[dpdk-dev] net: fix build with gcc 4.4.7 and strict aliasing

Message ID

1448377959-4440-1-git-send-email-danielx.t.mrzyglod@intel.com (mailing list archive)

State

Superseded, archived

Headers

From: Daniel Mrzyglod <danielx.t.mrzyglod@intel.com>
To: dev@dpdk.org
Date: Tue, 24 Nov 2015 16:12:39 +0100
Message-Id: <1448377959-4440-1-git-send-email-danielx.t.mrzyglod@intel.com>
Subject: [dpdk-dev] [PATCH] net: fix build with gcc 4.4.7 and strict aliasing
Precedence: list
Errors-To: dev-bounces@dpdk.org
Sender: "dev" <dev-bounces@dpdk.org>

Commit Message

Daniel Mrzyglod Nov. 24, 2015, 3:12 p.m. UTC

  This is fix for GCC 4.4.7.
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 <danielx.t.mrzyglod@intel.com>
---
 lib/librte_net/rte_ip.h | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

Comments

Daniel Mrzyglod Nov. 24, 2015, 3:47 p.m. UTC | #1

This error fix this situation for IPv6 checksum offload error on RHEL65
Any optimalisation above -O0 provide error in IPv6 checksum


Step 1 : start testpmd
./x86_64-native-linuxapp-gcc/app/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 : calculate correct checksum values of IPv6/TCP and IPv6/UDP by scapy
           Packets info:  IPv6/UDP:Ether(dst="02:00:00:00:00:00", src="90:e2:ba:4a:33:5c")/IPv6(src="::2")/UDP()/("X"*46)
                          IPv6/TCP:  Ether(src="52:00:00:00:00:00", dst="90:e2:ba:4a:33:5d")/IPv6(src="::1")/TCP()/("X"*46)

Step 4 : Send two packets with wrong checksum value,and calculate the right checksum value by port,packets received on another port
           Send packets info: IPv6/UDP：Ether(dst="90:e2:ba:4a:33:5d", src="52:00:00:00:00:00")/IPv6(src="::1")/UDP(chksum=0xf)/("X"*46)
                              IPv6/TCP：Ether(dst="90:e2:ba:4a:33:5d", src="52:00:00:00:00:00")/IPv6(src="::1")/TCP(chksum=0xf)/("X"*46)

RESULTS:
'IPv6/TCP': ['0xd41']}, 'IPv6/UDP': ['0x7d07'],

EXPECTED RESULTS:
'IPv6/TCP': ['0x9f5e']}, 'IPv6/UDP': ['0xf26']

Bruce Richardson Nov. 24, 2015, 3:49 p.m. UTC | #2

On Tue, Nov 24, 2015 at 03:47:28PM +0000, Mrzyglod, DanielX T wrote:
> This error fix this situation for IPv6 checksum offload error on RHEL65
> Any optimalisation above -O0 provide error in IPv6 checksum
> 
> 
> Step 1 : start testpmd
> ./x86_64-native-linuxapp-gcc/app/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 : calculate correct checksum values of IPv6/TCP and IPv6/UDP by scapy
>            Packets info:  IPv6/UDP:Ether(dst="02:00:00:00:00:00", src="90:e2:ba:4a:33:5c")/IPv6(src="::2")/UDP()/("X"*46)
>                           IPv6/TCP:  Ether(src="52:00:00:00:00:00", dst="90:e2:ba:4a:33:5d")/IPv6(src="::1")/TCP()/("X"*46)
> 
> Step 4 : Send two packets with wrong checksum value,and calculate the right checksum value by port,packets received on another port
>            Send packets info: IPv6/UDP：Ether(dst="90:e2:ba:4a:33:5d", src="52:00:00:00:00:00")/IPv6(src="::1")/UDP(chksum=0xf)/("X"*46)
>                               IPv6/TCP：Ether(dst="90:e2:ba:4a:33:5d", src="52:00:00:00:00:00")/IPv6(src="::1")/TCP(chksum=0xf)/("X"*46)
> 
> RESULTS:
> 'IPv6/TCP': ['0xd41']}, 'IPv6/UDP': ['0x7d07'],
> 
> EXPECTED RESULTS:
> 'IPv6/TCP': ['0x9f5e']}, 'IPv6/UDP': ['0xf26']

Hi Daniel,

this sort of detail - perhaps in abbreviated form - should be in the commit
message for the patch. Can you perhaps do a V2 to include it?

/Bruce

Daniel Mrzyglod Nov. 24, 2015, 4:31 p.m. UTC | #3

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(-)

Stephen Hemminger Nov. 24, 2015, 10:42 p.m. UTC | #4

On Tue, 24 Nov 2015 17:31:17 +0100
Daniel Mrzyglod <danielx.t.mrzyglod@intel.com> 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.

Ananyev, Konstantin Nov. 25, 2015, 6 p.m. UTC | #5

> From: dev [mailto:dev-bounces@dpdk.org] On Behalf Of Daniel Mrzyglod
> Sent: Tuesday, November 24, 2015 3:13 PM
> To: dev@dpdk.org
> Subject: [dpdk-dev] [PATCH] net: fix build with gcc 4.4.7 and strict aliasing
> 
> This is fix for GCC 4.4.7.
> 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 <danielx.t.mrzyglod@intel.com>
> ---

Acked-by: Konstantin Ananyev <konstantin.ananyev@intel.com>

> 2.5.0

Thomas Monjalon Nov. 25, 2015, 8:58 p.m. UTC | #6

2015-11-25 18:00, Ananyev, Konstantin:
> > From: dev [mailto:dev-bounces@dpdk.org] On Behalf Of Daniel Mrzyglod
> > Sent: Tuesday, November 24, 2015 3:13 PM
> > To: dev@dpdk.org
> > Subject: [dpdk-dev] [PATCH] net: fix build with gcc 4.4.7 and strict aliasing
> > 
> > This is fix for GCC 4.4.7.
> > 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 <danielx.t.mrzyglod@intel.com>
> 
> Acked-by: Konstantin Ananyev <konstantin.ananyev@intel.com>

Applied, thanks

Patch

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];