On 2022/05/13 22:50, Sergey Shtylyov wrote:
> The code multiplying the # of cylinders/heads/sectors in ata_id_n_sectors()
> to get a disk capacity implicitly uses the *int* type for that calculation
> and casting the result to 'u64' before returning ensues a sign extension.
> Explicitly casting the 'u16' typed multipliers to 'u32' results in avoiding
> a sign extension instruction and so in a more compact code...
>
> Found by Linux Verification Center (linuxtesting.org) with the SVACE static
> analysis tool.
>
> Signed-off-by: Sergey Shtylyov <s.shtylyov@xxxxxx>
>
> ---
> This patch is against the 'for-next' branch of Damien's 'libata.git' repo.
>
> drivers/ata/libata-core.c | 10 ++++++----
> 1 file changed, 6 insertions(+), 4 deletions(-)
>
> Index: libata/drivers/ata/libata-core.c
> ===================================================================
> --- libata.orig/drivers/ata/libata-core.c
> +++ libata/drivers/ata/libata-core.c
> @@ -1107,11 +1107,13 @@ static u64 ata_id_n_sectors(const u16 *i
> return ata_id_u32(id, ATA_ID_LBA_CAPACITY);
> } else {
> if (ata_id_current_chs_valid(id))
> - return id[ATA_ID_CUR_CYLS] * id[ATA_ID_CUR_HEADS] *
> - id[ATA_ID_CUR_SECTORS];
> + return (u32)id[ATA_ID_CUR_CYLS] *
> + (u32)id[ATA_ID_CUR_HEADS] *
> + (u32)id[ATA_ID_CUR_SECTORS];
> else
While at it, you can drop this useless "else". The 2 else above this one are
actually also useless...
> - return id[ATA_ID_CYLS] * id[ATA_ID_HEADS] *
> - id[ATA_ID_SECTORS];
> + return (u32)id[ATA_ID_CYLS] *
> + (u32)id[ATA_ID_HEADS] *
> + (u32)id[ATA_ID_SECTORS];
Given that the function returns an u64, I would cast everything to u64. That
will avoid overflows too, which was possible before, eventhough no problems seem
to have been reported... Who uses CHS these days :)
> }
> }
>
--
Damien Le Moal
Western Digital Research
