Re: [PATCH v2 0/1] libgomp: Fix gfortran detection when program is found via PATH

@Peter0x44 wrote in https://forge.sourceware.org/gcc/gcc-TEST/pulls/172#issue-415:
> The gfortran detection logic in libgomp's configure uses "test -x" to check whether the $GFORTRAN program is executable. However, "test -x" only succeeds for absolute or relative paths that name an existing file; it fails for bare program names (e.g. "x86_64-w64-mingw32-gfortran") that are found via $PATH lookup.

The latter is -- in my current understanding -- an invalid assumption: `GFORTRAN` is passed into libgomp `configure` via the top-level build system's `GFORTRAN_FOR_TARGET=$(STAGE_CC_WRAPPER) $$r/$(HOST_SUBDIR)/gcc/gfortran -B$$r/$(HOST_SUBDIR)/gcc/`, and `$$r/$(HOST_SUBDIR)/gcc/gfortran` always an absolute path, via `` r=`${PWD_COMMAND}` ``.  It should never be found "via $PATH lookup".

How are you `configure`ing your cross-compiler, could it be that it doesn't (effectively) include `--enable-languages=fortran`?  Because, in that case, you'd get: `GFORTRAN_FOR_TARGET=$(STAGE_CC_WRAPPER) [TARGET]-gfortran`, and with that:

> This causes FC to be incorrectly set to "no" in cross-compilation environments where $GFORTRAN is a bare command name rather than a full path. As a result, the Fortran OpenMP module (omp_lib.mod) is never installed, and programs that "use omp_lib" fail with:
> 
> Fatal Error: Cannot open module file 'omp_lib.mod' for reading

... this behavior is correct, as libgomp doesn't have a Fortran compiler available (as of the current GCC build).

It's not possible to use an external Fortran compiler; GCC target libraries are only to be built using the compilers of the current GCC build.

> The fix adds a "command -v" fallback for testing whether a command is available on $PATH.

So, that seems very dubious to be.

> The bug was introduced in r0-98199-g2122aa973ed (2010-01-26)

No, that commit just changed the `test -x` check from the full `"$GFORTRAN"` "path" (which includes compiler flags) to just its `$$r/$(HOST_SUBDIR)/gcc/gfortran` part.

> so the Fortran OpenMP module has been missing from cross-compiled installs for 16 years.

Quite likely even longer!  Because, `test -x "x86_64-w64-mingw32-gfortran [compiler flags here]"` is generally `false`.

Please first clarify how you're `configure`ing your cross-compiler.

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https://forge.sourceware.org/gcc/gcc-TEST/pulls/172#issuecomment-6635