Re: [PATCH] ata: libata-core: fix sloppy typing in ata_id_n_sectors()

[Sergey Shtylyov <s.shtylyov@omp.ru>]

On 6/8/22 9:47 AM, Damien Le Moal 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@omp.ru>
>>
>> ---
>> 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
>> -			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];
>>  	}
>>  }
>>  
> 
> Applied to for-5.20. Thanks !

   Actually I was going to redo it (changing the order of multiplications), but well,
it's OK as is...

MBR, Sergey