gdb: Trace File Format
Appendix I Trace File Format
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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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