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Date:   Wed, 10 Mar 2021 15:21:01 +0100 (CET)
From:   Miroslav Benes <mbenes@suse.cz>
To:     Masami Hiramatsu <mhiramat@kernel.org>
cc:     Steven Rostedt <rostedt@goodmis.org>,
        Ingo Molnar <mingo@kernel.org>, X86 ML <x86@kernel.org>,
        Daniel Xu <dxu@dxuuu.xyz>, linux-kernel@vger.kernel.org,
        bpf@vger.kernel.org, kuba@kernel.org, mingo@redhat.com,
        ast@kernel.org, tglx@linutronix.de, kernel-team@fb.com, yhs@fb.com
Subject: Re: [PATCH -tip 3/5] kprobes: treewide: Remove trampoline_address
 from kretprobe_trampoline_handler()
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References: <161495873696.346821.10161501768906432924.stgit@devnote2> <161495876994.346821.11468535974887762132.stgit@devnote2>
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Hi Masami,

> --- a/include/linux/kprobes.h
> +++ b/include/linux/kprobes.h
> @@ -205,15 +205,23 @@ extern void arch_prepare_kretprobe(struct kretprobe_instance *ri,
>  				   struct pt_regs *regs);
>  extern int arch_trampoline_kprobe(struct kprobe *p);
>  
> +void kretprobe_trampoline(void);
> +/*
> + * Since some architecture uses structured function pointer,
> + * use arch_deref_entry_point() to get real function address.

s/arch_deref_entry_point/dereference_function_descriptor/ ?

> + */
> +static nokprobe_inline void *kretprobe_trampoline_addr(void)
> +{
> +	return dereference_function_descriptor(kretprobe_trampoline);
> +}
> +

Would it make sense to use this in s390 and powerpc reliable unwinders?

Both

arch/s390/kernel/stacktrace.c:arch_stack_walk_reliable()
arch/powerpc/kernel/stacktrace.c:__save_stack_trace_tsk_reliable()

have

	if (state.ip == (unsigned long)kretprobe_trampoline)
		return -EINVAL;

which you wanted to hide previously if I am not mistaken.

Miroslav