% PT_QRY_SYNC_FORWARD(3)

NAME

pt_qry_sync_forward, pt_qry_sync_backward, pt_qry_sync_set - synchronize an Intel(R) Processor Trace query decoder

SYNOPSIS

Link with -lipt.

DESCRIPTION

These functions synchronize an Intel Processor Trace (Intel PT) query decoder pointed to by decoder onto the trace stream in decoder's trace buffer.

They search for a Packet Stream Boundary (PSB) packet in the trace stream and, if successful, set decoder's current position and synchronization position to that packet and start processing packets. For synchronization to be successfull, there must be a full PSB+ header in the trace stream.

If the ip argument is not NULL, these functions provide the code memory address at which tracing starts in the variable pointed to by ip. If tracing is disabled at the synchronization point, the lack of an IP is indicated in the return value by setting the pts_ip_suppressed bit.

pt_qry_sync_forward() searches in forward direction from decoder's current position towards the end of the trace buffer. If decoder has been newly allocated and has not been synchronized yet, the search starts from the beginning of the trace.

pt_qry_sync_backward() searches in backward direction from decoder's current position towards the beginning of the trace buffer. If decoder has been newly allocated and has not been synchronized yet, the search starts from the end of the trace.

pt_qry_sync_set() searches at offset bytes from the beginning of its trace buffer.

RETURN VALUE

All synchronization functions return zero or a positive value on success or a negative pt_error_code enumeration constant in case of an error.

On success, a bit-vector of pt_status_flag enumeration constants is returned. The pt_status_flag enumeration is declared as:

/** Decoder status flags. */
enum pt_status_flag {
    /** There is an event pending. */
    pts_event_pending   = 1 << 0,

    /** The address has been suppressed. */
    pts_ip_suppressed   = 1 << 1,

    /** There is no more trace data available. */
    pts_eos             = 1 << 2
};

ERRORS

pte_invalid

The decoder argument is NULL.

pte_eos

There is no (further) PSB+ header in the trace stream (pt_qry_sync_forward() and pt_qry_sync_backward()) or at offset bytes into the trace buffer (pt_qry_sync_set()).

pte_nosync

There is no PSB packet at offset bytes from the beginning of the trace (pt_qry_sync_set() only).

pte_bad_opc

The decoder encountered an unsupported Intel PT packet opcode.

pte_bad_packet

The decoder encountered an unsupported Intel PT packet payload.

EXAMPLE

The following example re-synchronizes an Intel PT query decoder after decode errors:

int foo(struct pt_query_decoder *decoder) {
    for (;;) {
        int errcode;

        errcode = pt_qry_sync_forward(decoder);
        if (errcode < 0)
            return errcode;

        do {
            errcode = decode(decoder);
        } while (errcode >= 0);
    }
}

SEE ALSO

pt_qry_alloc_decoder(3), pt_qry_free_decoder(3), pt_qry_get_offset(3), pt_qry_get_sync_offset(3), pt_qry_get_config(3), pt_qry_cond_branch(3), pt_qry_indirect_branch(3), pt_qry_event(3), pt_qry_time(3), pt_qry_core_bus_ratio(3)