ABI breakages in 4.4

[Tobias Burnus]

Thomas Koenig wrote:
>> just a heads-up: we have a couple of ABI breakages where 4.3-compiled
>> programs don't work correctly with the 4.4 library, namely PR 37498

The problem is that the struct passed for I/O has been modified to allow
Fortran 2003 features (UTF-8, rounding, decimal comma etc.). The problem
is that in libgfortran the new struct is expected, but gfortran 4.3
programs only passes a shorter struct. In the PR this causes that values
in an unrelated array are overwritten.

Do you have an idea how this should be solved?

a) Change the library number and thus be not backward compatible. (This
is likely needed for the next version again as we need to change the
internal array representation to fix some bugs, which should then be
compatible to the new C interoperability TR.)

b) Create special 4.3 versions of the procedure, making use of the
versioned symbols.

c) Something else?

Somehow, the interwoven nature of Fortran with its library makes it
difficult to maintain backwards compatibility without replicating large
parts of the code -- at least as soon as structs are involved. On the
other hand, having libgfortran backward compatibility is a useful goal,
e.g. to use AMD's ACML with newer gfortran compilers. So far we every
major version had an incompatible library: 4.0, 4.1, 4.2, 4.3 and 4.4 :-(

Tobias