A subroutine or function that calls itself recursively must be declared with the RECURSIVE attribute. gfortran should refuse to compile the subroutine below and return an error indicating that the RECURSIVE attribute must be specified.
>$ cat sub.f90 SUBROUTINE SUB() CALL SUB() END SUBROUTINE >$ gfortran -std=f95 -pedantic sub.f90 -c >$ gfortran -c -v Using built-in specs. Target: powerpc-apple-darwin8.1.0 Configured with: ../gcc-4.1-20050611/configure --enable-threads=posix --enable-languages=c++,f95 Thread model: posix gcc version 4.1.0 20050611 (experimental) For comparison, here is output from g95 and xlf90: >$ g95 -std=f95 -pedantic sub.f90 -c In file sub.f90:2 CALL SUB() 1 Error: SUBROUTINE 'sub' at (1) must be RECURSIVE in order to call itself >$ xlf90 -qsuffix=cpp=f90 -f95 sub.f90 -c "sub.f90", line 2.6: 1513-126 (S) Recursive calls are only permitted when the RECUR option is specified or the RECURSIVE keyword is specified. ** sub === End of Compilation 1 === 1501-511 Compilation failed for file sub.f90. On a related note, the limitations on RECURSIVE subroutines and functions should also be extended to any ENTRY statements within the subprogram. For example, the following code is also illegal but gfortran currently accepts it: >$ cat sub2.f90 SUBROUTINE SUB2() ENTRY ENT2() CALL ENT2() END SUBROUTINE >$ gfortran -std=f95 -pedantic sub2.f90 -c For comparison, xlf has the following output: >$ xlf90 -qsuffix=cpp=f90 -f95 sub2.f90 -c "sub2.f90", line 3.6: 1513-126 (S) Recursive calls are only permitted when the RECUR option is specified or the RECURSIVE keyword is specified. ** sub2 === End of Compilation 1 === 1501-511 Compilation failed for file sub2.f90. -- Summary: gfortran compiles recursive subroutines declared without the RECURSIVE attribute Product: gcc Version: unknown Status: UNCONFIRMED Severity: normal Priority: P3 Component: fortran AssignedTo: unassigned at gcc dot gnu dot org ReportedBy: bdtaylo1 at uiuc dot edu GCC build triplet: powerpc-apple-darwin8.1.0 GCC host triplet: powerpc-apple-darwin8.1.0 GCC target triplet: powerpc-apple-darwin8.1.0 http://gcc.gnu.org/bugzilla/show_bug.cgi?id=26551