https://gcc.gnu.org/bugzilla/show_bug.cgi?id=41227
--- Comment #22 from Tobias Burnus <burnus at gcc dot gnu.org> --- (In reply to rguent...@suse.de from comment #19) > > Well, Bill Long of Cray seems to agree with my interpretation, cf. > > http://mailman.j3-fortran.org/pipermail/j3/2010-February/003358.html > > But that answer suggests we get it wrong (currenty interoperating > with the C struct { int i; } works and with the plain decl it > doesn't). The answer specifically doesn't say that only (1) > is valid. As I stumbled over it again (and missed what I wrote 5 years ago in comment 0): One also needs to distinguish between common blocks with and without BIND(C). The Fortran standard only defines interoperability with C with Fortran 2003's C binding ("BIND(C)"). Thus, "external int i" interoperates with use iso_fortran_env, only: c_int integer(c_int) :: j common /i/ j bind(C) :: /i/ and for this construct, "struct {int i}" does not have to interoperate with it according to the standard. If the front-end produces the wrong code in this case, one can simply fix it. Seems as if we have to do this, including the output DWARF. [By the way, I assume that there is essentially no code out there, which uses BIND(C) with COMMON: Either it is pre-Fortran-2003 code - or it uses modules where one avoids all those issues with COMMON and either has "integer, bind(C) :: i" or "type(t), bind(C) :: i" and no ambiguity.] The other case is legacy code: There, programs can make the wildest assumptions what C code should interoperable with Fortran. See also T.S.'s comment 20. Seems as if a simple "struct" was the most common assumption - with a nonstruct being effectively interoperable with a one-variable struct; hence, also the latter seems to be used.
