linux-kernel - Re: [PATCH v14 08/19] tracing: Add ftrace_partial_regs() for converting ftrace_regs to pt

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Message-ID: <20240917101454.GC27384@willie-the-truck>
Date: Tue, 17 Sep 2024 11:14:54 +0100
From: Will Deacon <will@...nel.org>
To: Steven Rostedt <rostedt@...dmis.org>
Cc: Catalin Marinas <catalin.marinas@....com>,
	linux-arm-kernel@...ts.infradead.org,
	"Masami Hiramatsu (Google)" <mhiramat@...nel.org>,
	Florent Revest <revest@...omium.org>,
	linux-trace-kernel@...r.kernel.org,
	LKML <linux-kernel@...r.kernel.org>,
	Alexei Starovoitov <ast@...nel.org>, Jiri Olsa <jolsa@...nel.org>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Daniel Borkmann <daniel@...earbox.net>,
	Mark Rutland <mark.rutland@....com>
Subject: Re: [PATCH v14 08/19] tracing: Add ftrace_partial_regs() for
 converting ftrace_regs to pt_regs

On Sun, Sep 15, 2024 at 05:22:04AM -0400, Steven Rostedt wrote:
> On Fri, 13 Sep 2024 00:09:35 +0900
> "Masami Hiramatsu (Google)" <mhiramat@...nel.org> wrote:
> 
> > From: Masami Hiramatsu (Google) <mhiramat@...nel.org>
> > 
> > Add ftrace_partial_regs() which converts the ftrace_regs to pt_regs.
> > This is for the eBPF which needs this to keep the same pt_regs interface
> > to access registers.
> > Thus when replacing the pt_regs with ftrace_regs in fprobes (which is
> > used by kprobe_multi eBPF event), this will be used.
> > 
> > If the architecture defines its own ftrace_regs, this copies partial
> > registers to pt_regs and returns it. If not, ftrace_regs is the same as
> > pt_regs and ftrace_partial_regs() will return ftrace_regs::regs.
> > 
> > Signed-off-by: Masami Hiramatsu (Google) <mhiramat@...nel.org>
> > Acked-by: Florent Revest <revest@...omium.org>
> > ---
> >  Changes in v14:
> >   - Add riscv change.
> >  Changes in v8:
> >   - Add the reason why this required in changelog.
> >  Changes from previous series: NOTHING, just forward ported.
> > ---
> >  arch/arm64/include/asm/ftrace.h |   11 +++++++++++
> >  arch/riscv/include/asm/ftrace.h |   12 ++++++++++++
> >  include/linux/ftrace.h          |   17 +++++++++++++++++
> >  3 files changed, 40 insertions(+)
> > 
> > diff --git a/arch/arm64/include/asm/ftrace.h b/arch/arm64/include/asm/ftrace.h
> > index dffaab3dd1f1..5cd587afab6d 100644
> > --- a/arch/arm64/include/asm/ftrace.h
> > +++ b/arch/arm64/include/asm/ftrace.h
> > @@ -132,6 +132,17 @@ ftrace_regs_get_frame_pointer(const struct ftrace_regs *fregs)
> >  	return fregs->fp;
> >  }
> >  
> > +static __always_inline struct pt_regs *
> > +ftrace_partial_regs(const struct ftrace_regs *fregs, struct pt_regs *regs)
> > +{
> > +	memcpy(regs->regs, fregs->regs, sizeof(u64) * 9);
> > +	regs->sp = fregs->sp;
> > +	regs->pc = fregs->pc;
> > +	regs->regs[29] = fregs->fp;
> > +	regs->regs[30] = fregs->lr;
> > +	return regs;
> > +}

Ah, I guess this is where we pick up the lr that was set in patch 5.

Acked-by: Will Deacon <will@...nel.org>

Will