[PATCH] Fix PR56344

Richard Biener richard.guenther@gmail.com
Wed Feb 27 11:33:00 GMT 2013


On Wed, Feb 27, 2013 at 10:56 AM, Marek Polacek <polacek@redhat.com> wrote:
> On Tue, Feb 26, 2013 at 11:17:22PM +0000, Joseph S. Myers wrote:
>> On Tue, 26 Feb 2013, Marek Polacek wrote:
>>
>> > +         /* We don't allow passing huge (> 2^30 B) arguments
>> > +            by value.  It would cause an overflow later on.  */
>> > +         if (adjusted_args_size.constant >= (1 << 30))
>> > +           {
>> > +             error ("passing too large argument on stack");
>> > +             continue;
>>
>> This should be sorry () not error (), as a compiler limitation rather than
>> a defect in the user's program.  (And is input_location set to something
>> useful here so the diagnostic points to the argument in question rather
>> than e.g. to the end of the function containing the problem call?)
>
> Okay, changed back to sorry ().  I'd think that input_location is fine
> here, for e.g.
>
> struct S { unsigned char s[1 << 30]; } s;
> extern void foo (struct S);
>
> void
> bar (void)
> {
>   foo (s);
> }
>
> we get:
> pr56344.c: In function ‘bar’:
> pr56344.c:7:7: sorry, unimplemented: passing too large argument on stack
>    foo (s);
>        ^
>
> Ok now?

Wouldn't it be better to simply pass this using the variable size handling
code?  Thus, initialize args_size.var for too large constant size instead?
Also args_size.constant is HOST_WIDE_INT, so I'm not sure where you
derive the magic number 1<<30 from.  I'd expect it to be sth like

if (!host_integer_p (bit-size, 1))
  init variable-size

this has the advantage to move the error to runtime instead of compile-time
which is better than rejecting valid C code that will work when it is
not executed
at runtime.

Richard.

> 2013-02-27  Marek Polacek  <polacek@redhat.com>
>
>         PR middle-end/56344
>         * calls.c (expand_call): Disallow passing huge arguments
>         by value.
>
> --- gcc/calls.c.mp      2013-02-26 17:04:33.159555349 +0100
> +++ gcc/calls.c 2013-02-27 10:44:02.254461200 +0100
> @@ -3037,6 +3037,14 @@ expand_call (tree exp, rtx target, int i
>             {
>               rtx before_arg = get_last_insn ();
>
> +             /* We don't allow passing huge (> 2^30 B) arguments
> +                by value.  It would cause an overflow later on.  */
> +             if (adjusted_args_size.constant >= (1 << 30))
> +               {
> +                 sorry ("passing too large argument on stack");
> +                 continue;
> +               }
> +
>               if (store_one_arg (&args[i], argblock, flags,
>                                  adjusted_args_size.var != 0,
>                                  reg_parm_stack_space)
>
>         Marek



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