Connect with riscV-gdb to homebrewed openOCD

Following connection attempt fails. reiscV-gdb -> patched openOCD (see setup below). Following messages are displayed in gdb and openOCD

riscV-gdb output

(gdb) target remote 127.0.0.1:3333
Remote debugging using 127.0.0.1:3333
warning: Architecture rejected target-supplied description
warning: No executable has been specified and target does not support
determining executable automatically.  Try using the "file" command.
Truncated register 22 in remote 'g' packet

openOCD debug output of above attempt

Info : 543 2761051 server.c:100 add_connection(): accepting 'gdb' connection on tcp/3333
Debug: 544 2761052 breakpoints.c:354 breakpoint_clear_target_internal(): Delete all breakpoints for target: myOwnCPU.cpu
Debug: 545 2761052 breakpoints.c:494 watchpoint_clear_target(): Delete all watchpoints for target: myOwnCPU.cpu
Debug: 546 2761052 target.c:1581 target_call_event_callbacks(): target event 19 (gdb-attach)
Debug: 547 2761052 target.c:4535 target_handle_event(): target(0): myOwnCPU.cpu (myOwnCPU) event: 19 (gdb-attach) action: halt
Debug: 548 2761053 command.c:143 script_debug(): command - ocd_command ocd_command type ocd_halt
Debug: 549 2761055 command.c:143 script_debug(): command - halt ocd_halt
Debug: 551 2761057 target.c:3018 handle_halt_command(): -
Debug: 570 2761060 gdb_server.c:1014 gdb_new_connection(): New GDB Connection: 1, Target myOwnCPU.cpu, state: halted
Debug: 571 2761060 gdb_server.c:3160 gdb_input_inner(): received packet: 'qSupported:multiprocess+;swbreak+;hwbreak+;qRelocInsn+;fork-events+;vfork-events+;exec-events+;vContSupported+;QThreadEvents+;no-resumed+;xmlRegisters=i386'
Debug: 575 2761061 gdb_server.c:3160 gdb_input_inner(): received packet: 'vMustReplyEmpty'
Debug: 576 2761061 gdb_server.c:3160 gdb_input_inner(): received packet: 'QStartNoAckMode'
Debug: 577 2761061 gdb_server.c:639 gdb_get_packet_inner(): Received first acknowledgment after entering noack mode. Ignoring it.
Debug: 578 2761061 gdb_server.c:3160 gdb_input_inner(): received packet: 'Hg0'
Debug: 579 2761062 gdb_server.c:3160 gdb_input_inner(): received packet: 'qXfer:features:read:target.xml:0,1000'
Debug: 583 2761072 gdb_server.c:3160 gdb_input_inner(): received packet: 'qXfer:features:read:target.xml:1000,1000'
Debug: 584 2761073 gdb_server.c:3160 gdb_input_inner(): received packet: 'qXfer:features:read:target.xml:2000,1000'
Debug: 585 2761073 gdb_server.c:3160 gdb_input_inner(): received packet: 'qXfer:features:read:target.xml:3000,1000'
Debug: 586 2761074 gdb_server.c:3160 gdb_input_inner(): received packet: 'qXfer:features:read:target.xml:4000,1000'
Debug: 587 2761074 gdb_server.c:3160 gdb_input_inner(): received packet: 'qXfer:features:read:target.xml:5000,1000'
Debug: 588 2761077 gdb_server.c:3160 gdb_input_inner(): received packet: 'qTStatus'
Debug: 589 2761077 gdb_server.c:3160 gdb_input_inner(): received packet: '?'
Debug: 590 2761077 gdb_server.c:3160 gdb_input_inner(): received packet: 'qXfer:threads:read::0,1000'
Debug: 591 2761077 gdb_server.c:3160 gdb_input_inner(): received packet: 'Hc-1'
Debug: 592 2761078 gdb_server.c:3160 gdb_input_inner(): received packet: 'qC'
Debug: 593 2761078 gdb_server.c:3160 gdb_input_inner(): received packet: 'qAttached'
Debug: 594 2761078 gdb_server.c:3160 gdb_input_inner(): received packet: 'g'
Debug: 598 2761096 gdb_server.c:1046 gdb_connection_closed(): GDB Close, Target: myOwnCPU.cpu, state: halted, gdb_actual_connections=0
Debug: 599 2761096 target.c:1581 target_call_event_callbacks(): target event 6 (gdb-end)
Debug: 600 2761096 target.c:1581 target_call_event_callbacks(): target event 20 (gdb-detach)
Info : 601 2761096 server.c:577 server_loop(): dropped 'gdb' connection

• I don't know why the connection is dropped
• I guess I need to provide more information in my target.get_gdb_reg_list()
• Or I've provided wrong information in my target.get_gdb_reg_list()
• I need to know which information must be provided that riscV-gdb accepts the connection from the openOCD(acting as gdb-server).

Setup:

original riscv-gdb

openOCD from masterbranch

• added support for a new TAP-Controller (buggy part)
• chain: jtag(ftdi based) -- "new TAP" -- "riscV (zero riscy)"

Appendix:

connecting with the normal gdb (7.11.1) works in general:

(gdb) target remote 127.0.0.1:3333
Remote debugging using 127.0.0.1:3333
warning: Architecture rejected target-supplied description
0x000041b8 in ?? ()

I can start/stop the cpu, load images etc. My register view looks like

(gdb) info registers
eax            0x0  0
ecx            0x88aa   34986
edx            0x6fc4   28612
ebx            0x0  0
esp            0x0  0x0
ebp            0x0  0x0
esi            0x850    2128
edi            0x0  0
eip            0x41b8   0x41b8
eflags         0x0  [ ]
cs             0x40e4   16612
ss             0x4  4
ds             0xffffffff   -1
es             0x7f7f7f7f   2139062143
fs             0xa00    2560
gs             0x0  0

There should be much more registers. x00 to x31 + a couple of config registers. The program counter is correct.

Googling some error-messages from above leads to only on conclusion... Wrong GDB. But I've compiled the GDB from the riscv-repository with default options. This was not helping at all...

The following w2as the clue!

# cd into your destination folder and invoke a git clone of the riscV-OpenOCD
git clone https://github.com/riscv/riscv-binutils-gdb.git

# build gdb with riscv-support
mkdir build
cd build
../riscv-binutils-gdb/configure --prefix=${GDB_INSTALL_FOLDER} \
 --target=riscv-elf --program-prefix=riscv-elf-
# build
make all
# move build files into predefined install folder
make install

# to room up after build
# make distclean

--target=riscv-elf is the option you want. GDB expects a specific set of registers. As this is a clone from the original repository, the default is i386. It's also expecting registers definition and features from such a cpu.

To check the architecture your gdb supports run: (gdb) set architecture with no arguments. For my zero riscy from pulpino I had to select (gdb) set architecture riscv:rv32. Afterwards I cold connect to the target without loosing the connection.