| Debugging with GDB: 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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