Hello world,
the attached patch puts the workaround introduced by Jakub behind
a flag. I debated with myself what the name should be.
-fbroken-c-interfaces-die-die-die came to mind, but that would
have penalized people who wanted to disable the option :-)
Therefore, I have settled on -fbroken-callers and -fno-broken-callers,
respectively. If somebody has a better idea, please let the list know.
What we should do with this flag for gcc-10 is still up for discussion,
if we make it the default or not.
Regression-tested. "make info", "make dvi" and "make pdf" all
passed. OK for trunk?
Regards
Thomas
2019-05-18 Thomas Koenig <tkoe...@gcc.gnu.org>
PR fortran/90329
* invoke.texi: Document -fbroken-callers.
* lang.opt: Add -fbroken-callers.
* trans-decl.c (create_function_arglist): Only set
DECL_HIDDEN_STRING_LENGTH if flag_broken_callers is set.
Index: invoke.texi
===================================================================
--- invoke.texi (Revision 271371)
+++ invoke.texi (Arbeitskopie)
@@ -181,7 +181,7 @@ and warnings}.
@item Code Generation Options
@xref{Code Gen Options,,Options for code generation conventions}.
@gccoptlist{-faggressive-function-elimination -fblas-matmul-limit=@var{n} @gol
--fbounds-check -fcheck-array-temporaries @gol
+-fbounds-check -fbroken-callers -fcheck-array-temporaries @gol
-fcheck=@var{<all|array-temps|bounds|do|mem|pointer|recursion>} @gol
-fcoarray=@var{<none|single|lib>} -fexternal-blas -ff2c
-ffrontend-loop-interchange @gol
@@ -1617,6 +1617,30 @@ warnings for generated array temporaries.
@c Note: This option is also referred in gcc's manpage
Deprecated alias for @option{-fcheck=bounds}.
+@item -fbroken-callers
+@opindex @code{broken-callers}
+Some C interfaces to Fortran codes violate the gfortran ABI by
+omitting the hidden character length arguments as described in
+@xref{Argument passing conventions}. This can lead to crashes
+because pushing arguments for tail calls can overflow the stack.
+
+To provide a workaround for existing binary packages, this option
+disables tail call optimization for gfortran procedures with character
+arguments.
+
+Using this option can lead to problems including crashes due to
+insufficient stack space.
+
+It is @emph{very strongly} recommended to fix the code in question.
+Support for this option will likely be withdrawn in a future release
+of gfortran.
+
+The negative form, @option{-fno-broken-callers}, can be used to
+disable this option.
+
+Default is currently @option{-fbroken-callers}, this will change
+in future releases.
+
@item -fcheck-array-temporaries
@opindex @code{fcheck-array-temporaries}
Deprecated alias for @option{-fcheck=array-temps}.
Index: lang.opt
===================================================================
--- lang.opt (Revision 271371)
+++ lang.opt (Arbeitskopie)
@@ -397,6 +397,10 @@ fblas-matmul-limit=
Fortran RejectNegative Joined UInteger Var(flag_blas_matmul_limit) Init(30)
-fblas-matmul-limit=<n> Size of the smallest matrix for which matmul will use BLAS.
+fbroken-callers
+Fortran Var(flag_broken_callers) Init(1)
+Disallow tail call optimization when a calling routine may have omitted character lenghts.
+
fcheck-array-temporaries
Fortran
Produce a warning at runtime if a array temporary has been created for a procedure argument.
Index: trans-decl.c
===================================================================
--- trans-decl.c (Revision 271371)
+++ trans-decl.c (Arbeitskopie)
@@ -2516,7 +2516,11 @@ create_function_arglist (gfc_symbol * sym)
DECL_ARG_TYPE (length) = len_type;
TREE_READONLY (length) = 1;
gfc_finish_decl (length);
- if (f->sym->ts.u.cl
+
+ /* Marking the length DECL_HIDDEN_STRING_LENGTH will lead
+ to tail calls being disabled. Only do that if we
+ potentially have broken callers. */
+ if (flag_broken_callers && f->sym->ts.u.cl
&& f->sym->ts.u.cl->length
&& f->sym->ts.u.cl->length->expr_type == EXPR_CONSTANT)
DECL_HIDDEN_STRING_LENGTH (length) = 1;
