- ‘QTDP:n:addr:ena:step:pass[:Fflen][:Xlen,bytes][-]’
- Create a new tracepoint, number n, at addr. If ena
is ‘E’, then the tracepoint is enabled; if it is ‘D’, then
the tracepoint is disabled. The step gives the tracepoint's step
count, and pass gives its pass count. If an ‘F’ is present,
then the tracepoint is to be a fast tracepoint, and the flen is
the number of bytes that the target should copy elsewhere to make room
for the tracepoint. If an ‘X’ is present, it introduces a
tracepoint condition, which consists of a hexadecimal length, followed
by a comma and hex-encoded bytes, in a manner similar to action
encodings as described below. If the trailing ‘-’ is present,
further ‘QTDP’ packets will follow to specify this tracepoint's
actions.
Replies:
- ‘OK’
- The packet was understood and carried out.
- ‘qRelocInsn’
- See Relocate instruction reply packet.
- ‘’
- The packet was not recognized.
- ‘QTDP:-n:addr:[S]action...[-]’
- Define actions to be taken when a tracepoint is hit. The n and
addr must be the same as in the initial ‘QTDP’ packet for
this tracepoint. This packet may only be sent immediately after
another ‘QTDP’ packet that ended with a ‘-’. If the
trailing ‘-’ is present, further ‘QTDP’ packets will follow,
specifying more actions for this tracepoint.
In the series of action packets for a given tracepoint, at most one
can have an ‘S’ before its first action. If such a packet
is sent, it and the following packets define “while-stepping”
actions. Any prior packets define ordinary actions — that is, those
taken when the tracepoint is first hit. If no action packet has an
‘S’, then all the packets in the series specify ordinary
tracepoint actions.
The ‘action...’ portion of the packet is a series of
actions, concatenated without separators. Each action has one of the
following forms:
- ‘R mask’
- Collect the registers whose bits are set in mask,
a hexadecimal number whose i'th bit is set if register number
i should be collected. (The least significant bit is numbered
zero.) Note that mask may be any number of digits long; it may
not fit in a 32-bit word.
- ‘M basereg,offset,len’
- Collect len bytes of memory starting at the address in register
number basereg, plus offset. If basereg is
‘-1’, then the range has a fixed address: offset is the
address of the lowest byte to collect. The basereg,
offset, and len parameters are all unsigned hexadecimal
values (the ‘-1’ value for basereg is a special case).
- ‘X len,expr’
- Evaluate expr, whose length is len, and collect memory as
it directs. The agent expression expr is as described in
Agent Expressions. Each byte of the expression is encoded as a
two-digit hex number in the packet; len is the number of bytes
in the expression (and thus one-half the number of hex digits in the
packet).
Any number of actions may be packed together in a single ‘QTDP’
packet, as long as the packet does not exceed the maximum packet
length (400 bytes, for many stubs). There may be only one ‘R’
action per tracepoint, and it must precede any ‘M’ or ‘X’
actions. Any registers referred to by ‘M’ and ‘X’ actions
must be collected by a preceding ‘R’ action. (The
“while-stepping” actions are treated as if they were attached to a
separate tracepoint, as far as these restrictions are concerned.)
Replies:
- ‘OK’
- The packet was understood and carried out.
- ‘qRelocInsn’
- See Relocate instruction reply packet.
- ‘’
- The packet was not recognized.
- ‘QTDPsrc:n:addr:type:start:slen:bytes’
- Specify a source string of tracepoint n at address addr.
This is useful to get accurate reproduction of the tracepoints
originally downloaded at the beginning of the trace run. The type
is the name of the tracepoint part, such as ‘cond’ for the
tracepoint's conditional expression (see below for a list of types), while
bytes is the string, encoded in hexadecimal.
start is the offset of the bytes within the overall source
string, while slen is the total length of the source string.
This is intended for handling source strings that are longer than will
fit in a single packet.
The available string types are ‘at’ for the location,
‘cond’ for the conditional, and ‘cmd’ for an action command.
gdb sends a separate packet for each command in the action
list, in the same order in which the commands are stored in the list.
The target does not need to do anything with source strings except
report them back as part of the replies to the ‘qTfP’/‘qTsP’
query packets.
Although this packet is optional, and gdb will only send it
if the target replies with ‘TracepointSource’ See General Query Packets, it makes both disconnected tracing and trace files
much easier to use. Otherwise the user must be careful that the
tracepoints in effect while looking at trace frames are identical to
the ones in effect during the trace run; even a small discrepancy
could cause ‘tdump’ not to work, or a particular trace frame not
be found.
- ‘QTDV:n:value:builtin:name’
- Create a new trace state variable, number n, with an initial
value of value, which is a 64-bit signed integer. Both n
and value are encoded as hexadecimal values. gdb has
the option of not using this packet for initial values of zero; the
target should simply create the trace state variables as they are
mentioned in expressions. The value builtin should be 1 (one)
if the trace state variable is builtin and 0 (zero) if it is not builtin.
gdb only sets builtin to 1 if a previous ‘qTfV’ or
‘qTsV’ packet had it set. The contents of name is the
hex-encoded name (without the leading ‘$’) of the trace state
variable.
- ‘QTFrame:n’
- Select the n'th tracepoint frame from the buffer, and use the
register and memory contents recorded there to answer subsequent
request packets from gdb.
A successful reply from the stub indicates that the stub has found the
requested frame. The response is a series of parts, concatenated
without separators, describing the frame we selected. Each part has
one of the following forms:
- ‘F f’
- The selected frame is number n in the trace frame buffer;
f is a hexadecimal number. If f is ‘-1’, then there
was no frame matching the criteria in the request packet.
- ‘T t’
- The selected trace frame records a hit of tracepoint number t;
t is a hexadecimal number.
- ‘QTFrame:pc:addr’
- Like ‘QTFrame:n’, but select the first tracepoint frame after the
currently selected frame whose PC is addr;
addr is a hexadecimal number.
- ‘QTFrame:tdp:t’
- Like ‘QTFrame:n’, but select the first tracepoint frame after the
currently selected frame that is a hit of tracepoint t; t
is a hexadecimal number.
- ‘QTFrame:range:start:end’
- Like ‘QTFrame:n’, but select the first tracepoint frame after the
currently selected frame whose PC is between start (inclusive)
and end (inclusive); start and end are hexadecimal
numbers.
- ‘QTFrame:outside:start:end’
- Like ‘QTFrame:range:start:end’, but select the first
frame outside the given range of addresses (exclusive).
- ‘qTMinFTPILen’
- This packet requests the minimum length of instruction at which a fast
tracepoint (see Set Tracepoints) may be placed. For instance, on
the 32-bit x86 architecture, it is possible to use a 4-byte jump, but
it depends on the target system being able to create trampolines in
the first 64K of memory, which might or might not be possible for that
system. So the reply to this packet will be 4 if it is able to
arrange for that.
Replies:
- ‘0’
- The minimum instruction length is currently unknown.
- ‘length’
- The minimum instruction length is length, where length
is a hexadecimal number greater or equal to 1. A reply
of 1 means that a fast tracepoint may be placed on any instruction
regardless of size.
- ‘E’
- An error has occurred.
- ‘’
- An empty reply indicates that the request is not supported by the stub.
- ‘QTStart’
- Begin the tracepoint experiment. Begin collecting data from
tracepoint hits in the trace frame buffer. This packet supports the
‘qRelocInsn’ reply (see Relocate instruction reply packet).
- ‘QTStop’
- End the tracepoint experiment. Stop collecting trace frames.
- ‘QTEnable:n:addr’
- Enable tracepoint n at address addr in a started tracepoint
experiment. If the tracepoint was previously disabled, then collection
of data from it will resume.
- ‘QTDisable:n:addr’
- Disable tracepoint n at address addr in a started tracepoint
experiment. No more data will be collected from the tracepoint unless
‘QTEnable:n:addr’ is subsequently issued.
- ‘QTinit’
- Clear the table of tracepoints, and empty the trace frame buffer.
- ‘QTro:start1,end1:start2,end2:...’
- Establish the given ranges of memory as “transparent”. The stub
will answer requests for these ranges from memory's current contents,
if they were not collected as part of the tracepoint hit.
gdb uses this to mark read-only regions of memory, like those
containing program code. Since these areas never change, they should
still have the same contents they did when the tracepoint was hit, so
there's no reason for the stub to refuse to provide their contents.
- ‘QTDisconnected:value’
- Set the choice to what to do with the tracing run when gdb
disconnects from the target. A value of 1 directs the target to
continue the tracing run, while 0 tells the target to stop tracing if
gdb is no longer in the picture.
- ‘qTStatus’
- Ask the stub if there is a trace experiment running right now.
The reply has the form:
- ‘Trunning[;field]...’
- running is a single digit
1 if the trace is presently
running, or 0 if not. It is followed by semicolon-separated
optional fields that an agent may use to report additional status.
If the trace is not running, the agent may report any of several
explanations as one of the optional fields:
- ‘tnotrun:0’
- No trace has been run yet.
- ‘tstop[:text]:0’
- The trace was stopped by a user-originated stop command. The optional
text field is a user-supplied string supplied as part of the
stop command (for instance, an explanation of why the trace was
stopped manually). It is hex-encoded.
- ‘tfull:0’
- The trace stopped because the trace buffer filled up.
- ‘tdisconnected:0’
- The trace stopped because gdb disconnected from the target.
- ‘tpasscount:tpnum’
- The trace stopped because tracepoint tpnum exceeded its pass count.
- ‘terror:text:tpnum’
- The trace stopped because tracepoint tpnum had an error. The
string text is available to describe the nature of the error
(for instance, a divide by zero in the condition expression); it
is hex encoded.
- ‘tunknown:0’
- The trace stopped for some other reason.
Additional optional fields supply statistical and other information.
Although not required, they are extremely useful for users monitoring
the progress of a trace run. If a trace has stopped, and these
numbers are reported, they must reflect the state of the just-stopped
trace.
- ‘tframes:n’
- The number of trace frames in the buffer.
- ‘tcreated:n’
- The total number of trace frames created during the run. This may
be larger than the trace frame count, if the buffer is circular.
- ‘tsize:n’
- The total size of the trace buffer, in bytes.
- ‘tfree:n’
- The number of bytes still unused in the buffer.
- ‘circular:n’
- The value of the circular trace buffer flag.
1 means that the
trace buffer is circular and old trace frames will be discarded if
necessary to make room, 0 means that the trace buffer is linear
and may fill up.
- ‘disconn:n’
- The value of the disconnected tracing flag.
1 means that
tracing will continue after gdb disconnects, 0 means
that the trace run will stop.
- ‘qTP:tp:addr’
- Ask the stub for the current state of tracepoint number tp at
address addr.
Replies:
- ‘Vhits:usage’
- The tracepoint has been hit hits times so far during the trace
run, and accounts for usage in the trace buffer. Note that
while-stepping steps are not counted as separate hits, but the
steps' space consumption is added into the usage number.
- ‘qTV:var’
- Ask the stub for the value of the trace state variable number var.
Replies:
- ‘Vvalue’
- The value of the variable is value. This will be the current
value of the variable if the user is examining a running target, or a
saved value if the variable was collected in the trace frame that the
user is looking at. Note that multiple requests may result in
different reply values, such as when requesting values while the
program is running.
- ‘U’
- The value of the variable is unknown. This would occur, for example,
if the user is examining a trace frame in which the requested variable
was not collected.
- ‘qTfP’
- ‘qTsP’
- These packets request data about tracepoints that are being used by
the target. gdb sends
qTfP to get the first piece
of data, and multiple qTsP to get additional pieces. Replies
to these packets generally take the form of the QTDP packets
that define tracepoints. (FIXME add detailed syntax)
- ‘qTfV’
- ‘qTsV’
- These packets request data about trace state variables that are on the
target. gdb sends
qTfV to get the first vari of data,
and multiple qTsV to get additional variables. Replies to
these packets follow the syntax of the QTDV packets that define
trace state variables.
- ‘qTfSTM’
- ‘qTsSTM’
- These packets request data about static tracepoint markers that exist
in the target program. gdb sends
qTfSTM to get the
first piece of data, and multiple qTsSTM to get additional
pieces. Replies to these packets take the following form:
Reply:
- ‘m address:id:extra’
- A single marker
- ‘m address:id:extra,address:id:extra...’
- a comma-separated list of markers
- ‘l’
- (lower case letter ‘L’) denotes end of list.
- ‘E nn’
- An error occurred. The error number nn is given as hex digits.
- ‘’
- An empty reply indicates that the request is not supported by the
stub.
The address is encoded in hex;
id and extra are strings encoded in hex.
In response to each query, the target will reply with a list of one or
more markers, separated by commas. gdb will respond to each
reply with a request for more markers (using the ‘qs’ form of the
query), until the target responds with ‘l’ (lower-case ell, for
last).
- ‘qTSTMat:address’
- This packets requests data about static tracepoint markers in the
target program at address. Replies to this packet follow the
syntax of the ‘qTfSTM’ and
qTsSTM packets that list static
tracepoint markers.
- ‘QTSave:filename’
- This packet directs the target to save trace data to the file name
filename in the target's filesystem. The filename is encoded
as a hex string; the interpretation of the file name (relative vs
absolute, wild cards, etc) is up to the target.
- ‘qTBuffer:offset,len’
- Return up to len bytes of the current contents of trace buffer,
starting at offset. The trace buffer is treated as if it were
a contiguous collection of traceframes, as per the trace file format.
The reply consists as many hex-encoded bytes as the target can deliver
in a packet; it is not an error to return fewer than were asked for.
A reply consisting of just
l indicates that no bytes are
available.
- ‘QTBuffer:circular:value’
- This packet directs the target to use a circular trace buffer if
value is 1, or a linear buffer if the value is 0.
- ‘QTBuffer:size:size’
- This packet directs the target to make the trace buffer be of size
size if possible. A value of
-1 tells the target to
use whatever size it prefers.
- ‘QTNotes:[type:text][;type:text]...’
- This packet adds optional textual notes to the trace run. Allowable
types include
user, notes, and tstop, the
text fields are arbitrary strings, hex-encoded.
When installing fast tracepoints in memory, the target may need to
relocate the instruction currently at the tracepoint address to a
different address in memory. For most instructions, a simple copy is
enough, but, for example, call instructions that implicitly push the
return address on the stack, and relative branches or other
PC-relative instructions require offset adjustment, so that the effect
of executing the instruction at a different address is the same as if
it had executed in the original location.
In response to several of the tracepoint packets, the target may also
respond with a number of intermediate ‘qRelocInsn’ request
packets before the final result packet, to have gdb handle
this relocation operation. If a packet supports this mechanism, its
documentation will explicitly say so. See for example the above
descriptions for the ‘QTStart’ and ‘QTDP’ packets. The
format of the request is: