Re: [PATCH 1/2] riscv/ftrace: add DYNAMIC_FTRACE_WITH_DIRECT_CALLS support

[Song Shuai <suagrfillet@gmail.com>]

Guo Ren <guoren@kernel.org> 于2022年11月28日周一 13:17写道：
>
> On Wed, Nov 23, 2022 at 10:20 PM Song Shuai <suagrfillet@gmail.com> wrote:
> >
> > This patch adds DYNAMIC_FTRACE_WITH_DIRECT_CALLS support for RISC-V.
> >
> > select the DYNAMIC_FTRACE_WITH_DIRECT_CALLS to provide the
> > register_ftrace_direct[_multi] interfaces allowing users to register
> > the customed trampoline (direct_caller) as the mcount for one or
> > more target functions. And modify_ftrace_direct[_multi] are also
> > provided for modifying direct_caller.
> >
> > To make the direct_caller and the other ftrace hooks (eg. function/fgraph
> > tracer, k[ret]probes) co-exist, a temporary register is nominated to
> > store the address of direct_caller in ftrace_regs_caller. After the
> > setting of the address direct_caller by direct_ops->func and the
> > RESTORE_REGS in ftrace_regs_caller, direct_caller will be jumped to
> > by the `jr` inst.
> >
> > Signed-off-by: Song Shuai <suagrfillet@gmail.com>
> > ---
> >  arch/riscv/Kconfig              | 1 +
> >  arch/riscv/include/asm/ftrace.h | 6 ++++++
> >  arch/riscv/kernel/mcount-dyn.S  | 4 ++++
> >  3 files changed, 11 insertions(+)
> >
> > diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> > index 39ec8d628cf6..d083ec08d0b6 100644
> > --- a/arch/riscv/Kconfig
> > +++ b/arch/riscv/Kconfig
> > @@ -278,6 +278,7 @@ config ARCH_RV64I
> >         select ARCH_SUPPORTS_INT128 if CC_HAS_INT128
> >         select HAVE_DYNAMIC_FTRACE if !XIP_KERNEL && MMU && $(cc-option,-fpatchable-function-entry=8)
> >         select HAVE_DYNAMIC_FTRACE_WITH_REGS if HAVE_DYNAMIC_FTRACE
> > +       select HAVE_DYNAMIC_FTRACE_WITH_DIRECT_CALLS
> >         select HAVE_FTRACE_MCOUNT_RECORD if !XIP_KERNEL
> >         select HAVE_FUNCTION_GRAPH_TRACER
> >         select HAVE_FUNCTION_TRACER if !XIP_KERNEL && !PREEMPTION
> > diff --git a/arch/riscv/include/asm/ftrace.h b/arch/riscv/include/asm/ftrace.h
> > index 01bebb28eabe..be4d57566139 100644
> > --- a/arch/riscv/include/asm/ftrace.h
> > +++ b/arch/riscv/include/asm/ftrace.h
> > @@ -114,6 +114,12 @@ struct ftrace_regs;
> >  void ftrace_graph_func(unsigned long ip, unsigned long parent_ip,
> >                        struct ftrace_ops *op, struct ftrace_regs *fregs);
> >  #define ftrace_graph_func ftrace_graph_func
> > +
> > +static inline void arch_ftrace_set_direct_caller(struct pt_regs *regs, unsigned long addr)
> > +{
> > +               regs->t1 = addr;
> > +}
> > +
> >  #endif /* CONFIG_DYNAMIC_FTRACE_WITH_REGS */
> >
> >  #endif /* __ASSEMBLY__ */
> > diff --git a/arch/riscv/kernel/mcount-dyn.S b/arch/riscv/kernel/mcount-dyn.S
> > index 466c6ef217b1..b89c85a58569 100644
> > --- a/arch/riscv/kernel/mcount-dyn.S
> > +++ b/arch/riscv/kernel/mcount-dyn.S
> > @@ -233,6 +233,7 @@ ENDPROC(ftrace_caller)
> >  #else /* CONFIG_DYNAMIC_FTRACE_WITH_REGS */
> >  ENTRY(ftrace_regs_caller)
> >         SAVE_ABI_REGS 1
> > +       REG_S   x0, PT_T1(sp)
> ENTRY(ftrace_regs_caller)
> +    move t1, zero
>       SAVE_ABI_REGS 1
>       PREPARE_ARGS
>
> Shall we use a move here, instead?
That seems ok to me. Just move it.
>
> >         PREPARE_ARGS
> >
> >  ftrace_regs_call:
> > @@ -241,7 +242,10 @@ ftrace_regs_call:
> >
> >
> >         RESTORE_ABI_REGS 1
> > +       bnez    t1,.Ldirect
> >         jr t0
> > +.Ldirect:
> > +       jr t1
> >  ENDPROC(ftrace_regs_caller)
> >
> >  ENTRY(ftrace_caller)
> > --
> > 2.20.1
> >
>
>
> --
> Best Regards
>  Guo Ren



-- 
Thanks,
Song

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