When the underlying debugport transport is reliable, GDB's additional
checksums and acknowledgements are redundant. NoAckMode eliminates the
the acks and allows us to skip checking RX checksums. The GDB packet
framing does not change, so unfortunately (valid) checksums are still
included as message trailers.
The gdb(4) stub in FreeBSD advertises support for the feature in response to
the client's 'qSupported' request IFF the current debugport has the
gdb_dbfeatures flag GDB_DBGP_FEAT_RELIABLE set. Currently, only netgdb(4)
supports this feature.
If the remote GDB client supports the feature and does not have it disabled
via a GDB configuration knob, it may instruct our gdb(4) stub to enter
NoAckMode. Unless and until it issues that command, we must continue to
transmit acks as usual (and for now, we continue to wait until we receive
them as well, even if we know the debugport is on a reliable transport).
In the kernel sources, the sense of the flag representing the state of the
feature is reversed from that of the GDB command. (I.e., it is
'gdb_ackmode', not 'gdb_noackmode.') This is to avoid confusing double-
negative conditions.
For reference, see:
* https://sourceware.org/gdb/onlinedocs/gdb/Packet-Acknowledgment.html
* https://sourceware.org/gdb/onlinedocs/gdb/General-Query-Packets.html#QStartNoAckMode
Reviewed by: jhb, markj (both earlier version)
Differential Revision: https://reviews.freebsd.org/D21761
NetGDB(4) is a component of a system using a panic-time network stack to
remotely debug crashed FreeBSD kernels over the network, instead of
traditional serial interfaces.
There are three pieces in the complete NetGDB system.
First, a dedicated proxy server must be running to accept connections from
both NetGDB and gdb(1), and pass bidirectional traffic between the two
protocols.
Second, the NetGDB client is activated much like ordinary 'gdb' and
similarly to 'netdump' in ddb(4) after a panic. Like other debugnet(4)
clients (netdump(4)), the network interface on the route to the proxy server
must be online and support debugnet(4).
Finally, the remote (k)gdb(1) uses 'target remote <proxy>:<port>' (like any
other TCP remote) to connect to the proxy server.
The NetGDB v1 protocol speaks the literal GDB remote serial protocol, and
uses a 1:1 relationship between GDB packets and sequences of debugnet
packets (fragmented by MTU). There is no encryption utilized to keep
debugging sessions private, so this is only appropriate for local
segments or trusted networks.
Submitted by: John Reimer <john.reimer AT emc.com> (earlier version)
Discussed some with: emaste, markj
Relnotes: sure
Differential Revision: https://reviews.freebsd.org/D21568
This streams out an XML document over several GDB packets describing all
threads in the system; their ids, name, and any loosely defined "extra info"
we feel like including. For now, I have included a string version of the run
state, similar to some of the DDB logic to stringify thread state.
The benefit of supporting this in addition to the qfThreadInfo/qsThreadInfo
packing is that in this mode, the host gdb does not ask for every thread's
"qThreadExtraInfo," saving per-thread round-trips on "info threads."
To use this feature, (k)gdb needs to be built with the --with-expat option.
I would encourage enabling this option by default in our GDB port, if it is
not already.
Finally, there is another optional attribute you can specify per-thread
called a "handle." Handles are arbitrarily long sequences of bytes,
represented in the XML as hexadecimal. It is unclear to me how or if GDB
actually uses handles for anything. So I have left them out.
We suffer at least one round trip ACK latency every command / packet that
GDB has to send and receive, and the response format for 'info threads'
supports packing many threads IDs into a single packet, so do so.
Adds and uses a new API, gdb_txbuf_has_capacity(), which checks for a
certain number of bytes available in the outgoing txbuf.
On an example amd64 VM, the number of RTTs to transmit this list is reduced
by a factor of 110x. This is especially beneficial with recent GDB, which
seems to request the list at least twice during attach.
Mainly focus on files that use BSD 2-Clause license, however the tool I
was using misidentified many licenses so this was mostly a manual - error
prone - task.
The Software Package Data Exchange (SPDX) group provides a specification
to make it easier for automated tools to detect and summarize well known
opensource licenses. We are gradually adopting the specification, noting
that the tags are considered only advisory and do not, in any way,
superceed or replace the license texts.
This is a NFC patch to move around the Search:memory implementation so
that it doesn't exceed the standard column width and doesn't take so
much vertical space in gdb_trap.
Submitted by: Daniel O'Connor <darius@dons.net.au>
Reviewed by: cem, jhb
Sponsored by: Dell EMC Isilon
Differential Revision: https://reviews.freebsd.org/D12684
It is implemented via db_trace_thread() for DDB and not implemented
for GDB. This should have been part of r234190.
Pointy hat to: jhb
Reported by: jkim
MFC after: 1 week
the debugger back-end has changed. This means that switching from ddb
to gdb no longer requires a "step" which can be dangerous on an
already-crashed kernel.
Also add a capability to get from the gdb back-end back to ddb, by
typing ^C in the console window.
While here, simplify kdb_sysctl_available() by using
sbuf_new_for_sysctl(), and use strlcpy() instead of strncpy() since the
strlcpy semantic is desired.
MFC after: 1 month
specified register, but a pointer to the in-memory representation of
that value. The reason for this is twofold:
1. Not all registers can be represented by a register_t. In particular
FP registers fall in that category. Passing the new register value
by reference instead of by value makes this point moot.
2. When we receive a G or P packet, both are for writing a register,
the packet will have the register value in target-byte order and
in the memory representation (modulo the fact that bytes are sent
as 2 printable hexadecimal numbers of course). We only need to
decode the packet to have a pointer to the register value.
This change fixes the bug of extracting the register value of the P
packet as a hexadecimal number instead of as a bit array. The quick
(and dirty) fix to bswap the register value in gdb_cpu_setreg() as
it has been added on i386 and amd64 can therefore be removed and has
in fact been that.
Tested on: alpha, amd64, i386, ia64, sparc64
backend improves over the old GDB support in the following ways:
o Unified implementation with minimal MD code.
o A simple interface for devices to register themselves as debug
ports, ala consoles.
o Compression by using run-length encoding.
o Implements GDB threading support.
