[dpdk-dev] [PATCH v2] net: fix build with gcc 4.4.7 and strict aliasing
This fix is for IPv6 checksum offload error on RHEL65.
Any optimalisation above -O0 provide error in IPv6 checksum
flag "-fstrict-aliasing" is default for optimalisation above -O0.
Fixes: 2b039d5f20a3 ("net: fix build with gcc 4.4.7 and strict aliasing")
Signed-off-by: Daniel Mrzyglod
---
lib/librte_net/rte_ip.h | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/lib/librte_net/rte_ip.h b/lib/librte_net/rte_ip.h
index 71c519a..5b7554a 100644
--- a/lib/librte_net/rte_ip.h
+++ b/lib/librte_net/rte_ip.h
@@ -169,7 +169,8 @@ __rte_raw_cksum(const void *buf, size_t len, uint32_t sum)
{
/* workaround gcc strict-aliasing warning */
uintptr_t ptr = (uintptr_t)buf;
- const uint16_t *u16 = (const uint16_t *)ptr;
+ typedef uint16_t __attribute__((__may_alias__)) u16_p;
+ const u16_p *u16 = (const u16_p *)ptr;
while (len >= (sizeof(*u16) * 4)) {
sum += u16[0];
--
2.5.0
[dpdk-dev] [PATCH v2] net: fix build with gcc 4.4.7 and strict aliasing
This fix is for IPv6 checksum offload error on RHEL65.
Any optimalisation above -O0 provide error in IPv6 checksum
flag "-fstrict-aliasing" is default for optimalisation above -O0.
The solution is to add typedef with __attribute__((__may_alias__) for uint16_t.
Step 1 : start testpmd
./testpmd -c 0x6 -n 4 -- -i --portmask=0x3 --disable-hw-vlan --enable-rx-cksum
--crc-strip --txqflags=0
Step 2 : settings and start
set verbose 1
set fwd csum
start
Step 3 : send scapy with bad checksum IPv6/TCP packet
Ether(src="52:00:00:00:00:00",
dst="90:e2:ba:4a:33:5d")/IPv6(src="::1")/TCP(chksum=0xf)/("X"*46)
Step 4 : Recieved packets:
RESULTS:
IPv6/TCP': ['0xd41'] or other unexpected.
EXPECTED RESULTS:
IPv6/TCP': ['0x9f5e']
Daniel Mrzyglod (1):
net: fix build with gcc 4.4.7 and strict aliasing
lib/librte_net/rte_ip.h | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
--
2.5.0
[dpdk-dev] [PATCH v2] net: fix build with gcc 4.4.7 and strict aliasing
Hi Daniel,
So for my own curiosity: what went wrong here?
Did compiler avoid to generate a code for while {} loop?
Or something else?
BTW, it is an internal function, so instead of introducing new typedef,
we can just change the type of buf?
Let say to uint8_t *?
>From gcc manual page: " A character type may alias any other type."
Would that work?
Konstantin
> -Original Message-
> From: dev [mailto:dev-bounces at dpdk.org] On Behalf Of Daniel Mrzyglod
> Sent: Tuesday, November 24, 2015 4:31 PM
> To: dev at dpdk.org
> Subject: [dpdk-dev] [PATCH v2] net: fix build with gcc 4.4.7 and strict
> aliasing
>
> This fix is for IPv6 checksum offload error on RHEL65.
> Any optimalisation above -O0 provide error in IPv6 checksum
> flag "-fstrict-aliasing" is default for optimalisation above -O0.
>
> Fixes: 2b039d5f20a3 ("net: fix build with gcc 4.4.7 and strict aliasing")
>
> Signed-off-by: Daniel Mrzyglod
> ---
> lib/librte_net/rte_ip.h | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/lib/librte_net/rte_ip.h b/lib/librte_net/rte_ip.h
> index 71c519a..5b7554a 100644
> --- a/lib/librte_net/rte_ip.h
> +++ b/lib/librte_net/rte_ip.h
> @@ -169,7 +169,8 @@ __rte_raw_cksum(const void *buf, size_t len, uint32_t sum)
> {
> /* workaround gcc strict-aliasing warning */
> uintptr_t ptr = (uintptr_t)buf;
> - const uint16_t *u16 = (const uint16_t *)ptr;
> + typedef uint16_t __attribute__((__may_alias__)) u16_p;
> + const u16_p *u16 = (const u16_p *)ptr;
>
> while (len >= (sizeof(*u16) * 4)) {
> sum += u16[0];
> --
> 2.5.0
[dpdk-dev] [PATCH v2] net: fix build with gcc 4.4.7 and strict aliasing
On Tue, 24 Nov 2015 17:31:17 +0100
Daniel Mrzyglod wrote:
> This fix is for IPv6 checksum offload error on RHEL65.
> Any optimalisation above -O0 provide error in IPv6 checksum
> flag "-fstrict-aliasing" is default for optimalisation above -O0.
> The solution is to add typedef with __attribute__((__may_alias__) for
> uint16_t.
>
> Step 1 : start testpmd
> ./testpmd -c 0x6 -n 4 -- -i --portmask=0x3 --disable-hw-vlan
> --enable-rx-cksum --crc-strip --txqflags=0
>
> Step 2 : settings and start
>set verbose 1
>set fwd csum
>start
>
> Step 3 : send scapy with bad checksum IPv6/TCP packet
> Ether(src="52:00:00:00:00:00",
> dst="90:e2:ba:4a:33:5d")/IPv6(src="::1")/TCP(chksum=0xf)/("X"*46)
>
> Step 4 : Recieved packets:
> RESULTS:
> IPv6/TCP': ['0xd41'] or other unexpected.
>
> EXPECTED RESULTS:
> IPv6/TCP': ['0x9f5e']
>
> Daniel Mrzyglod (1):
> net: fix build with gcc 4.4.7 and strict aliasing
>
> lib/librte_net/rte_ip.h | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
An alternative way of fixing it (without resorting to attributes) would
be to use a union.
[dpdk-dev] [PATCH v2] net: fix build with gcc 4.4.7 and strict aliasing
If we change input buf:
xapp-gcc/include/rte_ip.h:211: error: dereferencing pointer 'u16' does break
strict-aliasing rules
/root/dpdk/x86_64-native-linuxapp-gcc/include/rte_ip.h:204: note: initialized
from here
/root/dpdk/x86_64-native-linuxapp-gcc/include/rte_ip.h:212: error:
dereferencing pointer '({anonymous})' does break strict-aliasing rules
/root/dpdk/x86_64-native-linuxapp-gcc/include/rte_ip.h:212: note: initialized
from here
/root/dpdk/x86_64-native-linuxapp-gcc/include/rte_ip.h:213: error:
dereferencing pointer '({anonymous})' does break strict-aliasing rules
/root/dpdk/x86_64-native-linuxapp-gcc/include/rte_ip.h:213: note: initialized
from here
/root/dpdk/x86_64-native-linuxapp-gcc/include/rte_ip.h:214: error:
dereferencing pointer '({anonymous})' does break strict-aliasing rules
/root/dpdk/x86_64-native-linuxapp-gcc/include/rte_ip.h:214: note: initialized
from here
The change was pointed out by Michael Qiu in patch:
2b039d5f20a34016ecaf9b26f8f8b6c4a81bf4b6
We can only cast void to uint8 but it would involve big endian/ little endian
macros:
static inline uint32_t __attribute__((__may_alias__))
__rte_raw_cksum(const void *buf, size_t len, uint32_t sum)
{
/* workaround gcc strict-aliasing warning */
const uint8_t *u8 = ((const uint8_t *)buf);
while (len >= (sizeof(*u8) * 8)) {
sum += *(u8+1) << 8 | *(u8);
sum += *(u8+3) << 8 | *(u8+2);
sum += *(u8+5) << 8 | *(u8+4);
sum += *(u8+7) << 8 | *(u8+6);
len -= sizeof(*u8) * 8;
u8 += 8;
}
while (len >= 2*sizeof(*u8)) {
sum += *u8 << 8 | *(u8+1);
len -= 2*sizeof(*u8);
u8 += 2;
}
/* if length is in odd bytes */
if (len == 1)
sum += *((const uint8_t *)u8);
return sum;
}
I will research about this union usage suggested by Stephen, but for this
moment local typedef & __attribute__((__may_alias__)) is the most clean
solution which work under gcc(4.4.7), clang, icc.
>-Original Message-
>From: Ananyev, Konstantin
>Sent: Tuesday, November 24, 2015 6:58 PM
>To: Mrzyglod, DanielX T
>Cc: dev at dpdk.org
>Subject: RE: [dpdk-dev] [PATCH v2] net: fix build with gcc 4.4.7 and strict
>aliasing
>
>Hi Daniel,
>So for my own curiosity: what went wrong here?
>Did compiler avoid to generate a code for while {} loop?
>Or something else?
>BTW, it is an internal function, so instead of introducing new typedef,
>we can just change the type of buf?
>Let say to uint8_t *?
>From gcc manual page: " A character type may alias any other type."
>Would that work?
>Konstantin
>
>> -Original Message-
>> From: dev [mailto:dev-bounces at dpdk.org] On Behalf Of Daniel Mrzyglod
>> Sent: Tuesday, November 24, 2015 4:31 PM
>> To: dev at dpdk.org
>> Subject: [dpdk-dev] [PATCH v2] net: fix build with gcc 4.4.7 and strict
>> aliasing
>>
>> This fix is for IPv6 checksum offload error on RHEL65.
>> Any optimalisation above -O0 provide error in IPv6 checksum
>> flag "-fstrict-aliasing" is default for optimalisation above -O0.
>>
>> Fixes: 2b039d5f20a3 ("net: fix build with gcc 4.4.7 and strict aliasing")
>>
>> Signed-off-by: Daniel Mrzyglod
>> ---
>> lib/librte_net/rte_ip.h | 3 ++-
>> 1 file changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/lib/librte_net/rte_ip.h b/lib/librte_net/rte_ip.h
>> index 71c519a..5b7554a 100644
>> --- a/lib/librte_net/rte_ip.h
>> +++ b/lib/librte_net/rte_ip.h
>> @@ -169,7 +169,8 @@ __rte_raw_cksum(const void *buf, size_t len, uint32_t
>sum)
>> {
>> /* workaround gcc strict-aliasing warning */
>> uintptr_t ptr = (uintptr_t)buf;
>> -const uint16_t *u16 = (const uint16_t *)ptr;
>> +typedef uint16_t __attribute__((__may_alias__)) u16_p;
>> +const u16_p *u16 = (const u16_p *)ptr;
>>
>> while (len >= (sizeof(*u16) * 4)) {
>> sum += u16[0];
>> --
>> 2.5.0
[dpdk-dev] [PATCH v2] net: fix build with gcc 4.4.7 and strict aliasing
> -Original Message-
> From: Mrzyglod, DanielX T
> Sent: Wednesday, November 25, 2015 5:07 PM
> To: Ananyev, Konstantin
> Cc: dev at dpdk.org
> Subject: RE: [dpdk-dev] [PATCH v2] net: fix build with gcc 4.4.7 and strict
> aliasing
>
> If we change input buf:
> xapp-gcc/include/rte_ip.h:211: error: dereferencing pointer 'u16' does break
> strict-aliasing rules
> /root/dpdk/x86_64-native-linuxapp-gcc/include/rte_ip.h:204: note: initialized
> from here
> /root/dpdk/x86_64-native-linuxapp-gcc/include/rte_ip.h:212: error:
> dereferencing pointer '({anonymous})' does break strict-aliasing rules
> /root/dpdk/x86_64-native-linuxapp-gcc/include/rte_ip.h:212: note: initialized
> from here
> /root/dpdk/x86_64-native-linuxapp-gcc/include/rte_ip.h:213: error:
> dereferencing pointer '({anonymous})' does break strict-aliasing rules
> /root/dpdk/x86_64-native-linuxapp-gcc/include/rte_ip.h:213: note: initialized
> from here
> /root/dpdk/x86_64-native-linuxapp-gcc/include/rte_ip.h:214: error:
> dereferencing pointer '({anonymous})' does break strict-aliasing rules
> /root/dpdk/x86_64-native-linuxapp-gcc/include/rte_ip.h:214: note: initialized
> from here
>
> The change was pointed out by Michael Qiu in patch:
> 2b039d5f20a34016ecaf9b26f8f8b6c4a81bf4b6
>
> We can only cast void to uint8 but it would involve big endian/ little endian
> macros:
>
> static inline uint32_t __attribute__((__may_alias__))
> __rte_raw_cksum(const void *buf, size_t len, uint32_t sum)
> {
> /* workaround gcc strict-aliasing warning */
> const uint8_t *u8 = ((const uint8_t *)buf);
> while (len >= (sizeof(*u8) * 8)) {
> sum += *(u8+1) << 8 | *(u8);
> sum += *(u8+3) << 8 | *(u8+2);
> sum += *(u8+5) << 8 | *(u8+4);
> sum += *(u8+7) << 8 | *(u8+6);
>
> len -= sizeof(*u8) * 8;
> u8 += 8;
> }
>
> while (len >= 2*sizeof(*u8)) {
> sum += *u8 << 8 | *(u8+1);
> len -= 2*sizeof(*u8);
> u8 += 2;
> }
>
> /* if length is in odd bytes */
> if (len == 1)
> sum += *((const uint8_t *)u8);
>
> return sum;
> }
So I misinterpreted gcc manual: it only allows conversion from any other type
to char, not visa-versa.
Sorry for wrong suggestion.
>
> I will research about this union usage suggested by Stephen, but for this
> moment local typedef & __attribute__((__may_alias__)) is the
> most clean solution which work under gcc(4.4.7), clang, icc.
Ok, if there is no other known way - let's stick with your original patch.
Konstantin
>
> >-Original Message-
> >From: Ananyev, Konstantin
> >Sent: Tuesday, November 24, 2015 6:58 PM
> >To: Mrzyglod, DanielX T
> >Cc: dev at dpdk.org
> >Subject: RE: [dpdk-dev] [PATCH v2] net: fix build with gcc 4.4.7 and strict
> >aliasing
> >
> >Hi Daniel,
> >So for my own curiosity: what went wrong here?
> >Did compiler avoid to generate a code for while {} loop?
> >Or something else?
> >BTW, it is an internal function, so instead of introducing new typedef,
> >we can just change the type of buf?
> >Let say to uint8_t *?
> >From gcc manual page: " A character type may alias any other type."
> >Would that work?
> >Konstantin
> >
> >> -Original Message-
> >> From: dev [mailto:dev-bounces at dpdk.org] On Behalf Of Daniel Mrzyglod
> >> Sent: Tuesday, November 24, 2015 4:31 PM
> >> To: dev at dpdk.org
> >> Subject: [dpdk-dev] [PATCH v2] net: fix build with gcc 4.4.7 and strict
> >> aliasing
> >>
> >> This fix is for IPv6 checksum offload error on RHEL65.
> >> Any optimalisation above -O0 provide error in IPv6 checksum
> >> flag "-fstrict-aliasing" is default for optimalisation above -O0.
> >>
> >> Fixes: 2b039d5f20a3 ("net: fix build with gcc 4.4.7 and strict aliasing")
> >>
> >> Signed-off-by: Daniel Mrzyglod
> >> ---
> >> lib/librte_net/rte_ip.h | 3 ++-
> >> 1 file changed, 2 insertions(+), 1 deletion(-)
> >>
> >> diff --git a/lib/librte_net/rte_ip.h b/lib/librte_net/rte_ip.h
> >> index 71c519a..5b7554a 100644
> >> --- a/lib/librte_net/rte_ip.h
> >> +++ b/lib/librte_net/rte_ip.h
> >> @@ -169,7 +169,8 @@ __rte_raw_cksum(const void *buf, size_t len, uint32_t
> >sum)
> >> {
> >>/* workaround gcc strict-aliasing warning */
> >>uintptr_t ptr = (uintptr_t)buf;
> >> - const uint16_t *u16 = (const uint16_t *)ptr;
> >> + typedef uint16_t __attribute__((__may_alias__)) u16_p;
> >> + const u16_p *u16 = (const u16_p *)ptr;
> >>
> >>while (len >= (sizeof(*u16) * 4)) {
> >>sum += u16[0];
> >> --
> >> 2.5.0
