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

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

[Arnd Bergmann]

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;
 
@@ -3521,6 +3523,8 @@ static int stmmac_request_irq_multi_msi(struct net_device *dev)
 
 	/* Request Tx MSI irq */
 	for (i = 0; i < priv->plat->tx_queues_to_use; i++) {
+		if (i > MTL_MAX_TX_QUEUES)
+			break;
 		if (priv->tx_irq[i] == 0)
 			continue;
 
-- 
2.29.2

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

[David Laight]

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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