D.4 General Query Packets

Packets starting with ‘q’ are general query packets; packets starting with ‘Q’ are general set packets. General query and set packets are a semi-unified form for retrieving and sending information to and from the stub.

The initial letter of a query or set packet is followed by a name indicating what sort of thing the packet applies to. For example, No value for GDBN may use a ‘qSymbol’ packet to exchange symbol definitions with the stub. These packet names follow some conventions:

• The name must not contain commas, colons or semicolons.
• Most No value for GDBN query and set packets have a leading upper case letter.
• The names of custom vendor packets should use a company prefix, in lower case, followed by a period. For example, packets designed at the Acme Corporation might begin with ‘qacme.foo’ (for querying foos) or ‘Qacme.bar’ (for setting bars).

The name of a query or set packet should be separated from any parameters by a ‘:’; the parameters themselves should be separated by ‘,’ or ‘;’. Stubs must be careful to match the full packet name, and check for a separator or the end of the packet, in case two packet names share a common prefix. New packets should not begin with ‘qC’, ‘qP’, or ‘qL’(9).

Like the descriptions of the other packets, each description here has a template showing the packet's overall syntax, followed by an explanation of the packet's meaning. We include spaces in some of the templates for clarity; these are not part of the packet's syntax. No No value for GDBN packet uses spaces to separate its components.

Here are the currently defined query and set packets:

‘qC’

Return the current thread id.

Reply:

‘QC pid’

Where pid is an unsigned hexadecimal process id.

‘(anything else)’

Any other reply implies the old pid.

‘qCRC:addr,length’

Compute the CRC checksum of a block of memory. Reply:

‘E NN’

An error (such as memory fault)

‘C crc32’

The specified memory region's checksum is crc32.

‘qfThreadInfo’

‘qsThreadInfo’

Obtain a list of all active thread ids from the target (OS). Since there may be too many active threads to fit into one reply packet, this query works iteratively: it may require more than one query/reply sequence to obtain the entire list of threads. The first query of the sequence will be the ‘qfThreadInfo’ query; subsequent queries in the sequence will be the ‘qsThreadInfo’ query.

NOTE: This packet replaces the ‘qL’ query (see below).

Reply:

‘m id’

A single thread id

‘m id,id…’

a comma-separated list of thread ids

‘l’

(lower case letter ‘L’) denotes end of list.

In response to each query, the target will reply with a list of one or more thread ids, in big-endian unsigned hex, separated by commas. No value for GDBN will respond to each reply with a request for more thread ids (using the ‘qs’ form of the query), until the target responds with ‘l’ (lower-case el, for last).

‘qGetTLSAddr:thread-id,offset,lm’

Fetch the address associated with thread local storage specified by thread-id, offset, and lm.

thread-id is the (big endian, hex encoded) thread id associated with the thread for which to fetch the TLS address.

offset is the (big endian, hex encoded) offset associated with the thread local variable. (This offset is obtained from the debug information associated with the variable.)

lm is the (big endian, hex encoded) OS/ABI-specific encoding of the the load module associated with the thread local storage. For example, a GNU/Linux system will pass the link map address of the shared object associated with the thread local storage under consideration. Other operating environments may choose to represent the load module differently, so the precise meaning of this parameter will vary.

Reply:

‘XX…’

Hex encoded (big endian) bytes representing the address of the thread local storage requested.

‘E nn’

An error occurred. nn are hex digits.

‘’

An empty reply indicates that ‘qGetTLSAddr’ is not supported by the stub.

‘qL startflag threadcount nextthread’

Obtain thread information from RTOS. Where: startflag (one hex digit) is one to indicate the first query and zero to indicate a subsequent query; threadcount (two hex digits) is the maximum number of threads the response packet can contain; and nextthread (eight hex digits), for subsequent queries (startflag is zero), is returned in the response as argthread.

Don't use this packet; use the ‘qfThreadInfo’ query instead (see above).

Reply:

‘qM count done argthread thread…’

Where: count (two hex digits) is the number of threads being returned; done (one hex digit) is zero to indicate more threads and one indicates no further threads; argthreadid (eight hex digits) is nextthread from the request packet; thread… is a sequence of thread IDs from the target. threadid (eight hex digits). See remote.c:parse_threadlist_response().

‘qOffsets’

Get section offsets that the target used when relocating the downloaded image.

Reply:

‘Text=xxx;Data=yyy[;Bss=zzz]’

Relocate the Text section by xxx from its original address. Relocate the Data section by yyy from its original address. If the object file format provides segment information (e.g. ELF ‘PT_LOAD’ program headers), No value for GDBN will relocate entire segments by the supplied offsets.

Note: while a Bss offset may be included in the response, No value for GDBN ignores this and instead applies the Data offset to the Bss section.

‘TextSeg=xxx[;DataSeg=yyy]’

Relocate the first segment of the object file, which conventionally contains program code, to a starting address of xxx. If ‘DataSeg’ is specified, relocate the second segment, which conventionally contains modifiable data, to a starting address of yyy. No value for GDBN will report an error if the object file does not contain segment information, or does not contain at least as many segments as mentioned in the reply. Extra segments are kept at fixed offsets relative to the last relocated segment.

‘qP mode threadid’

Returns information on threadid. Where: mode is a hex encoded 32 bit mode; threadid is a hex encoded 64 bit thread ID.

Don't use this packet; use the ‘qThreadExtraInfo’ query instead (see below).

Reply: see remote.c:remote_unpack_thread_info_response().

‘QPassSignals: signal [;signal]…’

Each listed signal should be passed directly to the inferior process. Signals are numbered identically to continue packets and stop replies (see section Stop Reply Packets). Each signal list item should be strictly greater than the previous item. These signals do not need to stop the inferior, or be reported to No value for GDBN. All other signals should be reported to No value for GDBN. Multiple ‘QPassSignals’ packets do not combine; any earlier ‘QPassSignals’ list is completely replaced by the new list. This packet improves performance when using ‘handle signal nostop noprint pass’.

Reply:

‘OK’

The request succeeded.

‘E nn’

An error occurred. nn are hex digits.

‘’

An empty reply indicates that ‘QPassSignals’ is not supported by the stub.

Use of this packet is controlled by the set remote pass-signals command (see section set remote pass-signals). This packet is not probed by default; the remote stub must request it, by supplying an appropriate ‘qSupported’ response (see qSupported).

‘qRcmd,command’

command (hex encoded) is passed to the local interpreter for execution. Invalid commands should be reported using the output string. Before the final result packet, the target may also respond with a number of intermediate ‘Ooutput’ console output packets. Implementors should note that providing access to a stubs's interpreter may have security implications.

Reply:

‘OK’

A command response with no output.

‘OUTPUT’

A command response with the hex encoded output string OUTPUT.

‘E NN’

Indicate a badly formed request.

‘’

An empty reply indicates that ‘qRcmd’ is not recognized.

(Note that the qRcmd packet's name is separated from the command by a ‘,’, not a ‘:’, contrary to the naming conventions above. Please don't use this packet as a model for new packets.)

‘qSupported [:gdbfeature [;gdbfeature]… ]’

Tell the remote stub about features supported by No value for GDBN, and query the stub for features it supports. This packet allows No value for GDBN and the remote stub to take advantage of each others' features. ‘qSupported’ also consolidates multiple feature probes at startup, to improve No value for GDBN performance—a single larger packet performs better than multiple smaller probe packets on high-latency links. Some features may enable behavior which must not be on by default, e.g. because it would confuse older clients or stubs. Other features may describe packets which could be automatically probed for, but are not. These features must be reported before No value for GDBN will use them. This “default unsupported” behavior is not appropriate for all packets, but it helps to keep the initial connection time under control with new versions of No value for GDBN which support increasing numbers of packets.

Reply:

‘stubfeature [;stubfeature]…’

The stub supports or does not support each returned stubfeature, depending on the form of each stubfeature (see below for the possible forms).

‘’

An empty reply indicates that ‘qSupported’ is not recognized, or that no features needed to be reported to No value for GDBN.

The allowed forms for each feature (either a gdbfeature in the ‘qSupported’ packet, or a stubfeature in the response) are:

‘name=value’

The remote protocol feature name is supported, and associated with the specified value. The format of value depends on the feature, but it must not include a semicolon.

‘name+’

The remote protocol feature name is supported, and does not need an associated value.

‘name-’

The remote protocol feature name is not supported.

‘name?’

The remote protocol feature name may be supported, and No value for GDBN should auto-detect support in some other way when it is needed. This form will not be used for gdbfeature notifications, but may be used for stubfeature responses.

Whenever the stub receives a ‘qSupported’ request, the supplied set of No value for GDBN features should override any previous request. This allows No value for GDBN to put the stub in a known state, even if the stub had previously been communicating with a different version of No value for GDBN.

No values of gdbfeature (for the packet sent by No value for GDBN) are defined yet. Stubs should ignore any unknown values for gdbfeature. Any No value for GDBN which sends a ‘qSupported’ packet supports receiving packets of unlimited length (earlier versions of No value for GDBN may reject overly long responses). Values for gdbfeature may be defined in the future to let the stub take advantage of new features in No value for GDBN, e.g. incompatible improvements in the remote protocol—support for unlimited length responses would be a gdbfeature example, if it were not implied by the ‘qSupported’ query. The stub's reply should be independent of the gdbfeature entries sent by No value for GDBN; first No value for GDBN describes all the features it supports, and then the stub replies with all the features it supports.

Similarly, No value for GDBN will silently ignore unrecognized stub feature responses, as long as each response uses one of the standard forms.

Some features are flags. A stub which supports a flag feature should respond with a ‘+’ form response. Other features require values, and the stub should respond with an ‘=’ form response.

Each feature has a default value, which No value for GDBN will use if ‘qSupported’ is not available or if the feature is not mentioned in the ‘qSupported’ response. The default values are fixed; a stub is free to omit any feature responses that match the defaults.

Not all features can be probed, but for those which can, the probing mechanism is useful: in some cases, a stub's internal architecture may not allow the protocol layer to know some information about the underlying target in advance. This is especially common in stubs which may be configured for multiple targets.

These are the currently defined stub features and their properties:

Feature Name	Value Required	Default	Probe Allowed
‘PacketSize’	Yes	‘-’	No
‘qXfer:auxv:read’	No	‘-’	Yes
‘qXfer:features:read’	No	‘-’	Yes
‘qXfer:libraries:read’	No	‘-’	Yes
‘qXfer:memory-map:read’	No	‘-’	Yes
‘qXfer:spu:read’	No	‘-’	Yes
‘qXfer:spu:write’	No	‘-’	Yes
‘QPassSignals’	No	‘-’	Yes

These are the currently defined stub features, in more detail:

‘PacketSize=bytes’

The remote stub can accept packets up to at least bytes in length. No value for GDBN will send packets up to this size for bulk transfers, and will never send larger packets. This is a limit on the data characters in the packet, including the frame and checksum. There is no trailing NUL byte in a remote protocol packet; if the stub stores packets in a NUL-terminated format, it should allow an extra byte in its buffer for the NUL. If this stub feature is not supported, No value for GDBN guesses based on the size of the ‘g’ packet response.

‘qXfer:auxv:read’

The remote stub understands the ‘qXfer:auxv:read’ packet (see qXfer auxiliary vector read).

‘qXfer:features:read’

The remote stub understands the ‘qXfer:features:read’ packet (see qXfer target description read).

‘qXfer:libraries:read’

The remote stub understands the ‘qXfer:libraries:read’ packet (see qXfer library list read).

‘qXfer:memory-map:read’

The remote stub understands the ‘qXfer:memory-map:read’ packet (see qXfer memory map read).

‘qXfer:spu:read’

The remote stub understands the ‘qXfer:spu:read’ packet (see qXfer spu read).

‘qXfer:spu:write’

The remote stub understands the ‘qXfer:spu:write’ packet (see qXfer spu write).

‘QPassSignals’

The remote stub understands the ‘QPassSignals’ packet (see QPassSignals).

‘qSymbol::’

Notify the target that No value for GDBN is prepared to serve symbol lookup requests. Accept requests from the target for the values of symbols.

Reply:

‘OK’

The target does not need to look up any (more) symbols.

‘qSymbol:sym_name’

The target requests the value of symbol sym_name (hex encoded). No value for GDBN may provide the value by using the ‘qSymbol:sym_value:sym_name’ message, described below.

‘qSymbol:sym_value:sym_name’

Set the value of sym_name to sym_value.

sym_name (hex encoded) is the name of a symbol whose value the target has previously requested.

sym_value (hex) is the value for symbol sym_name. If No value for GDBN cannot supply a value for sym_name, then this field will be empty.

Reply:

‘OK’

The target does not need to look up any (more) symbols.

‘qSymbol:sym_name’

The target requests the value of a new symbol sym_name (hex encoded). No value for GDBN will continue to supply the values of symbols (if available), until the target ceases to request them.

‘QTDP’

‘QTFrame’

See section Tracepoint Packets.

‘qThreadExtraInfo,id’

Obtain a printable string description of a thread's attributes from the target OS. id is a thread-id in big-endian hex. This string may contain anything that the target OS thinks is interesting for No value for GDBN to tell the user about the thread. The string is displayed in No value for GDBN's info threads display. Some examples of possible thread extra info strings are ‘Runnable’, or ‘Blocked on Mutex’.

Reply:

‘XX…’

Where ‘XX…’ is a hex encoding of ASCII data, comprising the printable string containing the extra information about the thread's attributes.

(Note that the qThreadExtraInfo packet's name is separated from the command by a ‘,’, not a ‘:’, contrary to the naming conventions above. Please don't use this packet as a model for new packets.)

‘QTStart’

‘QTStop’

‘QTinit’

‘QTro’

‘qTStatus’

See section Tracepoint Packets.

‘qXfer:object:read:annex:offset,length’

Read uninterpreted bytes from the target's special data area identified by the keyword object. Request length bytes starting at offset bytes into the data. The content and encoding of annex is specific to object; it can supply additional details about what data to access.

Here are the specific requests of this form defined so far. All ‘qXfer:object:read:…’ requests use the same reply formats, listed below.

‘qXfer:auxv:read::offset,length’

Access the target's auxiliary vector. See section auxiliary vector. Note annex must be empty.

This packet is not probed by default; the remote stub must request it, by supplying an appropriate ‘qSupported’ response (see qSupported).

‘qXfer:features:read:annex:offset,length’

Access the target description. See section Target Descriptions. The annex specifies which XML document to access. The main description is always loaded from the ‘target.xml’ annex.

This packet is not probed by default; the remote stub must request it, by supplying an appropriate ‘qSupported’ response (see qSupported).

‘qXfer:libraries:read:annex:offset,length’

Access the target's list of loaded libraries. See section Library List Format. The annex part of the generic ‘qXfer’ packet must be empty (see qXfer read).

Targets which maintain a list of libraries in the program's memory do not need to implement this packet; it is designed for platforms where the operating system manages the list of loaded libraries.

This packet is not probed by default; the remote stub must request it, by supplying an appropriate ‘qSupported’ response (see qSupported).

‘qXfer:memory-map:read::offset,length’

Access the target's memory-map. See section Memory Map Format. The annex part of the generic ‘qXfer’ packet must be empty (see qXfer read).

This packet is not probed by default; the remote stub must request it, by supplying an appropriate ‘qSupported’ response (see qSupported).

‘qXfer:spu:read:annex:offset,length’

Read contents of an spufs file on the target system. The annex specifies which file to read; it must be of the form ‘id/name’, where id specifies an SPU context ID in the target process, and name identifes the spufs file in that context to be accessed.

This packet is not probed by default; the remote stub must request it, by supplying an appropriate ‘qSupported’ response (see qSupported).

Reply:

‘m data’

Data data (see Binary Data) has been read from the target. There may be more data at a higher address (although it is permitted to return ‘m’ even for the last valid block of data, as long as at least one byte of data was read). data may have fewer bytes than the length in the request.

‘l data’

Data data (see Binary Data) has been read from the target. There is no more data to be read. data may have fewer bytes than the length in the request.

‘l’

The offset in the request is at the end of the data. There is no more data to be read.

‘E00’

The request was malformed, or annex was invalid.

‘E nn’

The offset was invalid, or there was an error encountered reading the data. nn is a hex-encoded errno value.

‘’

An empty reply indicates the object string was not recognized by the stub, or that the object does not support reading.

‘qXfer:object:write:annex:offset:data…’

Write uninterpreted bytes into the target's special data area identified by the keyword object, starting at offset bytes into the data. data… is the binary-encoded data (see Binary Data) to be written. The content and encoding of annex is specific to object; it can supply additional details about what data to access.

Here are the specific requests of this form defined so far. All ‘qXfer:object:write:…’ requests use the same reply formats, listed below.

‘qXfer:spu:write:annex:offset:data…’

Write data to an spufs file on the target system. The annex specifies which file to write; it must be of the form ‘id/name’, where id specifies an SPU context ID in the target process, and name identifes the spufs file in that context to be accessed.

This packet is not probed by default; the remote stub must request it, by supplying an appropriate ‘qSupported’ response (see qSupported).

Reply:

‘nn’

nn (hex encoded) is the number of bytes written. This may be fewer bytes than supplied in the request.

‘E00’

The request was malformed, or annex was invalid.

‘E nn’

The offset was invalid, or there was an error encountered writing the data. nn is a hex-encoded errno value.

‘’

An empty reply indicates the object string was not recognized by the stub, or that the object does not support writing.

‘qXfer:object:operation:…’

Requests of this form may be added in the future. When a stub does not recognize the object keyword, or its support for object does not recognize the operation keyword, the stub must respond with an empty packet.