linux-kernel - [PATCH] tty: rocket: reduce stack usage

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Date:   Fri, 18 Oct 2019 15:26:55 +0100
From:   Sudip Mukherjee <sudipm.mukherjee@...il.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jslaby@...e.com>
Cc:     linux-kernel@...r.kernel.org,
        Sudip Mukherjee <sudipm.mukherjee@...il.com>
Subject: [PATCH] tty: rocket: reduce stack usage

The build of xtensa allmodconfig gives warning of:
In function 'get_ports.isra.0':
warning: the frame size of 1040 bytes is larger than 1024 bytes

Allocate memory for 'struct rocket_ports' dynamically to reduce the
stack usage, as an added benifit we can remove the memset by using
kzalloc while allocating memory.

Signed-off-by: Sudip Mukherjee <sudipm.mukherjee@...il.com>
---
 drivers/tty/rocket.c | 29 ++++++++++++++++-------------
 1 file changed, 16 insertions(+), 13 deletions(-)

diff --git a/drivers/tty/rocket.c b/drivers/tty/rocket.c
index 5ba6816ebf81..cc1424b9a1e5 100644
--- a/drivers/tty/rocket.c
+++ b/drivers/tty/rocket.c
@@ -1222,22 +1222,25 @@ static int set_config(struct tty_struct *tty, struct r_port *info,
  */
 static int get_ports(struct r_port *info, struct rocket_ports __user *retports)
 {
-	struct rocket_ports tmp;
-	int board;
+	struct rocket_ports *tmp;
+	int board, ret = 0;
 
-	memset(&tmp, 0, sizeof (tmp));
-	tmp.tty_major = rocket_driver->major;
+	tmp = kzalloc(sizeof(*tmp), GFP_KERNEL);
+	tmp->tty_major = rocket_driver->major;
 
 	for (board = 0; board < 4; board++) {
-		tmp.rocketModel[board].model = rocketModel[board].model;
-		strcpy(tmp.rocketModel[board].modelString, rocketModel[board].modelString);
-		tmp.rocketModel[board].numPorts = rocketModel[board].numPorts;
-		tmp.rocketModel[board].loadrm2 = rocketModel[board].loadrm2;
-		tmp.rocketModel[board].startingPortNumber = rocketModel[board].startingPortNumber;
-	}
-	if (copy_to_user(retports, &tmp, sizeof (*retports)))
-		return -EFAULT;
-	return 0;
+		tmp->rocketModel[board].model = rocketModel[board].model;
+		strcpy(tmp->rocketModel[board].modelString,
+		       rocketModel[board].modelString);
+		tmp->rocketModel[board].numPorts = rocketModel[board].numPorts;
+		tmp->rocketModel[board].loadrm2 = rocketModel[board].loadrm2;
+		tmp->rocketModel[board].startingPortNumber =
+			rocketModel[board].startingPortNumber;
+	}
+	if (copy_to_user(retports, tmp, sizeof(*retports)))
+		ret = -EFAULT;
+	kfree(tmp);
+	return ret;
 }
 
 static int reset_rm2(struct r_port *info, void __user *arg)
-- 
2.11.0