flang: can't compile

[yannickulrich]

Nixpkgs version

• Stable (25.11)

Describe the bug

When invoking flang to compile and link a fortran program, the linker fails

/nix/store/i839kg98izahkn1iq17sn3wliliic7pm-binutils-2.44/bin/ld: cannot find Scrt1.o: No such file or directory
/nix/store/i839kg98izahkn1iq17sn3wliliic7pm-binutils-2.44/bin/ld: cannot find crti.o: No such file or directory
/nix/store/i839kg98izahkn1iq17sn3wliliic7pm-binutils-2.44/bin/ld: cannot find crtbeginS.o: No such file or directory
flang-20: error: linker command failed with exit code 1 (use -v to see invocation)

Steps to reproduce

Take a simple fortran program like

! test.f95
program test
  print*, 'test'
end program

and run

$ nix-shell -p flang
$ flang test.f95

Expected behaviour

Flang correctly identifies & links the runtime. For example,

$ flang -c test.f95 
/nix/store/kilyfvfmh9x9rlaj47ph1916lbc1pnsr-gcc-wrapper-14.3.0/bin/ld \
  --hash-style=gnu --eh-frame-hdr -m elf_x86_64 -pie -o a.out \
  /nix/store/pdwlyjkmc6icc0wb5gaw08m9ynqrg683-glibc-2.40-218/lib/Scrt1.o \
  /nix/store/pdwlyjkmc6icc0wb5gaw08m9ynqrg683-glibc-2.40-218/lib/crti.o \
  /nix/store/06409a3d2d3b1113zdk9rm5a3ns4rizz-gcc-14.3.0/lib/gcc/x86_64-unknown-linux-gnu/14.3.0/crtbeginS.o \
  -L/lib/../lib64 -L/lib test.o  \
  -L/nix/store/8rvn83lz6095k0rsqz958szcjb19687v-flang-20.1.8/lib \
  -L/nix/store/aas6l2pmz2wpd0lrk0cldnhzxvgjafik-gfortran-14.3.0-libgcc/lib \
  -L/nix/store/06409a3d2d3b1113zdk9rm5a3ns4rizz-gcc-14.3.0/lib/gcc/x86_64-unknown-linux-gnu/14.3.0/ \
  -lFortranRuntime -lFortranDecimal -lm -lgcc --as-needed -lgcc_s --no-as-needed -lc -lgcc --as-needed -lgcc_s --no-as-needed \
   /nix/store/06409a3d2d3b1113zdk9rm5a3ns4rizz-gcc-14.3.0/lib/gcc/x86_64-unknown-linux-gnu/14.3.0/crtendS.o \
  /nix/store/pdwlyjkmc6icc0wb5gaw08m9ynqrg683-glibc-2.40-218/lib/crtn.o

### Screenshots

_No response_

### Relevant log output

```console
flang version 20.1.8
Target: x86_64-unknown-linux-gnu
Thread model: posix
InstalledDir: /nix/store/8rvn83lz6095k0rsqz958szcjb19687v-flang-20.1.8/bin
 "/nix/store/8rvn83lz6095k0rsqz958szcjb19687v-flang-20.1.8/bin/flang" -fc1 -triple x86_64-unknown-linux-gnu -emit-obj -mrelocation-model pic -pic-level 2 -pic-is-pie -target-cpu x86-64 -resource-dir /nix/store/8rvn83lz6095k0rsqz958szcjb19687v-flang-20.1.8/lib/clang/20 -mframe-pointer=all -o /tmp/nix-shell-655059-1096684053/test-3f96cf.o -x f95-cpp-input test.f95
 "/nix/store/kilyfvfmh9x9rlaj47ph1916lbc1pnsr-gcc-wrapper-14.3.0/bin/ld" --hash-style=gnu --eh-frame-hdr -m elf_x86_64 -pie -o a.out Scrt1.o crti.o crtbeginS.o -L/lib/../lib64 -L/lib /tmp/nix-shell-655059-1096684053/test-3f96cf.o -L/nix/store/8rvn83lz6095k0rsqz958szcjb19687v-flang-20.1.8/lib -lFortranRuntime -lFortranDecimal -lm -lgcc --as-needed -lgcc_s --no-as-needed -lc -lgcc --as-needed -lgcc_s --no-as-needed crtendS.o crtn.o
/nix/store/i839kg98izahkn1iq17sn3wliliic7pm-binutils-2.44/bin/ld: cannot find Scrt1.o: No such file or directory
/nix/store/i839kg98izahkn1iq17sn3wliliic7pm-binutils-2.44/bin/ld: cannot find crti.o: No such file or directory
/nix/store/i839kg98izahkn1iq17sn3wliliic7pm-binutils-2.44/bin/ld: cannot find crtbeginS.o: No such file or directory
flang-20: error: linker command failed with exit code 1 (use -v to see invocation)

Additional context

No response

System metadata

• system: "x86_64-linux"
• host os: Linux 6.12.82, NixOS, 25.11 (Xantusia), 25.11.9476.e07580dae397
• multi-user?: yes
• sandbox: yes
• version: nix-env (Nix) 2.31.4
• channels(yannickulrich): ""
• channels(root): "home-manager-25.11.tar.gz, nixos-25.11, nixos-hardware, nixos-unstable"
• nixpkgs: /nix/store/k1k2aj8razdy1db8lrdpr9wgq9g2kqi3-nixos-25.11/nixos

Notify maintainers

@Acture

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[chopsticks-user]

Scrt1.o crti.o and crtn.o are provided by glibc while libgcc provides crtbeginS.o and crtendS.o along with gcc libraries. flang's source doesn't seem to have the two packages in buildInputs. A temporary solution for the time being:

nix shell nixpkgs#flang

alias flang-wrapped="flang -B/nix/store/jms7zxzm7w1whczwny5m3gkgdjghmi2r-glibc-2.42-51/lib -B/nix/store/wn351sdqain3snlj8snyqwg5wlwc2d2h-libgcc-x86_64-unknown-linux-gnu-15.2.0/lib/gcc/x86_64-unknown-linux-gnu/15.2.0 -L/nix/store/wn351sdqain3snlj8snyqwg5wlwc2d2h-libgcc-x86_64-unknown-linux-gnu-15.2.0/lib"

flang-wrapped test.f95

[Acture]

Thanks for the report. The root cause is that on 25.11 flang is shipped as the bare binary and is not run through cc-wrapper, so NIX_LDFLAGS (which would inject -L<glibc>/lib and -L<gcc-libs>/lib) never reaches the linker — hence the bare-named Scrt1.o / crti.o / crtbeginS.o cannot be located.

This is being fixed by #452306. The PR is large and touches the LLVM/clang package set, so it will take some time to land. As a workaround on current 25.11, you can either invoke the linker manually or use gfortran instead.