linux-kernel - Re: [PATCH 2/2] drm/imagination: avoid -Woverflow warning

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Message-ID: <9df9e4f87727399928c068dbbf614c9895ae15f9.camel@imgtec.com>
Date:   Wed, 29 Nov 2023 12:01:20 +0000
From:   Donald Robson <Donald.Robson@...tec.com>
To:     Frank Binns <Frank.Binns@...tec.com>,
        Matt Coster <Matt.Coster@...tec.com>,
        "arnd@...nel.org" <arnd@...nel.org>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "tzimmermann@...e.de" <tzimmermann@...e.de>,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        "airlied@...il.com" <airlied@...il.com>,
        "arnd@...db.de" <arnd@...db.de>,
        Sarah Walker <Sarah.Walker@...tec.com>,
        "maarten.lankhorst@...ux.intel.com" 
        <maarten.lankhorst@...ux.intel.com>,
        "daniel@...ll.ch" <daniel@...ll.ch>,
        "mripard@...nel.org" <mripard@...nel.org>
Subject: Re: [PATCH 2/2] drm/imagination: avoid -Woverflow warning

Hello Arnd,

Thanks for the patch.  I'm slightly concerned that we've not seen this warning when
building here.  I guess we need to check our CI settings...

Reviewed-by: Donald Robson <donald.robson@...tec.com>

On Wed, 2023-11-29 at 12:33 +0100, Arnd Bergmann wrote:
> From: Arnd Bergmann <arnd@...db.de>
> 
> The array size calculation in pvr_vm_mips_fini() appears to be incorrect based on
> taking the size of the pointer rather than the size of the array, which manifests
> as a warning about signed integer overflow:
> 
> In file included from include/linux/kernel.h:16,
>                  from drivers/gpu/drm/imagination/pvr_rogue_fwif.h:10,
>                  from drivers/gpu/drm/imagination/pvr_ccb.h:7,
>                  from drivers/gpu/drm/imagination/pvr_device.h:7,
>                  from drivers/gpu/drm/imagination/pvr_vm_mips.c:4:
> drivers/gpu/drm/imagination/pvr_vm_mips.c: In function 'pvr_vm_mips_fini':
> include/linux/array_size.h:11:25: error: overflow in conversion from 'long unsigned int' to 'int' changes value from '18446744073709551615' to '-1' [-Werror=overflow]
>    11 | #define ARRAY_SIZE(arr) (sizeof(arr) / sizeof((arr)[0]) + __must_be_array(arr))
>       |                         ^
> drivers/gpu/drm/imagination/pvr_vm_mips.c:106:24: note: in expansion of macro 'ARRAY_SIZE'
>   106 |         for (page_nr = ARRAY_SIZE(mips_data->pt_pages) - 1; page_nr >= 0; page_nr--) {
>       |                        ^~~~~~~~~~
> 
> Just use the number of array elements directly here, and in the corresponding
> init function for consistency.
> 
> Fixes: 927f3e0253c1 ("drm/imagination: Implement MIPS firmware processor and MMU support")
> Signed-off-by: Arnd Bergmann <arnd@...db.de>
> ---
>  drivers/gpu/drm/imagination/pvr_vm_mips.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/imagination/pvr_vm_mips.c b/drivers/gpu/drm/imagination/pvr_vm_mips.c
> index 7268cf6e630b..6c2e4cc4e6db 100644
> --- 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_dev)
>  	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;
> @@ -103,7 +103,7 @@ pvr_vm_mips_fini(struct pvr_device *pvr_dev)
>  	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);
>