ispc: unbreak on darwin

[yzx9]

ispc was broken on darwin for a month:

• aarch64-darwin: https://hydra.nixos.org/build/310588348
• x86_64-darwin: https://hydra.nixos.org/build/310588351

error:

/private/tmp/nix-build-ispc-1.28.2.drv-0/source/src/util.cpp:50:11: error: exception specification in declaration does not match previous declaration
   50 | void std::__libcpp_verbose_abort(char const *format, ...)
      |           ^
/nix/store/1h3bqrd2kvj4afq9xkaxvx4skdnfbql2-libcxx-19.1.2+apple-sdk-15.5/include/c++/v1/__verbose_abort:24:49: note: previous declaration is here
   24 | _LIBCPP_ATTRIBUTE_FORMAT(__printf__, 1, 2) void __libcpp_verbose_abort(const char* __format, ...);
      |                                                 ^
1 error generated.

ZHF: #457852

Things done

• Built on platform:
  • x86_64-linux
  • aarch64-linux
  • x86_64-darwin
  • aarch64-darwin
• Tested, as applicable:
  • NixOS tests in nixos/tests.
  • Package tests at passthru.tests.
  • Tests in lib/tests or pkgs/test for functions and "core" functionality.
• Ran nixpkgs-review on this PR. See nixpkgs-review usage.
• Tested basic functionality of all binary files, usually in ./result/bin/.
• Nixpkgs Release Notes
  • Package update: when the change is major or breaking.
• NixOS Release Notes
  • Module addition: when adding a new NixOS module.
  • Module update: when the change is significant.
• Fits CONTRIBUTING.md, pkgs/README.md, maintainers/README.md and other READMEs.

---

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[iedame]

nixpkgs-review result

Generated using nixpkgs-review-gha

Command: nixpkgs-review pr 458797
Commit: 699551b88170f4fd0c10ed8b7e957198094a7a48 (subsequent changes)
Merge: fa80d6f8251a5581ebcdfa00cbb706fa7f673657

Logs: https://github.com/iedame/nixpkgs-review-gha/actions/runs/19101402300

---

x86_64-linux

✅ No rebuilds

---

aarch64-linux

✅ No rebuilds

---

x86_64-darwin (sandbox = relaxed)

❌ 12 packages failed to build:

• embree
• f3d
• ispc
• meshlab
• openimagedenoise
• openusd
• python312Packages.f3d
• python312Packages.openusd
• python312Packages.pymeshlab (python313Packages.pymeshlab)
• python313Packages.f3d
• python313Packages.openusd
• rbdoom-3-bfg

---

Error logs: `x86_64-darwin`

ispc

PASSRATE (1565/1567) = 99% 
1565 / 1576 tests PASSED

2 / 1576 tests FAILED compilation

./tests/func-tests/round-float16-uniform.ispc

./tests/func-tests/round-float16-varying.ispc

0 / 1576 tests FAILED execution

9 / 1576 tests SKIPPED

./tests/func-tests/select-short-vec-func.ispc

./tests/func-tests/transcendentals-10-0.ispc

./tests/func-tests/transcendentals-sincos-uniform-float16.ispc

./tests/func-tests/transcendentals-sincos-uniform.ispc

./tests/func-tests/transcendentals-sincos-varying-float16.ispc

./tests/func-tests/transcendentals-sincos-varying.ispc

./tests/func-tests/xe-task-count.ispc

./tests/func-tests/xe-task-index-1.ispc

./tests/func-tests/xe-task-index.ispc

NEW COMPFAILS:

./tests/func-tests/round-float16-uniform.ispc

./tests/func-tests/round-float16-varying.ispc

---

aarch64-darwin (sandbox = relaxed)

❌ 7 packages failed to build:

• f3d
• meshlab
• openusd
• python312Packages.f3d
• python312Packages.pymeshlab (python313Packages.pymeshlab)
• python313Packages.f3d
• rbdoom-3-bfg

✅ 5 packages built:

• embree
• ispc
• openimagedenoise
• python312Packages.openusd
• python313Packages.openusd

---

Error logs: `aarch64-darwin`

meshlab

patching file src/external/levmar.cmake
patching file src/external/lib3mf.cmake
patching file src/external/libigl.cmake
patching file src/external/nexus.cmake
patching file src/CMakeLists.txt
patching file src/Config.cmake.in
patching file src/common/CMakeLists.txt
patching file src/meshlabplugins/io_base/CMakeLists.txt
applying patch /nix/store/cr374x9wf7qpfvwkjddf8kpjrmjcc2dh-no-plist.patch
can't find file to patch at input line 3
Perhaps you used the wrong -p or --strip option?
The text leading up to this was:
--------------------------
|--- src/meshlab/CMakeLists.txt.orig	2025-10-05 23:04:12.786192073 +0200
|+++ src/meshlab/CMakeLists.txt	2025-10-05 23:04:16.379256637 +0200
--------------------------
File to patch: 
Skip this patch? [y] 
Skipping patch.
1 out of 1 hunk ignored

rbdoom-3-bfg

[ 13%] Building CXX object extern/nvrhi/CMakeFiles/nvrhi_vk.dir/src/vulkan/vulkan-shader.cpp.o
[ 13%] Building CXX object idlib/CMakeFiles/idlib.dir/math/Polynomial.cpp.o
[ 13%] Building CXX object idlib/CMakeFiles/idlib.dir/math/Quat.cpp.o
[ 14%] Building CXX object idlib/CMakeFiles/idlib.dir/math/Rotation.cpp.o
[ 14%] Building CXX object idlib/CMakeFiles/idlib.dir/math/Simd.cpp.o
[ 14%] Building CXX object idlib/CMakeFiles/idlib.dir/math/Simd_Generic.cpp.o
[ 14%] Building CXX object idlib/CMakeFiles/idlib.dir/math/Simd_SSE.cpp.o
[ 14%] Building CXX object idlib/CMakeFiles/idlib.dir/math/VecX.cpp.o
[ 14%] Building CXX object idlib/CMakeFiles/idlib.dir/math/Vector.cpp.o
[ 15%] Building CXX object idlib/CMakeFiles/idlib.dir/sys/sys_assert.cpp.o
[ 15%] Building CXX object idlib/CMakeFiles/idlib.dir/sys/posix/posix_thread.cpp.o
[ 15%] Building CXX object extern/nvrhi/CMakeFiles/nvrhi_vk.dir/src/vulkan/vulkan-staging-texture.cpp.o
[ 16%] Building CXX object extern/nvrhi/CMakeFiles/nvrhi_vk.dir/src/vulkan/vulkan-state-tracking.cpp.o
[ 16%] Linking CXX static library libidlib.a
[ 16%] Built target idlib
[ 16%] Building CXX object extern/nvrhi/CMakeFiles/nvrhi_vk.dir/src/vulkan/vulkan-texture.cpp.o
[ 16%] Building CXX object extern/nvrhi/CMakeFiles/nvrhi_vk.dir/src/vulkan/vulkan-upload.cpp.o
[ 16%] Linking CXX static library libnvrhi_vk.a
[ 16%] Built target nvrhi_vk
make: *** [Makefile:136: all] Error 2

[yzx9]

Failures on aarch64-darwin are unrelated to this PR, while the x86_64-darwin error looks weird. Maybe we should mark x86_64-darwin again and wait for someone interested in investigating it, since I’m unable to fix it as I don’t have an x86_64-darwin device.

[alexfmpe]

Do we know why we need to workaround this way? #445934 had no issue so maybe an update of some dep hit an edge case and we exposed an upstream bug.
I'm running a bisect to try to find the nixpkgs commit that broke this.

I don’t have an x86_64-darwin device.

With Rosetta you can do nix-build -A ispc --argstr system "x86_64-darwin" to have build/host be treated as x86_64-darwin, which will also run tests

[yzx9]

I would suspect that #407738, which changed the default LLVM from 19 to 21, might be the cause.

Update: I can now confirm it's related — the build works fine with LLVM 19 without any patches. I suspect this is due to an LLVM version mismatch: the build uses libcxx 19 (from darwin stdenv), while LLVM 21 is provided as a runtime dependency.

[yzx9]

@alexfmpe Thanks for your help! I've built it with Rosetta. Here’s the error message on x86_64-darwin:

> nix log /nix/store/kyl4kf4zi6la53g6b602abj13xmy661b-ispc-1.28.2.drv | grep ".ispc failed" -B2 -A5
Running:  ./tests/func-tests/ptr-null-func-arg.ispc.run
Running: /nix/var/nix/builds/nix-34069-4230430288/source/build/bin/ispc  -I /nix/var/nix/builds/nix-34069-4230430288/source/tests --pic --woff /nix/var/nix/builds/nix-34069-4230430288/source/tests/func-tests/1546.ispc -o ./tests/func-tests/1546.ispc.o --arch=x86-64 --target=sse2-i32x4 -DTEST_SIG=1 -O2 -h /nix/var/nix/builds/nix-34069-4230430288/source/tests/func-tests/1546.ispc.h
Compilation of test ./tests/func-tests/round-float16-uniform.ispc failed            
Undefined symbols for architecture x86_64:
  "_roundevenf", referenced from:
      _f_f___un_3C_unf_3E_un_3C_unf_3E_ in round-float16-uniform.ispc.o
ld: symbol(s) not found for architecture x86_64
clang++: error: linker command failed with exit code 1 (use -v to see invocation)
--
Running: clang++ -O2 -I tests/ -m64 tests/test_static.cpp -DTEST_SIG=0 -DTEST_WIDTH=4 ./tests/func-tests/test-23.ispc.o -o ./tests/func-tests/test-23.ispc.run -fPIE -DTEST_HEADER="</nix/var/nix/builds/nix-34069-4230430288/source/tests/func-tests/test-23.ispc.h>"
Running: /nix/var/nix/builds/nix-34069-4230430288/source/build/bin/ispc  -I /nix/var/nix/builds/nix-34069-4230430288/source/tests --pic --woff /nix/var/nix/builds/nix-34069-4230430288/source/tests/func-tests/struct-forward-decl.ispc -o ./tests/func-tests/struct-forward-decl.ispc.o --arch=x86-64 --target=sse2-i32x4 -DTEST_SIG=1 -O2 -h /nix/var/nix/builds/nix-34069-4230430288/source/tests/func-tests/struct-forward-decl.ispc.h
Compilation of test ./tests/func-tests/round-float16-varying.ispc failed            
Undefined symbols for architecture x86_64:
  "_roundevenf", referenced from:
      _f_f___un_3C_unf_3E_un_3C_unf_3E_ in round-float16-varying.ispc.o
ld: symbol(s) not found for architecture x86_64
clang++: error: linker command failed with exit code 1 (use -v to see invocation)

I also tried switching to LLVM 19, but that didn’t fix the issue on x86_64-darwin. I found a similar issue (ispc/ispc#3529), so we might be able to just skip these tests on x86_64-darwin.