linux-kernel - Re: [PATCH v18 01/17] fgraph: Pass ftrace

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Message-ID: <20241101065023.72933d1b@gandalf.local.home>
Date: Fri, 1 Nov 2024 06:50:23 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: "Masami Hiramatsu (Google)" <mhiramat@...nel.org>
Cc: Alexei Starovoitov <alexei.starovoitov@...il.com>, Florent Revest
 <revest@...omium.org>, linux-trace-kernel@...r.kernel.org, LKML
 <linux-kernel@...r.kernel.org>, Martin KaFai Lau <martin.lau@...ux.dev>,
 bpf <bpf@...r.kernel.org>, Alexei Starovoitov <ast@...nel.org>, Jiri Olsa
 <jolsa@...nel.org>, Alan Maguire <alan.maguire@...cle.com>, Mark Rutland
 <mark.rutland@....com>, linux-arch@...r.kernel.org, Catalin Marinas
 <catalin.marinas@....com>, Will Deacon <will@...nel.org>, Huacai Chen
 <chenhuacai@...nel.org>, WANG Xuerui <kernel@...0n.name>, Michael Ellerman
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 <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>,
 Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
 Borislav Petkov <bp@...en8.de>, Dave Hansen <dave.hansen@...ux.intel.com>,
 x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>, Mathieu Desnoyers
 <mathieu.desnoyers@...icios.com>
Subject: Re: [PATCH v18 01/17] fgraph: Pass ftrace_regs to entryfunc

On Fri, 1 Nov 2024 10:51:02 +0900
Masami Hiramatsu (Google) <mhiramat@...nel.org> wrote:

> Ah, good catch! It should put the flag only when HAVE_DYNAMIC_FTRACE_WITH_ARGS
> is enabled.
> 
> static struct ftrace_ops graph_ops = {
> 	.func			= ftrace_graph_func,
> #ifdef CONFIG_DYNAMIC_FTRACE_WITH_ARGS
> 	.flags			= FTRACE_OPS_GRAPH_STUB | FTRACE_OPS_FL_SAVE_ARGS,
> #elif defined(CONFIG_DYNAMIC_FTRACE_WITH_ARGS)
> 	.flags			= FTRACE_OPS_GRAPH_STUB | FTRACE_OPS_FL_SAVE_REGS,
> #else
> 	.flags			= FTRACE_OPS_GRAPH_STUB,
> #endif
> 
> This will save fregs or regs or NULL according to the configuration.
> 

Please do not add that to the C code. It's really ugly. Just correct the
comment. Note, FTRACE_OPS_FL_SAVE_ARGS is already dynamic by configuration:

#ifndef CONFIG_DYNAMIC_FTRACE_WITH_ARGS
#define FTRACE_OPS_FL_SAVE_ARGS                        FTRACE_OPS_FL_SAVE_REGS
#else
#define FTRACE_OPS_FL_SAVE_ARGS                        0
#endif

I'm a bit confused at what you are trying to achieve here.

-- Steve