[v1] riscv: bpf: Fix uninitialized symbol 'retval_off'

[PATCH] riscv: bpf: Fix uninitialized symbol 'retval_off'

Posted by Chenghao Duan 5 months, 3 weeks ago

In __arch_prepare_bpf_trampoline(), retval_off is only meaningful when
save_ret is true, so the current logic is correct. However, in the
original logic, retval_off is only initialized under certain
conditions, which may cause a build warning.

So initialize retval_off unconditionally to fix it.

Signed-off-by: Chenghao Duan <duanchenghao@kylinos.cn>
---
 arch/riscv/net/bpf_jit_comp64.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/arch/riscv/net/bpf_jit_comp64.c b/arch/riscv/net/bpf_jit_comp64.c
index 10e01ff06312..49bbda8372b0 100644
--- a/arch/riscv/net/bpf_jit_comp64.c
+++ b/arch/riscv/net/bpf_jit_comp64.c
@@ -1079,10 +1079,9 @@ static int __arch_prepare_bpf_trampoline(struct bpf_tramp_image *im,
 	stack_size += 16;
 
 	save_ret = flags & (BPF_TRAMP_F_CALL_ORIG | BPF_TRAMP_F_RET_FENTRY_RET);
-	if (save_ret) {
+	if (save_ret)
 		stack_size += 16; /* Save both A5 (BPF R0) and A0 */
-		retval_off = stack_size;
-	}
+	retval_off = stack_size;
 
 	stack_size += nr_arg_slots * 8;
 	args_off = stack_size;
-- 
2.25.1

Re: [PATCH] riscv: bpf: Fix uninitialized symbol 'retval_off'

Posted by Pu Lehui 5 months, 3 weeks ago


On 2025/8/20 14:25, Chenghao Duan wrote:
> In __arch_prepare_bpf_trampoline(), retval_off is only meaningful when
> save_ret is true, so the current logic is correct. However, in the

lgtm, and same for `ip_off`, pls patch it together.

> original logic, retval_off is only initialized under certain
> conditions, which may cause a build warning.
> 
> So initialize retval_off unconditionally to fix it.
> 
> Signed-off-by: Chenghao Duan <duanchenghao@kylinos.cn>
> ---
>   arch/riscv/net/bpf_jit_comp64.c | 5 ++---
>   1 file changed, 2 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/riscv/net/bpf_jit_comp64.c b/arch/riscv/net/bpf_jit_comp64.c
> index 10e01ff06312..49bbda8372b0 100644
> --- a/arch/riscv/net/bpf_jit_comp64.c
> +++ b/arch/riscv/net/bpf_jit_comp64.c
> @@ -1079,10 +1079,9 @@ static int __arch_prepare_bpf_trampoline(struct bpf_tramp_image *im,
>   	stack_size += 16;
>   
>   	save_ret = flags & (BPF_TRAMP_F_CALL_ORIG | BPF_TRAMP_F_RET_FENTRY_RET);
> -	if (save_ret) {
> +	if (save_ret)
>   		stack_size += 16; /* Save both A5 (BPF R0) and A0 */
> -		retval_off = stack_size;
> -	}
> +	retval_off = stack_size;
>   
>   	stack_size += nr_arg_slots * 8;
>   	args_off = stack_size;

Re: [PATCH] riscv: bpf: Fix uninitialized symbol 'retval_off'

Posted by Chenghao Duan 5 months, 3 weeks ago

On Wed, Aug 20, 2025 at 02:52:01PM +0800, Pu Lehui wrote:
> 
> 
> On 2025/8/20 14:25, Chenghao Duan wrote:
> > In __arch_prepare_bpf_trampoline(), retval_off is only meaningful when
> > save_ret is true, so the current logic is correct. However, in the
> 
> lgtm, and same for `ip_off`, pls patch it together.

I also checked at the time that ip_off is only initialized and assigned
when flags & BPF_TRAMP_F_IP_ARG is true. However, I noticed that the use
of ip_off also requires this condition, so the compiler did not issue a
warning.

Chenghao

> 
> > original logic, retval_off is only initialized under certain
> > conditions, which may cause a build warning.
> > 
> > So initialize retval_off unconditionally to fix it.
> > 
> > Signed-off-by: Chenghao Duan <duanchenghao@kylinos.cn>
> > ---
> >   arch/riscv/net/bpf_jit_comp64.c | 5 ++---
> >   1 file changed, 2 insertions(+), 3 deletions(-)
> > 
> > diff --git a/arch/riscv/net/bpf_jit_comp64.c b/arch/riscv/net/bpf_jit_comp64.c
> > index 10e01ff06312..49bbda8372b0 100644
> > --- a/arch/riscv/net/bpf_jit_comp64.c
> > +++ b/arch/riscv/net/bpf_jit_comp64.c
> > @@ -1079,10 +1079,9 @@ static int __arch_prepare_bpf_trampoline(struct bpf_tramp_image *im,
> >   	stack_size += 16;
> >   	save_ret = flags & (BPF_TRAMP_F_CALL_ORIG | BPF_TRAMP_F_RET_FENTRY_RET);
> > -	if (save_ret) {
> > +	if (save_ret)
> >   		stack_size += 16; /* Save both A5 (BPF R0) and A0 */
> > -		retval_off = stack_size;
> > -	}
> > +	retval_off = stack_size;
> >   	stack_size += nr_arg_slots * 8;
> >   	args_off = stack_size;

Re: [PATCH] riscv: bpf: Fix uninitialized symbol 'retval_off'

Posted by Pu Lehui 5 months, 3 weeks ago


On 2025/8/20 17:26, Chenghao Duan wrote:
> On Wed, Aug 20, 2025 at 02:52:01PM +0800, Pu Lehui wrote:
>>
>>
>> On 2025/8/20 14:25, Chenghao Duan wrote:
>>> In __arch_prepare_bpf_trampoline(), retval_off is only meaningful when
>>> save_ret is true, so the current logic is correct. However, in the
>>
>> lgtm, and same for `ip_off`, pls patch it together.
> 
> I also checked at the time that ip_off is only initialized and assigned
> when flags & BPF_TRAMP_F_IP_ARG is true. However, I noticed that the use
> of ip_off also requires this condition, so the compiler did not issue a
> warning.
> 
> Chenghao
> 
>>
>>> original logic, retval_off is only initialized under certain

Can you show how to replay this warning? I guess the warning path is as 
follow. Compiler didn't know fmod_ret prog need BPF_TRAMP_F_CALL_ORIG.

```
if (fmod_ret->nr_links) {
	...
	emit_sd(RV_REG_FP, -retval_off, RV_REG_ZERO, ctx);
}
```

>>> conditions, which may cause a build warning.
>>>
>>> So initialize retval_off unconditionally to fix it.
>>>
>>> Signed-off-by: Chenghao Duan <duanchenghao@kylinos.cn>
>>> ---
>>>    arch/riscv/net/bpf_jit_comp64.c | 5 ++---
>>>    1 file changed, 2 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/arch/riscv/net/bpf_jit_comp64.c b/arch/riscv/net/bpf_jit_comp64.c
>>> index 10e01ff06312..49bbda8372b0 100644
>>> --- a/arch/riscv/net/bpf_jit_comp64.c
>>> +++ b/arch/riscv/net/bpf_jit_comp64.c
>>> @@ -1079,10 +1079,9 @@ static int __arch_prepare_bpf_trampoline(struct bpf_tramp_image *im,
>>>    	stack_size += 16;
>>>    	save_ret = flags & (BPF_TRAMP_F_CALL_ORIG | BPF_TRAMP_F_RET_FENTRY_RET);
>>> -	if (save_ret) {
>>> +	if (save_ret)
>>>    		stack_size += 16; /* Save both A5 (BPF R0) and A0 */
>>> -		retval_off = stack_size;
>>> -	}
>>> +	retval_off = stack_size;
>>>    	stack_size += nr_arg_slots * 8;
>>>    	args_off = stack_size;

Re: [PATCH] riscv: bpf: Fix uninitialized symbol 'retval_off'

Posted by Chenghao Duan 5 months, 3 weeks ago

On Wed, Aug 20, 2025 at 06:10:07PM +0800, Pu Lehui wrote:
> 
> 
> On 2025/8/20 17:26, Chenghao Duan wrote:
> > On Wed, Aug 20, 2025 at 02:52:01PM +0800, Pu Lehui wrote:
> > > 
> > > 
> > > On 2025/8/20 14:25, Chenghao Duan wrote:
> > > > In __arch_prepare_bpf_trampoline(), retval_off is only meaningful when
> > > > save_ret is true, so the current logic is correct. However, in the
> > > 
> > > lgtm, and same for `ip_off`, pls patch it together.
> > 
> > I also checked at the time that ip_off is only initialized and assigned
> > when flags & BPF_TRAMP_F_IP_ARG is true. However, I noticed that the use
> > of ip_off also requires this condition, so the compiler did not issue a
> > warning.
> > 
> > Chenghao
> > 
> > > 
> > > > original logic, retval_off is only initialized under certain
> 
> Can you show how to replay this warning? I guess the warning path is as
> follow. Compiler didn't know fmod_ret prog need BPF_TRAMP_F_CALL_ORIG.
> 
> ```
> if (fmod_ret->nr_links) {
> 	...
> 	emit_sd(RV_REG_FP, -retval_off, RV_REG_ZERO, ctx);
> }
> ```
> 

Exactly, the compiler sees the unconditional use of retval_off.

Chenghao

> > > > conditions, which may cause a build warning.
> > > > 
> > > > So initialize retval_off unconditionally to fix it.
> > > > 
> > > > Signed-off-by: Chenghao Duan <duanchenghao@kylinos.cn>
> > > > ---
> > > >    arch/riscv/net/bpf_jit_comp64.c | 5 ++---
> > > >    1 file changed, 2 insertions(+), 3 deletions(-)
> > > > 
> > > > diff --git a/arch/riscv/net/bpf_jit_comp64.c b/arch/riscv/net/bpf_jit_comp64.c
> > > > index 10e01ff06312..49bbda8372b0 100644
> > > > --- a/arch/riscv/net/bpf_jit_comp64.c
> > > > +++ b/arch/riscv/net/bpf_jit_comp64.c
> > > > @@ -1079,10 +1079,9 @@ static int __arch_prepare_bpf_trampoline(struct bpf_tramp_image *im,
> > > >    	stack_size += 16;
> > > >    	save_ret = flags & (BPF_TRAMP_F_CALL_ORIG | BPF_TRAMP_F_RET_FENTRY_RET);
> > > > -	if (save_ret) {
> > > > +	if (save_ret)
> > > >    		stack_size += 16; /* Save both A5 (BPF R0) and A0 */
> > > > -		retval_off = stack_size;
> > > > -	}
> > > > +	retval_off = stack_size;
> > > >    	stack_size += nr_arg_slots * 8;
> > > >    	args_off = stack_size;

Re: [PATCH] riscv: bpf: Fix uninitialized symbol 'retval_off'

Posted by Pu Lehui 5 months, 3 weeks ago


On 2025/8/20 18:35, Chenghao Duan wrote:
> On Wed, Aug 20, 2025 at 06:10:07PM +0800, Pu Lehui wrote:
>>
>>
>> On 2025/8/20 17:26, Chenghao Duan wrote:
>>> On Wed, Aug 20, 2025 at 02:52:01PM +0800, Pu Lehui wrote:
>>>>
>>>>
>>>> On 2025/8/20 14:25, Chenghao Duan wrote:
>>>>> In __arch_prepare_bpf_trampoline(), retval_off is only meaningful when
>>>>> save_ret is true, so the current logic is correct. However, in the

OK, I think we should make commit msg more explicit. Such like the 
follow. wdyt?

`However, in the fmod_ret logic, the compiler is not aware that the 
flags of the fmod_ret prog have set BPF_TRAMP_F_CALL_ORIG, resulting in 
an uninitialized symbol compilation warning.`

>>>>
>>>> lgtm, and same for `ip_off`, pls patch it together.
>>>
>>> I also checked at the time that ip_off is only initialized and assigned
>>> when flags & BPF_TRAMP_F_IP_ARG is true. However, I noticed that the use
>>> of ip_off also requires this condition, so the compiler did not issue a
>>> warning.
>>>
>>> Chenghao
>>>
>>>>
>>>>> original logic, retval_off is only initialized under certain
>>
>> Can you show how to replay this warning? I guess the warning path is as
>> follow. Compiler didn't know fmod_ret prog need BPF_TRAMP_F_CALL_ORIG.
>>
>> ```
>> if (fmod_ret->nr_links) {
>> 	...
>> 	emit_sd(RV_REG_FP, -retval_off, RV_REG_ZERO, ctx);
>> }
>> ```
>>
> 
> Exactly, the compiler sees the unconditional use of retval_off.
> 
> Chenghao
> 
>>>>> conditions, which may cause a build warning.
>>>>>
>>>>> So initialize retval_off unconditionally to fix it.
>>>>>
>>>>> Signed-off-by: Chenghao Duan <duanchenghao@kylinos.cn>
>>>>> ---
>>>>>     arch/riscv/net/bpf_jit_comp64.c | 5 ++---
>>>>>     1 file changed, 2 insertions(+), 3 deletions(-)
>>>>>
>>>>> diff --git a/arch/riscv/net/bpf_jit_comp64.c b/arch/riscv/net/bpf_jit_comp64.c
>>>>> index 10e01ff06312..49bbda8372b0 100644
>>>>> --- a/arch/riscv/net/bpf_jit_comp64.c
>>>>> +++ b/arch/riscv/net/bpf_jit_comp64.c
>>>>> @@ -1079,10 +1079,9 @@ static int __arch_prepare_bpf_trampoline(struct bpf_tramp_image *im,
>>>>>     	stack_size += 16;
>>>>>     	save_ret = flags & (BPF_TRAMP_F_CALL_ORIG | BPF_TRAMP_F_RET_FENTRY_RET);
>>>>> -	if (save_ret) {
>>>>> +	if (save_ret)
>>>>>     		stack_size += 16; /* Save both A5 (BPF R0) and A0 */
>>>>> -		retval_off = stack_size;
>>>>> -	}
>>>>> +	retval_off = stack_size;
>>>>>     	stack_size += nr_arg_slots * 8;
>>>>>     	args_off = stack_size;

Re: [PATCH] riscv: bpf: Fix uninitialized symbol 'retval_off'

Posted by Chenghao Duan 5 months, 3 weeks ago

On Thu, Aug 21, 2025 at 09:58:20AM +0800, Pu Lehui wrote:
> 
> 
> On 2025/8/20 18:35, Chenghao Duan wrote:
> > On Wed, Aug 20, 2025 at 06:10:07PM +0800, Pu Lehui wrote:
> > > 
> > > 
> > > On 2025/8/20 17:26, Chenghao Duan wrote:
> > > > On Wed, Aug 20, 2025 at 02:52:01PM +0800, Pu Lehui wrote:
> > > > > 
> > > > > 
> > > > > On 2025/8/20 14:25, Chenghao Duan wrote:
> > > > > > In __arch_prepare_bpf_trampoline(), retval_off is only meaningful when
> > > > > > save_ret is true, so the current logic is correct. However, in the
> 
> OK, I think we should make commit msg more explicit. Such like the follow.
> wdyt?
> 
> `However, in the fmod_ret logic, the compiler is not aware that the flags of
> the fmod_ret prog have set BPF_TRAMP_F_CALL_ORIG, resulting in an
> uninitialized symbol compilation warning.`
> 

Good idea

> > > > > 
> > > > > lgtm, and same for `ip_off`, pls patch it together.
> > > > 
> > > > I also checked at the time that ip_off is only initialized and assigned
> > > > when flags & BPF_TRAMP_F_IP_ARG is true. However, I noticed that the use
> > > > of ip_off also requires this condition, so the compiler did not issue a
> > > > warning.
> > > > 
> > > > Chenghao
> > > > 
> > > > > 
> > > > > > original logic, retval_off is only initialized under certain
> > > 
> > > Can you show how to replay this warning? I guess the warning path is as
> > > follow. Compiler didn't know fmod_ret prog need BPF_TRAMP_F_CALL_ORIG.
> > > 
> > > ```
> > > if (fmod_ret->nr_links) {
> > > 	...
> > > 	emit_sd(RV_REG_FP, -retval_off, RV_REG_ZERO, ctx);
> > > }
> > > ```
> > > 
> > 
> > Exactly, the compiler sees the unconditional use of retval_off.
> > 
> > Chenghao
> > 
> > > > > > conditions, which may cause a build warning.
> > > > > > 
> > > > > > So initialize retval_off unconditionally to fix it.
> > > > > > 
> > > > > > Signed-off-by: Chenghao Duan <duanchenghao@kylinos.cn>
> > > > > > ---
> > > > > >     arch/riscv/net/bpf_jit_comp64.c | 5 ++---
> > > > > >     1 file changed, 2 insertions(+), 3 deletions(-)
> > > > > > 
> > > > > > diff --git a/arch/riscv/net/bpf_jit_comp64.c b/arch/riscv/net/bpf_jit_comp64.c
> > > > > > index 10e01ff06312..49bbda8372b0 100644
> > > > > > --- a/arch/riscv/net/bpf_jit_comp64.c
> > > > > > +++ b/arch/riscv/net/bpf_jit_comp64.c
> > > > > > @@ -1079,10 +1079,9 @@ static int __arch_prepare_bpf_trampoline(struct bpf_tramp_image *im,
> > > > > >     	stack_size += 16;
> > > > > >     	save_ret = flags & (BPF_TRAMP_F_CALL_ORIG | BPF_TRAMP_F_RET_FENTRY_RET);
> > > > > > -	if (save_ret) {
> > > > > > +	if (save_ret)
> > > > > >     		stack_size += 16; /* Save both A5 (BPF R0) and A0 */
> > > > > > -		retval_off = stack_size;
> > > > > > -	}
> > > > > > +	retval_off = stack_size;
> > > > > >     	stack_size += nr_arg_slots * 8;
> > > > > >     	args_off = stack_size;