On Wed, Sep 9, 2020 at 11:49 AM Kent Gibson [off-list ref] wrote:

On Wed, Sep 09, 2020 at 11:41:35AM +0200, Bartosz Golaszewski wrote:

quoted

On Wed, Sep 9, 2020 at 11:35 AM Kent Gibson [off-list ref] wrote:

quoted

On Wed, Sep 09, 2020 at 11:26:00AM +0200, Bartosz Golaszewski wrote:

quoted

On Wed, Sep 9, 2020 at 11:24 AM Kent Gibson [off-list ref] wrote:

quoted

On Sat, Sep 05, 2020 at 09:35:36PM +0800, Kent Gibson wrote:

quoted

Add support for requesting lines using the GPIO_V2_GET_LINE_IOCTL, and
returning their current values using GPIO_V2_LINE_GET_VALUES_IOCTL.

The struct linereq implementation is based on the v1 struct linehandle
implementation.

Signed-off-by: Kent Gibson <warthog618@gmail.com>
---

[snip]

quoted

              if (copy_from_user(&offset, ip, sizeof(offset)))
                      return -EFAULT;

@@ -1104,6 +1505,25 @@ int gpiolib_cdev_register(struct gpio_device *gdev, dev_t devt)
               MAJOR(devt), gdev->id);

      return 0;
+     /*
+      * array sizes must ensure 64-bit alignment and not create holes in
+      * the struct packing.
+      */
+     BUILD_BUG_ON(IS_ALIGNED(GPIO_V2_LINES_MAX, 2));
+     BUILD_BUG_ON(IS_ALIGNED(GPIO_MAX_NAME_SIZE, 8));
+
+     /*
+      * check that uAPI structs are 64-bit aligned for 32/64-bit
+      * compatibility
+      */
+     BUILD_BUG_ON(IS_ALIGNED(sizeof(struct gpio_v2_line_attribute), 8));
+     BUILD_BUG_ON(IS_ALIGNED(sizeof(struct gpio_v2_line_config_attribute), 8));
+     BUILD_BUG_ON(IS_ALIGNED(sizeof(struct gpio_v2_line_config), 8));
+     BUILD_BUG_ON(IS_ALIGNED(sizeof(struct gpio_v2_line_request), 8));
+     BUILD_BUG_ON(IS_ALIGNED(sizeof(struct gpio_v2_line_info), 8));
+     BUILD_BUG_ON(IS_ALIGNED(sizeof(struct gpio_v2_line_info_changed), 8));
+     BUILD_BUG_ON(IS_ALIGNED(sizeof(struct gpio_v2_line_event), 8));
+     BUILD_BUG_ON(IS_ALIGNED(sizeof(struct gpio_v2_line_values), 8));
 }

A couple of things here - these should all be !IS_ALIGNED.
And the BUILD_BUG_ON gets compiled out, and so doesn't fail, if they are
after the return.

How would you like that fixed - v8 or a patch once v7 is in?

Cheers,
Kent.

v8 please. Why is it compiled out though? Does it need some config option?

Not sure - haven't looked into it.  I only noticed the condition was
inverted in passing, and when I flipped it it still compiled.
Moving the return to the end of the function made them all fail,
as they should if IS_ALIGNED is true.

Having BUILD_BUG_ON being able to compile out quietly is a problem in
itself.  Nothing special in my setup that I am aware of.

Cheers,
Kent.

From include/linux/compiler_types.h:

295 #ifdef __OPTIMIZE__
296 # define __compiletime_assert(condition, msg, prefix, suffix)           \
297         do {                                                            \
298                 extern void prefix ## suffix(void)
__compiletime_error(msg); \
299                 if (!(condition))                                       \
300                         prefix ## suffix();                             \
301         } while (0)
302 #else
303 # define __compiletime_assert(condition, msg, prefix, suffix) do {
} while (0)
304 #endif

__OPTIMIZE__ is a predefined macro. I'm not sure about your setup but
it it's defined for me in all my yocto SDK builds and BUILD_BUG_ON(1)
fails as expected.

Even when placed after the return, as was the case here?

Kent.

No of course not, I put it into a void function. Sorry for the noise.

I'm not sure how to disable optimizations for a macro.

For now putting it before return should be fine.

Bart