Re: [PATCH v4 05/12] arm64: Add call_break_hook() to early_brk64() for early kgdb

From: Doug Anderson <dianders@chromium.org>
To: Jason Wessel <jason.wessel@windriver.com>,
	Daniel Thompson <daniel.thompson@linaro.org>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Jonathan Corbet <corbet@lwn.net>,
	Frank Rowand <frowand.list@gmail.com>,
	Bjorn Andersson <bjorn.andersson@linaro.org>,
	linux-serial@vger.kernel.org, Ingo Molnar <mingo@redhat.com>,
	"H. Peter Anvin" <hpa@zytor.com>, Jiri Slaby <jslaby@suse.com>,
	kgdb-bugreport@lists.sourceforge.net,
	Sumit Garg <sumit.garg@linaro.org>, Will Deacon <will@kernel.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Andy Gross <agross@kernel.org>,
	Catalin Marinas <catalin.marinas@arm.com>,
	bp@alien8.de, Alexios Zavras <alexios.zavras@intel.com>,
	Allison Randal <allison@lohutok.net>,
	Dave Martin <Dave.Martin@arm.com>,
	Enrico Weigelt <info@metux.net>,
	"Eric W. Biederman" <ebiederm@xmission.com>,
	James Morse <james.morse@arm.com>,
	Mark Rutland <mark.rutland@arm.com>,
	Masami Hiramatsu <mhiramat@kernel.org>,
	jinho lim <jordan.lim@samsung.com>,
	Linux ARM <linux-arm-kernel@lists.infradead.org>,
	LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v4 05/12] arm64: Add call_break_hook() to early_brk64() for early kgdb
Date: Wed, 13 May 2020 16:12:11 -0700	[thread overview]
Message-ID: <CAD=FV=Wq1bnaMnUa09GZzQq5rZeQHUM9WAmxED3foc_Rjdsg2A@mail.gmail.com> (raw)
In-Reply-To: <20200507130644.v4.5.I22067ad43e77ddfd4b64c2d49030628480f9e8d9@changeid>

Hi,

On Thu, May 7, 2020 at 1:09 PM Douglas Anderson <dianders@chromium.org> wrote:
>
> In order to make early kgdb work properly we need early_brk64() to be
> able to call into it.  This is as easy as adding a call into
> call_break_hook() just like we do later in the normal brk_handler().
>
> Once we do this we can let kgdb know that it can break into the
> debugger a little earlier (specifically when parsing early_param's).
>
> NOTE: without this patch it turns out that arm64 can't do breakpoints
> even at dbg_late_init(), so if we decide something about this patch is
> wrong we might need to move dbg_late_init() a little later.
>
> Signed-off-by: Douglas Anderson <dianders@chromium.org>
> Cc: Catalin Marinas <catalin.marinas@arm.com>
> Cc: Will Deacon <will@kernel.org>
> Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> Reviewed-by: Daniel Thompson <daniel.thompson@linaro.org>
> ---
>
> Changes in v4:
> - Add "if KGDB" to "select ARCH_HAS_EARLY_DEBUG" in Kconfig.
>
> Changes in v3:
> - Change boolean weak function to KConfig.
>
> Changes in v2: None
>
>  arch/arm64/Kconfig                      | 1 +
>  arch/arm64/include/asm/debug-monitors.h | 2 ++
>  arch/arm64/kernel/debug-monitors.c      | 2 +-
>  arch/arm64/kernel/traps.c               | 3 +++
>  4 files changed, 7 insertions(+), 1 deletion(-)

As discussed in the replies to the v3 version of this patch [1], I
have posted a replacement patch for this one [2].  After the cut in
the replacement patch I talk about different ways it could land.
Hopefully that's not too confusing.  I can also re-spam everyone with
a v5 of the whole series if that makes it clearer.

[1] https://lore.kernel.org/r/20200428141218.v3.5.I22067ad43e77ddfd4b64c2d49030628480f9e8d9@changeid
[2] https://lore.kernel.org/r/20200513160501.1.I0b5edf030cc6ebef6ab4829f8867cdaea42485d8@changeid

-Doug