RE: [PATCH] [net-next] net: stmmac: fix gcc-10 -Wrestrict warning

[David Laight <David.Laight@ACULAB.COM>]

From: Arnd Bergmann
> Sent: 21 April 2021 14:47
> 
> From: Arnd Bergmann <arnd@arndb.de>
> 
> gcc-10 and later warn about a theoretical array overrun when
> accessing priv->int_name_rx_irq[i] with an out of bounds value
> of 'i':
> 
> drivers/net/ethernet/stmicro/stmmac/stmmac_main.c: In function 'stmmac_request_irq_multi_msi':
> drivers/net/ethernet/stmicro/stmmac/stmmac_main.c:3528:17: error: 'snprintf' argument 4 may overlap
> destination object 'dev' [-Werror=restrict]
>  3528 |                 snprintf(int_name, int_name_len, "%s:%s-%d", dev->name, "tx", i);
>       |                 ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> drivers/net/ethernet/stmicro/stmmac/stmmac_main.c:3404:60: note: destination object referenced by
> 'restrict'-qualified argument 1 was declared here
>  3404 | static int stmmac_request_irq_multi_msi(struct net_device *dev)
>       |                                         ~~~~~~~~~~~~~~~~~~~^~~
> 
> The warning is a bit strange since it's not actually about the array
> bounds but rather about possible string operations with overlapping
> arguments, but it's not technically wrong.
> 
> Avoid the warning by adding an extra bounds check.
> 
> Fixes: 8532f613bc78 ("net: stmmac: introduce MSI Interrupt routines for mac, safety, RX & TX")
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> ---
>  drivers/net/ethernet/stmicro/stmmac/stmmac_main.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
> b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
> index d1ca07c846e6..aadac783687b 100644
> --- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
> +++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
> @@ -3498,6 +3498,8 @@ static int stmmac_request_irq_multi_msi(struct net_device *dev)
> 
>  	/* Request Rx MSI irq */
>  	for (i = 0; i < priv->plat->rx_queues_to_use; i++) {
> +		if (i > MTL_MAX_RX_QUEUES)
> +			break;
>  		if (priv->rx_irq[i] == 0)
>  			continue;

It might be best to do:
	num_queues = min(priv->plat->rx_queues_to_use, MTL_MAX_RX_QUEUES);
	if (i = 0; i < num_queues; i++) {
		...

Or just give up - if rx_queues_to_use is too big it's all
gone horribly wrong already.

The compile must be smoking weed again.

	David

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