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 | 13 ++++++++-----
expression.c | 3 ---
validation/constexpr-offsetof.c | 21 +++++++++++++++++++++
3 files changed, 29 insertions(+), 8 deletions(-)
create mode 100644 validation/constexpr-offsetof.c
diff --git a/evaluate.c b/evaluate.c
index e3b08e4..d32f5a4 100644
--- a/evaluate.c
+++ b/evaluate.c
@@ -3001,7 +3001,6 @@ static struct symbol *evaluate_offsetof(struct expression *expr)
}
ctype = field;
expr->type = EXPR_VALUE;
- expr->flags = EXPR_FLAG_NONE;
expr_set_flag(&expr->flags, EXPR_FLAG_INT_CONST_EXPR);
expr->value = offset;
expr->taint = 0;
@@ -3020,7 +3019,6 @@ static struct symbol *evaluate_offsetof(struct expression *expr)
ctype = ctype->ctype.base_type;
if (!expr->index) {
expr->type = EXPR_VALUE;
- expr->flags = EXPR_FLAG_NONE;
expr_set_flag(&expr->flags, EXPR_FLAG_INT_CONST_EXPR);
expr->value = 0;
expr->taint = 0;
@@ -3028,13 +3026,18 @@ 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->flags;
idx = cast_to(idx, size_t_ctype);
+ idx->flags |= old_idx_flags;
+ expr_flags_decay_consts(&idx->flags);
m = alloc_const_expression(expr->pos,
bits_to_bytes(ctype->bit_size));
m->ctype = size_t_ctype;
@@ -3045,19 +3048,19 @@ static struct symbol *evaluate_offsetof(struct expression *expr)
expr->op = '*';
expr->ctype = size_t_ctype;
expr->flags = m->flags & idx->flags;
+ expr_flags_decay_consts(&expr->flags);
}
}
if (e) {
struct expression *copy = __alloc_expression(0);
- unsigned char flags_mask = EXPR_FLAG_NONE;
*copy = *expr;
if (e->type == EXPR_OFFSETOF)
e->in = ctype;
if (!evaluate_expression(e))
return NULL;
expr->type = EXPR_BINOP;
- expr_set_flag(&flags_mask, EXPR_FLAG_INT_CONST_EXPR);
- expr->flags = e->flags & copy->flags & flags_mask;
+ expr->flags = e->flags & copy->flags;
+ expr_flags_decay_consts(&expr->flags);
expr->op = '+';
expr->ctype = size_t_ctype;
expr->left = copy;
diff --git a/expression.c b/expression.c
index b82a036..4ecc865 100644
--- a/expression.c
+++ b/expression.c
@@ -199,7 +199,6 @@ 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);
- expr_set_flag(&e->flags, EXPR_FLAG_INT_CONST_EXPR);
e->op = '[';
*p = e;
p = &e->down;
@@ -207,7 +206,6 @@ static struct token *builtin_offsetof_expr(struct token *token,
case '.':
token = token->next;
e = alloc_expression(token->pos, EXPR_OFFSETOF);
- expr_set_flag(&e->flags, EXPR_FLAG_INT_CONST_EXPR);
e->op = '.';
if (token_type(token) != TOKEN_IDENT) {
sparse_error(token->pos, "Expected member name");
@@ -219,7 +217,6 @@ static struct token *builtin_offsetof_expr(struct token *token,
case '[':
token = token->next;
e = alloc_expression(token->pos, EXPR_OFFSETOF);
- expr_set_flag(&e->flags, EXPR_FLAG_INT_CONST_EXPR);
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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