linux-kernel - Re: [for-next][PATCH 4/4] ftrace: Consolidate ftrace_regs accessor functions for archs using pt

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Message-Id: <20241015085434.afeaac72d7cae61bf00af3b5@kernel.org>
Date: Tue, 15 Oct 2024 08:54:34 +0900
From: Masami Hiramatsu (Google) <mhiramat@...nel.org>
To: Steven Rostedt <rostedt@...dmis.org>
Cc: linux-kernel@...r.kernel.org, Masami Hiramatsu <mhiramat@...nel.org>,
 Mark Rutland <mark.rutland@....com>, Mathieu Desnoyers
 <mathieu.desnoyers@...icios.com>, Andrew Morton
 <akpm@...ux-foundation.org>, <linux-arch@...r.kernel.org>, "x86@...nel.org"
 <x86@...nel.org>, 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>, Catalin
 Marinas <catalin.marinas@....com>
Subject: Re: [for-next][PATCH 4/4] ftrace: Consolidate ftrace_regs accessor
 functions for archs using pt_regs

Hi Steve,

I found one problem on this patch while debugging my series;

On Fri, 11 Oct 2024 09:29:45 -0400
Steven Rostedt <rostedt@...dmis.org> wrote:

> -#define ftrace_regs_get_argument(fregs, n) \
> -	regs_get_kernel_argument(&arch_ftrace_regs(fregs)->regs, n)

As you can seem most arch uses "arch_ftrace_regs()" macro
for ftrace_regs_*() macros. This is because we are sure
this ftrace_regs is not fully compatible with pt_regs.


> +#define ftrace_regs_get_instruction_pointer(fregs) \
> +	instruction_pointer(arch_ftrace_get_regs(fregs))

However, these consolidated macros in ftrace_regs.h are
using "arch_ftrace_get_regs()" macro, which can return NULL
if FL_SAVE_REGS is not set.

So, those should use arch_ftrace_regs() as original code
does.

Thank you,

-- 
Masami Hiramatsu (Google) <mhiramat@...nel.org>