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

From: Anup Patel <anup@brainfault.org>
To: Vincent Chen <vincent.chen@sifive.com>
Cc: Daniel Thompson <daniel.thompson@linaro.org>,
	kgdb-bugreport@lists.sourceforge.net, jason.wessel@windriver.com,
	Douglas Anderson <dianders@chromium.org>,
	Palmer Dabbelt <palmer@dabbelt.com>,
	Paul Walmsley <paul.walmsley@sifive.com>,
	linux-riscv <linux-riscv@lists.infradead.org>
Subject: Re: [PATCH v2 0/5] riscv: Add KGDB and KDB support
Date: Mon, 6 Apr 2020 09:44:33 +0530	[thread overview]
Message-ID: <CAAhSdy2h0BsSQjL25tTZRx2JV1fnpnW9RgSO6keXopBJaJCsZw@mail.gmail.com> (raw)
In-Reply-To: <CABvJ_xh2pocd1xywyZ_4VQbs8eFO6ehQfsRkQTpdTDUJXbsXEg@mail.gmail.com>

On Mon, Apr 6, 2020 at 8:05 AM Vincent Chen <vincent.chen@sifive.com> wrote:
>
> 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 \

Majority of folks (including distros) have moved to OpenSBI instead
of BBL. In fact, QEMU releases ship with OpenSBI as default M-mode
firmware.

To boot Linux on QEMU Virt with OpenSBI as M-mode firmware refer:
https://github.com/riscv/opensbi/blob/master/docs/platform/qemu_virt.md

Regards,
Anup