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

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Message-Id: <20241002082616.e02d3f92968291fad7533b70@kernel.org>
Date: Wed, 2 Oct 2024 08:26:16 +0900
From: Masami Hiramatsu (Google) <mhiramat@...nel.org>
To: Will Deacon <will@...nel.org>
Cc: Steven Rostedt <rostedt@...dmis.org>, 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 Tue, 17 Sep 2024 11:14:54 +0100
Will Deacon <will@...nel.org> wrote:

> 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.

Yeah, this one also copies the fregs->pc to regs->pc, mainly for bpf.

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

Thank you!

> 
> Will


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