Fortran ABI issues with character arguments #650
Description
Hello,
this is a heads-up about an issue that appears to affect Julia based on a quick perusal of the source code (https://github.com/JuliaLang/julia/blob/master/stdlib/LinearAlgebra/src/blas.jl and https://github.com/JuliaLang/julia/blob/master/stdlib/LinearAlgebra/src/lapack.jl , maybe other files in the repo too).
When calling Fortran procedures that have character arguments, the character lengths have to be passed from the caller to the callee. Typically Fortran ABI's place these hidden (hidden in the sense that the Fortran programmer doesn't need to care about it, the compiler takes care of it behind the scenes) at the end of the argument list. Now, unfortunately it seems common to omit these hidden character length arguments when calling BLAS or LAPACK procedures with single-length characters.
While this has worked (apparently adequately?) for several decades, in light of increasingly sophisticated compiler optimizations, for instance interprocedural or link-time optimizations, such sins are unfortunately coming back to haunt us.
The upstream GFortran bug report: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=90329
CBLAS/LAPACKE bug report, which has become a sort of gathering-place for links to various incantations of this bug on github: Reference-LAPACK/lapack#339
There's even a LWN article: https://lwn.net/Articles/791393/
And one of the R developers who first discovered that this ABI mismatch could cause a (very subtle) problem wrote a nice overview: https://developer.r-project.org/Blog/public/2019/05/15/gfortran-issues-with-lapack/