linux-kernel - Re: [PATCH] drm/imagination: fix ARRAY

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Date: Thu, 18 Jan 2024 09:38:59 +0000
From: Matt Coster <Matt.Coster@...tec.com>
To: Randy Dunlap <rdunlap@...radead.org>
CC: Maxime Ripard <mripard@...nel.org>, Frank Binns <Frank.Binns@...tec.com>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Thomas Zimmermann
	<tzimmermann@...e.de>,
        David Airlie <airlied@...il.com>, Daniel Vetter
	<daniel@...ll.ch>,
        "dri-devel@...ts.freedesktop.org"
	<dri-devel@...ts.freedesktop.org>,
        "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] drm/imagination: fix ARRAY_SIZE build error

On 10/01/2024 00:23, Randy Dunlap wrote:
> Fix a build error when using GCC 13.2.0 from kernel.org crosstools
> by changing ARRAY_SIZE() to the macro PVR_MIPS_PT_PAGE_COUNT:

I assume you're referring to the x86_64 => aarch64 toolchain here?

> drivers/gpu/drm/imagination/pvr_vm_mips.c: In function 'pvr_vm_mips_fini':
> ../include/linux/array_size.h:11:25: warning: overflow in conversion from 'long unsigned int' to 'int' changes value from '18446744073709551615' to '-1' [-Woverflow]
>     11 | #define ARRAY_SIZE(arr) (sizeof(arr) / sizeof((arr)[0]) + __must_be_array(arr))
>        |                         ^
> drivers/gpu/drm/imagination/pvr_vm_mips.c:105:24: note: in expansion of macro 'ARRAY_SIZE'
>    105 |         for (page_nr = ARRAY_SIZE(mips_data->pt_pages) - 1; page_nr >= 0; page_nr--) {
>        |                        ^~~~~~~~~~

I can't seem to reproduce this using the above toolchain (or any other),
even with -Woverflow explicitly specified.

The use of ARRAY_SIZE() in loop bounds is a pretty common construction –
even within the pvr driver. Do you see similar warnings anywhere else?

Regards,
Matt

--
Matt Coster
Imagination Technologies

> Fixes: 927f3e0253c1 ("drm/imagination: Implement MIPS firmware processor and MMU support")
> Signed-off-by: Randy Dunlap <rdunlap@...radead.org>
> Cc: Donald Robson <donald.robson@...tec.com>
> Cc: Maxime Ripard <mripard@...nel.org>
> Cc: Frank Binns <frank.binns@...tec.com>
> Cc: Matt Coster <matt.coster@...tec.com>
> Cc: Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>
> Cc: Thomas Zimmermann <tzimmermann@...e.de>
> Cc: David Airlie <airlied@...il.com>
> Cc: Daniel Vetter <daniel@...ll.ch>
> Cc: dri-devel@...ts.freedesktop.org
> ---
>   drivers/gpu/drm/imagination/pvr_vm_mips.c |    4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff -- a/drivers/gpu/drm/imagination/pvr_vm_mips.c b/drivers/gpu/drm/imagination/pvr_vm_mips.c
> --- a/drivers/gpu/drm/imagination/pvr_vm_mips.c
> +++ b/drivers/gpu/drm/imagination/pvr_vm_mips.c
> @@ -46,7 +46,7 @@ pvr_vm_mips_init(struct pvr_device *pvr_
>   	if (!mips_data)
>   		return -ENOMEM;
>   
> -	for (page_nr = 0; page_nr < ARRAY_SIZE(mips_data->pt_pages); page_nr++) {
> +	for (page_nr = 0; page_nr < PVR_MIPS_PT_PAGE_COUNT; page_nr++) {
>   		mips_data->pt_pages[page_nr] = alloc_page(GFP_KERNEL | __GFP_ZERO);
>   		if (!mips_data->pt_pages[page_nr]) {
>   			err = -ENOMEM;
> @@ -102,7 +102,7 @@ pvr_vm_mips_fini(struct pvr_device *pvr_
>   	int page_nr;
>   
>   	vunmap(mips_data->pt);
> -	for (page_nr = ARRAY_SIZE(mips_data->pt_pages) - 1; page_nr >= 0; page_nr--) {
> +	for (page_nr = PVR_MIPS_PT_PAGE_COUNT - 1; page_nr >= 0; page_nr--) {
>   		dma_unmap_page(from_pvr_device(pvr_dev)->dev,
>   			       mips_data->pt_dma_addr[page_nr], PAGE_SIZE, DMA_TO_DEVICE);
>   

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