linux-kernel - [PATCH 3.16 017/204] gpio: acpi: work around false-positive -Wstring-overflow warning

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Date:   Thu, 28 Dec 2017 17:05:44 +0000
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, "Arnd Bergmann" <arnd@...db.de>,
        "Andy Shevchenko" <andriy.shevchenko@...ux.intel.com>,
        "Mika Westerberg" <mika.westerberg@...ux.intel.com>,
        "Linus Walleij" <linus.walleij@...aro.org>
Subject: [PATCH 3.16 017/204] gpio: acpi: work around false-positive
 -Wstring-overflow warning

3.16.52-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Arnd Bergmann <arnd@...db.de>

commit e40a3ae1f794a35c4af3746291ed6fedc1fa0f6f upstream.

gcc-7 notices that the pin_table is an array of 16-bit numbers,
but fails to take the following range check into account:

drivers/gpio/gpiolib-acpi.c: In function 'acpi_gpiochip_request_interrupt':
drivers/gpio/gpiolib-acpi.c:206:24: warning: '%02X' directive writing between 2 and 4 bytes into a region of size 3 [-Wformat-overflow=]
   sprintf(ev_name, "_%c%02X",
                        ^~~~
drivers/gpio/gpiolib-acpi.c:206:20: note: directive argument in the range [0, 65535]
   sprintf(ev_name, "_%c%02X",
                    ^~~~~~~~~
drivers/gpio/gpiolib-acpi.c:206:3: note: 'sprintf' output between 5 and 7 bytes into a destination of size 5
   sprintf(ev_name, "_%c%02X",
   ^~~~~~~~~~~~~~~~~~~~~~~~~~~
    agpio->triggering == ACPI_EDGE_SENSITIVE ? 'E' : 'L',
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    pin);
    ~~~~

As suggested by Andy, this changes the format string to have a fixed length.
Since modifying the range check did not help, I also opened a bug against
gcc, see link below.

Fixes: 0d1c28a449c6 ("gpiolib-acpi: Add ACPI5 event model support to gpio.")
Cc: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Link: https://patchwork.kernel.org/patch/9840801/
Link: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82123
Signed-off-by: Arnd Bergmann <arnd@...db.de>
Acked-by: Mika Westerberg <mika.westerberg@...ux.intel.com>
Signed-off-by: Linus Walleij <linus.walleij@...aro.org>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 drivers/gpio/gpiolib-acpi.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/drivers/gpio/gpiolib-acpi.c
+++ b/drivers/gpio/gpiolib-acpi.c
@@ -130,7 +130,7 @@ static acpi_status acpi_gpiochip_request
 
 	if (pin <= 255) {
 		char ev_name[5];
-		sprintf(ev_name, "_%c%02X",
+		sprintf(ev_name, "_%c%02hhX",
 			agpio->triggering == ACPI_EDGE_SENSITIVE ? 'E' : 'L',
 			pin);
 		if (ACPI_SUCCESS(acpi_get_handle(handle, ev_name, &evt_handle)))