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* [dpdk-dev] [PATCH] hash: fix breaking strict-aliasing rules
@ 2015-03-18 16:51 Yerden Zhumabekov
  2015-03-19 16:25 ` Bruce Richardson
                   ` (3 more replies)
  0 siblings, 4 replies; 10+ messages in thread
From: Yerden Zhumabekov @ 2015-03-18 16:51 UTC (permalink / raw)
  To: dev

Fix rte_hash_crc() function. Casting uint64_t pointer to uin32_t
may trigger a compiler warning about breaking strict-aliasing rules.
To avoid that, introduce a lookup table which is used to mask out
a remainder of data.

See issue #1, http://dpdk.org/ml/archives/dev/2015-March/015174.html

Signed-off-by: Yerden Zhumabekov <e_zhumabekov@sts.kz>
---
 lib/librte_hash/rte_hash_crc.h |   31 +++++++++++++++----------------
 1 file changed, 15 insertions(+), 16 deletions(-)

diff --git a/lib/librte_hash/rte_hash_crc.h b/lib/librte_hash/rte_hash_crc.h
index 3dcd362..e81920f 100644
--- a/lib/librte_hash/rte_hash_crc.h
+++ b/lib/librte_hash/rte_hash_crc.h
@@ -323,6 +323,16 @@ static const uint32_t crc32c_tables[8][256] = {{
  0xE54C35A1, 0xAC704886, 0x7734CFEF, 0x3E08B2C8, 0xC451B7CC, 0x8D6DCAEB, 0x56294D82, 0x1F1530A5
 }};
 
+static const uint64_t odd_8byte_mask[] = {
+	0x00FFFFFFFFFFFFFF,
+	0x0000FFFFFFFFFFFF,
+	0x000000FFFFFFFFFF,
+	0x00000000FFFFFFFF,
+	0x0000000000FFFFFF,
+	0x000000000000FFFF,
+	0x00000000000000FF,
+};
+
 #define CRC32_UPD(crc, n) \
 	(crc32c_tables[(n)][(crc) & 0xFF] ^ \
 	 crc32c_tables[(n)-1][((crc) >> 8) & 0xFF])
@@ -535,38 +545,27 @@ static inline uint32_t
 rte_hash_crc(const void *data, uint32_t data_len, uint32_t init_val)
 {
 	unsigned i;
-	uint64_t temp = 0;
+	uint64_t temp;
 	const uint64_t *p64 = (const uint64_t *)data;
 
 	for (i = 0; i < data_len / 8; i++) {
 		init_val = rte_hash_crc_8byte(*p64++, init_val);
 	}
 
-	switch (7 - (data_len & 0x07)) {
+	i = 7 - (data_len & 0x07);
+	switch (i) {
 	case 0:
-		temp |= (uint64_t) *((const uint8_t *)p64 + 6) << 48;
-		/* Fallthrough */
 	case 1:
-		temp |= (uint64_t) *((const uint8_t *)p64 + 5) << 40;
-		/* Fallthrough */
 	case 2:
-		temp |= (uint64_t) *((const uint8_t *)p64 + 4) << 32;
-		temp |= *((const uint32_t *)p64);
+		temp = odd_8byte_mask[i] & *p64;
 		init_val = rte_hash_crc_8byte(temp, init_val);
 		break;
 	case 3:
-		init_val = rte_hash_crc_4byte(*(const uint32_t *)p64, init_val);
-		break;
 	case 4:
-		temp |= *((const uint8_t *)p64 + 2) << 16;
-		/* Fallthrough */
 	case 5:
-		temp |= *((const uint8_t *)p64 + 1) << 8;
-		/* Fallthrough */
 	case 6:
-		temp |= *((const uint8_t *)p64);
+		temp = odd_8byte_mask[i] & *p64;
 		init_val = rte_hash_crc_4byte(temp, init_val);
-		/* Fallthrough */
 	default:
 		break;
 	}
-- 
1.7.9.5

^ permalink raw reply	[flat|nested] 10+ messages in thread

* Re: [dpdk-dev] [PATCH] hash: fix breaking strict-aliasing rules
  2015-03-18 16:51 [dpdk-dev] [PATCH] hash: fix breaking strict-aliasing rules Yerden Zhumabekov
@ 2015-03-19 16:25 ` Bruce Richardson
  2015-03-19 16:31   ` Bruce Richardson
  2015-03-20 12:41 ` Pawel Wodkowski
                   ` (2 subsequent siblings)
  3 siblings, 1 reply; 10+ messages in thread
From: Bruce Richardson @ 2015-03-19 16:25 UTC (permalink / raw)
  To: Yerden Zhumabekov; +Cc: dev

On Wed, Mar 18, 2015 at 10:51:12PM +0600, Yerden Zhumabekov wrote:
> Fix rte_hash_crc() function. Casting uint64_t pointer to uin32_t
> may trigger a compiler warning about breaking strict-aliasing rules.
> To avoid that, introduce a lookup table which is used to mask out
> a remainder of data.
> 
> See issue #1, http://dpdk.org/ml/archives/dev/2015-March/015174.html
> 
> Signed-off-by: Yerden Zhumabekov <e_zhumabekov@sts.kz>

Looks ok to me. Couple of minor suggestions below.

/Bruce

> ---
>  lib/librte_hash/rte_hash_crc.h |   31 +++++++++++++++----------------
>  1 file changed, 15 insertions(+), 16 deletions(-)
> 
> diff --git a/lib/librte_hash/rte_hash_crc.h b/lib/librte_hash/rte_hash_crc.h
> index 3dcd362..e81920f 100644
> --- a/lib/librte_hash/rte_hash_crc.h
> +++ b/lib/librte_hash/rte_hash_crc.h
> @@ -323,6 +323,16 @@ static const uint32_t crc32c_tables[8][256] = {{
>   0xE54C35A1, 0xAC704886, 0x7734CFEF, 0x3E08B2C8, 0xC451B7CC, 0x8D6DCAEB, 0x56294D82, 0x1F1530A5
>  }};
>  
> +static const uint64_t odd_8byte_mask[] = {

Where does the name of this variable come from, it seems unclear to me?

> +	0x00FFFFFFFFFFFFFF,
> +	0x0000FFFFFFFFFFFF,
> +	0x000000FFFFFFFFFF,
> +	0x00000000FFFFFFFF,
> +	0x0000000000FFFFFF,
> +	0x000000000000FFFF,
> +	0x00000000000000FF,
> +};
> +
>  #define CRC32_UPD(crc, n) \
>  	(crc32c_tables[(n)][(crc) & 0xFF] ^ \
>  	 crc32c_tables[(n)-1][((crc) >> 8) & 0xFF])
> @@ -535,38 +545,27 @@ static inline uint32_t
>  rte_hash_crc(const void *data, uint32_t data_len, uint32_t init_val)
>  {
>  	unsigned i;
> -	uint64_t temp = 0;
> +	uint64_t temp;

It is worth keeping variable "temp" at all, it looks to me like it could be done
away with without seriously affecting readability.

>  	const uint64_t *p64 = (const uint64_t *)data;
>  
>  	for (i = 0; i < data_len / 8; i++) {
>  		init_val = rte_hash_crc_8byte(*p64++, init_val);
>  	}
>  
> -	switch (7 - (data_len & 0x07)) {
> +	i = 7 - (data_len & 0x07);

i is not a terribly meaningful variable name, perhaps a slightly longer, more
meaningful name might improve readability.

> +	switch (i) {
>  	case 0:
> -		temp |= (uint64_t) *((const uint8_t *)p64 + 6) << 48;
> -		/* Fallthrough */
>  	case 1:
> -		temp |= (uint64_t) *((const uint8_t *)p64 + 5) << 40;
> -		/* Fallthrough */
>  	case 2:
> -		temp |= (uint64_t) *((const uint8_t *)p64 + 4) << 32;
> -		temp |= *((const uint32_t *)p64);
> +		temp = odd_8byte_mask[i] & *p64;
>  		init_val = rte_hash_crc_8byte(temp, init_val);
>  		break;
>  	case 3:
> -		init_val = rte_hash_crc_4byte(*(const uint32_t *)p64, init_val);
> -		break;
>  	case 4:
> -		temp |= *((const uint8_t *)p64 + 2) << 16;
> -		/* Fallthrough */
>  	case 5:
> -		temp |= *((const uint8_t *)p64 + 1) << 8;
> -		/* Fallthrough */
>  	case 6:
> -		temp |= *((const uint8_t *)p64);
> +		temp = odd_8byte_mask[i] & *p64;
>  		init_val = rte_hash_crc_4byte(temp, init_val);
> -		/* Fallthrough */
>  	default:
>  		break;
>  	}
> -- 
> 1.7.9.5
> 

^ permalink raw reply	[flat|nested] 10+ messages in thread

* Re: [dpdk-dev] [PATCH] hash: fix breaking strict-aliasing rules
  2015-03-19 16:25 ` Bruce Richardson
@ 2015-03-19 16:31   ` Bruce Richardson
  2015-03-20  3:29     ` Yerden Zhumabekov
  0 siblings, 1 reply; 10+ messages in thread
From: Bruce Richardson @ 2015-03-19 16:31 UTC (permalink / raw)
  To: Yerden Zhumabekov; +Cc: dev

On Thu, Mar 19, 2015 at 04:25:47PM +0000, Bruce Richardson wrote:
> On Wed, Mar 18, 2015 at 10:51:12PM +0600, Yerden Zhumabekov wrote:
> > Fix rte_hash_crc() function. Casting uint64_t pointer to uin32_t
> > may trigger a compiler warning about breaking strict-aliasing rules.
> > To avoid that, introduce a lookup table which is used to mask out
> > a remainder of data.
> > 
> > See issue #1, http://dpdk.org/ml/archives/dev/2015-March/015174.html
> > 
> > Signed-off-by: Yerden Zhumabekov <e_zhumabekov@sts.kz>
> 
> Looks ok to me. Couple of minor suggestions below.
> 
> /Bruce

Other than the below suggestions:

Acked-by: Bruce Richardson <bruce.richardson@intel.com>
> 
> > ---
> >  lib/librte_hash/rte_hash_crc.h |   31 +++++++++++++++----------------
> >  1 file changed, 15 insertions(+), 16 deletions(-)
> > 
> > diff --git a/lib/librte_hash/rte_hash_crc.h b/lib/librte_hash/rte_hash_crc.h
> > index 3dcd362..e81920f 100644
> > --- a/lib/librte_hash/rte_hash_crc.h
> > +++ b/lib/librte_hash/rte_hash_crc.h
> > @@ -323,6 +323,16 @@ static const uint32_t crc32c_tables[8][256] = {{
> >   0xE54C35A1, 0xAC704886, 0x7734CFEF, 0x3E08B2C8, 0xC451B7CC, 0x8D6DCAEB, 0x56294D82, 0x1F1530A5
> >  }};
> >  
> > +static const uint64_t odd_8byte_mask[] = {
> 
> Where does the name of this variable come from, it seems unclear to me?
> 
> > +	0x00FFFFFFFFFFFFFF,
> > +	0x0000FFFFFFFFFFFF,
> > +	0x000000FFFFFFFFFF,
> > +	0x00000000FFFFFFFF,
> > +	0x0000000000FFFFFF,
> > +	0x000000000000FFFF,
> > +	0x00000000000000FF,
> > +};
> > +
> >  #define CRC32_UPD(crc, n) \
> >  	(crc32c_tables[(n)][(crc) & 0xFF] ^ \
> >  	 crc32c_tables[(n)-1][((crc) >> 8) & 0xFF])
> > @@ -535,38 +545,27 @@ static inline uint32_t
> >  rte_hash_crc(const void *data, uint32_t data_len, uint32_t init_val)
> >  {
> >  	unsigned i;
> > -	uint64_t temp = 0;
> > +	uint64_t temp;
> 
> It is worth keeping variable "temp" at all, it looks to me like it could be done
> away with without seriously affecting readability.
> 
> >  	const uint64_t *p64 = (const uint64_t *)data;
> >  
> >  	for (i = 0; i < data_len / 8; i++) {
> >  		init_val = rte_hash_crc_8byte(*p64++, init_val);
> >  	}
> >  
> > -	switch (7 - (data_len & 0x07)) {
> > +	i = 7 - (data_len & 0x07);
> 
> i is not a terribly meaningful variable name, perhaps a slightly longer, more
> meaningful name might improve readability.
> 
> > +	switch (i) {
> >  	case 0:
> > -		temp |= (uint64_t) *((const uint8_t *)p64 + 6) << 48;
> > -		/* Fallthrough */
> >  	case 1:
> > -		temp |= (uint64_t) *((const uint8_t *)p64 + 5) << 40;
> > -		/* Fallthrough */
> >  	case 2:
> > -		temp |= (uint64_t) *((const uint8_t *)p64 + 4) << 32;
> > -		temp |= *((const uint32_t *)p64);
> > +		temp = odd_8byte_mask[i] & *p64;
> >  		init_val = rte_hash_crc_8byte(temp, init_val);
> >  		break;
> >  	case 3:
> > -		init_val = rte_hash_crc_4byte(*(const uint32_t *)p64, init_val);
> > -		break;
> >  	case 4:
> > -		temp |= *((const uint8_t *)p64 + 2) << 16;
> > -		/* Fallthrough */
> >  	case 5:
> > -		temp |= *((const uint8_t *)p64 + 1) << 8;
> > -		/* Fallthrough */
> >  	case 6:
> > -		temp |= *((const uint8_t *)p64);
> > +		temp = odd_8byte_mask[i] & *p64;
> >  		init_val = rte_hash_crc_4byte(temp, init_val);
> > -		/* Fallthrough */
> >  	default:
> >  		break;
> >  	}
> > -- 
> > 1.7.9.5
> > 

^ permalink raw reply	[flat|nested] 10+ messages in thread

* Re: [dpdk-dev] [PATCH] hash: fix breaking strict-aliasing rules
  2015-03-19 16:31   ` Bruce Richardson
@ 2015-03-20  3:29     ` Yerden Zhumabekov
  0 siblings, 0 replies; 10+ messages in thread
From: Yerden Zhumabekov @ 2015-03-20  3:29 UTC (permalink / raw)
  To: Bruce Richardson; +Cc: dev

Hi Bruce,

Answers below.

19.03.2015 22:25, Bruce Richardson пишет:
> On Wed, Mar 18, 2015 at 10:51:12PM +0600, Yerden Zhumabekov wrote:
>> Fix rte_hash_crc() function. Casting uint64_t pointer to uin32_t
>> may trigger a compiler warning about breaking strict-aliasing rules.
>> To avoid that, introduce a lookup table which is used to mask out
>> a remainder of data.
>>
>> See issue #1, http://dpdk.org/ml/archives/dev/2015-March/015174.html
>>
>> Signed-off-by: Yerden Zhumabekov <e_zhumabekov@sts.kz>
> Looks ok to me. Couple of minor suggestions below.
>
> /Bruce
>
>> ---
>>  lib/librte_hash/rte_hash_crc.h |   31 +++++++++++++++----------------
>>  1 file changed, 15 insertions(+), 16 deletions(-)
>>
>> diff --git a/lib/librte_hash/rte_hash_crc.h b/lib/librte_hash/rte_hash_crc.h
>> index 3dcd362..e81920f 100644
>> --- a/lib/librte_hash/rte_hash_crc.h
>> +++ b/lib/librte_hash/rte_hash_crc.h
>> @@ -323,6 +323,16 @@ static const uint32_t crc32c_tables[8][256] = {{
>>   0xE54C35A1, 0xAC704886, 0x7734CFEF, 0x3E08B2C8, 0xC451B7CC, 0x8D6DCAEB, 0x56294D82, 0x1F1530A5
>>  }};
>>  
>> +static const uint64_t odd_8byte_mask[] = {
> Where does the name of this variable come from, it seems unclear to me?

If the number of bytes in data for CRC hashing cannot be evenly divided
by 8, the remainder is extracted with these masks. Hence, we have 'odd'
bytes to mask out. Maybe my poor english. :) Suggestions are welcome.
What about remainder_8byte_mask?

>> +	0x00FFFFFFFFFFFFFF,
>> +	0x0000FFFFFFFFFFFF,
>> +	0x000000FFFFFFFFFF,
>> +	0x00000000FFFFFFFF,
>> +	0x0000000000FFFFFF,
>> +	0x000000000000FFFF,
>> +	0x00000000000000FF,
>> +};
>> +
>>  #define CRC32_UPD(crc, n) \
>>  	(crc32c_tables[(n)][(crc) & 0xFF] ^ \
>>  	 crc32c_tables[(n)-1][((crc) >> 8) & 0xFF])
>> @@ -535,38 +545,27 @@ static inline uint32_t
>>  rte_hash_crc(const void *data, uint32_t data_len, uint32_t init_val)
>>  {
>>  	unsigned i;
>> -	uint64_t temp = 0;
>> +	uint64_t temp;
> It is worth keeping variable "temp" at all, it looks to me like it could be done
> away with without seriously affecting readability.

Noted.

>>  	const uint64_t *p64 = (const uint64_t *)data;
>>  
>>  	for (i = 0; i < data_len / 8; i++) {
>>  		init_val = rte_hash_crc_8byte(*p64++, init_val);
>>  	}
>>  
>> -	switch (7 - (data_len & 0x07)) {
>> +	i = 7 - (data_len & 0x07);
> i is not a terribly meaningful variable name, perhaps a slightly longer, more
> meaningful name might improve readability.

Noted, I'll declare a new one.

-- 
Sincerely,

Yerden Zhumabekov
State Technical Service
Astana, KZ

^ permalink raw reply	[flat|nested] 10+ messages in thread

* Re: [dpdk-dev] [PATCH] hash: fix breaking strict-aliasing rules
  2015-03-18 16:51 [dpdk-dev] [PATCH] hash: fix breaking strict-aliasing rules Yerden Zhumabekov
  2015-03-19 16:25 ` Bruce Richardson
@ 2015-03-20 12:41 ` Pawel Wodkowski
  2015-03-20 12:47 ` Pawel Wodkowski
  2015-03-24 13:31 ` [dpdk-dev] [PATCH v2] " Yerden Zhumabekov
  3 siblings, 0 replies; 10+ messages in thread
From: Pawel Wodkowski @ 2015-03-20 12:41 UTC (permalink / raw)
  To: dev

On 2015-03-18 17:51, Yerden Zhumabekov wrote:
> Fix rte_hash_crc() function. Casting uint64_t pointer to uin32_t
> may trigger a compiler warning about breaking strict-aliasing rules.
> To avoid that, introduce a lookup table which is used to mask out
> a remainder of data.
>
> See issue #1, http://dpdk.org/ml/archives/dev/2015-March/015174.html
>
> Signed-off-by: Yerden Zhumabekov <e_zhumabekov@sts.kz>
> ---
>   lib/librte_hash/rte_hash_crc.h |   31 +++++++++++++++----------------
>   1 file changed, 15 insertions(+), 16 deletions(-)
>
> diff --git a/lib/librte_hash/rte_hash_crc.h b/lib/librte_hash/rte_hash_crc.h
> index 3dcd362..e81920f 100644
> --- a/lib/librte_hash/rte_hash_crc.h
> +++ b/lib/librte_hash/rte_hash_crc.h
> @@ -323,6 +323,16 @@ static const uint32_t crc32c_tables[8][256] = {{
>    0xE54C35A1, 0xAC704886, 0x7734CFEF, 0x3E08B2C8, 0xC451B7CC, 0x8D6DCAEB, 0x56294D82, 0x1F1530A5
>   }};
>
> +static const uint64_t odd_8byte_mask[] = {
> +	0x00FFFFFFFFFFFFFF,
> +	0x0000FFFFFFFFFFFF,
> +	0x000000FFFFFFFFFF,
> +	0x00000000FFFFFFFF,
> +	0x0000000000FFFFFF,
> +	0x000000000000FFFF,
> +	0x00000000000000FF,
> +};
> +
>   #define CRC32_UPD(crc, n) \
>   	(crc32c_tables[(n)][(crc) & 0xFF] ^ \
>   	 crc32c_tables[(n)-1][((crc) >> 8) & 0xFF])
> @@ -535,38 +545,27 @@ static inline uint32_t
>   rte_hash_crc(const void *data, uint32_t data_len, uint32_t init_val)
>   {
>   	unsigned i;
> -	uint64_t temp = 0;
> +	uint64_t temp;
>   	const uint64_t *p64 = (const uint64_t *)data;
>
>   	for (i = 0; i < data_len / 8; i++) {
>   		init_val = rte_hash_crc_8byte(*p64++, init_val);
>   	}
>
> -	switch (7 - (data_len & 0x07)) {
> +	i = 7 - (data_len & 0x07);

Great idea with lookup table!
Only one question here: why keeping this magic at all now?
If you sort odd_8byte_mask opposite direction you can do something like that

	data_len &= 0x07;
	switch (data_len & 0x07) {
	case 1:
	case 2:
	case 3:
	case 4:
		temp = odd_8byte_mask[data_len] & *p64;
		init_val = rte_hash_crc_4byte(temp, init_val);
	case 5:
	case 6:
	case 7:
		temp = odd_8byte_mask[data_len] & *p64;
		init_val = rte_hash_crc_8byte(temp, init_val);
		break;
	default:
		break;
	}
Or

	data_len &= 0x07;
	if (data_len > 0) {
		temp = odd_8byte_mask[data_len] & *p64;
		if (data_len <= 4)
			init_val = rte_hash_crc_4byte(temp, init_val);
		else
			init_val = rte_hash_crc_8byte(temp, init_val);
	}
	
Is there something obvious what I am not seeing here?

Pawel

> +	switch (i) {
>   	case 0:
> -		temp |= (uint64_t) *((const uint8_t *)p64 + 6) << 48;
> -		/* Fallthrough */
>   	case 1:
> -		temp |= (uint64_t) *((const uint8_t *)p64 + 5) << 40;
> -		/* Fallthrough */
>   	case 2:
> -		temp |= (uint64_t) *((const uint8_t *)p64 + 4) << 32;
> -		temp |= *((const uint32_t *)p64);
> +		temp = odd_8byte_mask[i] & *p64;
>   		init_val = rte_hash_crc_8byte(temp, init_val);
>   		break;
>   	case 3:
> -		init_val = rte_hash_crc_4byte(*(const uint32_t *)p64, init_val);
> -		break;
>   	case 4:
> -		temp |= *((const uint8_t *)p64 + 2) << 16;
> -		/* Fallthrough */
>   	case 5:
> -		temp |= *((const uint8_t *)p64 + 1) << 8;
> -		/* Fallthrough */
>   	case 6:
> -		temp |= *((const uint8_t *)p64);
> +		temp = odd_8byte_mask[i] & *p64;
>   		init_val = rte_hash_crc_4byte(temp, init_val);
> -		/* Fallthrough */
>   	default:
>   		break;
>   	}
>


-- 
Pawel

^ permalink raw reply	[flat|nested] 10+ messages in thread

* Re: [dpdk-dev] [PATCH] hash: fix breaking strict-aliasing rules
  2015-03-18 16:51 [dpdk-dev] [PATCH] hash: fix breaking strict-aliasing rules Yerden Zhumabekov
  2015-03-19 16:25 ` Bruce Richardson
  2015-03-20 12:41 ` Pawel Wodkowski
@ 2015-03-20 12:47 ` Pawel Wodkowski
  2015-03-21  6:57   ` Жумабеков Ерден Мирзагулович
  2015-03-24 13:31 ` [dpdk-dev] [PATCH v2] " Yerden Zhumabekov
  3 siblings, 1 reply; 10+ messages in thread
From: Pawel Wodkowski @ 2015-03-20 12:47 UTC (permalink / raw)
  To: Yerden Zhumabekov, dev

On 2015-03-18 17:51, Yerden Zhumabekov wrote:

>
> -	switch (7 - (data_len & 0x07)) {
> +	i = 7 - (data_len & 0x07);
> +	switch (i) {
>   	case 0:
> -		temp |= (uint64_t) *((const uint8_t *)p64 + 6) << 48;
> -		/* Fallthrough */
>   	case 1:
> -		temp |= (uint64_t) *((const uint8_t *)p64 + 5) << 40;
> -		/* Fallthrough */
>   	case 2:
> -		temp |= (uint64_t) *((const uint8_t *)p64 + 4) << 32;
> -		temp |= *((const uint32_t *)p64);
> +		temp = odd_8byte_mask[i] & *p64;
>   		init_val = rte_hash_crc_8byte(temp, init_val);
>   		break;
>   	case 3:
> -		init_val = rte_hash_crc_4byte(*(const uint32_t *)p64, init_val);
> -		break;
>   	case 4:
> -		temp |= *((const uint8_t *)p64 + 2) << 16;
> -		/* Fallthrough */
>   	case 5:
> -		temp |= *((const uint8_t *)p64 + 1) << 8;
> -		/* Fallthrough */
>   	case 6:
> -		temp |= *((const uint8_t *)p64);
> +		temp = odd_8byte_mask[i] & *p64;
>   		init_val = rte_hash_crc_4byte(temp, init_val);
> -		/* Fallthrough */
>   	default:
>   		break;
>   	}
>

Second thought: is this not an issue here reading 8 bytes by 
dereferencing *p64 if there is less bytes in buffer?

-- 
Pawel

^ permalink raw reply	[flat|nested] 10+ messages in thread

* Re: [dpdk-dev] [PATCH] hash: fix breaking strict-aliasing rules
  2015-03-20 12:47 ` Pawel Wodkowski
@ 2015-03-21  6:57   ` Жумабеков Ерден Мирзагулович
  0 siblings, 0 replies; 10+ messages in thread
From: Жумабеков Ерден Мирзагулович @ 2015-03-21  6:57 UTC (permalink / raw)
  To: Pawel Wodkowski, dev

Hi Pawel,

Oops, thanks for the clue. I have a buffer over-read here leading to undefined behaviour.
The only solution I see here is to declare uint32_t pointer and evaluate it to (uint8_t *) data + data_len - (data_len & 0x07). Ideas are welcome. That would resolve strict-aliasing violation.
_____________________
From: Pawel Wodkowski [pawelx.wodkowski@intel.com]
Sent: Friday, March 20, 2015 18:47
To: Жумабеков Ерден Мирзагулович; dev@dpdk.org
Subject: Re: [dpdk-dev] [PATCH] hash: fix breaking strict-aliasing rules

On 2015-03-18 17:51, Yerden Zhumabekov wrote:

>
> -     switch (7 - (data_len & 0x07)) {
> +     i = 7 - (data_len & 0x07);
> +     switch (i) {
>       case 0:
> -             temp |= (uint64_t) *((const uint8_t *)p64 + 6) << 48;
> -             /* Fallthrough */
>       case 1:
> -             temp |= (uint64_t) *((const uint8_t *)p64 + 5) << 40;
> -             /* Fallthrough */
>       case 2:
> -             temp |= (uint64_t) *((const uint8_t *)p64 + 4) << 32;
> -             temp |= *((const uint32_t *)p64);
> +             temp = odd_8byte_mask[i] & *p64;
>               init_val = rte_hash_crc_8byte(temp, init_val);
>               break;
>       case 3:
> -             init_val = rte_hash_crc_4byte(*(const uint32_t *)p64, init_val);
> -             break;
>       case 4:
> -             temp |= *((const uint8_t *)p64 + 2) << 16;
> -             /* Fallthrough */
>       case 5:
> -             temp |= *((const uint8_t *)p64 + 1) << 8;
> -             /* Fallthrough */
>       case 6:
> -             temp |= *((const uint8_t *)p64);
> +             temp = odd_8byte_mask[i] & *p64;
>               init_val = rte_hash_crc_4byte(temp, init_val);
> -             /* Fallthrough */
>       default:
>               break;
>       }
>

Second thought: is this not an issue here reading 8 bytes by
dereferencing *p64 if there is less bytes in buffer?

--
Pawel

^ permalink raw reply	[flat|nested] 10+ messages in thread

* [dpdk-dev] [PATCH v2] hash: fix breaking strict-aliasing rules
  2015-03-18 16:51 [dpdk-dev] [PATCH] hash: fix breaking strict-aliasing rules Yerden Zhumabekov
                   ` (2 preceding siblings ...)
  2015-03-20 12:47 ` Pawel Wodkowski
@ 2015-03-24 13:31 ` Yerden Zhumabekov
  2015-03-26 17:47   ` De Lara Guarch, Pablo
  3 siblings, 1 reply; 10+ messages in thread
From: Yerden Zhumabekov @ 2015-03-24 13:31 UTC (permalink / raw)
  To: dev

Fix rte_hash_crc() function by making use of uintptr_t variable
to hold a pointer to data being hashed. In this way, casting uint64_t
pointer to uint32_t avoided.

Signed-off-by: Yerden Zhumabekov <e_zhumabekov@sts.kz>
---
 lib/librte_hash/rte_hash_crc.h |   21 +++++++++++----------
 1 file changed, 11 insertions(+), 10 deletions(-)

diff --git a/lib/librte_hash/rte_hash_crc.h b/lib/librte_hash/rte_hash_crc.h
index 1cd626c..abdbd9a 100644
--- a/lib/librte_hash/rte_hash_crc.h
+++ b/lib/librte_hash/rte_hash_crc.h
@@ -513,35 +513,36 @@ rte_hash_crc(const void *data, uint32_t data_len, uint32_t init_val)
 {
 	unsigned i;
 	uint64_t temp = 0;
-	const uint64_t *p64 = (const uint64_t *)data;
+	uintptr_t pd = (uintptr_t) data;
 
 	for (i = 0; i < data_len / 8; i++) {
-		init_val = rte_hash_crc_8byte(*p64++, init_val);
+		init_val = rte_hash_crc_8byte(*(const uint64_t *)pd, init_val);
+		pd += 8;
 	}
 
 	switch (7 - (data_len & 0x07)) {
 	case 0:
-		temp |= (uint64_t) *((const uint8_t *)p64 + 6) << 48;
+		temp |= (uint64_t) *((const uint8_t *)pd + 6) << 48;
 		/* Fallthrough */
 	case 1:
-		temp |= (uint64_t) *((const uint8_t *)p64 + 5) << 40;
+		temp |= (uint64_t) *((const uint8_t *)pd + 5) << 40;
 		/* Fallthrough */
 	case 2:
-		temp |= (uint64_t) *((const uint8_t *)p64 + 4) << 32;
-		temp |= *((const uint32_t *)p64);
+		temp |= (uint64_t) *((const uint8_t *)pd + 4) << 32;
+		temp |= *(const uint32_t *)pd;
 		init_val = rte_hash_crc_8byte(temp, init_val);
 		break;
 	case 3:
-		init_val = rte_hash_crc_4byte(*(const uint32_t *)p64, init_val);
+		init_val = rte_hash_crc_4byte(*(const uint32_t *)pd, init_val);
 		break;
 	case 4:
-		temp |= *((const uint8_t *)p64 + 2) << 16;
+		temp |= *((const uint8_t *)pd + 2) << 16;
 		/* Fallthrough */
 	case 5:
-		temp |= *((const uint8_t *)p64 + 1) << 8;
+		temp |= *((const uint8_t *)pd + 1) << 8;
 		/* Fallthrough */
 	case 6:
-		temp |= *((const uint8_t *)p64);
+		temp |= *(const uint8_t *)pd;
 		init_val = rte_hash_crc_4byte(temp, init_val);
 		/* Fallthrough */
 	default:
-- 
1.7.9.5

^ permalink raw reply	[flat|nested] 10+ messages in thread

* Re: [dpdk-dev] [PATCH v2] hash: fix breaking strict-aliasing rules
  2015-03-24 13:31 ` [dpdk-dev] [PATCH v2] " Yerden Zhumabekov
@ 2015-03-26 17:47   ` De Lara Guarch, Pablo
  2015-03-27  9:26     ` Thomas Monjalon
  0 siblings, 1 reply; 10+ messages in thread
From: De Lara Guarch, Pablo @ 2015-03-26 17:47 UTC (permalink / raw)
  To: Yerden Zhumabekov, dev



> -----Original Message-----
> From: dev [mailto:dev-bounces@dpdk.org] On Behalf Of Yerden
> Zhumabekov
> Sent: Tuesday, March 24, 2015 1:32 PM
> To: dev@dpdk.org
> Subject: [dpdk-dev] [PATCH v2] hash: fix breaking strict-aliasing rules
> 
> Fix rte_hash_crc() function by making use of uintptr_t variable
> to hold a pointer to data being hashed. In this way, casting uint64_t
> pointer to uint32_t avoided.
> 
> Signed-off-by: Yerden Zhumabekov <e_zhumabekov@sts.kz>

Acked-by: Pablo de Lara <pablo.de.lara.guarch@intel.com>

^ permalink raw reply	[flat|nested] 10+ messages in thread

* Re: [dpdk-dev] [PATCH v2] hash: fix breaking strict-aliasing rules
  2015-03-26 17:47   ` De Lara Guarch, Pablo
@ 2015-03-27  9:26     ` Thomas Monjalon
  0 siblings, 0 replies; 10+ messages in thread
From: Thomas Monjalon @ 2015-03-27  9:26 UTC (permalink / raw)
  To: Yerden Zhumabekov; +Cc: dev

> > Fix rte_hash_crc() function by making use of uintptr_t variable
> > to hold a pointer to data being hashed. In this way, casting uint64_t
> > pointer to uint32_t avoided.
> > 
> > Signed-off-by: Yerden Zhumabekov <e_zhumabekov@sts.kz>
> 
> Acked-by: Pablo de Lara <pablo.de.lara.guarch@intel.com>

Applied, thanks

^ permalink raw reply	[flat|nested] 10+ messages in thread

end of thread, other threads:[~2015-03-27  9:26 UTC | newest]

Thread overview: 10+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2015-03-18 16:51 [dpdk-dev] [PATCH] hash: fix breaking strict-aliasing rules Yerden Zhumabekov
2015-03-19 16:25 ` Bruce Richardson
2015-03-19 16:31   ` Bruce Richardson
2015-03-20  3:29     ` Yerden Zhumabekov
2015-03-20 12:41 ` Pawel Wodkowski
2015-03-20 12:47 ` Pawel Wodkowski
2015-03-21  6:57   ` Жумабеков Ерден Мирзагулович
2015-03-24 13:31 ` [dpdk-dev] [PATCH v2] " Yerden Zhumabekov
2015-03-26 17:47   ` De Lara Guarch, Pablo
2015-03-27  9:26     ` Thomas Monjalon

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