linux-kernel - Re: [PATCH v3 05/11] arm64: Add call_break_hook() to early

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Date:   Mon, 11 May 2020 15:59:09 +0100
From:   Will Deacon <will@...nel.org>
To:     Douglas Anderson <dianders@...omium.org>
Cc:     jason.wessel@...driver.com, daniel.thompson@...aro.org,
        gregkh@...uxfoundation.org, agross@...nel.org,
        kgdb-bugreport@...ts.sourceforge.net, catalin.marinas@....com,
        linux-serial@...r.kernel.org, sumit.garg@...aro.org,
        corbet@....net, mingo@...hat.com, hpa@...or.com,
        tglx@...utronix.de, frowand.list@...il.com, bp@...en8.de,
        bjorn.andersson@...aro.org, jslaby@...e.com,
        Alexios Zavras <alexios.zavras@...el.com>,
        Allison Randal <allison@...utok.net>,
        Dave Martin <Dave.Martin@....com>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        James Morse <james.morse@....com>,
        Mark Rutland <mark.rutland@....com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        jinho lim <jordan.lim@...sung.com>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 05/11] arm64: Add call_break_hook() to early_brk64()
 for early kgdb

Hi Doug,

On Tue, Apr 28, 2020 at 02:13:45PM -0700, Douglas Anderson wrote:
> diff --git a/arch/arm64/kernel/debug-monitors.c b/arch/arm64/kernel/debug-monitors.c
> index 48222a4760c2..59c353dfc8e9 100644
> --- a/arch/arm64/kernel/debug-monitors.c
> +++ b/arch/arm64/kernel/debug-monitors.c
> @@ -297,7 +297,7 @@ void unregister_kernel_break_hook(struct break_hook *hook)
>  	unregister_debug_hook(&hook->node);
>  }
>  
> -static int call_break_hook(struct pt_regs *regs, unsigned int esr)
> +int call_break_hook(struct pt_regs *regs, unsigned int esr)
>  {
>  	struct break_hook *hook;
>  	struct list_head *list;
> diff --git a/arch/arm64/kernel/traps.c b/arch/arm64/kernel/traps.c
> index cf402be5c573..a8173f0c1774 100644
> --- a/arch/arm64/kernel/traps.c
> +++ b/arch/arm64/kernel/traps.c
> @@ -1044,6 +1044,9 @@ int __init early_brk64(unsigned long addr, unsigned int esr,
>  	if ((comment & ~KASAN_BRK_MASK) == KASAN_BRK_IMM)
>  		return kasan_handler(regs, esr) != DBG_HOOK_HANDLED;
>  #endif
> +	if (call_break_hook(regs, esr) == DBG_HOOK_HANDLED)
> +		return 0;

I think this just means we're not running debug_traps_init() early enough,
and actually the KASAN early handler is unnecessary too.

If we call debug_traps_init() directly from setup_arch() and drop the
arch_initcall(), can we then drop early_brk64 entirely?

Will