% PT_QRY_ALLOC_DECODER(3)

NAME

pt_qry_alloc_decoder, pt_qry_free_decoder - allocate/free an Intel(R) Processor Trace query decoder

SYNOPSIS

Link with -lipt.

DESCRIPTION

A query decoder decodes raw Intel Processor Trace (Intel PT) and provides functions for querying the decoder about:

• whether the next conditional branch was taken (or not taken)
• the destination of the next indirect branch

This information can be used to reconstruct the execution flow of the traced code. As long as the flow is clear, follow the flow. If the flow cannot be determined by examining the current instruction, ask the query decoder.

In addition, the query decoder indicates asynchronous events via the return value of its query functions and provides an additional function to query for such asynchronous events. See pt_qry_cond_branch(3), pt_qry_indirect_branch(3), and pt_qry_event(3).

pt_qry_alloc_decoder() allocates a new query decoder and returns a pointer to it. The config argument points to a pt_config object. See pt_config(3). The config argument will not be referenced by the returned decoder but the trace buffer defined by the config argument's begin and end fields will.

The returned query decoder needs to be synchronized onto the trace stream before it can be used. To synchronize the query decoder, use pt_qry_sync_forward(3), pt_qry_sync_backward(3), or pt_qry_sync_set(3).

pt_qry_free_decoder() frees the Intel PT query decoder pointed to by decoder. The decoder argument must be NULL or point to a decoder that has been allocated by a call to pt_qry_alloc_decoder().

RETURN VALUE

pt_qry_alloc_decoder() returns a pointer to a pt_query_decoder object on success or NULL in case of an error.

EXAMPLE

int foo(const struct pt_config *config) {
    struct pt_query_decoder *decoder;
    errcode;

    decoder = pt_qry_alloc_decoder(config);
    if (!decoder)
        return pte_nomem;

    errcode = bar(decoder);

    pt_qry_free_decoder(decoder);
    return errcode;
}

SEE ALSO

pt_config(3), pt_qry_sync_forward(3), pt_qry_sync_backward(3), pt_qry_sync_set(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)