[U-Boot] [PATCH v1] gcc-9: silence 'address-of-packed-member' warning

[Tom Rini]

On Fri, Nov 29, 2019 at 07:47:59PM +0200, Andy Shevchenko wrote:

> GCC 9.x starts complaining about potential misalignment of the pointer to
> the array (in this case alignment=2) in the packed (alignment=1) structures.
> 
> Repeating Linus' Torvalds commit 6f303d60534c in the Linux kernel.
> 
> Original commit message:
> 
>   We already did this for clang, but now gcc has that warning too.
>   Yes, yes, the address may be unaligned.  And that's kind of the point.
> 
> This in particular hides the warnings like
> 
> drivers/usb/gadget/composite.c:545:23: warning: taking address of packed member of ‘struct usb_string_descriptor’ may result in an unaligned pointer value [-Waddress-of-packed-member]
>   545 |    collect_langs(sp, s->wData);
> 
> drivers/usb/gadget/composite.c:550:24: warning: taking address of packed member of ‘struct usb_string_descriptor’ may result in an unaligned pointer value [-Waddress-of-packed-member]
>   550 |     collect_langs(sp, s->wData);
> 
> drivers/usb/gadget/composite.c:555:25: warning: taking address of packed member of ‘struct usb_string_descriptor’ may result in an unaligned pointer value [-Waddress-of-packed-member]
>   555 |      collect_langs(sp, s->wData);
> 
> Signed-off-by: Andy Shevchenko <andriy.shevchenko at linux.intel.com>
> ---
>  Makefile | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/Makefile b/Makefile
> index 7485bc2594..a0469f6a9c 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -672,11 +672,12 @@ endif
>  endif
>  
>  KBUILD_CFLAGS += $(call cc-option,-Wno-format-nonliteral)
> +KBUILD_CFLAGS += $(call cc-disable-warning, address-of-packed-member)
> +
>  ifeq ($(cc-name),clang)
>  KBUILD_CPPFLAGS += $(call cc-option,-Qunused-arguments,)
>  KBUILD_CFLAGS += $(call cc-disable-warning, format-invalid-specifier)
>  KBUILD_CFLAGS += $(call cc-disable-warning, gnu)
> -KBUILD_CFLAGS += $(call cc-disable-warning, address-of-packed-member)
>  KBUILD_CFLAGS += $(call cc-option, -fcatch-undefined-behavior)
>  endif

Ooh, I wish I had thought to look at the kernel a while ago.  I very
much like this idea and need to run a test to see how much space we
re-grain with this patch and reverting the handful of reworks that might
not make as much long term sense to do.  Thanks!

-- 
Tom
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