On Mon, Jun 09, 2014 at 06:34:24AM -0700, Josh Triplett wrote:
Thanks for the quick response.
> On Mon, Jun 09, 2014 at 02:58:01PM +0300, Phil Carmody wrote:
> > Consider the operation of rounding up to the nearest multiple of a power of 2.
> > e.g. #define ALLOC_SIZE(t) ((sizeof(t) + ASIZE - 1) & ~(ASIZE - 1))
> >
> > If ASIZE is unfortunately defined as an unsigned type smaller than size_t,
> > then the ~ will not undergo sign-bit extension, and the incorrect mask will
> > be used. If used in a memory allocation context this could be fatal.
> >
> > Warn about such dubious 'large op ~short' usage.
> >
> > Signed-off-by: Phil Carmody <phil@xxxxxxxxxx>
> > ---
> > evaluate.c | 21 +++++++++++++++++++++
> > 1 file changed, 21 insertions(+)
> >
> > diff --git a/evaluate.c b/evaluate.c
> > index 9052962..c0f3c91 100644
> > --- a/evaluate.c
> > +++ b/evaluate.c
> > @@ -189,6 +189,14 @@ left:
> > return left;
> > }
> >
> > +static int is_bigger_int_type(struct symbol *left, struct symbol *right)
> > +{
> > + left = integer_promotion(left);
> > + right = integer_promotion(right);
> > +
> > + return (left->bit_size > right->bit_size);
> > +}
> > +
> > static int same_cast_type(struct symbol *orig, struct symbol *new)
> > {
> > return orig->bit_size == new->bit_size &&
> > @@ -927,6 +935,19 @@ static struct symbol *evaluate_binop(struct expression *expr)
> > op,
> > right_not ? "!" : "");
> >
> > + left_not = expr->left->type == EXPR_PREOP
> > + && expr->left->op == '~';
> > + right_not = expr->right->type == EXPR_PREOP
> > + && expr->right->op == '~';
>
> Ah, now I see why you wanted these to not use "const". Fair enough.
> "bool" still seems like the right type, though.
There did seem to be general bool-avoidance in the code, it would have been
my preference too.
> > + if ((left_not && is_bigger_int_type(rtype, ltype)
> > + && (ltype->ctype.modifiers & MOD_UNSIGNED)) ||
> > + (right_not && is_bigger_int_type(ltype, rtype)
> > + && (rtype->ctype.modifiers & MOD_UNSIGNED)))
>
> You might consider wrapping the common expression here, along with the
> corresponding previous _not expression, into a function, and then
> calling it twice, flipping the arguments around for the second call.
Yes, that makes sense.
> > + warning(expr->pos, "dubious: %sx %c %sy",
> > + left_not ? "~" : "",
> > + op,
> > + right_not ? "~" : "");
>
> What happens here if left_not && right_not? Should this warning still
> occur? I *think* it still makes sense for it to, but the warning
> message might prove less informative.
You're right, the message wouldn't identify which was the operand that
was not being sign extended. I can pull the warning itself into the helper
function I create for the test.
> > +
> > ltype = usual_conversions(op, expr->left, expr->right,
> > lclass, rclass, ltype, rtype);
> > ctype = rtype = ltype;
Thanks for your comments. A v2 will be forthcoming...
Cheers,
Phil
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