pt_blk_next man page

pt_blk_next, pt_block — iterate over blocks of traced instructions

Synopsis

#include <intel-pt.h>

struct pt_block;

int pt_blk_next(struct pt_blk_decoder *decoder,

                 struct pt_blk *blk, size_t size);

int pt_blk_next(struct pt_block_decoder *decoder,

                struct pt_block *block, size_t size);

Link with -lipt.

Description

pt_blk_next() provides the next block of instructions in execution order, which is described by the pt_block structure.

The size argument must be set to sizeof(struct pt_block). The function will provide at most size bytes of the pt_block structure. A newer decoder library may truncate an extended pt_block object to size bytes.

An older decoder library may provide less pt_block fields. Fields that are not provided will be zero-initialized. For fields where zero is a valid value (e.g. for bit-fields), check the decoder library version to determine which fields are valid. See pt_library_version(3).

On success, the next block of instructions is provided in the pt_block object pointed to by the block argument. The pt_block structure is declared as:

/** A block of instructions.
 *
 * Instructions in this block are executed sequentially but are not necessarily
 * contiguous in memory.  Users are expected to follow direct branches.
 */
struct pt_block {
    /** The IP of the first instruction in this block. */
    uint64_t ip;

    /** The IP of the last instruction in this block.
     *
     * This can be used for error-detection.
     */
    uint64_t end_ip;

    /** The image section that contains the instructions in this block.
     *
     * A value of zero means that the section did not have an identifier.
     * The section was not added via an image section cache or the memory
     * was read via the read memory callback.
     */
    int isid;

    /** The execution mode for all instructions in this block. */
    enum pt_exec_mode mode;

    /** The instruction class for the last instruction in this block.
     *
     * This field may be set to ptic_error to indicate that the instruction
     * class is not available.  The block decoder may choose to not provide
     * the instruction class in some cases for performance reasons.
     */
    enum pt_insn_class iclass;

    /** The number of instructions in this block. */
    uint16_t ninsn;

    /** The raw bytes of the last instruction in this block in case the
     * instruction does not fit entirely into this block's section.
     *
     * This field is only valid if \@truncated is set.
     */
    uint8_t raw[pt_max_insn_size];

    /** The size of the last instruction in this block in bytes.
     *
     * This field is only valid if \@truncated is set.
     */
    uint8_t size;

    /** A collection of flags giving additional information about the
     * instructions in this block.
     *
     * - all instructions in this block were executed speculatively.
     */
    uint32_t speculative:1;

    /** - the last instruction in this block is truncated.
     *
     *    It starts in this block's section but continues in one or more
     *    other sections depending on how fragmented the memory image is.
     *
     *    The raw bytes for the last instruction are provided in \@raw and
     *    its size in \@size in this case.
     */
    uint32_t truncated:1;
};

The fields of the pt_block structure are described in more detail below:

ip

The virtual address of the first instruction in the block. The address should be interpreted in the current address space context.

end_ip

The virtual address of the last instruction in the block. The address should be interpreted in the current address space context.

This can be used for error detection. Reconstruction of the instructions in a block should end with the last instruction at end_ip.

isid

The image section identifier of the section from which the block of instructions originated. This will be zero unless the instructions came from a section that was added via an image section cache. See pt_image_add_cached(3).

The image section identifier can be used for reading the memory containing an instruction in order to decode it and for tracing an instruction back to its binary file and from there to source code.

mode

The execution mode at which the instructions in the block were executed. The pt_exec_mode enumeration is declared as:

/** An execution mode. */
enum pt_exec_mode {
    ptem_unknown,
    ptem_16bit,
    ptem_32bit,
    ptem_64bit
};
iclass

A coarse classification of the last instruction in the block. This may be ptic_error to indicate that the classification is not available.

The block decoder knows the instruction class of the instruction that ended the block most of the time. If it does, it provides this information to save the caller the effort of decoding the instruction in some cases.

ninsn

The number of instructions contained in this block.

The instructions are sequential in the sense that no trace is required for reconstructing them. They are not necessarily contiguous in memory.

The IP of the first instruction is given in the ip field and the IP of other instructions can be determined by decoding and examining the previous instruction.

raw

If the last instruction of this block can not be read entirely from this block’s section, this field provides the instruction’s raw bytes.

It is only valid if the truncated flag is set.

size

If the last instruction of this block can not be read entirely from this block’s section, this field provides the instruction’s size in bytes.

It is only valid if the truncated flag is set.

speculative

A flag giving the speculative execution status of all instructions in the block. If set, the instructions were executed speculatively. Otherwise, the instructions were executed normally.

truncated

A flag saying whether the last instruction in this block can not be read entirely from this block’s section. Some bytes need to be read from one or more other sections. This can happen when an image section is partially overwritten by another image section.

If set, the last instruction’s memory is provided in raw and its size in size.

Return Value

pt_blk_next() returns 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
};

The pts_event_pending flag indicates that one or more events are pending. Use pt_blk_event(3) to process pending events before calling pt_blk_next() again.

The pt_eos flag indicates that the information contained in the Intel PT stream has been consumed. Further calls to pt_blk_next() will continue to provide blocks for instructions as long as the instruction’s addresses can be determined without further trace.

Errors

pte_invalid

The decoder or block argument is NULL or the size argument is too small.

pte_eos

Decode reached the end of the trace stream.

pte_nosync

The decoder has not been synchronized onto the trace stream. Use pt_blk_sync_forward(3), pt_blk_sync_backward(3), or pt_blk_sync_set(3) to synchronize decoder.

pte_bad_opc

The decoder encountered an unsupported Intel PT packet opcode.

pte_bad_packet

The decoder encountered an unsupported Intel PT packet payload.

pte_bad_query

Execution flow reconstruction and trace got out of sync.

This typically means that, on its way to the virtual address of the next event, the decoder encountered a conditional or indirect branch for which it did not find guidance in the trace.

See Also

pt_blk_alloc_decoder(3), pt_blk_free_decoder(3), pt_blk_sync_forward(3), pt_blk_sync_backward(3), pt_blk_sync_set(3), pt_blk_time(3), pt_blk_core_bus_ratio(3), pt_blk_event(3)

Referenced By

pt_blk_alloc_decoder(3), pt_blk_get_offset(3), pt_blk_sync_forward(3), pt_insn_get_image(3), pt_qry_event(3), pt_qry_time(3).

The man page pt_block(3) is an alias of pt_blk_next(3).