Curious linker error for libgsl past GHC 9.6

tmplt · December 18, 2025, 1:33pm

I’m working on a library that uses hmatrix-gsl. Past GHC 9.6 I’m getting confusing linker errors for libgsl.so: undefined symbol: cblas_ctrmv. An LD_PRELOAD=/nix/store/<HASH>-gsl-2.8/lib/libgslcblas.so fixes the issue, but I do not understand why the symbol is no longer resolved in later toolchain versions; the same libgslcblas.so shows up in ldd for both builds, after all.

I’m using Nix and haskell-flake, and have an MWE available via GitHub - tmplt/hmatrix-gsl-mwe

This issue was originally posted at libgslcblas link issue past GHC 9.6 · srid/haskell-flake · Discussion #464 · GitHub , but this feels more like a Cabal issue, so I’m trying here.

Any help appreciated!

sergv · December 23, 2025, 11:43pm

After briefly looking around I notice that hmatrix-gsl package does have an onlygsl flag. When enabled it will use linking flags obtained from pkg-config which seem to specify gslcblas which is what you seem to be after.

github.com/haskell-numerics/hmatrix

packages/gsl/hmatrix-gsl.cabal

master


      
          flag onlygsl
              description:    don't link gslcblas
              default:        False

Your hunch about cabal (meaning cabal-install, the executable) might be correct - cabal might or may not decide to turn this flag on when you upgrade to a different cabal version. The fix is to pass the flags you want explicitly. How to do it with nix is another matter.

tmplt · January 8, 2026, 4:13pm

Thanks for the suggestion. I’ve updated the MWE to include development environments for both builds: both use cabal 3.16.0.0. Turning flags on/off yielded the same results. Perhaps this is a Nix issue. I’ll leave this open until I find the source of the issue.