linux-kernel - [RFC PATCH 2/2] tty: serial/8250: Fix build warning in serial8250_probe

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Message-ID: <20250805195155.742004-2-abinashsinghlalotra@gmail.com>
Date: Wed,  6 Aug 2025 01:21:55 +0530
From: Abinash Singh <abinashsinghlalotra@...il.com>
To: gregkh@...uxfoundation.org
Cc: jirislaby@...nel.org,
	andriy.shevchenko@...ux.intel.com,
	sunilvl@...tanamicro.com,
	arnd@...db.de,
	u.kleine-koenig@...libre.com,
	linux-kernel@...r.kernel.org,
	linux-serial@...r.kernel.org,
	abinashsinghlalotra@...il.com
Subject: [RFC PATCH 2/2]  tty: serial/8250: Fix build warning in serial8250_probe_platform()

    The function serial8250_probe_platform() in 8250_platform.c triggered a
        frame size warning:
    drivers/tty/serial/8250/8250_platform.c: In function ‘serial8250_probe_platform.isra’:
drivers/tty/serial/8250/8250_platform.c:201:1: warning: the frame size of 1184 bytes is larger than 1024 bytes [-Wframe-larger-than=]

This patch reduces the stack usage by dynamically allocating the
`uart` structure using kmalloc(), rather than placing it on
the stack. This eliminates the overflow warning and improves kernel
robustness.

Signed-off-by: Abinash Singh <abinashsinghlalotra@...il.com>
---
The stack usage was further confirmed by using -fstack-usage flag.
it was usiing 1248 bytes:
..............................
drivers/tty/serial/8250/8250_platform.c:154:12:serial8250_probe_platform.isra	1248	dynamic,bounded
drivers/tty/serial/8250/8250_platform.c:208:12:serial8250_probe	16	static
......................................
After applying the patch it becomes :
.........
It doesn't show up in stack usage  and warning is fixed.
.......
This function is used for probing . So dynamic allocation will not create
any issues.

Thank You
---
 drivers/tty/serial/8250/8250_platform.c | 63 +++++++++++++------------
 1 file changed, 33 insertions(+), 30 deletions(-)

diff --git a/drivers/tty/serial/8250/8250_platform.c b/drivers/tty/serial/8250/8250_platform.c
index f7f9c5036d39..86816d9b32ce 100644
--- a/drivers/tty/serial/8250/8250_platform.c
+++ b/drivers/tty/serial/8250/8250_platform.c
@@ -158,43 +158,46 @@ static int serial8250_probe_acpi(struct platform_device *pdev)
 
 static int serial8250_probe_platform(struct platform_device *dev, struct plat_serial8250_port *p)
 {
-	struct uart_8250_port uart;
+	struct uart_8250_port *uart __free(kfree) = NULL;
 	int ret, i, irqflag = 0;
 
-	memset(&uart, 0, sizeof(uart));
+	uart = kmalloc(sizeof(*uart), GFP_KERNEL);
+	if (!uart)
+		return -ENOMEM;
+	memset(uart, 0, sizeof(*uart));
 
 	if (share_irqs)
 		irqflag = IRQF_SHARED;
 
 	for (i = 0; p && p->flags != 0; p++, i++) {
-		uart.port.iobase	= p->iobase;
-		uart.port.membase	= p->membase;
-		uart.port.irq		= p->irq;
-		uart.port.irqflags	= p->irqflags;
-		uart.port.uartclk	= p->uartclk;
-		uart.port.regshift	= p->regshift;
-		uart.port.iotype	= p->iotype;
-		uart.port.flags		= p->flags;
-		uart.port.mapbase	= p->mapbase;
-		uart.port.mapsize	= p->mapsize;
-		uart.port.hub6		= p->hub6;
-		uart.port.has_sysrq	= p->has_sysrq;
-		uart.port.private_data	= p->private_data;
-		uart.port.type		= p->type;
-		uart.bugs		= p->bugs;
-		uart.port.serial_in	= p->serial_in;
-		uart.port.serial_out	= p->serial_out;
-		uart.dl_read		= p->dl_read;
-		uart.dl_write		= p->dl_write;
-		uart.port.handle_irq	= p->handle_irq;
-		uart.port.handle_break	= p->handle_break;
-		uart.port.set_termios	= p->set_termios;
-		uart.port.set_ldisc	= p->set_ldisc;
-		uart.port.get_mctrl	= p->get_mctrl;
-		uart.port.pm		= p->pm;
-		uart.port.dev		= &dev->dev;
-		uart.port.irqflags	|= irqflag;
-		ret = serial8250_register_8250_port(&uart);
+		uart->port.iobase	= p->iobase;
+		uart->port.membase	= p->membase;
+		uart->port.irq		= p->irq;
+		uart->port.irqflags	= p->irqflags;
+		uart->port.uartclk	= p->uartclk;
+		uart->port.regshift	= p->regshift;
+		uart->port.iotype	= p->iotype;
+		uart->port.flags		= p->flags;
+		uart->port.mapbase	= p->mapbase;
+		uart->port.mapsize	= p->mapsize;
+		uart->port.hub6		= p->hub6;
+		uart->port.has_sysrq	= p->has_sysrq;
+		uart->port.private_data	= p->private_data;
+		uart->port.type		= p->type;
+		uart->bugs		= p->bugs;
+		uart->port.serial_in	= p->serial_in;
+		uart->port.serial_out	= p->serial_out;
+		uart->dl_read		= p->dl_read;
+		uart->dl_write		= p->dl_write;
+		uart->port.handle_irq	= p->handle_irq;
+		uart->port.handle_break	= p->handle_break;
+		uart->port.set_termios	= p->set_termios;
+		uart->port.set_ldisc	= p->set_ldisc;
+		uart->port.get_mctrl	= p->get_mctrl;
+		uart->port.pm		= p->pm;
+		uart->port.dev		= &dev->dev;
+		uart->port.irqflags	|= irqflag;
+		ret = serial8250_register_8250_port(uart);
 		if (ret < 0) {
 			dev_err(&dev->dev, "unable to register port at index %d "
 				"(IO%lx MEM%llx IRQ%d): %d\n", i,
-- 
2.50.1