linux-kernel - RE: [PATCH] arm64: Show three registers per line

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Message-ID: <c3ef59f1c06b42ecaa05a84beb7321b3@AcuMS.aculab.com>
Date:   Wed, 21 Apr 2021 08:31:32 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     "'Matthew Wilcox (Oracle)'" <willy@...radead.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Peter Zijlstra <peterz@...radead.org>,
        Kees Cook <keescook@...omium.org>,
        Marc Zyngier <maz@...nel.org>,
        Vincenzo Frascino <vincenzo.frascino@....com>
CC:     "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH] arm64: Show three registers per line

From: Matthew Wilcox
> Sent: 20 April 2021 18:23
>
> Displaying two registers per line takes 15 lines.  That improves to just
> 10 lines if we display three registers per line, which reduces the amount
> of information lost when oopses are cut off.  It stays within 80 columns
> and matches x86-64.
> 
> Signed-off-by: Matthew Wilcox (Oracle) <willy@...radead.org>
> ---
>  arch/arm64/kernel/process.c | 9 +++------
>  1 file changed, 3 insertions(+), 6 deletions(-)
> 
> diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c
> index 6e60aa3b5ea9..aff5a2c12297 100644
> --- a/arch/arm64/kernel/process.c
> +++ b/arch/arm64/kernel/process.c
> @@ -294,13 +294,10 @@ void __show_regs(struct pt_regs *regs)
>  	i = top_reg;
> 
>  	while (i >= 0) {
> -		printk("x%-2d: %016llx ", i, regs->regs[i]);
> -		i--;
> +		printk("x%-2d: %016llx", i, regs->regs[i]);
> 
> -		if (i % 2 == 0) {
> -			pr_cont("x%-2d: %016llx ", i, regs->regs[i]);
> -			i--;
> -		}
> +		while (i-- % 3)
> +			pr_cont(" x%-2d: %016llx", i, regs->regs[i]);
> 
>  		pr_cont("\n");
>  	}

I think I'd avoid pr_cont() to avoid 'mishaps' during concurrent oops.
This probably needs something like:
	for (; i >= 0; i -= 3) {
		switch (i) {
		case 0:
			printk("x%-2d: %016llx\n", i, regs->regs[i]);
			break;
		case 1:
			printk("x%-2d: %016llx x%-2d: %016llx\n",
			       i, regs->regs[i], i - 1, regs->regs[i - 1]);
			break;
		default:
			printk("x%-2d: %016llx x%-2d: %016llx x%-2d: %016llx\n",
			       i, regs->regs[i], i - 1, regs->regs[i - 1],
				 i - 2, regs->regs[i - 2]);
			continue;
		}
		break;
	}

	David

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