[dtrace-discuss] invalid alignment error message

[Ryan Johnson]

Priya Krishnan wrote:
> I need help in understanding this alignment error. The error message is
> dtrace: error on enabled probe ID 14 (ID 24380: 
> iscsi:idm:idm_pdu_rx_forward_ffp:nop-receive): invalid alignment 
> (0xffffff03df31b06c) in action #1 at DIF offset 32
>
> This is a new probe that has two arguments - conninfo_t and iscsiinfo_t
> In my D script, I print out just the datalen field from argument 1.
> iscsi:::
> {
>   printf("datalen[%d],", args[1]->ii_datalen);
> }
>
> I use a translator to translate from C struct iscsi_nop_out_hdr_t to D 
> struct iscsiinfo_t
>
> The D struct iscsiinfo_t is defined as
> typedef struct iscsiinfo {
>        string ii_target;       /* target iqn */
>        string ii_initiator;    /* initiator iqn */
>        string ii_isid;         /* initiator session identifier */
>        string ii_tsih;         /* target session identifying handle */
>        string ii_transport;    /* transport type ("iser-ib", 
> "sockets") */
>
>        uint64_t ii_lun;        /* target logical unit number */
>
>        uint32_t ii_itt;        /* initiator task tag */
>        uint32_t ii_ttt;        /* target transfer tag */
>
>        uint32_t ii_cmdsn;      /* command sequence number */
>        uint32_t ii_statsn;     /* status sequence number */
>        uint32_t ii_datasn;     /* data sequence number */
>
>        uint32_t ii_datalen;    /* length of data payload */
>        uint32_t ii_flags;      /* probe-specific flags */
> } iscsiinfo_t;
>
> The native structure is defined as
> /* NOP-Out Message */
> typedef struct _iscsi_nop_out_hdr {
>        uint8_t opcode;
>        uint8_t flags;
>        uint16_t rsvd2;
>        uint8_t rsvd3;
>        uint8_t dlength[3];
>        uint8_t lun[8];
>        uint32_t itt;   /* Initiator Task Tag */
>        uint32_t ttt;   /* Target Transfer Tag */
>        uint32_t cmdsn;
>        uint32_t expstatsn;
>        uint8_t rsvd4[16];
> } iscsi_nop_out_hdr_t;
>
> My translator looks like this
>
> #pragma D binding "1.5" translator
> translator iscsiinfo_t < iscsi_nop_out_hdr_t *P > {
>        <snip>
>        <snip>
>        ii_datalen = P->dlength[0] << 16 || P->dlength[1] << 8 || 
> P->dlength[2];
> };
>
> Any hints on how I can debug this problem is appreciated
Hmm... nothing jumps out at me right off -- the address is 
4-byte-aligned and you don't access any 8-byte values that I can see. 
Unless struct iscsiinfo somehow doesn't get 8-byte-aligned and you 
actually croak while initializing ii_lun? What happens if you move 
ii_lun to be the first member of the struct? Those strings are just 
char[256] (unless you've changed the size limit), and don't impose any 
alignment constraints. It shouldn't matter, but who knows... You could 
also try not initializing ii_lun at all to see if the error disappears, 
though that's obviously not a permanent solution.

BTW, you are using logical '||' instead bitwise '|' to reconstruct 
ii_datalen, which is probably not what you want.

Regards,
Ryan