Re: [PATCH] drm/format-helper: fix build

[Thomas Zimmermann <tzimmermann@suse.de>]

Hi

Am 02.04.25 um 12:44 schrieb Matthew Auld:
> Build fails with:
>
> error: multiple unsequenced modifications to 'sbuf32'
> [-Werror,-Wunsequenced]
>    264 |                         le32_to_cpup(sbuf32++),
>        |                                            ^
>    265 |                         le32_to_cpup(sbuf32++),
>        |                                            ~~
>
> With that move the increment of the sbuf32 pointer to the end of the
> loop, instead of inside the array list initializer, where the
> order/sequence of the sbuf32 pointer modifications is not defined.
>
> Fixes: 58523a25cbf7 ("drm/format-helper: Optimize 32-to-24-bpp conversion")
> Fixes: 3f31a017ddbc ("drm/format-helper: Optimize 32-to-16-bpp conversion")
> Fixes: 65931bbc5177 ("drm/format-helper: Optimize 32-to-8-bpp conversion")
> Signed-off-by: Matthew Auld <matthew.auld@intel.com>
> Cc: Thomas Zimmermann <tzimmermann@suse.de>
> Cc: Jocelyn Falempe <jfalempe@redhat.com>

Reviewed-by: Thomas Zimmermann <tzimmermann@suse.de>

Thanks for the fix. I build with W=1 but never saw this error. Do you 
use other build flags?

Best regards
Thomas

> ---
>   drivers/gpu/drm/drm_format_helper.c | 32 ++++++++++++++++-------------
>   1 file changed, 18 insertions(+), 14 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_format_helper.c b/drivers/gpu/drm/drm_format_helper.c
> index fc7347caf600..d36e6cacc575 100644
> --- a/drivers/gpu/drm/drm_format_helper.c
> +++ b/drivers/gpu/drm/drm_format_helper.c
> @@ -261,10 +261,10 @@ static __always_inline void drm_fb_xfrm_line_32to8(void *dbuf, const void *sbuf,
>   	/* write 4 pixels at once */
>   	while (sbuf32 < ALIGN_DOWN_PIXELS(send32, pixels, 4)) {
>   		u32 pix[4] = {
> -			le32_to_cpup(sbuf32++),
> -			le32_to_cpup(sbuf32++),
> -			le32_to_cpup(sbuf32++),
> -			le32_to_cpup(sbuf32++),
> +			le32_to_cpup(sbuf32),
> +			le32_to_cpup(sbuf32 + 1),
> +			le32_to_cpup(sbuf32 + 2),
> +			le32_to_cpup(sbuf32 + 3),
>   		};
>   		/* write output bytes in reverse order for little endianness */
>   		u32 val32 = xfrm_pixel(pix[0]) |
> @@ -272,6 +272,7 @@ static __always_inline void drm_fb_xfrm_line_32to8(void *dbuf, const void *sbuf,
>   			   (xfrm_pixel(pix[2]) << 16) |
>   			   (xfrm_pixel(pix[3]) << 24);
>   		*dbuf32++ = cpu_to_le32(val32);
> +		sbuf32 += ARRAY_SIZE(pix);
>   	}
>   
>   	/* write trailing pixels */
> @@ -294,10 +295,10 @@ static __always_inline void drm_fb_xfrm_line_32to16(void *dbuf, const void *sbuf
>   	/* write 4 pixels at once */
>   	while (sbuf32 < ALIGN_DOWN_PIXELS(send32, pixels, 4)) {
>   		u32 pix[4] = {
> -			le32_to_cpup(sbuf32++),
> -			le32_to_cpup(sbuf32++),
> -			le32_to_cpup(sbuf32++),
> -			le32_to_cpup(sbuf32++),
> +			le32_to_cpup(sbuf32),
> +			le32_to_cpup(sbuf32 + 1),
> +			le32_to_cpup(sbuf32 + 2),
> +			le32_to_cpup(sbuf32 + 3),
>   		};
>   		/* write output bytes in reverse order for little endianness */
>   		u64 val64 = ((u64)xfrm_pixel(pix[0])) |
> @@ -305,6 +306,7 @@ static __always_inline void drm_fb_xfrm_line_32to16(void *dbuf, const void *sbuf
>   			    ((u64)xfrm_pixel(pix[2]) << 32) |
>   			    ((u64)xfrm_pixel(pix[3]) << 48);
>   		*dbuf64++ = cpu_to_le64(val64);
> +		sbuf32 += ARRAY_SIZE(pix);
>   	}
>   #endif
>   
> @@ -312,13 +314,14 @@ static __always_inline void drm_fb_xfrm_line_32to16(void *dbuf, const void *sbuf
>   	dbuf32 = (__le32 __force *)dbuf64;
>   	while (sbuf32 < ALIGN_DOWN_PIXELS(send32, pixels, 2)) {
>   		u32 pix[2] = {
> -			le32_to_cpup(sbuf32++),
> -			le32_to_cpup(sbuf32++),
> +			le32_to_cpup(sbuf32),
> +			le32_to_cpup(sbuf32 + 1),
>   		};
>   		/* write output bytes in reverse order for little endianness */
>   		u32 val32 = xfrm_pixel(pix[0]) |
>   			   (xfrm_pixel(pix[1]) << 16);
>   		*dbuf32++ = cpu_to_le32(val32);
> +		sbuf32 += ARRAY_SIZE(pix);
>   	}
>   
>   	/* write trailing pixel */
> @@ -339,10 +342,10 @@ static __always_inline void drm_fb_xfrm_line_32to24(void *dbuf, const void *sbuf
>   	/* write pixels in chunks of 4 */
>   	while (sbuf32 < ALIGN_DOWN_PIXELS(send32, pixels, 4)) {
>   		u32 val24[4] = {
> -			xfrm_pixel(le32_to_cpup(sbuf32++)),
> -			xfrm_pixel(le32_to_cpup(sbuf32++)),
> -			xfrm_pixel(le32_to_cpup(sbuf32++)),
> -			xfrm_pixel(le32_to_cpup(sbuf32++)),
> +			xfrm_pixel(le32_to_cpup(sbuf32)),
> +			xfrm_pixel(le32_to_cpup(sbuf32 + 1)),
> +			xfrm_pixel(le32_to_cpup(sbuf32 + 2)),
> +			xfrm_pixel(le32_to_cpup(sbuf32 + 3)),
>   		};
>   		u32 out32[3] = {
>   			/* write output bytes in reverse order for little endianness */
> @@ -363,6 +366,7 @@ static __always_inline void drm_fb_xfrm_line_32to24(void *dbuf, const void *sbuf
>   		*dbuf32++ = cpu_to_le32(out32[0]);
>   		*dbuf32++ = cpu_to_le32(out32[1]);
>   		*dbuf32++ = cpu_to_le32(out32[2]);
> +		sbuf32 += ARRAY_SIZE(val24);
>   	}
>   
>   	/* write trailing pixel */

-- 
--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Frankenstrasse 146, 90461 Nuernberg, Germany
GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman
HRB 36809 (AG Nuernberg)