no_builtin flag isn't always respected. #32125

Zig Version

0.17.0-dev.135+9df02121d

Steps to Reproduce and Observed Behavior

I'm building my kernel module with the following config but when trying to do floating point computation Zig emits builtin calls which shall not happen with the .no_builtin = true flag.

varkernel_target=target;kernel_target.query.cpu_arch=kernel_target.query.cpu_archorelse@import("builtin").cpu.arch;kernel_target.query=switch(kernel_target.query.cpu_arch.?){.x86_64=>.{.cpu_arch=.x86_64,.os_tag=.freestanding,.abi=.none,.cpu_features_add=std.Target.x86.featureSet(&.{.soft_float,.retpoline,.retpoline_external_thunk}),.cpu_features_sub=std.Target.x86.featureSet(&.{.mmx,.sse,.sse2,.avx,.avx2}),},else=>@panic("Correct feature flags unimplemented for target arch..."),};constobject_options:std.Build.ObjectOptions=.{.name="pside_zig",.use_llvm=true,.root_module=b.createModule(.{.root_source_file=b.path("src/kernelspace/main.zig"),.target=kernel_target,.optimize=kernel_optimize,.link_libc=false,.link_libcpp=false,.single_threaded=true,.strip=false,.unwind_tables=.none,.code_model=.kernel,.stack_protector=false,.stack_check=false,.pic=false,.red_zone=false,.omit_frame_pointer=false,.error_tracing=false,.no_builtin=true,.imports=&.{.{.name="communications",.module=communications_mod},.{.name="kernel",.module=bindings_mod},.{.name="serialization",.module=serialization_mod},},}),};

❯ zig build
make -C /lib/modules/6.19.14-arch1-1/build M=/home/giuseppe/Documents/pside/.zig-cache/o/f179c7b7eaad6c04f3dd98eccb0cdd4b modules
make[1]: Entering directory '/usr/lib/modules/6.19.14-arch1-1/build'
make[2]: Entering directory '/home/giuseppe/Documents/pside/.zig-cache/o/f179c7b7eaad6c04f3dd98eccb0cdd4b'
 MODPOST Module.symvers
ERROR: modpost: "__divsf3" [pside.ko] undefined!
ERROR: modpost: "__floatundisf" [pside.ko] undefined!
make[4]: *** [/usr/lib/modules/6.19.14-arch1-1/build/scripts/Makefile.modpost:147: Module.symvers] Error 1
make[3]: *** [/usr/lib/modules/6.19.14-arch1-1/build/Makefile:2015: modpost] Error 2
make[2]: *** [/usr/lib/modules/6.19.14-arch1-1/build/Makefile:248: __sub-make] Error 2
make[2]: Leaving directory '/home/giuseppe/Documents/pside/.zig-cache/o/f179c7b7eaad6c04f3dd98eccb0cdd4b'
make[1]: *** [Makefile:248: __sub-make] Error 2
make[1]: Leaving directory '/usr/lib/modules/6.19.14-arch1-1/build'
make: *** [Makefile:8: all] Error 2

Expected Behavior

If I'm not mistaken, such functions shall be included in the binary itself and not be treated as provided externally. Moreover, I feel like this is a regression since some time ago I was doing this exact thing and everything was compiling.

Well, in all fairness, I'm not sure what LLVM should be expected to do if it's directed to emit soft float code but also not emit libcalls. An error might have been nice, but ultimately there's nothing useful to do.

Understandable, but then which configuration would give access to the builtins without external dependencies? Because even turning no_builtin = false, soft floating point symbols are not found and I feel like I did not prevent the linkage of any library that would be necessary for such definitions in my build.zig.

Here is a minimal repo which shows the behavior.

You'd need to bundle compiler-rt into your object file. That's zig build-obj -fcompiler-rt on the command line, but I forget the corresponding build system field.

Thank you and sorry for the wrongful report.

For reference

constobj=b.addObject(...);// or could be any other b.addExe or addLibrary or similarobj.bundle_compiler_rt=true;// the methods don't have an option for this