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Date: Fri, 18 Aug 2023 20:01:48 +0900
From: Masami Hiramatsu (Google) <mhiramat@kernel.org>
To: Florent Revest <revest@chromium.org>
Cc: Alexei Starovoitov <alexei.starovoitov@gmail.com>, Steven Rostedt
 <rostedt@goodmis.org>, linux-trace-kernel@vger.kernel.org, LKML
 <linux-kernel@vger.kernel.org>, Martin KaFai Lau <martin.lau@linux.dev>,
 bpf <bpf@vger.kernel.org>, Sven Schnelle <svens@linux.ibm.com>, Alexei
 Starovoitov <ast@kernel.org>, Jiri Olsa <jolsa@kernel.org>, Arnaldo
 Carvalho de Melo <acme@kernel.org>, Daniel Borkmann <daniel@iogearbox.net>,
 Alan Maguire <alan.maguire@oracle.com>, Mark Rutland
 <mark.rutland@arm.com>, Peter Zijlstra <peterz@infradead.org>, Thomas
 Gleixner <tglx@linutronix.de>
Subject: Re: [PATCH v3 4/8] fprobe: rethook: Use ftrace_regs in fprobe exit
 handler and rethook
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On Thu, 17 Aug 2023 10:57:40 +0200
Florent Revest <revest@chromium.org> wrote:

> On Sat, Aug 12, 2023 at 7:37 AM Masami Hiramatsu (Google)
> <mhiramat@kernel.org> wrote:
> >
> > diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig
> > index 976fd594b446..d56304276318 100644
> > --- a/kernel/trace/Kconfig
> > +++ b/kernel/trace/Kconfig
> > @@ -57,6 +57,13 @@ config HAVE_DYNAMIC_FTRACE_WITH_ARGS
> >          This allows for use of ftrace_regs_get_argument() and
> >          ftrace_regs_get_stack_pointer().
> >
> > +config HAVE_PT_REGS_TO_FTRACE_REGS_CAST
> > +       bool
> > +       help
> > +        If this is set, the memory layout of the ftrace_regs data structure
> > +        is the same as the pt_regs. So the pt_regs is possible to be casted
> > +        to ftrace_regs.
> 
> What would you think of introducing a:
> 
> #ifdef HAVE_PT_REGS_TO_FTRACE_REGS_CAST
> static_assert(sizeof(struct pt_regs) == sizeof(struct ftrace_regs);
> #endif // HAVE_PT_REGS_TO_FTRACE_REGS_CAST
> 
> somewhere in ftrace.h just as a small extra safety net ? It doesn't
> exactly guarantee all we want but it should give an early warning of
> mistakes.

That's a good idea :)
OK, I'll add it in the next version.

Thank you,


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