Build-system question: Making known to gcc/fortran's CPP call: TARGET_SYSTEM_ROOT / @TARGET_SYSTEM_ROOT_DEFINE@

[Tobias Burnus]

Dear all,

I have a question to the GCC build-system experts to make 
TARGET_SYSTEM_ROOT available to gfortran (see PR54725); it's required to 
have the proper "<system_root>/usr/include" directory when using CPP.

That's partially cured by the patch below, however, it is not sufficient 
as "TARGET_SYSTEM_ROOT" is not available. The bug reporter suggests the 
following (see PR). What's the recommend GCC way?

(The first option, seems to be the cleanest, but it adds gcc/fortran 
dependency to gcc/Makefile.in; I have the feeling that the second option 
is wrong and that the last one won't work as it mixes driver and compiler.)

  Mike Frysinger wrote (in PR54725 comment 6):
> in gcc/Makefile.in, they do:
>    CFLAGS-c-family/c-opts.o += @TARGET_SYSTEM_ROOT_DEFINE@
>
> but you can't do that in gcc/fortran/Make-lang.in.  you can't use
> $(TARGET_SYSTEM_ROOT_DEFINE) either because the variable is only AC_SUBST().
>
> so you could add this line to gcc/Makefile.in:
>    CFLAGS-fortran/cpp.o += @TARGET_SYSTEM_ROOT_DEFINE@
> and it'd work.  this seems to be how they propagate the define into the
> CFLAGS-c-family/c-opts.o variable, so maybe this is OK.
>
> alternatively, gcc/Makefile.in does setup $(COMPILER_DEFINES), so adding this
> to gcc/fortran/Make-lang.in works:
>    CFLAGS-fortran/cpp.o += $(DRIVER_DEFINES)
> but i'm sure that's the wrong answer.
>
> the other alternative is to declare a "static const char *sysroot" inside of
> gcc/fortran/gfortranspec.c and then initialize gfc_cpp_option.sysroot via that.
>   this works because gfortranspec.c is compiled already with
> $(COMPILER_DEFINES).


Tobias

PS: The following patch does the same as c-family/c-opts.c does:

--- a/gcc/fortran/cpp.c
+++ b/gcc/fortran/cpp.c
@@ -40,0 +41,4 @@ along with GCC; see the file COPYING3.  If not see
+#ifndef TARGET_SYSTEM_ROOT
+# define TARGET_SYSTEM_ROOT NULL
+#endif
+
@@ -270 +274 @@ gfc_cpp_init_options (unsigned int decoded_options_count,
-  gfc_cpp_option.sysroot = NULL;
+  gfc_cpp_option.sysroot = TARGET_SYSTEM_ROOT;