On Wed, 2023-09-27 at 14:23 +0200, Thomas Haller wrote:
> With gcc-13.2.1-1.fc38.x86_64:
>
> $ gcc -Iinclude -c -o tmp.o src/netlink_linearize.c -Werror -
> Wstrict-overflow=5 -O3
> src/netlink_linearize.c: In function ‘netlink_gen_bitwise’:
> src/netlink_linearize.c:1790:1: error: assuming signed overflow
> does not occur when changing X +- C1 cmp C2 to X cmp C2 -+ C1 [-
> Werror=strict-overflow]
> 1790 | }
> | ^
> cc1: all warnings being treated as errors
>
> It also makes more sense this way, where "n" is the hight of the
> "binops" stack, and we check for a non-empty stack with "n > 0" and
> pop
> the last element with "binops[--n]".
>
> Signed-off-by: Thomas Haller <thaller@xxxxxxxxxx>
> ---
> src/netlink_linearize.c | 7 +++----
> 1 file changed, 3 insertions(+), 4 deletions(-)
>
> diff --git a/src/netlink_linearize.c b/src/netlink_linearize.c
> index c91211582b3d..f2514b012a9d 100644
> --- a/src/netlink_linearize.c
> +++ b/src/netlink_linearize.c
> @@ -712,14 +712,13 @@ static void netlink_gen_bitwise(struct
> netlink_linearize_ctx *ctx,
> while (left->etype == EXPR_BINOP && left->left != NULL &&
> (left->op == OP_AND || left->op == OP_OR || left->op
> == OP_XOR))
> binops[n++] = left = left->left;
I wanted to ask, what ensures that binops buffer does not overflow?
> - n--;
>
> - netlink_gen_expr(ctx, binops[n--], dreg);
> + netlink_gen_expr(ctx, binops[--n], dreg);
>
> mpz_bitmask(mask, expr->len);
> mpz_set_ui(xor, 0);
> - for (; n >= 0; n--) {
> - i = binops[n];
> + while (n > 0) {
> + i = binops[--n];
> mpz_set(val, i->right->value);
>
> switch (i->op) {
