Re: [PATCH v14 08/19] tracing: Add ftrace_partial_regs() for converting ftrace_regs to pt_regs

Will Deacon
2024-09-17T10:15:00Z

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@kernel.org> wrote:
>
> > From: Masami Hiramatsu (Google) <mhiramat@kernel.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@kernel.org>
> > Acked-by: Florent Revest <revest@chromium.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@kernel.org>

Will