% PT_QRY_SYNC_FORWARD(3)

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# NAME

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


# SYNOPSIS

| **\#include `<intel-pt.h>`**
|
| **int pt_qry_sync_forward(struct pt_query_decoder \**decoder*,**
|                         **uint64_t \**ip*);**
| **int pt_qry_sync_backward(struct pt_query_decoder \**decoder*,**
|                          **uint64_t \**ip*);**
| **int pt_qry_sync_set(struct pt_query_decoder \**decoder*,**
|                     **uint64_t \**ip*, uint64_t *offset*);**

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:

~~~{.c}
/** 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:

~~~{.c}
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)