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## Appendix I Trace File Format

The trace file comes in three parts: a header, a textual description section, and a trace frame section with binary data.

The header has the form `\x7fTRACE0\n`. The first byte is `0x7f` so as to indicate that the file contains binary data, while the `0` is a version number that may have different values in the future.

The description section consists of multiple lines of ASCII text separated by newline characters (`0xa`). The lines may include a variety of optional descriptive or context-setting information, such as tracepoint definitions or register set size. GDB will ignore any line that it does not recognize. An empty line marks the end of this section.

`R size`

  Specifies the size of a register block in bytes. This is equal to the size of a `g` packet payload in the remote protocol. size is an ascii decimal number. There should be only one such line in a single trace file.

`status status`

  Trace status. status has the same format as a `qTStatus` remote packet reply. There should be only one such line in a single trace file.

`tp payload`

  Tracepoint definition. The payload has the same format as `qTfP`/`qTsP` remote packet reply payload. A single tracepoint may take multiple lines of definition, corresponding to the multiple reply packets.

`tsv payload`

  Trace state variable definition. The payload has the same format as `qTfV`/`qTsV` remote packet reply payload. A single variable may take multiple lines of definition, corresponding to the multiple reply packets.

`tdesc payload`

  Target description in XML format. The payload is a single line of the XML file. All such lines should be concatenated together to get the original XML file. This file is in the same format as `qXfer` `features` payload, and corresponds to the main `target.xml` file. Includes are not allowed.

The trace frame section consists of a number of consecutive frames. Each frame begins with a two-byte tracepoint number, followed by a four-byte size giving the amount of data in the frame. The data in the frame consists of a number of blocks, each introduced by a character indicating its type (at least register, memory, and trace state variable). The data in this section is raw binary, not a hexadecimal or other encoding; its endianness matches the target’s endianness.

`R bytes`

  Register block. The number and ordering of bytes matches that of a `g` packet in the remote protocol. Note that these are the actual bytes, in target order, not a hexadecimal encoding.

`M address length bytes...`

  Memory block. This is a contiguous block of memory, at the 8-byte address address, with a 2-byte length length, followed by length bytes.

`V number value`

  Trace state variable block. This records the 8-byte signed value value of trace state variable numbered number.

Future enhancements of the trace file format may include additional types of blocks.

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