE_UMASK=007
              export CCACHE_SLOPPINESS=random_seed
              if [ ! -d "$CCACHE_DIR" ]; then
                echo "====="
                echo "Directory '$CCACHE_DIR' does not exist"
                echo "Please create it with:"
                echo "  sudo mkdir -m0770 '$CCACHE_DIR'"
                echo "  sudo chown root:nixbld '$CCACHE_DIR'"
                echo "====="
                exit 1
              fi
              if [ ! -w "$CCACHE_DIR" ]; then
                echo "====="
                echo "Directory '$CCACHE_DIR' is not accessible for user $(whoami)"
                echo "Please verify its access permissions"
                echo "====="
                exit 1
              fi
            '';
          };
        })
        (final: super: {
          llvmPackages_custom = super.llvmPackages_git.override (prev: {
            monorepoSrc = (fetchGit /home/user/dev/llvm) // {
              passthru = {
                owner = "";
                repo = "";
                rev = "";
              };
            };
            version = "22.0.0";
            doCheck = false;
            dontUnpack = true;
            stdenv = super.ccacheStdenv;
          });
        })
      ];
      pkgs = import nixpkgs {
        inherit system overlays;
      };
    in
    {
      packages.${system}.default = pkgs.stdenv.mkDerivation {
        name = "test";
        src = ./.;
        buildInputs = [
          pkgs.llvmPackages_custom.clang-tools
        ];
      };
    };
}

I mean, it failed, because that test derivation of yours doesn’t produce any output, but the LLVM itself built successfully.

All I need is a dev env where I can test changes I made to tools on external projects (e.g., fmtlib). I’m not trying to package anything, so direnv with use flake /home/user/dev/flake-test --impure is what I am using (just with more packages in buildInputs for the set of projects I want to test).

Patryk27 · August 9, 2025, 3:19pm

Okie, let me try to build this flake as well and we’ll see

Patryk27 · August 9, 2025, 4:28pm

Got the same error, interesting - let’s see what’s going on…

Patryk27 · August 9, 2025, 8:54pm

Okie, another approach - could you try this?

(final: super: {
  llvm_custom = super.llvmPackages_git.llvm.override (prev: {
    src = /home/user/dev/llvm-project;
  });

  llvmPackages_custom = super.llvmPackages_git.override (prev: {
    llvm = final.llvm_custom;
  });
})

(possibly with doCheck = false; to avoid running those tons of tests)

5chmidti · August 9, 2025, 10:21pm

That successfully builds the project (but not with the specified path, it builds the git version specified in nixpkgs, explained in the next post), but sadly ignores the doCheck:

      overlays = [
        (self: super: {
          ccacheWrapper = super.ccacheWrapper.override {
            extraConfig = ''
              export CCACHE_COMPRESS=1
              export CCACHE_DIR="/var/cache/ccache"
              export CCACHE_UMASK=007
              export CCACHE_SLOPPINESS=random_seed
              if [ ! -d "$CCACHE_DIR" ]; then
                echo "====="
                echo "Directory '$CCACHE_DIR' does not exist"
                echo "Please create it with:"
                echo "  sudo mkdir -m0770 '$CCACHE_DIR'"
                echo "  sudo chown root:nixbld '$CCACHE_DIR'"
                echo "====="
                exit 1
              fi
              if [ ! -w "$CCACHE_DIR" ]; then
                echo "====="
                echo "Directory '$CCACHE_DIR' is not accessible for user $(whoami)"
                echo "Please verify its access permissions"
                echo "====="
                exit 1
              fi
            '';
          };
        })
        (final: super: {
          llvm_custom = super.llvmPackages_git.llvm.override (prev: {
            src = /home/user/dev/llvm-project;
            doCheck = false;
            stdenv = super.ccacheStdenv;
          });
          llvmPackages_custom = super.llvmPackages_git.override (prev: {
            llvm = final.llvm_custom;
            doCheck = false;
            stdenv = super.ccacheStdenv;
          });
        })
      ];

building llvm-22.0.0-unstable-2025-08-03 (checkPhase): PASS ...

5chmidti · August 9, 2025, 10:57pm

Alright, so this one actually built the llvmPackages_git version, not the specified one. I noticed that the date in the package name was from a week ago and confirmed it in nixpkgs (either way my changes were not present):

which clang-tidy
/nix/store/jsjydl7sc4gr9j96iqvs7r4cvbpjkban-clang-tools-22.0.0-unstable-2025-08-03/bin/clang-tidy

github.com/NixOS/nixpkgs

pkgs/development/compilers/llvm/default.nix

nixos-unstable


      
            "14.0.6".officialRelease.sha256 = "sha256-vffu4HilvYwtzwgq+NlS26m65DGbp6OSSne2aje1yJE=";
            "15.0.7".officialRelease.sha256 = "sha256-wjuZQyXQ/jsmvy6y1aksCcEDXGBjuhpgngF3XQJ/T4s=";
            "16.0.6".officialRelease.sha256 = "sha256-fspqSReX+VD+Nl/Cfq+tDcdPtnQPV1IRopNDfd5VtUs=";
            "17.0.6".officialRelease.sha256 = "sha256-8MEDLLhocshmxoEBRSKlJ/GzJ8nfuzQ8qn0X/vLA+ag=";
            "18.1.8".officialRelease.sha256 = "sha256-iiZKMRo/WxJaBXct9GdAcAT3cz9d9pnAcO1mmR6oPNE=";
            "19.1.7".officialRelease.sha256 = "sha256-cZAB5vZjeTsXt9QHbP5xluWNQnAHByHtHnAhVDV0E6I=";
            "20.1.6".officialRelease.sha256 = "sha256-PfCzECiCM+k0hHqEUSr1TSpnII5nqIxg+Z8ICjmMj0Y=";
            "21.1.0-rc2".officialRelease.sha256 = "sha256-7qE5MAYuB+gr5NmQm+7jJWCarIjoDUtyd8SDiJwvITw=";
            "22.0.0-git".gitRelease = {
              rev = "144cd87088dc82263b25e816c77fc03f29fd1288";
              rev-version = "22.0.0-unstable-2025-08-03";
              sha256 = "sha256-DtY1OcpquPQ+dXTyuVggrK5gO7H5xgoZajf/ZONCQ7o=";
            };
          }
          // llvmVersions;
          
          mkPackage =
            {
              name ? null,
              officialRelease ? null,
              gitRelease ? null,

Using monorepoSrc again did also not work

tmayoff · October 24, 2025, 11:50pm

Were you able to get llvm overridden I’m trying to do something similar but with this fork. I tried all sorts of things including this fork of nixpkgs. No matter what I try it builds the original llvm (if I override llvmPackages_21 it’s clang 21, if I try llvmPackages_git it’ll be what’s in the git version, currently 22.0.0). The changes and flake I’m trying to do this in is here