[V9,3/4] riscv: ftrace: Add DYNAMIC_FTRACE_WITH_DIRECT_CALLS support

Commit Message

Song Shuai May 10, 2023, 10:18 a.m. UTC

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 <[e-mail]>
Tested-by: Guo Ren <[e-mail]>
Signed-off-by: Guo Ren <[e-mail]>
---
 arch/riscv/Kconfig              |  1 +
 arch/riscv/include/asm/ftrace.h |  8 ++++++++
 arch/riscv/kernel/mcount-dyn.S  | 10 ++++++++++
 3 files changed, 19 insertions(+)

Comments

Björn Töpel May 11, 2023, 7:19 a.m. UTC | #1

Song Shuai <[e-mail]> writes:

> 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 <[e-mail]>
> Tested-by: Guo Ren <[e-mail]>
> Signed-off-by: Guo Ren <[e-mail]>
> ---
>  arch/riscv/Kconfig              |  1 +
>  arch/riscv/include/asm/ftrace.h |  8 ++++++++
>  arch/riscv/kernel/mcount-dyn.S  | 10 ++++++++++
>  3 files changed, 19 insertions(+)
>
> diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> index e0632493482f..fdf0b219a02c 100644
> --- a/arch/riscv/Kconfig
> +++ b/arch/riscv/Kconfig
> @@ -144,6 +144,7 @@ config RISCV
>  	select UACCESS_MEMCPY if !MMU
>  	select ZONE_DMA32 if 64BIT
>  	select HAVE_DYNAMIC_FTRACE if !XIP_KERNEL && MMU && (CLANG_SUPPORTS_DYNAMIC_FTRACE || GCC_SUPPORTS_DYNAMIC_FTRACE)
> +	select HAVE_DYNAMIC_FTRACE_WITH_DIRECT_CALLS
>  	select HAVE_DYNAMIC_FTRACE_WITH_REGS if HAVE_DYNAMIC_FTRACE
>  	select HAVE_FTRACE_MCOUNT_RECORD if !XIP_KERNEL
>  	select HAVE_FUNCTION_GRAPH_TRACER
> diff --git a/arch/riscv/include/asm/ftrace.h b/arch/riscv/include/asm/ftrace.h
> index 84f856a3286e..84904c1e4369 100644
> --- a/arch/riscv/include/asm/ftrace.h
> +++ b/arch/riscv/include/asm/ftrace.h
> @@ -114,6 +114,14 @@ 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;
> +}
> +#define arch_ftrace_set_direct_caller(fregs, addr) \
> +	__arch_ftrace_set_direct_caller(&(fregs)->regs, 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 f26e9f6e2fed..9d405baedb52 100644
> --- a/arch/riscv/kernel/mcount-dyn.S
> +++ b/arch/riscv/kernel/mcount-dyn.S
> @@ -231,6 +231,7 @@ ENDPROC(ftrace_caller)
>  
>  #else /* CONFIG_DYNAMIC_FTRACE_WITH_REGS */
>  ENTRY(ftrace_regs_caller)
> +	move	t1, zero

Please use "mv", and not "move" [1].

>  	SAVE_ABI_REGS 1
>  	PREPARE_ARGS
>  
> @@ -239,7 +240,10 @@ ftrace_regs_call:
>  	call	ftrace_stub
>  
>  	RESTORE_ABI_REGS 1
> +	bnez	t1,.Ldirect
>  	jr t0
> +.Ldirect:
> +	jr t1

Again, while you're doing changes here, please try to align op/operands.

Wearing my BPF hat, I'm happy to finally get DIRECT_CALLS support!

This does not take the WITH_CALL_OPS approach Mark suggested in the v7
threads, but given that text patching story on RISC-V is still a bit sad
(inconsistency in the RV tree, no specification, cannot work with
preempt, ...) I'd say this approach is OK for now, and we can change to
WITH_CALL_OPS later in a wider "let's improve RISC-V textpatching" work.

Thoughts?


Björn

[1] https://github.com/riscv-non-isa/riscv-asm-manual/blob/master/riscv-asm.md#-a-listing-of-standard-risc-v-pseudoinstructions

Song Shuai May 11, 2023, 9:18 a.m. UTC | #2

Björn Töpel <[e-mail]> 于2023年5月11日周四 07:19写道：

>
> Song Shuai <[e-mail]> writes:
>
> > 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 <[e-mail]>
> > Tested-by: Guo Ren <[e-mail]>
> > Signed-off-by: Guo Ren <[e-mail]>
> > ---
> >  arch/riscv/Kconfig              |  1 +
> >  arch/riscv/include/asm/ftrace.h |  8 ++++++++
> >  arch/riscv/kernel/mcount-dyn.S  | 10 ++++++++++
> >  3 files changed, 19 insertions(+)
> >
> > diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> > index e0632493482f..fdf0b219a02c 100644
> > --- a/arch/riscv/Kconfig
> > +++ b/arch/riscv/Kconfig
> > @@ -144,6 +144,7 @@ config RISCV
> >       select UACCESS_MEMCPY if !MMU
> >       select ZONE_DMA32 if 64BIT
> >       select HAVE_DYNAMIC_FTRACE if !XIP_KERNEL && MMU && (CLANG_SUPPORTS_DYNAMIC_FTRACE || GCC_SUPPORTS_DYNAMIC_FTRACE)
> > +     select HAVE_DYNAMIC_FTRACE_WITH_DIRECT_CALLS
> >       select HAVE_DYNAMIC_FTRACE_WITH_REGS if HAVE_DYNAMIC_FTRACE
> >       select HAVE_FTRACE_MCOUNT_RECORD if !XIP_KERNEL
> >       select HAVE_FUNCTION_GRAPH_TRACER
> > diff --git a/arch/riscv/include/asm/ftrace.h b/arch/riscv/include/asm/ftrace.h
> > index 84f856a3286e..84904c1e4369 100644
> > --- a/arch/riscv/include/asm/ftrace.h
> > +++ b/arch/riscv/include/asm/ftrace.h
> > @@ -114,6 +114,14 @@ 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;
> > +}
> > +#define arch_ftrace_set_direct_caller(fregs, addr) \
> > +     __arch_ftrace_set_direct_caller(&(fregs)->regs, 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 f26e9f6e2fed..9d405baedb52 100644
> > --- a/arch/riscv/kernel/mcount-dyn.S
> > +++ b/arch/riscv/kernel/mcount-dyn.S
> > @@ -231,6 +231,7 @@ ENDPROC(ftrace_caller)
> >
> >  #else /* CONFIG_DYNAMIC_FTRACE_WITH_REGS */
> >  ENTRY(ftrace_regs_caller)
> > +     move    t1, zero
>
> Please use "mv", and not "move" [1].
Will fix it up in the next version
>
> >       SAVE_ABI_REGS 1
> >       PREPARE_ARGS
> >
> > @@ -239,7 +240,10 @@ ftrace_regs_call:
> >       call    ftrace_stub
> >
> >       RESTORE_ABI_REGS 1
> > +     bnez    t1,.Ldirect
> >       jr t0
> > +.Ldirect:
> > +     jr t1
>
> Again, while you're doing changes here, please try to align op/operands.
>
> Wearing my BPF hat, I'm happy to finally get DIRECT_CALLS support!
>
> This does not take the WITH_CALL_OPS approach Mark suggested in the v7
> threads, but given that text patching story on RISC-V is still a bit sad
> (inconsistency in the RV tree, no specification, cannot work with
> preempt, ...) I'd say this approach is OK for now, and we can change to
> WITH_CALL_OPS later in a wider "let's improve RISC-V textpatching" work.
>
> Thoughts?
>
>
> Björn
>
> [1] https://github.com/riscv-non-isa/riscv-asm-manual/blob/master/riscv-asm.md#-a-listing-of-standard-risc-v-pseudoinstructions



--
Thanks,
Song

Evgenii Shatokhin May 11, 2023, 1:30 p.m. UTC | #3

Hi,

On 11.05.2023 10:19, Björn Töpel wrote:
> Song Shuai <[e-mail]> writes:
> 
>> 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 <[e-mail]>
>> Tested-by: Guo Ren <[e-mail]>
>> Signed-off-by: Guo Ren <[e-mail]>
>> ---
>>   arch/riscv/Kconfig              |  1 +
>>   arch/riscv/include/asm/ftrace.h |  8 ++++++++
>>   arch/riscv/kernel/mcount-dyn.S  | 10 ++++++++++
>>   3 files changed, 19 insertions(+)
>>
>> diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
>> index e0632493482f..fdf0b219a02c 100644
>> --- a/arch/riscv/Kconfig
>> +++ b/arch/riscv/Kconfig
>> @@ -144,6 +144,7 @@ config RISCV
>>        select UACCESS_MEMCPY if !MMU
>>        select ZONE_DMA32 if 64BIT
>>        select HAVE_DYNAMIC_FTRACE if !XIP_KERNEL && MMU && (CLANG_SUPPORTS_DYNAMIC_FTRACE || GCC_SUPPORTS_DYNAMIC_FTRACE)
>> +     select HAVE_DYNAMIC_FTRACE_WITH_DIRECT_CALLS
>>        select HAVE_DYNAMIC_FTRACE_WITH_REGS if HAVE_DYNAMIC_FTRACE
>>        select HAVE_FTRACE_MCOUNT_RECORD if !XIP_KERNEL
>>        select HAVE_FUNCTION_GRAPH_TRACER
>> diff --git a/arch/riscv/include/asm/ftrace.h b/arch/riscv/include/asm/ftrace.h
>> index 84f856a3286e..84904c1e4369 100644
>> --- a/arch/riscv/include/asm/ftrace.h
>> +++ b/arch/riscv/include/asm/ftrace.h
>> @@ -114,6 +114,14 @@ 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;
>> +}
>> +#define arch_ftrace_set_direct_caller(fregs, addr) \
>> +     __arch_ftrace_set_direct_caller(&(fregs)->regs, 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 f26e9f6e2fed..9d405baedb52 100644
>> --- a/arch/riscv/kernel/mcount-dyn.S
>> +++ b/arch/riscv/kernel/mcount-dyn.S
>> @@ -231,6 +231,7 @@ ENDPROC(ftrace_caller)
>>
>>   #else /* CONFIG_DYNAMIC_FTRACE_WITH_REGS */
>>   ENTRY(ftrace_regs_caller)
>> +     move    t1, zero
> 
> Please use "mv", and not "move" [1].
> 
>>        SAVE_ABI_REGS 1
>>        PREPARE_ARGS
>>
>> @@ -239,7 +240,10 @@ ftrace_regs_call:
>>        call    ftrace_stub
>>
>>        RESTORE_ABI_REGS 1
>> +     bnez    t1,.Ldirect
>>        jr t0
>> +.Ldirect:
>> +     jr t1
> 
> Again, while you're doing changes here, please try to align op/operands.
> 
> Wearing my BPF hat, I'm happy to finally get DIRECT_CALLS support!
> 
> This does not take the WITH_CALL_OPS approach Mark suggested in the v7
> threads, but given that text patching story on RISC-V is still a bit sad
> (inconsistency in the RV tree, no specification, cannot work with
> preempt, ...) I'd say this approach is OK for now, and we can change to
> WITH_CALL_OPS later in a wider "let's improve RISC-V textpatching" work.
> 
> Thoughts?

The WITH_CALL_OPS approach seems to need much more time and effort, so, 
yes, I'd also use this implementation of DIRECT_CALLS for now. Other 
improvements could wait for the future "big patching rework".

FWIW, the implementation of kprobes for RISC-V has been improving 
gradually too, not everything was done in the first very patchset, but 
it was usable nonetheless.

I have not tested this particular version of this 
DYNAMIC_FTRACE_WITH_DIRECT_CALLS series, only some previous ones - there 
were no outstanding problems there. The code looks sane to me.

> 
> 
> Björn
> 
> [1] https://github.com/riscv-non-isa/riscv-asm-manual/blob/master/riscv-asm.md#-a-listing-of-standard-risc-v-pseudoinstructions
> 

Regards,
Evgenii

Guo Ren May 21, 2023, 3:22 p.m. UTC | #4

On Thu, May 11, 2023 at 9:30 PM Evgenii Shatokhin <[e-mail]> wrote:
>
> Hi,
>
> On 11.05.2023 10:19, Björn Töpel wrote:
> > Song Shuai <[e-mail]> writes:
> >
> >> 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 <[e-mail]>
> >> Tested-by: Guo Ren <[e-mail]>
> >> Signed-off-by: Guo Ren <[e-mail]>
> >> ---
> >>   arch/riscv/Kconfig              |  1 +
> >>   arch/riscv/include/asm/ftrace.h |  8 ++++++++
> >>   arch/riscv/kernel/mcount-dyn.S  | 10 ++++++++++
> >>   3 files changed, 19 insertions(+)
> >>
> >> diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> >> index e0632493482f..fdf0b219a02c 100644
> >> --- a/arch/riscv/Kconfig
> >> +++ b/arch/riscv/Kconfig
> >> @@ -144,6 +144,7 @@ config RISCV
> >>        select UACCESS_MEMCPY if !MMU
> >>        select ZONE_DMA32 if 64BIT
> >>        select HAVE_DYNAMIC_FTRACE if !XIP_KERNEL && MMU && (CLANG_SUPPORTS_DYNAMIC_FTRACE || GCC_SUPPORTS_DYNAMIC_FTRACE)
> >> +     select HAVE_DYNAMIC_FTRACE_WITH_DIRECT_CALLS
> >>        select HAVE_DYNAMIC_FTRACE_WITH_REGS if HAVE_DYNAMIC_FTRACE
> >>        select HAVE_FTRACE_MCOUNT_RECORD if !XIP_KERNEL
> >>        select HAVE_FUNCTION_GRAPH_TRACER
> >> diff --git a/arch/riscv/include/asm/ftrace.h b/arch/riscv/include/asm/ftrace.h
> >> index 84f856a3286e..84904c1e4369 100644
> >> --- a/arch/riscv/include/asm/ftrace.h
> >> +++ b/arch/riscv/include/asm/ftrace.h
> >> @@ -114,6 +114,14 @@ 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;
> >> +}
> >> +#define arch_ftrace_set_direct_caller(fregs, addr) \
> >> +     __arch_ftrace_set_direct_caller(&(fregs)->regs, 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 f26e9f6e2fed..9d405baedb52 100644
> >> --- a/arch/riscv/kernel/mcount-dyn.S
> >> +++ b/arch/riscv/kernel/mcount-dyn.S
> >> @@ -231,6 +231,7 @@ ENDPROC(ftrace_caller)
> >>
> >>   #else /* CONFIG_DYNAMIC_FTRACE_WITH_REGS */
> >>   ENTRY(ftrace_regs_caller)
> >> +     move    t1, zero
> >
> > Please use "mv", and not "move" [1].
> >
> >>        SAVE_ABI_REGS 1
> >>        PREPARE_ARGS
> >>
> >> @@ -239,7 +240,10 @@ ftrace_regs_call:
> >>        call    ftrace_stub
> >>
> >>        RESTORE_ABI_REGS 1
> >> +     bnez    t1,.Ldirect
> >>        jr t0
> >> +.Ldirect:
> >> +     jr t1
> >
> > Again, while you're doing changes here, please try to align op/operands.
> >
> > Wearing my BPF hat, I'm happy to finally get DIRECT_CALLS support!
> >
> > This does not take the WITH_CALL_OPS approach Mark suggested in the v7
> > threads, but given that text patching story on RISC-V is still a bit sad
> > (inconsistency in the RV tree, no specification, cannot work with
> > preempt, ...) I'd say this approach is OK for now, and we can change to
> > WITH_CALL_OPS later in a wider "let's improve RISC-V textpatching" work.
> >
> > Thoughts?
>
> The WITH_CALL_OPS approach seems to need much more time and effort, so,
> yes, I'd also use this implementation of DIRECT_CALLS for now. Other
> improvements could wait for the future "big patching rework".
I agree to make DIRECT_CALLS merged first, WITH_CALL_OPS is another
"big patching rework".

>
> FWIW, the implementation of kprobes for RISC-V has been improving
> gradually too, not everything was done in the first very patchset, but
> it was usable nonetheless.
>
> I have not tested this particular version of this
> DYNAMIC_FTRACE_WITH_DIRECT_CALLS series, only some previous ones - there
> were no outstanding problems there. The code looks sane to me.
>
> >
> >
> > Björn
> >
> > [1] https://github.com/riscv-non-isa/riscv-asm-manual/blob/master/riscv-asm.md#-a-listing-of-standard-risc-v-pseudoinstructions
> >
>
> Regards,
> Evgenii
>
>

Patch

diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
index e0632493482f..fdf0b219a02c 100644
--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig
@@ -144,6 +144,7 @@  config RISCV
 	select UACCESS_MEMCPY if !MMU
 	select ZONE_DMA32 if 64BIT
 	select HAVE_DYNAMIC_FTRACE if !XIP_KERNEL && MMU && (CLANG_SUPPORTS_DYNAMIC_FTRACE || GCC_SUPPORTS_DYNAMIC_FTRACE)
+	select HAVE_DYNAMIC_FTRACE_WITH_DIRECT_CALLS
 	select HAVE_DYNAMIC_FTRACE_WITH_REGS if HAVE_DYNAMIC_FTRACE
 	select HAVE_FTRACE_MCOUNT_RECORD if !XIP_KERNEL
 	select HAVE_FUNCTION_GRAPH_TRACER
diff --git a/arch/riscv/include/asm/ftrace.h b/arch/riscv/include/asm/ftrace.h
index 84f856a3286e..84904c1e4369 100644
--- a/arch/riscv/include/asm/ftrace.h
+++ b/arch/riscv/include/asm/ftrace.h
@@ -114,6 +114,14 @@  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;
+}
+#define arch_ftrace_set_direct_caller(fregs, addr) \
+	__arch_ftrace_set_direct_caller(&(fregs)->regs, 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 f26e9f6e2fed..9d405baedb52 100644
--- a/arch/riscv/kernel/mcount-dyn.S
+++ b/arch/riscv/kernel/mcount-dyn.S
@@ -231,6 +231,7 @@  ENDPROC(ftrace_caller)
 
 #else /* CONFIG_DYNAMIC_FTRACE_WITH_REGS */
 ENTRY(ftrace_regs_caller)
+	move	t1, zero
 	SAVE_ABI_REGS 1
 	PREPARE_ARGS
 
@@ -239,7 +240,10 @@  ftrace_regs_call:
 	call	ftrace_stub
 
 	RESTORE_ABI_REGS 1
+	bnez	t1,.Ldirect
 	jr t0
+.Ldirect:
+	jr t1
 ENDPROC(ftrace_regs_caller)
 
 ENTRY(ftrace_caller)
@@ -254,3 +258,9 @@  ftrace_call:
 	jr t0
 ENDPROC(ftrace_caller)
 #endif /* CONFIG_DYNAMIC_FTRACE_WITH_REGS */
+
+#ifdef CONFIG_DYNAMIC_FTRACE_WITH_DIRECT_CALLS
+SYM_CODE_START(ftrace_stub_direct_tramp)
+	jr	t0
+SYM_CODE_END(ftrace_stub_direct_tramp)
+#endif /* CONFIG_DYNAMIC_FTRACE_WITH_DIRECT_CALLS */