Re: [PATCH] c: [PR32122] Require pointer types for computed gotos

[Andrew Pinski <pinskia@gmail.com>]

On Fri, Oct 1, 2021 at 4:03 AM Eric Gallager via Gcc-patches
<gcc-patches@gcc.gnu.org> wrote:
>
> On Mon, Sep 20, 2021 at 12:15 AM apinski--- via Gcc-patches
> <gcc-patches@gcc.gnu.org> wrote:
> >
> > From: Andrew Pinski <apinski@marvell.com>
> >
> > So GCC has always accepted non-pointer types in computed gotos but
> > that was wrong based on the documentation:
> > Any expression of type void * is allowed.
> >
> > So this fixes the problem by requiring the type to
> > be a pointer type.
> >
> > OK? Bootstrapped and tested on x86_64-linux-gnu with no regressions.
> >
> >         PR c/32122
> >
> > gcc/c/ChangeLog:
> >
> >         * c-parser.c (c_parser_statement_after_labels): Pass
> >         the c_expr instead of the tree to c_finish_goto_ptr.
> >         * c-typeck.c (c_finish_goto_ptr): Change the second
> >         argument type to c_expr.
> >         * c-tree.h (c_finish_goto_ptr): Likewise.
> >         Error out if the expression was not of a pointer type.
> >
> > gcc/testsuite/ChangeLog:
> >
> >         * gcc.dg/comp-goto-5.c: New test.
> >         * gcc.dg/comp-goto-6.c: New test.
> > ---
> >  gcc/c/c-parser.c                   |  2 +-
> >  gcc/c/c-tree.h                     |  2 +-
> >  gcc/c/c-typeck.c                   | 11 ++++++++++-
> >  gcc/testsuite/gcc.dg/comp-goto-5.c | 11 +++++++++++
> >  gcc/testsuite/gcc.dg/comp-goto-6.c |  6 ++++++
> >  5 files changed, 29 insertions(+), 3 deletions(-)
> >  create mode 100644 gcc/testsuite/gcc.dg/comp-goto-5.c
> >  create mode 100644 gcc/testsuite/gcc.dg/comp-goto-6.c
> >
> > diff --git a/gcc/c/c-parser.c b/gcc/c/c-parser.c
> > index fb1399e300d..bcd8a05489f 100644
> > --- a/gcc/c/c-parser.c
> > +++ b/gcc/c/c-parser.c
> > @@ -6141,7 +6141,7 @@ c_parser_statement_after_labels (c_parser *parser, bool *if_p,
> >               c_parser_consume_token (parser);
> >               val = c_parser_expression (parser);
> >               val = convert_lvalue_to_rvalue (loc, val, false, true);
> > -             stmt = c_finish_goto_ptr (loc, val.value);
> > +             stmt = c_finish_goto_ptr (loc, val);
> >             }
> >           else
> >             c_parser_error (parser, "expected identifier or %<*%>");
> > diff --git a/gcc/c/c-tree.h b/gcc/c/c-tree.h
> > index d50d0cb7f2d..a046c6b0926 100644
> > --- a/gcc/c/c-tree.h
> > +++ b/gcc/c/c-tree.h
> > @@ -746,7 +746,7 @@ extern tree c_finish_expr_stmt (location_t, tree);
> >  extern tree c_finish_return (location_t, tree, tree);
> >  extern tree c_finish_bc_stmt (location_t, tree, bool);
> >  extern tree c_finish_goto_label (location_t, tree);
> > -extern tree c_finish_goto_ptr (location_t, tree);
> > +extern tree c_finish_goto_ptr (location_t, c_expr val);
> >  extern tree c_expr_to_decl (tree, bool *, bool *);
> >  extern tree c_finish_omp_construct (location_t, enum tree_code, tree, tree);
> >  extern tree c_finish_oacc_data (location_t, tree, tree);
> > diff --git a/gcc/c/c-typeck.c b/gcc/c/c-typeck.c
> > index 49d1bb067a0..b472e448011 100644
> > --- a/gcc/c/c-typeck.c
> > +++ b/gcc/c/c-typeck.c
> > @@ -10783,10 +10783,19 @@ c_finish_goto_label (location_t loc, tree label)
> >     the GOTO.  */
> >
> >  tree
> > -c_finish_goto_ptr (location_t loc, tree expr)
> > +c_finish_goto_ptr (location_t loc, c_expr val)
> >  {
> > +  tree expr = val.value;
> >    tree t;
> >    pedwarn (loc, OPT_Wpedantic, "ISO C forbids %<goto *expr;%>");
> > +  if (expr != error_mark_node
> > +      && !POINTER_TYPE_P (TREE_TYPE (expr))
> > +      && !null_pointer_constant_p (expr))
> > +    {
> > +      error_at (val.get_location (),
> > +               "computed goto must be pointer type");
> > +      expr = build_zero_cst (ptr_type_node);
> > +    }
> >    expr = c_fully_fold (expr, false, NULL);
> >    expr = convert (ptr_type_node, expr);
> >    t = build1 (GOTO_EXPR, void_type_node, expr);
> > diff --git a/gcc/testsuite/gcc.dg/comp-goto-5.c b/gcc/testsuite/gcc.dg/comp-goto-5.c
> > new file mode 100644
> > index 00000000000..d487729a5d4
> > --- /dev/null
> > +++ b/gcc/testsuite/gcc.dg/comp-goto-5.c
> > @@ -0,0 +1,11 @@
> > +/* PR c/32122 */
> > +/* { dg-do compile } */
> > +/* { dg-options "" } */
> > +
> > +enum {a=1};
> > +void foo()
> > +{
> > +  goto *
> > +        a; /* { dg-error "computed goto must be pointer type" } */
> > +}
> > +
> > diff --git a/gcc/testsuite/gcc.dg/comp-goto-6.c b/gcc/testsuite/gcc.dg/comp-goto-6.c
> > new file mode 100644
> > index 00000000000..497f6cd76ca
> > --- /dev/null
> > +++ b/gcc/testsuite/gcc.dg/comp-goto-6.c
> > @@ -0,0 +1,6 @@
> > +/* PR c/32122 */
> > +/* { dg-do compile } */
> > +/* { dg-options "" } */
> > +void foo(void *a) { goto *10000000; } /* { dg-error "computed goto must be pointer type" } */
> > +void foo1(void *a) { goto *a; }
> > +
> > --
> > 2.17.1
> >
>
> Maybe add to one of the testcases a test to ensure that the
> cast-to-void workaround works successfully?
> e.g.
> void foo2(void *a) { goto *(void *)10000000; } /* { dg-bogus "computed
> goto must be pointer type" } */

There actually were a few testcases which needed to be fixed up so
there is no need for another one :).

Thanks,
Andrew