Re: [PATCH] ftrace: Make ftrace_regs abstract from direct use

From: Catalin Marinas <catalin.marinas@arm.com>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: LKML <linux-kernel@vger.kernel.org>,
	Linux Trace Kernel <linux-trace-kernel@vger.kernel.org>,
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	WANG Xuerui <kernel@xen0n.name>,
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	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@kernel.org>, Borislav Petkov <bp@alien8.de>,
	Dave Hansen <dave.hansen@linux.intel.com>
Subject: Re: [PATCH] ftrace: Make ftrace_regs abstract from direct use
Date: Tue, 8 Oct 2024 11:03:57 +0100	[thread overview]
Message-ID: <ZwUDjbrYZNC7HLZS@arm.com> (raw)
In-Reply-To: <20241007204743.41314f1d@gandalf.local.home>

On Mon, Oct 07, 2024 at 08:47:43PM -0400, Steven Rostedt wrote:
> From: Steven Rostedt <rostedt@goodmis.org>
> 
> ftrace_regs was created to hold registers that store information to save
> function parameters, return value and stack. Since it is a subset of
> pt_regs, it should only be used by its accessor functions. But because
> pt_regs can easily be taken from ftrace_regs (on most archs), it is
> tempting to use it directly. But when running on other architectures, it
> may fail to build or worse, build but crash the kernel!
> 
> Instead, make struct ftrace_regs an empty structure and have the
> architectures define __arch_ftrace_regs and all the accessor functions
> will typecast to it to get to the actual fields. This will help avoid
> usage of ftrace_regs directly.
> 
> Link: https://lore.kernel.org/all/20241007171027.629bdafd@gandalf.local.home/
> 
> Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
> ---
> Note, I tried to cros-compile the affected architectures,
> but my builds failed for 32 bit powerpc and s390 (without this patch).
> It mostly compiled, and the affected files seemed to build.
> 
>  arch/arm64/include/asm/ftrace.h          | 20 +++++++++--------
>  arch/arm64/kernel/asm-offsets.c          | 22 +++++++++----------
>  arch/arm64/kernel/ftrace.c               | 10 ++++-----

For arm64:

Acked-by: Catalin Marinas <catalin.marinas@arm.com>