linux-kernel - Re: [tip: core/kprobes] arm/ftrace: Use __patch

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Date:   Fri, 7 Feb 2020 19:47:28 +0300
From:   Dmitry Osipenko <digetx@...il.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     linux-kernel@...r.kernel.org,
        tip-bot2 for Peter Zijlstra <tip-bot2@...utronix.de>,
        linux-tip-commits@...r.kernel.org, Will Deacon <will@...nel.org>,
        Thierry Reding <thierry.reding@...il.com>,
        Jon Hunter <jonathanh@...dia.com>,
        Andy Lutomirski <luto@...nel.org>,
        Borislav Petkov <bp@...en8.de>,
        Brian Gerst <brgerst@...il.com>,
        Denys Vlasenko <dvlasenk@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Mark Rutland <mark.rutland@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        ard.biesheuvel@...aro.org, james.morse@....com, rabin@....in,
        Ingo Molnar <mingo@...nel.org>, x86 <x86@...nel.org>,
        "linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [tip: core/kprobes] arm/ftrace: Use __patch_text()

07.02.2020 14:27, Peter Zijlstra пишет:
>> NVIDIA Tegra20/30 are not booting with CONFIG_FTRACE=y, but even with
>> CONFIG_FTRACE=n things are not working well.
> 
> Ooh, I think I see. Can you try this:
> 
> diff --git a/arch/arm/kernel/ftrace.c b/arch/arm/kernel/ftrace.c
> index 2a5ff69c28e6..10499d44964a 100644
> --- a/arch/arm/kernel/ftrace.c
> +++ b/arch/arm/kernel/ftrace.c
> @@ -78,13 +78,10 @@ static int ftrace_modify_code(unsigned long pc, unsigned long old,
>  {
>  	unsigned long replaced;
>  
> -	if (IS_ENABLED(CONFIG_THUMB2_KERNEL)) {
> +	if (IS_ENABLED(CONFIG_THUMB2_KERNEL))
>  		old = __opcode_to_mem_thumb32(old);
> -		new = __opcode_to_mem_thumb32(new);
> -	} else {
> +	else
>  		old = __opcode_to_mem_arm(old);
> -		new = __opcode_to_mem_arm(new);
> -	}
>  
>  	if (validate) {
>  		if (probe_kernel_read(&replaced, (void *)pc, MCOUNT_INSN_SIZE))
> 

Hello Peter,

It fixes the problem, at least kernel is booting fine now and I can't
notice any problems. Thank you very much! :)

Tested-by: Dmitry Osipenko <digetx@...il.com>