linux-kernel - Re: [PATCH] ftrace: Make ftrace

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Message-ID: <ZwUDjbrYZNC7HLZS@arm.com>
Date: Tue, 8 Oct 2024 11:03:57 +0100
From: Catalin Marinas <catalin.marinas@....com>
To: Steven Rostedt <rostedt@...dmis.org>
Cc: LKML <linux-kernel@...r.kernel.org>,
	Linux Trace Kernel <linux-trace-kernel@...r.kernel.org>,
	linux-arm-kernel@...ts.infradead.org, loongarch@...ts.linux.dev,
	linuxppc-dev@...ts.ozlabs.org, linux-riscv@...ts.infradead.org,
	linux-s390@...r.kernel.org,
	"linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
	"x86@...nel.org" <x86@...nel.org>,
	Masami Hiramatsu <mhiramat@...nel.org>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Mark Rutland <mark.rutland@....com>, Will Deacon <will@...nel.org>,
	Huacai Chen <chenhuacai@...nel.org>,
	WANG Xuerui <kernel@...0n.name>,
	Michael Ellerman <mpe@...erman.id.au>,
	Nicholas Piggin <npiggin@...il.com>,
	Christophe Leroy <christophe.leroy@...roup.eu>,
	Naveen N Rao <naveen@...nel.org>,
	Madhavan Srinivasan <maddy@...ux.ibm.com>,
	Paul Walmsley <paul.walmsley@...ive.com>,
	Palmer Dabbelt <palmer@...belt.com>,
	Albert Ou <aou@...s.berkeley.edu>,
	Heiko Carstens <hca@...ux.ibm.com>,
	Vasily Gorbik <gor@...ux.ibm.com>,
	Alexander Gordeev <agordeev@...ux.ibm.com>,
	Christian Borntraeger <borntraeger@...ux.ibm.com>,
	Sven Schnelle <svens@...ux.ibm.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...nel.org>, Borislav Petkov <bp@...en8.de>,
	Dave Hansen <dave.hansen@...ux.intel.com>
Subject: Re: [PATCH] ftrace: Make ftrace_regs abstract from direct use

On Mon, Oct 07, 2024 at 08:47:43PM -0400, Steven Rostedt wrote:
> From: Steven Rostedt <rostedt@...dmis.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@...dmis.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@....com>