Dear Nitin, First off: exactly which LDXR / STXR instruction variant pairs is generated? I begin to wonder if __sync_lock_test_and_set(...) might not be doing you any favors. Given that dq->interrupt_pending is a u32, I would have expected a 4-byte instruction with (at worst) a 4-byte alignment requirement.
Are there any alignment restrictions on the 1-byte variants LDXRB / STXRB? If not: since we use dq->interrupt_pending as a one-bit flag, declaring it as a u8 - or casting &dq->interrupt_pending to (u8 *) in an arch-dependent fashion - might make the pain go away. Aligning every vector in the system will waste memory, and will not legislate this class of problem out of existence. So, I wouldn't want to force 8-byte alignment in the way you mention. Anyhow, aligning the first vector element to an 8-byte boundary says little about the layout of elements within each vector element, especially if the structure is packed. If dq->interrupt_pending needs to be aligned to a specific boundary without fail, the only completely reliable method would be to pack and pad the structure e.g. to a multiple of 8 octets and ensure that interrupt_pending lands on the required boundary. Then use vec_add2_ha (...) to manipulate the vector. HTH... Dave From: vpp-dev-boun...@lists.fd.io [mailto:vpp-dev-boun...@lists.fd.io] On Behalf Of Saxena, Nitin Sent: Thursday, September 28, 2017 4:53 AM To: vpp-dev@lists.fd.io Cc: Narayana, Prasad Athreya <prasadathreya.naray...@cavium.com> Subject: [vpp-dev] [v17.07.01]: vec_add2() causing crash on ARMv8 Hi All, I got a crash with vpp v17.07.01 on ARMv8 Soc @src/vnet/devices/virtio/vhost-user.c: Line no: 1852 if (clib_smp_swap (&dq->interrupt_pending, 0) || (node->state == VLIB_NODE_STATE_POLLING)){ } While debugging it turns out that value of (&dq->interrupt_pending) was not 8 byte aligned hence causing SIGBUS error on ARMv8 SoC. Further debugging tells that dq was added in vector using vec_add2 (src/vnet/devices/devices.c Line no: 152) vec_add2 (rt->devices_and_queues, dq, 1) which uses 0 byte alignment. Changing vec_add2 to vec_add2_aligned() fixed the problem. My question is can we completely define vec_add2() as #define vec_add2(V,P,N) vec_add2_ha(V,P,N,0,8) instead of #define vec_add2(V,P,N) vec_add2_ha(V,P,N,0,0) This can be helpful for all architecture. Thanks, Nitin
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