PDBG

pdbg is a simple application to allow debugging of the host POWER processors from the BMC. It works in a similar way to JTAG programmers for embedded system development in that it allows you to access GPRs, SPRs and system memory.

A remote gdb sever is under development to allow integration with standard debugging tools.

Building

The output of autoconf is not included in the git tree so it needs to be generated using autoreconf. This can be done by running ./bootstrap.sh in the top level directory. Static linking is supported and can be performed by adding CFLAGS=-static to the command line passed to configure.

Cross compiling for BMC (ARM)

apt-get install gcc-arm-linux-gnueabi
./bootstrap.sh
./configure --host=arm-linux-gnueabi CFLAGS="-static"
make
rsync pdbg root@bmc:/usr/local/bin

Usage

Several backends are supported depending on which system you are using and are selected using the -b option:

POWER8 Backends:

i2c (default): Uses an i2c connection between BMC and host processor
fsi: Uses a bit-banging GPIO backend which accesses BMC registers directly via /dev/mem/. Requires -d p8 to specify you are running on a POWER8 system.

POWER9 Backends:

kernel (default): Uses the in kernel OpenFSI driver provided by OpenBMC
fsi: Uses a bit-banging GPIO backend which accesses BMC registers directly via /dev/mem. Requiers -d p9w/p9r/p9z as appropriate for the system.

When using the fsi backend POWER8 AMI based BMC's must first be put into debug mode to allow access to the relevant GPIOs:

ipmitool -H <host> -U <username> -P <password> raw 0x3a 0x01

On POWER9 when using the fsi backend it is also a good idea to put the BMC into debug mode to prevent conflicts with the OpenFSI driver. On the BMC run:

systemctl start fsi-disable.service && systemctl stop host-failure-reboots@0.service

Usage is straight forward. Note that if the binary is not statically linked all commands need to be prefixed with LD_LIBRARY_PATH= in addition to the arguments for selecting a backend.

Examples

$ ./pdbg --help
Usage: ./pdbg [options] command ...

 Options:
        -p, --processor=processor-id
        -c, --chip=chiplet-id
        -t, --thread=thread
        -a, --all
                Run command on all possible processors/chips/threads (default)
        -b, --backend=backend
                fsi:    An experimental backend that uses
                        bit-banging to access the host processor
                        via the FSI bus.
                i2c:    The P8 only backend which goes via I2C.
                kernel: The default backend which goes the kernel FSI driver.
        -d, --device=backend device
                For I2C the device node used by the backend to access the bus.
                For FSI the system board type, one of p8 or p9w
                Defaults to /dev/i2c4 for I2C
        -s, --slave-address=backend device address
                Device slave address to use for the backend. Not used by FSI
                and defaults to 0x50 for I2C
        -V, --version
        -h, --help

 Commands:
        getcfam <address>
        putcfam <address> <value> [<mask>]
        getscom <address>
        putscom <address> <value> [<mask>]
        getmem <address> <count>
        putmem <address>
        getvmem <virtual address>
        getgpr <gpr>
        putgpr <gpr> <value>
        getnia
        putnia <value>
        getspr <spr>
        putspr <spr> <value>
        start
        step <count>
        stop
        threadstatus
        probe

Probe chip/processor/thread numbers

$ ./pdbg -a probe
    BMC GPIO bit-banging FSI master
        CFAM hMFSI Port
            p1: POWER FSI2PIB
                POWER9 ADU
                c16: POWER9 Core
                    t0: POWER9 Thread
                    t1: POWER9 Thread
                    t2: POWER9 Thread
                    t3: POWER9 Thread
                c17: POWER9 Core
                    t0: POWER9 Thread
                    t1: POWER9 Thread
                    t2: POWER9 Thread
                    t3: POWER9 Thread
                c18: POWER9 Core
                    t0: POWER9 Thread
                    t1: POWER9 Thread
                    t2: POWER9 Thread
                    t3: POWER9 Thread
                c19: POWER9 Core
                    t0: POWER9 Thread
                    t1: POWER9 Thread
                    t2: POWER9 Thread
                    t3: POWER9 Thread
                c20: POWER9 Core
                    t0: POWER9 Thread
                    t1: POWER9 Thread
                    t2: POWER9 Thread
                    t3: POWER9 Thread
                c21: POWER9 Core
                    t0: POWER9 Thread
                    t1: POWER9 Thread
                    t2: POWER9 Thread
                    t3: POWER9 Thread
                c22: POWER9 Core
                    t0: POWER9 Thread
                    t1: POWER9 Thread
                    t2: POWER9 Thread
                    t3: POWER9 Thread
                c23: POWER9 Core
                    t0: POWER9 Thread
                    t1: POWER9 Thread
                    t2: POWER9 Thread
                    t3: POWER9 Thread
        p0: POWER FSI2PIB
            POWER9 ADU
            c5: POWER9 Core
                t0: POWER9 Thread
                t1: POWER9 Thread
                t2: POWER9 Thread
                t3: POWER9 Thread
            c7: POWER9 Core
                t0: POWER9 Thread
                t1: POWER9 Thread
                t2: POWER9 Thread
                t3: POWER9 Thread
            c14: POWER9 Core
                t0: POWER9 Thread
                t1: POWER9 Thread
                t2: POWER9 Thread
                t3: POWER9 Thread
            c15: POWER9 Core
                t0: POWER9 Thread
                t1: POWER9 Thread
                t2: POWER9 Thread
                t3: POWER9 Thread
            c19: POWER9 Core
                t0: POWER9 Thread
                t1: POWER9 Thread
                t2: POWER9 Thread
                t3: POWER9 Thread
            c20: POWER9 Core
                t0: POWER9 Thread
                t1: POWER9 Thread
                t2: POWER9 Thread
                t3: POWER9 Thread
            c21: POWER9 Core
                t0: POWER9 Thread
                t1: POWER9 Thread
                t2: POWER9 Thread
                t3: POWER9 Thread
            c22: POWER9 Core
                t0: POWER9 Thread
                t1: POWER9 Thread
                t2: POWER9 Thread
                t3: POWER9 Thread

Note that only selected targets will be shown above. If none are shown
try adding '-a' to select all targets

Core-IDs are core/chip numbers which should be passed as arguments to -c when performing operations such as getgpr that operate on particular cores. Processor-IDs should be passed as arguments to -p to operate on different processor chips. Specifying no targets is an error and will result in the following error message:

Note that only selected targets will be shown above. If none are shown
try adding '-a' to select all targets

If the above error occurs even though targets were specified it means the specified targets were not found when probing the system.

Read SCOM register

$ ./pdbg -a getscom 0xf000f
p0:0xf000f = 0x220ea04980000000
p1:0xf000f = 0x220ea04980800000

Write SCOM register on secondary processor

$ ./pdbg -p1 putscom 0x8013c02 0x0

Get thread status

$ ./pdbg -a threadstatus

p0t: 0 1 2 3 4 5 6 7
c22: A A A A
c21: A A A A
c20: A A A A
c19: A A A A
c15: A A A A
c14: A A A A
c07: A A A A
c05: A A A A 

p1t: 0 1 2 3 4 5 6 7
c23: A A A A
c22: A A A A
c21: A A A A
c20: A A A A
c19: A A A A
c18: A A A A
c17: A A A A
c16: A A A A

Stop thread execution on thread 0-4 of processor 0 core/chip 22

Reading thread register values requires all threads on a given core to be in the quiesced state.

$ ./pdbg -p0 -c22 -t0 -t1 -t2 -t3 stop
$ ./pdbg -p0 -c22 -t0 -t1 -t2 -t3 threadstatus

p0t: 0 1 2 3 4 5 6 7
c22: Q Q Q Q

Read GPR on thread 0 of processor 0 core/chip 22

$ ./pdbg -p0 -c22 -t0 getgpr 2
p0:c22:t0:gpr02: 0xc000000000f09900

Read SPR 8 (LR) on thread 0 of processor 0 core/chip 22

$ ./pdbg -p0 -c22 -t0 getspr 8
p0:c22:t0:spr008: 0xc0000000008a97f0

Restart thread 0-4 execution on processor 0 core/chip 22

./pdbg -p0 -c22 -t0 -t1 -t2 -t3 start
./pdbg -p0 -c22 -t0 -t1 -t2 -t3 threadstatus

p0t: 0 1 2 3 4 5 6 7
c22: A A A A

Write to memory through processor 1

$ echo hello | sudo ./pdbg -p 1 putmem 0x250000001
Wrote 6 bytes starting at 0x0000000250000001

Read 6 bytes from memory through processor 1

$ sudo ./pdbg -p 1 getmem 0x250000001 6 | hexdump -C
00000000  68 65 6c 6c 6f 0a                                 |hello.|
00000006

Write to cache-inhibited memory through processor 1

$ echo hello | sudo ./pdbg -p 1 putmem -ci 0x3fe88202
Wrote 6 bytes starting at 0x000000003fe88202

Read from cache-inhibited memory through processor 1

$ sudo ./pdbg -p 1 getmem -ci 0x3fe88202 6 | hexdump -C
00000000  68 65 6c 6c 6f 0a                                 |hello.|
00000006

Read 4 bytes from the hardware RNG

$ lsprop /proc/device-tree/hwrng@3ffff40000000/
ibm,chip-id      00000000
compatible       "ibm,power-rng"
reg              0003ffff 40000000 00000000 00001000
phandle          100003bd (268436413)
name             "hwrng"

$ sudo ./pdbg -p 0  getmem -ci 0x0003ffff40000000 4 |hexdump -C
00000000  01 c0 d1 79                                       |...y|
00000004
$  sudo ./pdbg -p 0  getmem -ci 0x0003ffff40000000 4 |hexdump -C
00000000  77 9b ab ce                                       |w...|
00000004
$  sudo ./pdbg -p 0  getmem -ci 0x0003ffff40000000 4 |hexdump -C
00000000  66 8d fb 42                                       |f..B|
00000004
$  sudo ./pdbg -p 0  getmem -ci 0x0003ffff40000000 4 |hexdump -C
00000000  fa 9b e3 44                                       |...D|
00000004

Hardware Trace Macro

Expoitation of HTM is limited to POWER9 NestHTM from the powerpc host. POWER8 (core and nest( is currently experimental. The dump files should be correct but have not been confirmed to be.

Using HTM requires a kernel built with both CONFIG_PPC_MEMTRACE=y (v4.14) and CONFIG_SCOM_DEBUGFS=y. debugfs should be mounted at /sys/kernel/debug.

pdbg provides a htm command with a variety of subcommands:

trace will configure the hardware and start tracing
analyse which still stop the trace and dump the result to a file

./pdbg -b host -d p9 -a htm trace
[allow test to run]
./pdbg -b host -d p9 -a htm analyse

If you are running into a checkstop issue, htm trace will print the physical address of the buffer it is tracing into and the BMC can be used to recover this memory after checkstop see getmem.

pdbg also provides some of the basic functionality to use HTM, such as htm reset, htm start and htm stop to perform each step manually if required.

mikey / pdbg