Re: [PATCH v2 0/5] riscv: Add KGDB and KDB support

[Vincent Chen <vincent.chen@sifive.com>]

On Fri, Apr 3, 2020 at 6:12 PM Daniel Thompson
<daniel.thompson@linaro.org> wrote:
>
> On Tue, Mar 31, 2020 at 11:23:06PM +0800, Vincent Chen wrote:
> > This patch set implements required ports to enable RISC-V kernel to support
> > KGDB and KDB features. Because there is no immediate value in the RISC-V
> > trap instruction, the kernel cannot identify the purpose of each trap
> > exception through the opcode. This makes the existing identification
> > schemes in other architecture unsuitable for the RISC-V kernel. In order
> > to solve this problem, this patch adds the kgdb_has_hit_break() to kgdb.c
> > to help the RISC-V kernel identify the KGDB trap exception. In addition,
> > the XML target description was introduced in this patch set to enable KGDB
> > to report the contents of the status, cause and steal registers.
> >
> > This patchset has passed the kgdbts test suite provided by Linux kernel on
> > HiFive unleashed board and QEMU.
>
> Can you share the defconfig and qemu boot lines used for testing.
>
> I'd like to see if they can easily be integrated into kgdbtest. Normally
> figuring out the qemu boot line is the hardest bit of adding support for
> an architecture one is not familar with.
>
The process of building a RISC-V kernel is a bit different from other
architecture. Maybe you can refer the steps in
https://risc-v-getting-started-guide.readthedocs.io/en/latest/linux-qemu.html
to build the kernel image and run it.

For the Linux configuration used by KGDB, I just enable KGDB related
configuration based on riscv defconfig. The riscv defconfig can
founded in arch/riscv/configs/defconfig

The QEMU boot lines are listed in the following.

qemu-system-riscv64 -M virt -m 256M -nographic \
-kernel <bbl image>\
-append "debug root=/dev/vda rw console=ttyS0" \
-drive file=<root file system>,format=raw,id=hd0 \
-serial tcp:localhost:2345,server \
-gdb tcp::1133 \
-device virtio-blk-device,drive=hd0 \

>
> Daniel.
>
>
> PS At the moment it helps kgdbtest a lot if qemu is configured with two
>    serial ports but I really should get round to relaxing that!
>
> >
> > Changes since v1:
> > 1. Replace the magic number with macro when filling the gdb_regs[].
> > 2. Only support GDB XML packet instead of all query packets.
> > 3. Move the macros used to parse instrcuton to parse_asm.h
> >
> >
> > Vincent Chen (5):
> >   kgdb: Add kgdb_has_hit_break function
> >   riscv: Add KGDB support
> >   kgdb: enable arch to support XML packet support.
> >   riscv: Use the XML target descriptions to report 3 system registers
> >   riscv: Add SW single-step support for KDB
> >
> >  arch/riscv/Kconfig                 |   2 +
> >  arch/riscv/include/asm/Kbuild      |   1 -
> >  arch/riscv/include/asm/gdb_xml.h   | 117 ++++++++++++
> >  arch/riscv/include/asm/kdebug.h    |  12 ++
> >  arch/riscv/include/asm/kgdb.h      | 113 +++++++++++
> >  arch/riscv/include/asm/parse_asm.h | 214 +++++++++++++++++++++
> >  arch/riscv/kernel/Makefile         |   1 +
> >  arch/riscv/kernel/kgdb.c           | 382 +++++++++++++++++++++++++++++++++++++
> >  arch/riscv/kernel/traps.c          |   5 +
> >  include/linux/kgdb.h               |   9 +
> >  kernel/debug/debug_core.c          |  12 ++
> >  kernel/debug/gdbstub.c             |  13 ++
> >  lib/Kconfig.kgdb                   |   5 +
> >  13 files changed, 885 insertions(+), 1 deletion(-)
> >  create mode 100644 arch/riscv/include/asm/gdb_xml.h
> >  create mode 100644 arch/riscv/include/asm/kdebug.h
> >  create mode 100644 arch/riscv/include/asm/kgdb.h
> >  create mode 100644 arch/riscv/include/asm/parse_asm.h
> >  create mode 100644 arch/riscv/kernel/kgdb.c
> >
> > --
> > 2.7.4
> >