linux-kernel - Re: [PATCH] riscv: bpf: Fix uninitialized symbol 'retval

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Message-ID: <20250820092628.GA1289807@chenghao-pc>
Date: Wed, 20 Aug 2025 17:26:28 +0800
From: Chenghao Duan <duanchenghao@...inos.cn>
To: Pu Lehui <pulehui@...wei.com>
Cc: ast@...nel.org, bjorn@...nel.org, puranjay@...nel.org,
	paul.walmsley@...ive.com, palmer@...belt.com, aou@...s.berkeley.edu,
	daniel@...earbox.net, andrii@...nel.org, martin.lau@...ux.dev,
	eddyz87@...il.com, song@...nel.org, yonghong.song@...ux.dev,
	john.fastabend@...il.com, kpsingh@...nel.org, sdf@...ichev.me,
	haoluo@...gle.com, jolsa@...nel.org, alex@...ti.fr,
	bpf@...r.kernel.org, linux-riscv@...ts.infradead.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] riscv: bpf: Fix uninitialized symbol 'retval_off'

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@...inos.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;