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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.

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 and GDB register 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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