Currently, the determination of a __builtin_offsetof() expressions'
constness flags is done in two steps:
- Several flags are speculatively set at expression parsing time
- and possibly cleared again at evaluation if the member expression
includes a non-const array index like in
__builtin_offsetof(struct A, a.b[non_const_foo])
For consistency with other expression types' evaluation, defer the
determination of a __builtin_offsetof() expression's constness to
evaluation time, too.
Furthermore, carry an array index expression's constness flags
through the implicit cast to size_t type.
Signed-off-by: Nicolai Stange <nicstange@xxxxxxxxx>
---
evaluate.c | 10 +++++++---
expression.c | 6 ------
validation/constexpr-offsetof.c | 21 +++++++++++++++++++++
3 files changed, 28 insertions(+), 9 deletions(-)
create mode 100644 validation/constexpr-offsetof.c
diff --git a/evaluate.c b/evaluate.c
index 7a4af39..0101e61 100644
--- a/evaluate.c
+++ b/evaluate.c
@@ -3031,25 +3031,29 @@ static struct symbol *evaluate_offsetof(struct expression *expr)
} else {
struct expression *idx = expr->index, *m;
struct symbol *i_type = evaluate_expression(idx);
+ unsigned old_idx_flags;
int i_class = classify_type(i_type, &i_type);
+
if (!is_int(i_class)) {
expression_error(expr, "non-integer index");
return NULL;
}
unrestrict(idx, i_class, &i_type);
+ old_idx_flags = idx->constexpr_flags;
idx = cast_to(idx, size_t_ctype);
+ idx->constexpr_flags = old_idx_flags;
m = alloc_const_expression(expr->pos,
bits_to_bytes(ctype->bit_size));
m->ctype = size_t_ctype;
- m->constexpr_flags |=
- CONSTEXPR_FLAG_INT_CONST_EXPR_SET_MASK;
+ m->constexpr_flags = CONSTEXPR_FLAG_INT_CONST_SET_MASK;
expr->type = EXPR_BINOP;
expr->left = idx;
expr->right = m;
expr->op = '*';
expr->ctype = size_t_ctype;
expr->constexpr_flags = m->constexpr_flags &
- idx->constexpr_flags;
+ idx->constexpr_flags &
+ ~CONSTEXPR_FLAG_DECAY_CONSTS_MASK;
}
}
if (e) {
diff --git a/expression.c b/expression.c
index ac6cf43..c3d54fe 100644
--- a/expression.c
+++ b/expression.c
@@ -200,8 +200,6 @@ static struct token *builtin_offsetof_expr(struct token *token,
return expect(token, ')', "at end of __builtin_offset");
case SPECIAL_DEREFERENCE:
e = alloc_expression(token->pos, EXPR_OFFSETOF);
- e->constexpr_flags =
- CONSTEXPR_FLAG_INT_CONST_EXPR_SET_MASK;
e->op = '[';
*p = e;
p = &e->down;
@@ -209,8 +207,6 @@ static struct token *builtin_offsetof_expr(struct token *token,
case '.':
token = token->next;
e = alloc_expression(token->pos, EXPR_OFFSETOF);
- e->constexpr_flags =
- CONSTEXPR_FLAG_INT_CONST_EXPR_SET_MASK;
e->op = '.';
if (token_type(token) != TOKEN_IDENT) {
sparse_error(token->pos, "Expected member name");
@@ -222,8 +218,6 @@ static struct token *builtin_offsetof_expr(struct token *token,
case '[':
token = token->next;
e = alloc_expression(token->pos, EXPR_OFFSETOF);
- e->constexpr_flags =
- CONSTEXPR_FLAG_INT_CONST_EXPR_SET_MASK;
e->op = '[';
token = parse_expression(token, &e->index);
token = expect(token, ']',
diff --git a/validation/constexpr-offsetof.c b/validation/constexpr-offsetof.c
new file mode 100644
index 0000000..d1697b0
--- /dev/null
+++ b/validation/constexpr-offsetof.c
@@ -0,0 +1,21 @@
+struct A {
+ int a[1];
+ int b;
+};
+
+extern int c;
+
+static int o[] = {
+ [__builtin_offsetof(struct A, b)] = 0, // OK
+ [__builtin_offsetof(struct A, a[0])] = 0, // OK
+ [__builtin_offsetof(struct A, a[0*0])] = 0, // OK
+ [__builtin_offsetof(struct A, a[c])] = 0 // KO
+};
+
+/*
+ * check-name: __builtin_offsetof() constness verification.
+ *
+ * check-error-start
+constexpr-offsetof.c:12:39: error: bad constant expression
+ * check-error-end
+ */
--
2.7.0
--
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