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 an incorrect mask will
be used. If used in a memory allocation context this could be fatal.
Warn about such dubious 'large op ~short' usage.
v2: pulled noisy repeated parts into a helper
Signed-off-by: Phil Carmody <phil@xxxxxxxxxx>
---
evaluate.c | 26 ++++++++++++++++++++++++++
1 file changed, 26 insertions(+)
diff --git a/evaluate.c b/evaluate.c
index 9052962..a16aa45 100644
--- a/evaluate.c
+++ b/evaluate.c
@@ -886,6 +886,25 @@ static struct symbol *evaluate_logical(struct expression *expr)
return &int_ctype;
}
+static int int_size_cmp(struct symbol *left, struct symbol *right)
+{
+ left = integer_promotion(left);
+ right = integer_promotion(right);
+
+ return (left->bit_size > right->bit_size) ? 1 :
+ (right->bit_size > left->bit_size) ? -1 : 0;
+}
+
+static void check_masking(struct expression *expr, int op, int is_l,
+ struct expression *sexpr, struct symbol *stype)
+{
+ if ((sexpr->type == EXPR_PREOP)
+ && (sexpr->op == '~')
+ && (stype->ctype.modifiers & MOD_UNSIGNED))
+ warning(expr->pos, "dubious zero-extended '~': %sx %c %sy",
+ "~"+!is_l, op, "~"+!!is_l);
+}
+
static struct symbol *evaluate_binop(struct expression *expr)
{
struct symbol *ltype, *rtype, *ctype;
@@ -917,6 +936,7 @@ static struct symbol *evaluate_binop(struct expression *expr)
rtype = integer_promotion(rtype);
} else {
// The rest do usual conversions
+ int size_cmp;
int left_not = expr->left->type == EXPR_PREOP
&& expr->left->op == '!';
int right_not = expr->right->type == EXPR_PREOP
@@ -927,6 +947,12 @@ static struct symbol *evaluate_binop(struct expression *expr)
op,
right_not ? "!" : "");
+ size_cmp = int_size_cmp(ltype, rtype);
+ if (size_cmp > 0)
+ check_masking(expr, op, 0, expr->right, rtype);
+ else if (size_cmp < 0)
+ check_masking(expr, op, 1, expr->left, ltype);
+
ltype = usual_conversions(op, expr->left, expr->right,
lclass, rclass, ltype, rtype);
ctype = rtype = ltype;
--
2.0.0
--
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