On Fri, Jul 14, 2017 at 2:52 PM, Andy Shevchenko
[off-list ref] wrote:

On Fri, 2017-07-14 at 14:07 +0200, Arnd Bergmann wrote:

quoted

gcc-7 notices that the pin_table is an array of 16-bit numbers,
but we assume it can be printed as a two-character hexadecimal
string:

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);
    ~~~~

This is obviously a false positive warning.

Here we have
int pin = u16 pin_table[0] <= 255 (implying >= 0).

I see few options how to make it more clear
1) your proposal;
2) use "%02hhX" instead;
3) use if (ret >= 0 && ret <= 255) condition.

I would choose one of the 2-3.

In case gcc will complain about 3), file a bug to gcc crazy warning.

Makes sense. I didn't remember the syntax for 2) and couldn't find
it in the man page when I first looked. This seems like a good solution
here.

I'm pretty sure I tried 3) a few times when the warning first showed
up last year, but couldn't get that to work. Filing a gcc bug also seems
like a good idea, but I should first see if it's already fixed. The version
I use for testing at the moment is from late April, and others may
have complained about that already.

      Arnd