Re: [PATCH] riscv: bpf: Fix uninitialized symbol 'retval_off'
From: Pu Lehui
Date: Wed Aug 20 2025 - 21:59:46 EST
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@xxxxxxxxxx>
---
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;